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1.
  • Ahlstrom Silversand, AF, et al. (författare)
  • Combustion of methane over a Pd-Al2O3/SiO2 catalyst, catalyst activity and stability
  • 1997
  • Ingår i: Applied Catalysis A: General. - 0926-860X. ; 153:1-2, s. 157-175
  • Tidskriftsartikel (refereegranskat)abstract
    • Palladium supported on Si-stabilised alumina has been demonstrated to be an active and durable catalyst for the combustion of methane. Si is more effective in stabilising alumina than La or Ba when the elements are added through an impregnation technique. Multiple stabilisation with combinations of La, Ba and Si does not increase further the stability against sintering. The stability increases logarithmically with the amount of Si added (0.5-8 atomic%). The rate of sintering is not affected by an increase of the water vapour content of the atmosphere from 1 to 20 vol.%. Doping palladium with rhodium or platinum increases the activity of the catalyst for methane combustion. The high-temperature stability of pure Pd is however superior to the stabilities of the Rh- and Pt-doped catalysts. Addition of La or Ce to the Pd-catalyst increases its stability against thermal deactivation but leads to an overall decrease in activity. The activity of the as-prepared catalysts are affected by the Pd-content below a value corresponding to 5% of the monolayer capacity. Thermally deactivated catalysts show a stronger activity dependence of the Pd-content than as-prepared catalysts. The combustion reaction is first order with respect to methane and zero-order with respect to oxygen (>2 vol.% of oxygen). Carbon dioxide has no inhibitory effects on the combustion. The activity of the Pd-catalyst is decreased by a factor of 5 through deactivation at 1473 K for 768 h. The decrease in activity is linearly correlated to the decrease in specific surface area.
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2.
  • Ahlstrom Silversand, AF, et al. (författare)
  • Thermally sprayed wire-mesh catalysts for the purification of flue gases from small-scale combustion of bio-fuel - Catalyst preparation and activity studies
  • 1997
  • Ingår i: Applied Catalysis A: General. - 0926-860X. ; 153:1-2, s. 177-201
  • Tidskriftsartikel (refereegranskat)abstract
    • Catalytically active wire meshes were used to combust different pollutants present in flue gases from bio-fuel combustion, e.g. CO, propylene, terpenes and tar. Alumina was spray-deposited onto wire meshes of Kanthal AF (8-20 Tayler mesh) with a plasma spray equipment. The specific surface area of the ceramic layer was increased through wash coating, in-situ precipitation or sol-treatment. The catalytically active materials consisted of precious metals (Pd/Pt) or metal oxides (V2O5/CuO) and were added to the ceramic matrix through an impregnation technique. The combustion was in most cases severely limited by external mass transfer. The effects of the specific surface area and the loading of catalytically active material were only significant in the reaction controlled domain. In the mass transfer controlled domain the conversion was affected only by the flow conditions and the external surface area of the wire meshes. CO and most hydrocarbons were effectively combusted at temperatures below 773 on a Pd/Pt-catalyst. The catalyst performance was not affected by the presence of water vapour or carbon dioxide or by low oxygen concentrations. Similar combustion experiments were performed with a commercial monolith and it can be concluded that the performance of the catalytically active wire meshes in the mass-transfer controlled domain was superior. Tar-residues, soot particulates and charcoal particles were effectively combusted over a Pd/Pt-doped oxide-catalyst (V2O5/CuO).
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3.
  • Andersson, Arne, et al. (författare)
  • Surface Characterization and Reactivity in Ammoxidation Reactions of Vanadium Antimonate Catalysts
  • 1994
  • Ingår i: Applied Catalysis A: General. - 0926-860X. ; 113:1, s. 43-57
  • Tidskriftsartikel (refereegranskat)abstract
    • Unsupported vanadium antimonate catalysts with Sb/V ratios of 1 and 5 and samples with the latter ratio supported on alumina were studied in toluene and propane ammoxidation to benzonitrile and acrylonitrile, respectively, and were characterized by X-ray photoelectron spectroscopy (XPS) analysis before and after catalytic tests. Activity data for toluene ammoxidation suggest that excess antimony with respect to the stoichiometric amount required for forming the VSbO4 rutile phase affects the dispersion of the latter phase giving smaller particles. Vanadium sites are involved both in the activation of toluene and in the insertion of nitrogen in this reaction, whereas antimony does not play a specific role in the reaction mechanism. In propane ammoxidation, on the other hand, due to a higher reaction temperature with respect to toluene (500°C vs. 370°C), free vanadia on the surface of the catalyst has a negative influence on the selectivity because it promotes the conversion of ammonia to nitrogen, decreasing the surface nitrogenous species required for the selective formation of acrylonitrile. Excess antimony is thus necessary for completing the reaction between antimony and vanadium oxides, but antimony also participates in the reaction mechanism. In propane ammoxidation, in fact, XPS data show that both vanadium and antimony sites are reduced. Tentatively, vanadium sites are involved in the activation of propane, while antimony sites insert nitrogen. The differences between the toluene and propane ammoxidation mechanisms are interpreted to be primarily related to the different reaction temperatures.
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4.
  • Huuhtanen, Jane, et al. (författare)
  • Catalytic and Spectroscopic Studies of Vanadium Oxide Supported on Group IVb and Vb Metal Oxides for Oxidation of Toluene
  • 1993
  • Ingår i: Applied Catalysis A: General. - 0926-860X. ; 97:2, s. 197-221
  • Tidskriftsartikel (refereegranskat)abstract
    • Vanadia was deposited on TiO2, ZrO2, HfO2, Nb2O5, and Ta2O5 supports using impregnation with either an oxalic acid solution of NH4VO3 or a solution of vanadyl acetylacetonate in ethanol. Prepared samples, with a nominal vanadia content in the range 0.5–2 monolayers, were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopy, and were used in toluene oxidation. XRD did not reveal formation of any vanadia phase. XPS spectra showed deposited vanadium to be present mainly as V5+ on all the supports. A plot of the V:( support metal) ratio determined by XPS showed agglomeration of vanadia on TiO2, ZrO2, HfO2, and Nb2O5 to occur at loadings above 0.5 monolayer, while for Ta2O5 the dispersion seemed independent of the loading. Preparations from vanadyl acetylacetonate gave superior dispersion. Raman spectra showed bands from crystalline V2O5 on all the supports except Nb2O5. Raman and infrared bands from dispersed vanadia were present in the spectra of TiO2 (three species), ZrO2 and HfO2 (both one species) supported catalysts. No bands from vanadium-oxygen vibrational modes were seen in the spectra of Nb2O5 supported samples, but a V-OH band was observed, suggesting an amorphous structure. Some evidence was obtained for formation of amorphous VTa9O25 on Ta205. The activity for toluene oxidation increased with vanadia loading for each support, and the activity varied with respect to support at all loadings in the order TiO2 > ZrO2 > Nb2O5 > HfO2 > Ta2O5. The selectivity for formation of benzaldehyde was the highest using TiO2 and Nb2O5 supports, while for benzoic acid TiO2 was the best support.
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5.
  • Lif, Johan, 1964, et al. (författare)
  • Sintering of nickel particles supported on gamma-alumina in ammonia
  • 2002
  • Ingår i: Applied Catalysis A: General. - 1873-3875 .- 0926-860X. ; 228:1-2, s. 145-154
  • Tidskriftsartikel (refereegranskat)abstract
    • Sintering of nickel on gamma-alumina in hydrogen, ammonia, ammonia + hydrogen and ammonia + nitrogen was investigated isocoric in the temperature range 483 to 523 K. The sintering process was followed by hydrogen chemisorption, specific surface area measurements, X-ray diffraction and transmission electron microscopy. After exposure to ammonia + hydrogen, hydrogen chemisorption revealed a fast decline of the nickel surface area. The results from X-ray diffraction and transmission electron microscopy are consistent with the result from the chemisorption experiments. The BET analysis showed that there are no losses of the total surface area. The sintering rate was significantly slower if the heat treatment was performed in the presence of only one of the gases, ammonia or hydrogen, or in ammonia + nitrogen. This indicates that the sintering in the temperature range 483 to 523 K only occurs with reduced nickel particles in ammonia + hydrogen. The prevailing mechanism for the sintering seems to be sintering by particle migration. The kinetics of the sintering process indicates that the rate constant is correlated to more factors than the temperature.
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6.
  • Sanati, Mehri, et al. (författare)
  • Zirconia-Supported Vanadium Oxide Catalysts for Ammoxidation and Oxidation of Toluene: A Characterization and Activity Study
  • 1993
  • Ingår i: Applied Catalysis A: General. - 0926-860X. ; 106:1, s. 51-72
  • Tidskriftsartikel (refereegranskat)abstract
    • A series of samples of vanadia supported on monoclinic zirconia were prepared with nominal loadings from a half up to sixteen theoretical vanadia layers. The samples were characterized with X-ray diffraction, scanning electron microscopy combined with energy dispersive X-ray analysis, high-resolution electron microscopy, Raman and diffuse reflectance infrared spectroscopy, and were used in the oxidation and the ammoxidation of toluene. At loadings in the monolayer range, Raman and infrared bands from decavanadate-like and dehydrated tetrahedral vanadia species were at ca. 990 and ca. 1025 cm−1, respectively. Raman bands at 821 and 880 cm−1 were present only at the lowest loading and are characteristic of orthovanadate and pyrovanadate species, respectively. X-ray diffraction, Raman and infrared spectroscopic results revealed formation of some crystalline V2O5 and ZrV2O7 at loadings exceeding a theoretical monolayer. In this case, consideration of Raman intensity variations allowed the conclusion that additional non-crystalline vanadia must be present. According to high-resolution electron micrographs, this vanadia consists of an amorphous overlayer, 4–8 atomic layers thick. In toluene oxidation zirconia-supported vanadia compared with crystalline V2O5 was found less selective for benzaldehyde formation. In toluene ammoxidation, on the other hand, vanadia on zirconia was found to possess good activity and selectivity for benzonitrile formation. Amorphous vanadia was the most active structure on zirconia, while the selectivities for nitrile and aldehyde formations were almost independent of the loading for one theoretical layer and above.
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7.
  • Agrell, J., et al. (författare)
  • Production of hydrogen by partial oxidation of methanol over Cu/ZnO catalysts prepared by microemulsion technique
  • 2001
  • Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 211:2, s. 239-250
  • Tidskriftsartikel (refereegranskat)abstract
    • Production of hydrogen by partial oxidation of methanol, using air as oxidant. has been studied over a series of Cu/ZnO catalysts prepared by microemulsion technique. The catalytic activity was compared to that of a reference catalyst prepared by conventional co-precipitation. The BET surface areas of the microemulsion catalysts (30-70 wt.% Cu) ranged from 22 to 36 m(2)/g and were considerably lower than that of the reference (60 m(2)/g). Nevertheless, the microemulsion catalysts were more active in the partial oxidation reaction and exhibited high hydrogen and carbon dioxide selectivities. At a molar O-2/CH3OH ratio of 0.1, hydrogen production was initiated at about 185 degreesC over the microemulsion catalysts. Over the reference, hydrogen production began at 215 degreesC under the same conditions. The catalytic activity was Found to be strongly dependent on the partial pressure of oxygen, which also plays an important role in determining the product distribution. By increasing the O-2/CH3OH ratio, the methanol conversion and carbon dioxide selectivity increase. while production of water occurs at the expense of hydrogen. By TEM and TPR, it was observed that Cu is less well-dispersed in the microemulsion catalysts than in the reference. The higher catalytic activity is not expected considering the lower number of exposed Cu sites, i.e, the turnover frequencies are substantially higher over the microemulsion catalysts. It is possible that, a strong interaction between a small part of CuO and the ZnO lattice is responsible for the higher turnover frequencies of the microemulsion catalysts, or that particular crystallographic Cu planes or surface imperfections are the active sites of the reaction.
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8.
  • Agrell, J., et al. (författare)
  • Production of hydrogen by partial oxidation of methanol over ZnO-supported palladium catalysts prepared by microemulsion technique
  • 2003
  • Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 242:2, s. 233-245
  • Tidskriftsartikel (refereegranskat)abstract
    • Selective production of hydrogen by partial oxidation of methanol, using air as oxidant, was studied over a series of ZnO-supported Pd catalysts. Microemulsion-assisted synthesis and conventional impregnation techniques were used for preparation of catalysts containing Pd particles of different sizes. Catalyst characterisation included BET, XRD and TEM analyses. The influence of Pd particle size on catalytic activity and product distribution was studied by carrying out activity measurements at temperatures between 230 and 300 degreesC using a stoichiometric feed composition. All catalysts performed well with respect to methanol conversion and hydrogen yield. Both methanol conversion and hydrogen selectivity increased with increasing reaction temperature, the latter at the expense of water formation. Oxygen conversion was complete throughout the examined temperature range. These selectivity trends, with a strong dependence of hydrogen and carbon monoxide selectivities on methanol conversion and reaction temperature, support a reaction scheme consisting of consecutive methanol combustion, steam reforming and decomposition. More importantly, a correlation between Pd particle size and carbon monoxide selectivity was found. When the microemulsion catalysts are compared, carbon monoxide formation increases with increasing particle size. This was not observed over the impregnated reference catalysts, which exhibited high carbon monoxide-levels throughout the examined temperature range. Bimetallic PdZn particles were detected in spent catalysts by means of XRD and it is suggested that the catalytic activity is dependent on the formation of PdZn, the catalytic function being different from that of Pd-0.
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9.
  • Agrell, J., et al. (författare)
  • Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part I. Catalyst preparation and characterisation
  • 2003
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 253:1, s. 201-211
  • Tidskriftsartikel (refereegranskat)abstract
    • Mixed copper-zinc oxide catalysts (Cu/ZnO) were prepared by two different techniques, i.e. from hydroxycarbonate precursors formed in aqueous solution and from oxalate precursors formed in water-in-oil microemulsion. Their physicochemical properties were characterised by nitrogen adsorption-desorption, N2O chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and oxidation (TPO). The BET surface areas ranged from 34 to 87 m(2)/g, depending on the method of preparation. Cu surface areas between 6.6 and 22 m(2)/g were measured. It was a general observation that catalysts prepared by microemulsion technique had lower Cu dispersions than expected (3.4-5.7%), due to a proposed partial embedding of Cu in ZnO. The catalyst prepared by carbonate co-precipitation exhibited a significantly higher Cu dispersion (10.3%). In addition, this catalyst displayed better resistance to successive TPR/TPO than the microemulsion catalysts, which exhibited significant Cu crystallite growth. However, the microemulsion route provided well-mixed materials with a narrow particle size distribution and the possibility to obtain high BET surface areas (up to 87 m(2)/g) by controlling the water/surfactant ratio in the microemulsion. XPS measurements revealed the existence of Cu+ species on the surface of both types of catalysts after exposure to a O-2/CH3OH mixture. The surface composition of the hydroxycarbonate-derived sample was unaffected by reduction in hydrogen and exposure to O-2/CH3OH, while Zn-enrichment on the surface was observed in the microemulsion catalysts after reduction, indicating sintering of the Cu particles. These observations were consistent with the TPR/TPO measurements.
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10.
  • Agrell, J., et al. (författare)
  • Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part II. Catalytic activity and reaction pathways
  • 2003
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 253:1, s. 213-223
  • Tidskriftsartikel (refereegranskat)abstract
    • The activity for conversion of methanol into hydrogen was investigated over binary Cu/ZnO catalysts derived from precursors prepared by two different techniques, viz. oxalates formed in microemulsion and hydroxycarbonates formed in aqueous solution. Some distinct differences in the reaction pathways were observed. During partial oxidation of methanol under a sub-stoichiometric oxygen/methanol ratio, the microemulsion materials exhibited considerably higher combustion activity in the low-temperature region than a catalyst prepared in aqueous solution. Over the former, oxygen was quickly converted by methanol combustion, after which steam reforming was initiated, producing hydrogen at the expense of water and gradually decreasing the net heat of reaction. Hence, a reaction sequence for the partial oxidation reaction over microemulsion catalysts is proposed. consisting of consecutive methanol combustion and steam reforming, followed by decomposition when all oxygen has been consumed. Over the hydroxycarbonate catalyst, the reaction ignited at a higher temperature, directly producing hydrogen by partial oxidation of methanol. When the two types of catalysts were evaluated in the steam reforming reaction, all catalysts displayed the typical S-shaped dependence of methanol conversion on temperature. However, there was a downward shift in the temperature at which methanol reached complete conversion, favouring the hydroxycarbonate, material. Hydrogen was produced selectively over all catalysts, but carbon monoxide formation was more pronounced over the microemulsion materials. The differences in catalytic behaviour are discussed in terms of catalyst morphology and the valence state of Cu in the working catalyst.
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11.
  • Amandusson, H., et al. (författare)
  • Alcohol dehydrogenation over Pd versus PdAg membranes
  • 2001
  • Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 217:1-2, s. 157-164
  • Tidskriftsartikel (refereegranskat)abstract
    • The dehydrogenation of methanol and ethanol and the subsequent permeation of hydrogen through Pd and Pd70Ag30 membranes, respectively, have been studied. In order to keep a continuous hydrogen permeation rate, oxygen needs to be added to the alcohol supply. Without oxygen, the decomposition products will form a contaminating layer on the upstream membrane surface. The extraction of hydrogen from ethanol is six times more effective through a Pd70Ag30 membrane than through a pure Pd membrane (at optimum conditions). For methanol, the hydrogen permeation is 30% larger through a Pd70Ag30 membrane than through a membrane of pure Pd. The increased hydrogen permeation yield through Pd70Ag30 compared to Pd can be attributed mainly to a lower upstream consumption of hydrogen due to water formation, but also to an increased conversion of the alcohol in the presence of oxygen. © 2001 Elsevier Science B.V.
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12.
  • Creaser, Derek, et al. (författare)
  • Transient study of oxidative dehydrogenation of propane
  • 1999
  • Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 187:1, s. 147-160
  • Tidskriftsartikel (refereegranskat)abstract
    • Kinetics and the mechanism of the oxidative dehydrogenation of propane were investigated using various transient techniques. Results support a redox reaction mechanism in which propane and intermediate products react with lattice oxygen, reducing the catalyst surface, which is reoxidized by gas-phase O2. Partial reduction of the catalyst occurs during the start-up to a steady state. Successive pulsing with C3H8 reduced V5+ in the magnesium ortho-vanadate phase to V2+. Carbon-containing species were observed upon interruption of the reaction, although only minute amounts were formed. Cycling increases the amount of the carbon deposited, but this carbon is reactive and most of it is oxidized in the succeeding O2 pulse. Temperature-programmed oxidation (TPO) experiments on the catalyst used in steady-state operation revealed mainly strongly bound carbonaceous matter on the catalyst, but this carbon deposition did not affect catalyst activity. Thus, adsorbed oxygen is an important source of total combustion. Our experiments show, however, that lattice oxygen also produces total oxidation. Propene selectivity of the reaction in the absence of gas-phase O2 was superior to steady-state selectivity, at the same propane conversion. Propene selectivity could be further improved by increasing the degree of reduction of the catalyst
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13.
  • Lindström, B., et al. (författare)
  • Activity and characterization of Cu/Zn, Cu/Cr and Cu/Zr on gamma-alumina for methanol reforming for fuel cell vehicles
  • 2002
  • Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 234:02-jan, s. 111-125
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of catalyst properties on the activity and selectivity of hydrogen generation by methanol reforming over copper-based catalysts impregnated on gamma-alumina pellets has been investigated. In the experiments, three sets of copper-based catalysts with various compositions were tested: Cu/Zn/Al2O3, Cu/Cr/Al2O3 and Cu/Zr/Al2O3. The catalysts were characterized using temperature programmed reduction (TPR), temperature programmed oxidation (TPO), SEM-EDS, Brunauer-Emmett-Teller (BET) surface area measurement and X-ray diffraction (XRD). The copper surface area was determined by pulse chemisorption using N2O. We found a correlation between the copper surface area and catalytic activity. The activity tests were performed in a fixed bed reactor with 15 g of spherical catalyst pellets using a gas hourly space velocity (GHSV) of 25,000. The results of the activity tests indicate that the choice of promoter and the catalyst composition greatly influence the activity as well as the selectivity for CO2 formation. The highest conversions were achieved for the zinc-containing catalysts (Cu/Zn/Al2O3) for both steam reforming and the combined reforming process. Complete conversion of methanol was only obtained for the zinc-containing catalysts when running the steam reforming process. The combined reforming process generally yielded A product stream containing lower carbon monoxide concentrations compared to steam reforming at the equivalent reactor temperature for all of the catalysts tested.
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14.
  • Persson, K., et al. (författare)
  • Preparation of alumina-supported palladium catalysts for complete oxidation of methane
  • 2003
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 249:1, s. 165-174
  • Tidskriftsartikel (refereegranskat)abstract
    • Alumina-supported palladium catalysts (Pd/Al2O3) have been prepared by incipient wetness (IW), grafting (G) and microemulsion techniques (ME). Two slightly different microemulsion methods have been used (ME1) and (ME2). The catalysts have been calcined at 1000 degreesC for 4 h. The catalysts have then been examined with respect to their activity for the combustion of methane, during heating and cooling ramps. Pd/Al2O3-IW and Pd/Al2O3-ME2 exhibit the highest activity whereas Pd/Al2O3-ME1 and Pd/Al2O3-G are the less active. There is not much of a difference in activity between Pd/Al2O3-IW and Pd/Al2O3-ME2, despite strong differences in palladium particle size observed by TEM analysis. TPO experiments show that Pd/Al2O3-IW and Pd/Al2O3-ME2 present a higher PdO/Pd ratio than the other samples exhibit. The preparation technique affects the reoxidation ability of palladium during cooling, hence the combustion activity of the fresh catalyst, as PdO is more active than Pd for the complete oxidation of methane under lean conditions.
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15.
  • Thevenin, P. O., et al. (författare)
  • Deactivation of high temperature combustion catalysts
  • 2001
  • Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 212:02-jan, s. 189-197
  • Tidskriftsartikel (refereegranskat)abstract
    • The main objective of catalytic combustion is to attain a flame temperature 300-400 Klower than in thermal or non-catalyzed combustion; this substantially reduces the direct combination of nitrogen and oxygen in air to form the so-called thermal NOx. In this way, catalytic combustion is a preventive solution to the problem of nitrogen oxides emissions. The focus of attention here is its application in gas turbines, both for power production and for transportation by road, sea and air. Any catalyst for catalytic combustion, however, has to face extreme demands: continuous operation above 1000 degreesC in the presence of oxygen and steam for preferably 30,000 h, resistance to poisons in the fuel and/or process air, and ability to withstand large thermal and mechanical shocks. While material/catalyst advances are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid reactors. The deactivation of catalyst supports, washcoats, and active materials is briefly reviewed here: sintering, vaporization, phase transformation, thermal shock and poisoning.
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16.
  • Van Den Hark,, et al. (författare)
  • Hydrogenation of oleochemicals at supercritical single-phase conditions : Influence of hydrogen and substrate concentrations on the process
  • 2001
  • Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 210:42006, s. 207-215
  • Tidskriftsartikel (refereegranskat)abstract
    • Fatty alcohols can be produced by catalytic hydrogenation of fatty acid methyl esters. This heterogeneous catalytic reaction is normally performed in a multi-phase system. In such a system, with a low hydrogen solubility in the liquid substrate and a large mass transport resistance, the hydrogen concentration at the catalyst is low and limits the reaction rate. To overcome this limitation, we have used the unique properties of supercritical fluids, properties which are in between those of liquids and gases, making them a very suitable medium for reactions. By adding propane to the reaction mixture of hydrogen and fatty acid methyl esters (C18) we have created supercritical single-phase conditions. At these single-phase conditions the concentrations of all the reactants at the catalyst surface can be controlled, and an excess of hydrogen becomes possible. In this way, extremely rapid hydrogenation can be combined with a high product selectivity. In our lab-scale experiments the catalyst performance was studied as a function of hydrogen concentration, substrate concentration and temperature. Complete conversion of the liquid substrate was reached in a few seconds. As long as single-phase conditions remain, we have, in our experiments, tested up to 15 wt.% substrate, vapor-phase like reaction rates can be maintained. However, at these high substrate concentrations, mass transport becomes important again. Our results show that performing hydrogenation at supercritical single-phase conditions has a large potential for this and other catalytic processes where the hydrogen concentration at the catalyst is the limiting factor.
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17.
  • Ying, Zhong-Shu, et al. (författare)
  • Hydrodemetallisation of residual oil with catalysts using fibrillar alumina as carrier material
  • 1997
  • Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 153:1-2, s. 69-82
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydroprocessing catalysts were prepared using fibrillar aluminas as carrier materials and sulphides of nickel and molybdenum as active substances. The fibrillar aluminas were obtained from fibrillar boehmite samples prepared at three different synthesis conditions resulting in different fibril sizes. After extrudation and deposition of metals, catalysts combining large surface areas with large average pore diameters were obtained. The catalysts were tested for hydrodemetallisation of an atmospheric residue and the results were compared with those obtained for a commercial reference catalyst with a similar loading of nickel and molybdenum. Two of the catalysts prepared using fibrillar alumina as carrier material were more active than the commercial catalyst. The third catalyst containing the largest alumina fibrils was inferior to the other catalysts in all respects. Catalyst deactivation was investigated in a long-term hydroprocessing experiment using a heavy vacuum residue containing large amounts of metals as a feed oil. The catalyst prepared using fibrillar alumina used in this test showed a constant level of hydrodemetallisation even after 500 h on stream whereas the reference catalyst was completely deactivated after 350 h.
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18.
  • Ahlkvist, Johan, et al. (författare)
  • One-pot catalytic conversion of Nordic pulp media into green platform chemicals
  • 2013
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 454, s. 21-29
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, both sulphite and sulphate (Kraft) cellulose from Nordic pulp mills were used as raw materials in the catalytic one-pot synthesis of green platform chemicals, levulinic and formic acids, respectively. The catalyst of choice was a macro-porous, cationic ion-exchange resin, Amberlyst 70. The optimal reaction conditions were determined and the influence of various gas atmospheres was investigated. The maximum yields of 53% formic acid and 57% of levulinic acid were separately obtained in a straight-forward conversion system only containing cellulose, water and the heterogeneous catalyst. The concept introduces a one-pot procedure providing a feasible route to green platform chemicals obtained via conversion of coniferous soft wood pulp to levulinic and formic acids, respectively.
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19.
  • Ajaikumar, Samikannu, et al. (författare)
  • Oxidation of α-pinene over gold containing bimetallic nanoparticles supported on reducible TiO2 by DPU method
  • 2011
  • Ingår i: Applied Catalysis A. - Amsterdam : Elsevier. - 0926-860X .- 1873-3875. ; 392:1-2, s. 11-18
  • Tidskriftsartikel (refereegranskat)abstract
    • A series of bimetallic catalysts Au–M (where M = Cu, Co and Ru) were supported on a reducible TiO2 oxide via deposition-precipitation (DP) method with a slow decomposition of urea as the precipitating agent. The characteristic structural features of the prepared materials were characterized by various physico-chemical techniques such as X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). XPS results indicated the formation of alloyed bimetallic particles on the TiO2 support. TEM results confirmed the fine dispersion of metal nanoparticles on the support with an average particle size in the range of 3–5 nm. An industrially important process, oxy-functionalization of α-pinene was carried out over the prepared bimetallic heterogeneous catalysts under liquid phase conditions. Reaction parameters such as the reaction time, temperature, and the effect of solvent were studied for optimal conversion of α-pinene into verbenone. The major products obtained were verbenone, verbenol, α-pinene oxide and alkyl-pinene peroxide. The activity of the catalysts followed the order; AuCu/TiO2 > AuCo/TiO2 > Cu/TiO2 > Au/TiO2 > AuRu/TiO2. Upon comparison of the various catalysts, AuCu/TiO2 was found to be an active and selective catalyst towards the formation of verbenone. The temperature, nature of the catalysts and the choice of solvents greatly influenced the reaction rate.
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20.
  • Andersson, Robert, et al. (författare)
  • Correlation patterns and effect of syngas conversion level for product selectivity to alcohols and hydrocarbons over molybdenum sulfide based catalysts
  • 2012
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 417, s. 119-128
  • Tidskriftsartikel (refereegranskat)abstract
    • The focus of the present study was to investigate the effect of the operation conditions, space velocity and temperature, on product distribution for a K-Ni-MoS2 catalyst for mixed alcohol synthesis from syngas. All experiments were performed at 91 bar pressure and constant H-2/CO=1 syngas feed ratio. For comparison, results from a non-promoted MoS2 catalyst are presented. It was found that the CO conversion level for the K-Ni-MoS2 catalyst very much decides the alcohol and hydrocarbon selectivities. Increased CO conversion by means of increased temperature (tested between 330 and 370 degrees C) or decreased space velocity (tested between 2400 and 18,000 ml/(g(cat) h)), both have the same effect on the product distribution with decreased alcohol selectivity and increased hydrocarbon selectivity. Increased CO conversion also leads to a greater long-to-short alcohol chain ratio. This indicates that shorter alcohols are building blocks for longer alcohols and that those alcohols can be converted to hydrocarbons by secondary reactions. At high temperature (370 degrees C) and low space velocity (2400 ml/(g(cat) h)) the selectivity to isobutanol is much greater than previously reported (9%C). The promoted catalyst (K-Ni-MoS2) is also compared to a non-promoted (MoS2) catalyst: the promoted catalyst has quite high alcohol selectivity, while almost only hydrocarbons are produced with the non-promoted catalyst. Another essential difference between the two catalysts is that the paraffin to olefin ratio within the hydrocarbon group is significantly different. For the non-promoted catalyst virtually no olefins are produced, only paraffins, while the promoted catalyst produces approximately equal amounts of C-2-C-6 olefins and paraffins. Indications of olefins being produced by dehydration of alcohols were found. The selectivity to other non-alcohol oxygenates (mostly short esters and aldehydes) is between 5 and 10%C and varies little with space velocity but decreases slightly with increased temperature. Very strong correlation patterns (identical chain growth probability) and identical deviations under certain reaction conditions between aldehyde and alcohol selectivities (for the same carbon chain length) indicate that they derive from the same intermediate. Also olefin selectivity is correlated to alcohol selectivity, but the correlation is not as strong as between aldehydes and alcohols. The selectivity to an ester is correlated to the selectivity to the two corresponding alcohols, in the same way as an ester can be thought of as built from two alcohol chains put together (with some H-2 removed). This means that, e.g. methyl acetate selectivity (C-3) is correlated to the combination of methanol (C-1) and ethanol (C-2) selectivities.
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21.
  • Andrae, Johan, et al. (författare)
  • High-pressure catalytic combustion of gasified biomass in a hybrid combustor
  • 2005
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 293:1-2, s. 129-136
  • Tidskriftsartikel (refereegranskat)abstract
    • Catalytic combustion of synthetic gasified biomass was conducted in a high-pressure facility at pressures ranging from 5 to 16 bars. The catalytic combustor design considered was a hybrid monolith (400 cpsi, diameter 3.5 cm, length 3.6 cm and every other channel coated). The active phase consisted of 1 wt.% Pt/gamma-Al2O3 With wash coat loading of total monolith 15 wt.%. In the interpretation of the experiments, a twodimensional boundary layer model was applied successfully to model a single channel of the monolith. At constant inlet velocity to the monolith the combustion efficiency decreased with increasing pressure. A multi-step surface mechanism predicted that the flux of carbon dioxide and water from the surface increased with pressure. However, as the pressure (i.e. the Reynolds number) was increased, unreacted gas near the center of the channel penetrated significantly longer into the channel compared to lower pressures. For the conditions studied (lambda = 46, T-in = 218-257 degrees C and residence time similar to 5 ms), conversion of hydrogen and carbon monoxide were diffusion limited after ignition, while methane never ignited and was kinetically controlled. According to the kinetic model surface coverage of major species changed from CO, H and CO2 before ignition to O, OH, CO2 and free surface sites after ignition. The model predicted further that for constant mass flow combustion efficiency increased with pressure, and was more pronounced at lower pressures (2.5-10 bar) than at higher pressures (> 10 bar).
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22.
  • Barrientos, Javier, et al. (författare)
  • CO methanation over TiO2-supported nickel catalysts : A carbon formation study
  • 2015
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 502, s. 276-286
  • Tidskriftsartikel (refereegranskat)abstract
    • A systematic study on titania-supported nickel catalysts was performed in order to evaluate the effect of different process conditions on catalyst stability. Reaction tests and temperature-programmed-hydrogenation analyses were used in order to evaluate the effect of temperature, feed composition, water and reduction conditions on catalyst deactivation and carbon deposition. It was shown that high H-2/CO ratios and syngas partial pressures decrease the rate of carbon formation. Moreover, increasing temperature enhanced the formation of more stable carbon species and thus catalyst deactivation. The temperature-programmed hydrogenation analyses also revealed that water reduces the rate of carbon deposition. However, water enhanced catalyst deactivation when the catalysts were reduced at high temperatures. This negative effect of water is probably due to a progressive destruction of the strong-metal-support interaction characteristic of titania-supported nickel catalysts reduced at high temperatures. (C) 2015 Elsevier B.V. All rights reserved.
  •  
23.
  • Barrientos, Javier, et al. (författare)
  • Deactivation of supported nickel catalysts during CO methanation
  • 2014
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 486, s. 143-149
  • Tidskriftsartikel (refereegranskat)abstract
    • Deactivation of Ni-based catalysts was investigated during CO methanation over different supported catalysts. X-ray diffraction and temperature-programmed hydrogenation analyses were used to investigate nickel particle sintering and carbon formation during the first 24 h on stream. Titania-supported catalysts presented high resistance towards carbon deposition and nickel particle growth in comparison with the other tested catalysts. Particle size effects on these two deactivation causes were also evaluated. It was shown that carbon formation rates are higher on bigger crystal particles. However, it was found that titania-supported nickel catalysts reduced at high temperatures show the opposite effect. This difference is most probably due to a stronger interaction between nickel and TiOx (x < 2) species on smaller crystals which changes the CO dissociation properties and, in consequence, carbon formation rates.
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24.
  • Barrientos, Javier, et al. (författare)
  • The effect of catalyst pellet size on nickel carbonyl-induced particle sintering under low temperature CO methanation
  • 2016
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 514, s. 91-102
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract The present work aims to evaluate the effect of catalyst pellet size on deactivation due to nickel carbonyl-induced particle sintering. For that purpose, a γ-Al2O3-supported nickel catalyst was prepared and tested under low temperature and high CO partial pressure. A total of four different pellet sizes were employed in the present study. It was found that the deactivation rate decreases with increasing pellet size. A very severe deactivation was observed when using small pellets. Large pellets exhibited instead a more stable performance. This difference in catalyst stability was explained by X-ray diffraction analyses which revealed that the growth of the nickel particles was very severe when using small pellets. An evaluation of heat and mass transfer phenomena in these four pellets was also conducted. It was found that, under the present low temperature reaction conditions, the temperature at the catalyst external surface can greatly differ from that in the bulk gas when using sufficiently large pellets. It was also shown that, for large pellets, the major part of the interior of the catalyst is exposed to negligible CO partial pressures and high temperatures, fact that can reduce the potential for nickel carbonyl formation.
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25.
  • Björk, Emma, et al. (författare)
  • Mesoporous silica and carbon based catalysts for esterification and biodiesel fabrication-The effect of matrix surface composition and porosity
  • 2017
  • Ingår i: Applied Catalysis A. - : ELSEVIER SCIENCE BV. - 0926-860X .- 1873-3875. ; 533, s. 49-58
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of catalyst matrix porosity composition on the catalytic performance have been studied using sulfonated mesoporous SBA-15 silica. The matrix was sulfonated with three different methods grafting, in situ oxidation, and carbon infiltration. Additionally, unordered sulfonated mesoporous carbon, and the commercial catalysts Amberlite IR-120 and Nafion 117 were tested. The catalytic performance was evaluated in a Fischer esterification using acetic acid and ethanol, as well as in a transesterification of triglycerides (sunflower oil) and ethanol to produce biodiesel. The study shows that for long carbon chains, the effective wetting of the porous catalyst matrix by the reactants is most important for the catalytic efficiency, while for shorter carbon chain, the mass transport of the reagents trough the porous structure is more important. The catalysts were analysed using electron microscopy and physisorption. The study shows that the reactions are faster with carbon infiltrated materials than the silica materials due to a higher concentration of sulfonic groups linked to the carbon. The in situ functionalized SBA-15 is a more efficient catalyst compared to the post grafted one. All the synthesized catalysts outperform the commercial ones in both reactions in terms of conversion. (C) 2017 Elsevier B.V. All rights reserved.
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26.
  • Bukhanko, Natalia, et al. (författare)
  • Gas phase synthesis of isopropyl chloride from isopropanol and HCl over alumina and flexible 3-D carbon foam supported catalysts
  • 2017
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 542:25, s. 212-225
  • Tidskriftsartikel (refereegranskat)abstract
    • Isopropyl chloride synthesis from isopropanol and HCl in gas phase over ZnCl2 catalysts supported on Al2O3 as well as flexible carbon foam was studied in a continuous reactor. A series of catalytic materials were synthesised and characterised by BET, XPS, SEM, TEM, XRD and NH3-TPD methods. Catalytic activity tests (product selectivity and conversion of reactants) were performed for all materials and optimal reaction conditions (temperature and feedstock flow rates) were found. The results indicate that the highest yield of isopropyl chloride was obtained over 5 wt.% ZnCl2 on commercial Al2O3 (No. II) (95.3%). Determination of product mixture compositions and by-product identification were done using a GC-MS method. Carbon foam variant catalyst, 5 wt.% ZnCl2/C, was found to perform best out of the carbon-supported materials, achieving ∼75% yield of isopropyl chloride. The kinetic model describing the process in a continuous packed bed reactor was proposed and kinetic parameters were calculated. The activation energy for the formation of isopropyl chloride reaction directly from isopropanol and HCl was found to be ∼58 kJ/mol.
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27.
  • Chaoquan, Hu, 1981, et al. (författare)
  • Methyl crotonate hydrogenation over Pt: Effects of support and metal dispersion
  • 2016
  • Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 511, s. 106-116
  • Tidskriftsartikel (refereegranskat)abstract
    • Gas-phase hydrogenation of methyl crotonate (MC) has been studied over Pt supported on Al2O3, C, SiO2,and TiO2. The physicochemical properties of the catalysts were characterized by use of N2 physisorption,transmission electron microscopy and CO chemisorption. The effects of Pt dispersion and nature of the support on the catalytic properties of the catalysts were determined by measurements of the kinetic parameters for MC hydrogenation. The results clearly display MC inhibition effects on the hydrogenation over the catalysts. However, the degree of MC-inhibition is found to depend on both the Pt dispersion and the support used. For alumina a high Pt dispersion can promote the resistance of the catalyst against MC-inhibition, and even allow hydrogen adsorption to become equilibrated on the Pt surface. Compared to SiO2 and C supports, Al2O3 improves the resistance of the Pt surface against MC inhibition, whereas TiO2reduces the resistance. Possible reasons are suggested to understand the positive effect of Al2O3 on Pt against MC inhibition.
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28.
  • Creaser, Derek, 1966, et al. (författare)
  • Modeling study of 5 kWe-scale autothermal diesel fuel reformer
  • 2011
  • Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 404, s. 129-140
  • Tidskriftsartikel (refereegranskat)abstract
    • A model was developed that successfully describes key operating features of a 5 kWe-scale autothermal diesel fuel reformer with an engineered monolith-supported Rh based catalyst. The model consisted of a kinetic model comprised of four overall reactions including total oxidation, fuel steam reforming, methane formation via fuel decomposition and the water–gas shift reaction. The model also accounted for heat and mass transport effects that were of importance when coupling the exothermic oxidation reactions with endothermic steam reforming reactions in a full-scale reformer. According to the model, the total oxidation and steam reforming reactions occurred simultaneously, however the heat effects of the oxidation reaction dominated near the reactor inlet resulting in a local hot spot. Transport resistances were found to hinder the rates of the main reactions, especially at higher temperature operating conditions. The model was primarily based on experimental data for a commercial low-sulphur diesel fuel (MK1), however it was found to also reasonably well describe the operation of the reactor with a diesel surrogate (n-tetradecane).
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29.
  • Danish, Muhammad, et al. (författare)
  • An efficient catalytic degradation of trichloroethene in a percarbonate system catalyzed by ultra-fine heterogeneous zeolite supported zero valent iron-nickel bimetallic composite
  • 2017
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 531, s. 177-186
  • Tidskriftsartikel (refereegranskat)abstract
    • Zeolite supported nano iron-nickel bimetallic composite (Z-nZVI-Ni) was prepared using a liquid-phase reduction process. The corresponding surface morphologies and physico-chemical properties of the Z-nZVI-Ni composite were determined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Energy dispersive X-ray spectra (EDS), Brunauer Emmett Teller (BET) adsorption, wide angle X-ray diffractometry (WA-XRD), and Fourier transform infrared spectroscopy (FTIR). The results indicated high dispersion of iron and nickel nano particles on the zeolite sheet with an enhanced surface area. Complete destruction of trichloroethene (TCE) and efficient removal of total organic carbon (TOC) were observed by using Z-nZVI-Ni as a heterogeneous catalyst for a Fenton-like oxidation process employing sodium percarbonate (SPC) as an oxidant. The electron spin resonance (ESR) of Z-nZVI-Ni verified the generation and intensity of hydroxyl radicals (OH center dot). The quantification of OH center dot elucidated by using p-chlorobenzoic acid, a probe indicator, confirmed the higher intensity of OH center dot. The transformation products were identified using GC-MS. The slow iron and nickel leaching offered higher stability and better catalytic activity of Z-nZVI-Ni, demonstrating its prospective long term applications in groundwater for TCE degradation. (C) 2016 Elsevier B.V. All rights reserved.
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30.
  • Danwittayakul, Supamas, et al. (författare)
  • Enhanced hydrogen selectivity via photo-engineered surface defects for methanol steam reformation using zinc oxide-copper nanocomposite catalysts
  • 2014
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 471, s. 63-69
  • Tidskriftsartikel (refereegranskat)abstract
    • Methanol steam reformation (MSR) to produce hydrogen (H-2) gas using copper on zinc oxide (Cu/ZnO) supported catalysts is attractive due to the simple and low cost preparation process of the catalyst. H-2 yield from MSR is proportional to total catalyst loading which can be tuned during catalyst preparation. By creating UV-c light induced surface defects on ZnO nanorods, we have shown improved copper (Cu) nano-particle distribution on the ZnO nanorods leading to better H-2 yield. Increase in Cu nanoparticle adsorption is achieved by in situ reduction of Cu ions by photo-generated electrons, facilitated by ZnO surface defects that act as high energy sites favorable for Cu ion adsorption and their subsequent growth into nanoparticles. The modulated Cu/ZnO catalyst increases H-2 selectivity by 57% along with a corresponding increase in CO content, which can be controlled by adjusting H2O:MeOH ratio in the precursor solution.
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31.
  • DAWODY, JAZAER, 1959, et al. (författare)
  • Platinum dispersion measurements for Pt/BaO/Al2O3, NOx storage catalysts
  • 2005
  • Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 296:2, s. 157-168
  • Tidskriftsartikel (refereegranskat)abstract
    • In this investigation different experimental methods to determine the platinum dispersion of Pt/BaO/Al2O3 NOx storage catalysts are compared. The dispersion of platinum is determined independently using temperature programmed desorption of CO, dissociation of N2O, static volumetric CO and H2 chemisorption, dynamic CO chemisorption and transmission electron microscopy. For Pt/BaO/Al2O3, reproducible results are obtained when the platinum dispersion is determined from N2O dissociation, CO and H2 chemisorption. However, repeated CO-TPD experiments result in decreased amount of desorbed CO, which limits this method to determine platinum dispersion for Pt/BaO/Al2O3 samples. For Pt/Al2O3, similar values for platinum dispersion are obtained for all methods used in the study.In addition to the platinum dispersion investigations, the surface morphology of Pt/BaO/Al2O3 samples and the distribution of different elements are studied using SEM-EDS. The SEM-EDS analyses show that the platinum is evenly distributed over the entire sample surface, while the distribution of barium is more uneven.
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32.
  • Eriksson, Sara, et al. (författare)
  • Catalytic combustion of methane in steam and carbon dioxide-diluted reaction mixtures
  • 2006
  • Ingår i: Applied Catalysis. - : Elsevier BV. - 0166-9834 .- 1873-3867. ; 312, s. 95-101
  • Tidskriftsartikel (refereegranskat)abstract
    • Supported palladium catalysts have been tested for methane combustion under lean conditions in the temperature range of 200-800 degrees C. The effect of diluting the reaction mixture with high amounts of water and carbon dioxide was studied in order to simulate a combustion process with exhaust gas recirculation. The influence of support material, i.e. ZrO2 or doped CeO2, on the catalytic performance was also investigated. The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order: Pd/ZrO2 < Pd/Zr-CeO2 < Pd/La-CeO2. The order of activity changed at higher temperatures resulting in Pd/La-CeO2 being the most active catalyst above 670 degrees C. This catalyst also shows a more stable performance with no distinct deactivation occurring at higher temperatures during cooling. Both water and CO2 were found to have a negative influence on the catalytic activity. The inhibitory effect was, however, more pronounced for water. This inhibitory effect was present in the entire temperature range investigated. Adding CO2 in the presence of water resulted in conversions similar to the ones observed when feeding water alone for Pd/ZrO2 and Pd/La-CeO2, On the contrary, the activity of Pd/Zr-CeO2 was further decreased when co-feeding water and CO2.
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33.
  • Eriksson, Sara, et al. (författare)
  • Effect of Ce-doping on Rh/ZrO2 catalysts for partial oxidation of methane
  • 2007
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 326:1, s. 8-16-
  • Tidskriftsartikel (refereegranskat)abstract
    • The partial oxidation of methane over supported (ZrO2, CeO2-ZrO2) rhodium catalysts was investigated at atmospheric pressure. The effect of temperature, CH4/O-2 ratio, catalyst composition and pre-treatment was studied. Ceria doping of the support material resulted in significant improvements concerning the methane conversion and syngas selectivity, which could be related to a higher noble metal dispersion on the Rh/CeO2-ZrO2 catalyst. In addition, the light-off temperature was decreased by 128 degrees C when using CeO2-ZrO2, as support. X-ray photoelectron spectroscopy revealed the presence of different Rh oxidation states depending on catalyst composition and pre-treatment. A stabilization of partially oxidized (Rh delta+) species by ceria could be detected. An active and stable catalyst behavior could be observed for Rh/CeO2-ZrO2, irrespectively of catalyst pre-treatment, whereas an activation period was required for stabilizing the activity of the Rh/ZrO2 catalyst. The activity tests indicate that the indirect reaction mechanism, consisting of methane combustion followed by steam and dry reforming, prevails under the experimental conditions studied.
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34.
  • Eriksson, Sara, et al. (författare)
  • Preparation of catalysts from microemulsions and their applications in heterogeneous catalysis
  • 2004
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 265:2, s. 207-219
  • Tidskriftsartikel (refereegranskat)abstract
    • Microemulsions have a wide range of applications from oil recovery to synthesis of nanoparticles. The first implementation of water-in-oil (w/o) microemulsions for synthesis of nanoparticles was introduced in 1982 and concerns nanoparticles of noble metals for catalytic uses. Since this time, the method has been employed quite extensively in the field of catalysis, from room-temperature reactions such as butene isomerisation to high-temperature reactions such as catalytic combustion of methane.The present review paper will introduce the term microemulsion with emphasis on the microemulsion properties essential for heterogeneous catalyst preparation followed by a general description of the mode of catalytic materials prepared from microemulsions. Several examples of the use of these materials in heterogeneous catalysis are then described. It is shown that nanoparticles obtained from microemulsions have specific properties with respect to size, size distribution and surface structure. Consequently, these particles are in some cases superior regarding catalytic activity and/or selectivity
  •  
35.
  • Eta, Valerie, et al. (författare)
  • Kinetics of dimethyl carbonate synthesis from methanol and carbon dioxide over ZrO2–MgO catalyst in the presence of butylene oxide as additive
  • 2011
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 404:1-2, s. 39-46
  • Tidskriftsartikel (refereegranskat)abstract
    • A kinetic investigation of dimethyl carbonate (DMC) synthesis from methanol and CO2 over ZrO2–MgO was performed by using butylene oxide as a chemical trap for the water formed during the reaction. The effect of the catalyst amount, the stirring speed, the temperature, as well as the amount of butylene oxide on the reaction rate and the selectivity to DMC was studied. The analysis of the reaction pathway suggests that DMC and butylene glycol are formed via the reaction of adsorbed mono-methoxycarbonate intermediate and methoxybutanol or methanol. A kinetic model was developed based on the reaction mechanism and it was in agreement with the experimental data. The apparent activation energy for the formation of DMC was 62 kJ/mol.
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36.
  • Farooq, U., et al. (författare)
  • Efficient transformation in characteristics of cations supported-reduced graphene oxide nanocomposites for the destruction of trichloroethane
  • 2017
  • Ingår i: Applied Catalysis A. - : Elsevier B.V.. - 0926-860X .- 1873-3875. ; 544, s. 10-20
  • Tidskriftsartikel (refereegranskat)abstract
    • Experiments were conducted to investigate the use of graphene-oxide supported metallic nanocomposites for improving the degradation of trichloroethane (TCA) by sodium percarbonate (SPC). Two methods of production, chemical reduction (CR) and solvo-thermal (ST), were tested for preparation of single (Fe) and binary (Fe-Cu) nanocomposites supported by reduced graphene oxide (rGO). A variety of analytical techniques including N2 adsorption Brunauer-Emmett-Teller (BET), x-ray diffraction (XRD), fourier-transfrom infrared spectroscopy (FTIR), and transmisison electron microscopy (TEM) were applied to characterize the physicochemical and microstructural properties of the synthesized nanocomposites. The characterization indicated that the CR method produced nanocomposites that comprised only mesoporous structure. Conversely, both micro and mesoporous structures were present for samples produced with the ST method. The synthesized single and bimetallic composites produced from the ST method showed higher surface areas, i.e. 93.6 m2/g and 119.2 m2/g as compared to the ones synthesized via the CR method, i.e. 13.8 m2/g and 38.0 m2/g respectively. The results of FTIR and XRD analyses confirmed that the ST method produced highly crystalline nanocomposites. SEM and TEM analysis validated that metallic particles with definite morphology well distributed on the surface of rGO. X-ray photoelectron spectroscopy (XPS) analysis confirmed the homogeneity nanocomposites and occurrence of variation in copper oxidation states during degradation process. EDS mapping validate the homogeneous distribution of Cu and Fe at reduced graphene oxide surface. The Fe-Cu/rGO (ST) activated SPC system effectively degraded TCA (92%) in 2.5 h at low nanocomposite dose compared to the Fe-Cu/rGO (CR) and only Fe, for which the maximum degradation efficiencies achieved were 81% and 34%. In conclusion, excellent catalytic characteristics were observed for the ST-synthesized single and bimetallic (Fe/rGO, Fe-Cu/rGO) catalysts. These catalysts were successful in improving the degradation of TCA via activated SPC. 
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37.
  • Garlisi, Corrado, et al. (författare)
  • E-beam evaporated TiO2 and Cu-TiO2 on glass : Performance in the discoloration of methylene blue and 2-propanol oxidation
  • 2016
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 526, s. 191-199
  • Tidskriftsartikel (refereegranskat)abstract
    • TiO2 and Cu-TiO2 thin films were deposited by e-beam evaporation and then annealed at 350 and 500 degrees C. Their structure, surface morphology and optical properties were studied by X-ray diffraction, scanning electron microscopy, cross-sectional TEM, UV-vis, FT-IR spectroscopy and X-ray absorption spectroscopy. A single-phase source material was used for the first time in the deposition process, thus avoiding preferential evaporation of Cu with respect to TiO2, and resulting in an even concentration of Cu in the doped films. The photocatalytic activity was evaluated by degradation of pre-adsorbed methylene blue (MB) in dry conditions and gaseous 2-propanol in oxygen atmosphere under visible and simulated solar light, respectively. Results suggested that high surface hydroxylation of the as-deposited films is an important factor for MB oxidation occurring through a dye-sensitized mechanism activated by visible light absorption. Conversely, the rate of photodegradation of 2-propanol is enhanced in annealed samples due to the greater crystallinity and less electron-hole recombination, with the TiO2 annealed at 500 degrees C being the most efficient photocatalyst. However, Cu-doped samples resulted the most active samples during the degradation of MB under visible radiation. Finally, the performance at increasing thickness (250, 500, 1000, up to 2000 nm) was tested for the most reactive films revealing a marked rise in photocatalytic activity up to 1000 nm.
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38.
  • Golets, Mikhail, 1987-, et al. (författare)
  • Liquid phase acetoxylation of α-pinene over Amberlyst-70 ion-exchange resin
  • 2012
  • Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 435-436, s. 43-50
  • Tidskriftsartikel (refereegranskat)abstract
    • Heterogeneously-catalyzed and solvent-catalyzed liquid phase acetoxylation of α-pinene with acetic acid acting as both a solvent and a reagent was studied. Both solvent-catalyzed and catalytic experiments were carried out and various reaction conditions were studied. The influence of temperature, pressure, solvent and gas milieu were taken into account. Bornyl, fenchyl, verbenyl as well as α-terpinyl acetates, limonene, camphene and γ-terpinene were found among reaction products. The addition of the catalyst allowed for maximization of the yield of bornyl acetate. The predominant products obtained were α-terpinyl, verbenyl and bornyl acetates. The reaction pathways were identified and evaluated. The aim of this work was to study the feasibility of batch acetoxylation of α-pinene. The analysis of the complex product distribution is not trivial and, consequently, resolving the reaction network was important. The optimized reaction conditions were searched for aiming at an efficient conversion of α-pinene to a mixture of valuable products.
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39.
  • González Arcos, Angélica Viviana, et al. (författare)
  • Promoted RhPt bimetallic catalyst supported on δ-Al2O3 and CeO2-ZrO2 during full-scale autothermal reforming for automotive applications: Post-mortem characterization
  • 2015
  • Ingår i: Applied Catalysis A. - : Angélica González. - 0926-860X .- 1873-3875. ; 491, s. 8-16
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of sulfur and coke formation on the steam reforming of diesel was evaluated for two promoted RhPt bimetallic catalysts, composed of 1:1 Rh:Pt/10:10 La2O3: CeO2/ δ-Al2O3 (CAT 1) and 1:1 Rh:Pt/4:5 MgO: Y2O3/CeO2 − ZrO2 (CAT 2). The intrinsic activity is related to the total Rh and Pt area observed after the exposure to sulfur. Therefore, the degree of deactivation is related to the amount of sulfur deposited on the active metal sites. Sulfur analysis on the aged catalyst washcoat showed a decreasing sulfur concentration in the axial direction of the reformer. The estimated sulfur coverage related to metal surface area after 40 h on stream reached values of 0.145 in CAT 2, below the equilibrated sulfur coverage of 0.19 after tests with DIN 590. Thus, showing a partial deactivation due to sulfur poisoning. Further catalyst characterization on carbon deposits and thermal aging was performed by TPO, TGA, BET, CO chemisorption, and TEM analysis.
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40.
  • Guo, X. W., et al. (författare)
  • Effects of SiO2/Al2O3, MgO modification and hydrothermal treatment on the catalytic activity of HZSM-5 zeolites in the methylation of 4-methylbiphenyl with methanol
  • 2004
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 261:2, s. 183-189
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of this work is to study the effects Of SiO2/Al2O3 of HZSM-5, MgO modification and hydrothermal treatment on methylation of 4-methylbiphenyl (4-MBP) with methanol under fixed-bed down-flow conditions. The results show that, with an increase in the SiO2/Al2O3 of HZSM-5 (from 50 to 150, molar ratio), the selectivity to 4,4'-dimethylbiphenyl (4,4'-DMBP) increases from 25 to 79%. MgO modification also increases the selectivity to 4,4'-DMBP, but leads as well to low catalyst activity and rapid deactivation. Hydrothermal treatment not only increases the selectivity, but also improves the stability. When CBV1502 (SiO2/Al2O3 = 150) catalyst was hydrothermally treated at 500degreesC, the selectivity to 4,4'-DMBP increased to 85%. The selectivity to 4,4'-DMBP was further improved to about 90% by the increasing in the amount of mesitylene in the feed as solvent.
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41.
  • Holmberg, Johan, et al. (författare)
  • Catalytic behaviour of M1, M2, and M1/M2 physical mixtures of the Mo-V-Nb-Te-oxide system in propane and propene ammoxidation
  • 2004
  • Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 0926-860X. ; 270:1-2, s. 121-134
  • Tidskriftsartikel (refereegranskat)abstract
    • Essentially pure orthorhombic M1 and pseudo-hexagonal M2 phases were prepared using the precursor method. Consistent with literature the M1 phase was shown to be effective for propane ammoxidation to acrylonitrile while the M2 phase was essentially inert for propane activation. Both phases convert propene efficiently to acrylonitrile. Both phases show a significant selectivity dependence on the ammonia and oxygen concentrations in the feed, revealing thereby additional insights into the reaction mechanism. Physical mixtures of the two separately prepared phases exhibited symbiosis in the ammoxidation of propane when finally divided (similar to5 mum), thoroughly mixed and brought into intimate contact with each other. Acrylonitrile yields significantly higher than those obtained with the M1 phase alone were demonstrated with a 50 wt.% M1/50 wt.% M2 physical mixture having a corresponding Surface area ratio of about 4:1. The phase cooperation effect is particularly large at high propane conversions and non-existent when the particle size of the phases is too large (e.g. >250 mum) and the inter-particle contact is poor. Published by Elsevier B.V.
  •  
42.
  • Jogunola, Olatunde, et al. (författare)
  • Qualitative treatment of catalytic hydrolysis of alkyl formates
  • 2010
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 384:1-2, s. 36-44
  • Tidskriftsartikel (refereegranskat)abstract
    • Liquid-phase hydrolysis of alkyl formates was performed in a stirred batch reactor using formic acid as a homogenous catalyst, cation exchange resin as heterogeneous catalyst and an additive as a complexation agent. The catalysts increased the rate of the reaction considerably, but the equilibrium conversion was slightly suppressed by the homogenous catalyst. The additive not only accelerated the reaction rate, but also improved the yield significantly. The effect of external and internal mass transfer limitations present in the heterogeneous reaction steps was investigated and it was observed that there is the existence of internal diffusion limitation for the largest catalyst particles. Other parameters such as temperature, catalyst pre-treatment, catalyst loading and stirring speed were investigated in order to optimize the process. The experiments also demonstrated that the ion exchange resin can be reused more than once.
  •  
43.
  • Jonsson, Rasmus, 1989, et al. (författare)
  • Chemical poisoning by zinc and phosphorous of Pt/Ba/Al2O3 NOx storage catalysts
  • 2019
  • Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 571, s. 158-169
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of phosphorous and zinc on the performance of Pt/Ba/Al2O3 catalysts were investigated through wet impregnation of ammonium phosphate and zinc acetate aqueous solutions. Six different sample combinations were studied; 1 wt-% P, 1 wt-% Zn, 1 wt-% P with 1 wt-% Zn, 2 wt-% P, 2 wt-% Zn, 2 wt-% P with 2 wt-% Zn. NOx storage and reduction (NSR) activity and NO2 temperature programmed desorption (TPD) profiles were measured before and after impregnation of P and Zn. Samples containing P performed significantly worse than samples only containing Zn in both NSR activity and TPD measurements. The increased NOx slip during lean phase in activity measurements for P-poisoned samples is mainly related to an increased slip of NO2. This was found for both NO and NO2 in the gas feed during lean phase and suggests that it is mainly the storage component that is poisoned and not the noble metal. Furthermore, the combination (1 wt-% P and 1 wt-% Zn) proved to result in slightly worse performance than only 1 wt-% P, however this was not the case for samples containing 2 wt-%, where the addition of zinc reduced the negative effect of phosphorous. Measurements from NO2-TPD experiments showed that NOx release at low temperature was not affected by the addition of P, while desorption in the temperature range 425–475 °C was significantly reduced. It can therefore be concluded that the poisoning mainly is related to barium NOx storage sites and not to alumina sites. Moreover, X-ray diffraction measurements indicate that some of the barium species are affected by phosphorous. Images from scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX) mapping were in line with the results seen in both the activity tests and NO2-TPD experiments. Phosphorous was concentrated at the same position as barium in the observed images, whereas zinc was more evenly distributed over the surface. For the sample with both 2 wt-% P and 2 wt-% Zn, X-ray photoelectron spectroscopy measurements indicate that Zn and P have a low interaction and this suggests that most of the zinc and phosphorous are separated. However, STEM-EDX showed agglomerates of some zinc and phosphorous, which could be zinc phosphates. This is a plausible explanation of the decreased deactivation observed after introducing 2 wt-% Zn compared to the sample only containing 2 wt-% P.
  •  
44.
  • Keller, Martin, 1985, et al. (författare)
  • Chemical Looping Tar reforming with Fe,Sr-doped La2Zr2O7 pyrochlore supported on ZrO2
  • 2018
  • Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 550, s. 105-112
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemical Looping Reforming (CLR) has been proposed as a new technology for tar removal from hot raw gas derived from biomass gasification. In this two-reactor fluidized bed process at atmospheric pressure, the bed material is circulating between a reformer, in which the bed material is in contact with the raw synthesis gas, and a regenerator, in which the bed material is regenerated by oxidizing coke deposits and sulfides with air. In this study Fe,Sr-doped La 2 Zr 2 O 7 pyrochlores supported on ZrO 2 with different Fe and Sr loadings were investigated for their use as a catalyst in CLR. By decreasing the Fe loading to Fe/La = 0.25 the benzene-to-syngas conversion could be improved by about 50% at T = 800 °C in comparison with the reference material with Fe/La = 1.25. With this material, benzene and ethylene conversion could be further improved by co-feeding O 2 with the gasification gas, achieving a benzene conversion of up to 80% and an ethylene conversion of about 95% at a temperature of 850 °C and a Gas Hourly Space Velocity of 6800 h −1 . The performance of the bed material was found stable over at least 3 redox cycles. Considering the expected lower costs and non-toxicity of this material compared to precious metal- and Nickel-containing catalysts, normally used in fixed-bed systems, it is a promising material for a fluidized CLR system for tar removal.
  •  
45.
  • Kirilin, Alexey V, et al. (författare)
  • Aqueous phase reforming of xylitol and sorbitol : comparison and influence of substrate structure
  • 2012
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 435-436, s. 172-180
  • Tidskriftsartikel (refereegranskat)abstract
    • The behavior of abundant polyol stemming from hemicelluloses, xylitol, was investigated in the aqueous phase reforming (APR) over supported Pt/Al2O3. The data obtained in the case of xylitol was compared to aqueous phase reforming of sorbitol under the same operating conditions. The effect of weight hour space velocity on the performance of a catalytic system as well as on selectivity towards hydrogen and alkanes was studied. The catalyst showed stable performance with insignificant deactivation over 160 hours time-on-stream. The selectivity towards H2 diminished from 86 to 70% within 120 hours. The regeneration of the catalytic system in a H2 flow allowed to recover the catalyst activity and to improve selectivity towards H2 to 75%. It was found that both polyols demonstrated similar behavior in the APR in the whole range of space velocities studied. The selectivity towards H2 went through a maximum in the case of xylitol and sorbitol when changing a space velocity. This behavior was attributed to a number of side reactions which involved hydrogen thus leading to its consumption. Additionally, the yields of target APR product, hydrogen, were higher in the case of xylitol compared to sorbitol due to the longer carbon chain in the latter substrate. The plausible reaction network based on the hypothesis that APR process proceeds through the terminal position of polyol was proposed to explain similarity in the gas and liquid product composition in the APR of xylitol and sorbitol. The reaction scheme describing formation of the main gas and liquid products via various pathways was proposed and discussed. The results obtained and explanations provided are in perfect coincidence with the results obtained for different substrates in the literature.
  •  
46.
  • Konwar, Lakhya Jyoti, 1987-, et al. (författare)
  • Carbon support effects on metal (Pd, Pt and Ru) catalyzed hydrothermal decarboxylation/deoxygenation of triglycerides
  • 2022
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 638
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, we show that textural properties of carbon supports have limited influence on the activity and stability of carbon supported Pd, Pt and Ru catalysts upon decarboxylation of a model triglyceride (tristearin) in the presence of subcritical water (256–326 °C). In contrast, surface acid-base properties of carbon supports were found to have a marked impact on the performance and stability of these catalysts. More precisely, for Pt group (Pt and Pd) a positive correlation could be observed between the concentration of surface basic sites and catalyst deoxygenation activity and durability while acid sites had the opposite effect. On the other hand, the activity of Ru-based catalysts were not analogously affected by the acid-base properties of carbon supports, even so a positive correlation was found between surface basicity and durability (reusability). Further, the activity of metals in decreasing order of TOF was Ru>Pt>Pd, irrespective of carbon support.
  •  
47.
  • Kopyscinski, J., et al. (författare)
  • Synthetic natural gas from wood: Reactions of ethylene in fluidised bed methanation
  • 2013
  • Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 462-463, s. 150-156
  • Tidskriftsartikel (refereegranskat)abstract
    • The synthesis step in the production of synthetic natural gas from wood, i.e. the methanation, was investigated by systematic experiments with commercial nickel catalyst in a micro-fluidised bed reactor. Ethylene in the feed is always converted completely; dominantly serial reactions of ethylene to ethane and further to methane under isothermal fluidised bed methanation conditions could be shown. Lower temperatures favour the production of the intermediate ethane while high temperatures cause the formation of carbon depositions and carbon whiskers. Applying optimal operation conditions, the hydrogenation of the unsaturated olefin not only avoids the deposition of carbon or coke, but also leads to an increase of the higher heating value (HHV) of the produced (raw) SNG. © 2013 Elsevier B.V. All rights reserved.
  •  
48.
  • Kumar, N., et al. (författare)
  • Bi-reforming of methane on Ni-based pyrochlore catalyst
  • 2016
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 517, s. 211-216
  • Tidskriftsartikel (refereegranskat)abstract
    • A Ni-based pyrochlore catalyst was synthesized using the modified Pechini method. In this method, 1 wt% Ni was doped into the La2Zr2O7 pyrochlore structure. The catalyst was characterized by H2-TPR, TPO, XRD, and EXAFS, and tested for its methane reforming activity under bi-reforming reaction conditions; i.e.; in the presence of CO2 and steam: 3CH4+CO2+2H2O⇌4CO+8H2 Repeated TPR/TPO cycles showed that the two consecutive TPR spectra do not change, showing that the catalyst is stable at high temperatures, and that the nickel oxidation/reduction process is reversible. The catalyst showed constant activity with time at all temperatures in the range of 700-950 °C over a cumulative period of 170 h. After this series of bi-reforming tests, TPO of the spent catalyst was carried out, which showed detectable but unquantifiable carbon deposition. The presence of steam in bi-reforming greatly limits carbon deposition compared to directly related dry-reforming tests on this same catalyst.
  •  
49.
  • Lanza, Roberto, et al. (författare)
  • Methane partial oxidation over Pt-Ru catalyst : An investigation on the mechanism
  • 2010
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 375:1, s. 92-100
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanism of the partial oxidation of methane has been investigated over a bimetallic Pt-Ru catalyst. Dedicated experiments aimed to separate and quantify the relative contribution of single reactions included in the so-called "combustion and reforming" mechanism using the same catalyst. The catalyst is 0.5% Ru and 0.5% Pt (w/w) supported on mixture of alumina, ceria and zirconia (75/4.4/20.6%, w/w), washcoated on a ceramic monolith. Steam reforming, dry reforming, direct and reverse water-gas shift reactions were investigated. The temperature range investigated is 300 < T < 800 degrees C, while the space velocity range is 25.000 < GHSV < 100.000 h(-1). Conditions at which single side reactions are expected to occur during the partial oxidation process, were approximated by tuning the reactant composition. The experimental results are also compared with thermodynamic equilibrium calculations. The CO and H-2 yields of partial oxidation have been quantitatively connected with steam and dry reforming, while the persistent water-gas shift reaction always rearranges the products and intermediates.
  •  
50.
  • Lanza, Roberto, et al. (författare)
  • Microemulsion-prepared ruthenium catalyst for syngas production via methane partial oxidation
  • 2008
  • Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 337:1, s. 10-18
  • Tidskriftsartikel (refereegranskat)abstract
    • Partial oxidation of methane (POxM) was studied over Ru catalyst supported on alumina (1%, w/w). The catalyst was prepared via microemulsion (ME) and coated onto cordierite monoliths. Samples were characterized by XRD, BET surface area, SEM-EDS and TPR and TPO analyses. The catalyst showed high methane conversion with very good selectivity towards CO and H-2 under every condition tested. The effects of GHSV and heating rate (HR) were investigated, recording composition data both during heating and cooling. This allowed to evidence hysteresis cycles and to obtain additional information on the reactions occurring within the monolith.
  •  
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