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1.
  • Amberntsson, Annika, 1974, et al. (författare)
  • Investigations of sulphur deactivation of NOx storage catalysts: influence of sulphur carrier and exposure conditions
  • 2002
  • Ingår i: Catalysis Today. - 0920-5861. ; 73:3-4, s. 279-286
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of SO2, H2S and COS in low concentrations on the deactivation of PURh/BaO/Al2O3 NOx storage catalysts was investigated. Different samples of the catalyst were exposed to synthetic gas mixtures mimicking lean/rich engine cycling in a mixed lean application at 400degreesC. The lean gas mixture contained 8 vol.% O2, 500 vol-ppm C3H6 and 400 vol-ppm NO balanced to 100 vol.% with Ar. The rich excursions were performed by switching off the oxygen supply. Sulphur, 25 vol-ppm of either SO2, H2S or COS, was added to the gas flow either during the lean, the rich or both periods. This procedure aimed at investigating the influence of the exposure conditions and therefore the lean and rich periods were kept equally long (5 min). In addition, thermodynamical calculations for the prevailing conditions were performed.
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2.
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3.
  • Blanco, J, et al. (författare)
  • Lean-DeNO(x) titania based monolithic catalysts
  • 1998
  • Ingår i: Catalysis Today. - 0920-5861. ; 45:1-4, s. 103-108
  • Tidskriftsartikel (refereegranskat)abstract
    • The activity of titania based copper and platinum monolithic catalysts in the reduction of nitrogen oxides was studied with exhaust gases from a Diesel engine injecting fuel as reductant. Combining both catalysts, a two-stage system was designed, studying the influence of the copper catalysts composition on its performance with synthetic gas mixtures. The influence of reactants concentration and operating conditions was also investigated. Taking into account these results, a double-bed system with a cell density of 33 cell cm(-2) (210 c.p.s.i.) was prepared. Linear velocity had a strong influence on the performance of the Pt catalyst and of the double-bed. Two NOx conversion maxima were observed with Pt/TiO2 at 225 degrees C and 350 degrees C operating at 6.6 m s(-1). Promising NOx conversions were achieved in the temperature range 200-450 degrees C. (C) 1998 Elsevier Science B.V. All rights reserved.
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4.
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5.
  • Carlsson, Per-Anders, 1972, et al. (författare)
  • Induced low temperature catalytic ignition by transient changes in the gas composition
  • 2002
  • Ingår i: Catalysis Today. - 0920-5861. ; 73:3-4, s. 307-313
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of gas composition changes on the low temperature activity for supported platinum model catalysts has been studied. By introducing well-controlled periodic O2 pulses to a simple diluted gas mixture of CO and O2, a substantial improvement of the low temperature oxidation activity was observed. The reason for low activity on noble metals at low temperatures is often attributed to self-poisoning by CO. The improved catalytic performance observed is proposed to origin from the transients causing a surface reactant composition that is favourable for the reaction rate, i.e. lower degree of self-poisoning. This was also confirmed by in situ Fourier transform infrared spectroscopy in combination with mass spectrometry measurements, which gave evidence for the existence of a strong interplay between the gas phase concentration and the adsorbate composition for these catalysts.
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6.
  • Hammarstrom, L., et al. (författare)
  • Mimicking photosystem II reactions in artificial photosynthesis : Ru(II)-polypyridine photosensitisers linked to tyrosine and manganese electron donors
  • 2000
  • Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 58:03-feb, s. 57-69
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper describes a project aiming at constructing functional mimics of the oxygen evolving complex in photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors, manganese complexes and tyrosine, have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photooxidised Ru(III) complex was demonstrated using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn(III,III)-->tyrosine-->Ru(III) was demonstrated, in analogy to the reaction on the donor side of photosystem II. Electron transfer from the tyrosine to Ru(III) was coupled to tyrosine deprotonation. This resulted in a large reorganisation energy and thus a slow reaction rate, unless the tyrosine was hydrogen bonded or already deprotonated. A comparison with analogous reaction in photosystem II is made. Finally, light-induced oxidation of a manganese dimer linked to a Ru(II)-photosensitiser was observed. Preliminary results suggest the possibility of photooxidising manganese dimers in several steps, which is an important step towards water oxidation,
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7.
  • Larsson, PO, et al. (författare)
  • Supported metal oxides for catalytic combustion of CO and VOCs emissions: Preparation of titania overlayers on a macroporous support
  • 1997
  • Ingår i: Catalysis Today. - 0920-5861. ; 35:1-2, s. 137-144
  • Tidskriftsartikel (refereegranskat)abstract
    • TiO2 (anatase), SiO2 and gamma-Al2O3 were used as supports for Co-, Cu-, Fe- and Mn-oxide with a loading of active phase corresponding to one theoretical layer. The catalysts were tested for the combustion of CO and toluene, and the best combinations with active phase and support were submitted to a deactivation test in a waste gas incinerator for 50 days. The catalyst screening showed that CuOx/TiO2 was the most promising system. To design a catalyst with good activity and transport properties, a macroporous substrate was coated with TiO2 for use as a support for Cu-oxide, Titania overlayers were prepared by precipitation from oxychloride, tetrachloride and alkoxide, and stabilisation with ZrO2 and SiO2 was tried. The results show that precipitation from oxychloride gives the best properties and that addition of ZrO2 gives enhanced activity to the catalyst, while SiO2 addition produces increased stability.
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8.
  • Nilsson, J, et al. (författare)
  • Catalysis and structure of the SbVO4/Sb2O4 system for propane ammoxidation
  • 1997
  • Ingår i: Catalysis Today. - 0920-5861. ; 33:1-3, s. 97-108
  • Tidskriftsartikel (refereegranskat)abstract
    • Pure Sb0.9V0.9O4 and various preparations with excess of either vanadia or antimony oxide, including mechanical mixtures, have been investigated for propane ammoxidation to acrylonitrile. The catalysts were characterized before and after use in catalysis by various methods, including electron microscopy, infrared spectroscopy and XPS. The catalytic data show that preparations with approximate to SbVO4 and alpha-Sb2O4, compared with the single phases, are more selective to acrylonitrile formation on the condition that the excess antimony oxide is present while synthesising the approximate to SbVO, phase. Considering the catalytic data together with the results from the characterisations, various possibilities are discussed to explain the role of excess alpha-Sb2O4 in propane ammoxidation. Possibilities that can be excluded on rational grounds are catalysis on two phases, or, at grain boundaries, an influence on the morphology of approximate to SbVO4 from alpha-Sb2O4, the formation of alpha-Sb2O4 containing vanadium, defect formation, creation of active sites by the spillover of oxygen, and formation of VSb2O5. Instead, the observed synergy effect is due to the formation of approximate to SbVO4 enriched with antimony at the surface, creating isolation to a suitable level of the V-centres. The explanation is consistent with several observations including catalytic data for a series of vanadium compounds with different vanadium content, showing that structural isolation of the vanadium is necessary for obtaining high selectivity to acrylonitrile.
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9.
  • Nilsson, Roland, et al. (författare)
  • The Transient Response Technique for the Study of Hydrocarbon Oxidation on Metal Oxides: Simulation of the Responses for Various Propene Oxidation Mechanism
  • 1996
  • Ingår i: Catalysis Today. - 0920-5861. ; 32:1-4, s. 11-20
  • Tidskriftsartikel (refereegranskat)abstract
    • Partial differential equations, describing the consumption of reactants and the formation of products, have been solved numerically for a step change from inert to reactant feed considering different variants of propene oxidation mechanisms. The response features and their dependency on the rate limiting step have been rationalised in terms of conclusions, which can serve as general guidelines for mechanistic interpretation of experimental transients from hydrocarbon oxidation over metal oxides. Though the response pattern is characteristic of the rate limiting step, it is demonstrated that different variants of mechanisms can give identical response features. In that case complementary investigation with other techniques, or more detailed mathematical analysis is necessary.
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10.
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11.
  • Olsson, Louise, 1974, et al. (författare)
  • Mean Field Modelling of NOx Storage on Pt/BaO/Al2O3
  • 2002
  • Ingår i: Catalysis Today. - 0920-5861. ; 73:3-4, s. 263-270
  • Tidskriftsartikel (refereegranskat)abstract
    • A mean field model, for storage and desorption of NOx in a Pt/BaO/Al2O3 catalyst is developed using data from flow reactor experiments. This relatively complex system is divided into five smaller sub-systems and the model is divided into the following steps: (i) NO oxidation on Pt/Al2O3; (ii) NO oxidation on Pt/BaO/Al2O3; (iii) NOx storage on BaO/Al2O3; (iv) NOx storage on Pt/BaO/Al2O3 with thermal regeneration and (v) NOx storage on Pt/BaO/Al2O3 with regeneration using C3H6. In this paper, we focus on the last sub-system. The kinetic model for NO, storage on Pt/BaO/Al2O3 was constructed with kinetic parameters obtained from the NO oxidation model together with a NO, storage model on BaO/Al2O3. This model was not sufficient to describe the NO, storage experiments for the Pt/BaO/Al2O3, because the NO, desorption in TPD experiments was larger for Pt/BaO/Al2O3, compared to BaO/Al2O3. The model was therefore modified by adding a reversible spill-over step. Further, the model was validated with additional experiments, which showed that NO significantly promoted desorption of NOx from Pt/BaO/Al2O3. To this NOx storage model, additional steps were added to describe the reduction by hydrocarbon in experiments with NO2 and C3H6. The main reactions for continuous reduction of NOx occurs on Pt by reactions between hydrocarbon species and NO in the model. The model is also able to describe the reduction phase, the storage and NO breakthrough peaks, observed in experiments.
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12.
  • Otamiri, J, et al. (författare)
  • Kinetics and mechanisms in the ammoxidation of toluene over a V2O5 catalyst. Part 1: Selective reactions
  • 1988
  • Ingår i: Catalysis Today. - 0920-5861. ; 3:2-3, s. 211-222
  • Tidskriftsartikel (refereegranskat)abstract
    • A thorough kinetic investigation of the ammoxidation of toluene over a V2O5 catalyst was carried out. Pressures of reactants were varied and rates for formation of benzonitrile and benzaldehyde were determined. Kinetic expressions completely describing experimental data were derived. A mechanisms is proposed on basis of both rate equations and other types of information published in the literature. The (010) plane of V2O5 is considered to be the active plane. An ensemble of 4 V=O species, having neighbouring vanadium ions exposed, is the active site. The rate-determining step for formation of aldehyde is the abstraction of a hydrogen atom from the methyl group. Nitrile is formed from two routes. In one of the routes, the active site reacts with one ammonia molecule, which constitutes a rate-limiting step. In the second route, the active site chemisorbs two ammonia species, and the rate-determining step is the hydrogen abstraction from the methyl group. The results indicate that the electronic properties of the surface are greatly affected by adsorption of ammonia.
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13.
  • Otamiri, J, et al. (författare)
  • Kinetics and mechanisms in the ammoxidation of toluene over a V2O5 catalyst. Part 2: Non-selective reactions
  • 1988
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 3:2-3, s. 223-234
  • Tidskriftsartikel (refereegranskat)abstract
    • In the ammoxidation of toluene over a V2O5 catalyst, the variation of initial rates with partial pressures of oxygen, toluene and ammonia was determined for formation of carbon oxides. Dependencies obtained were analyzed and expressed in terms of rate equations. It was found that CO and CO2 are initial products formed at different sites, none of which are involved in selective reactions. The mechanisms derived for the formation of the two oxides have many features in common. In each mechanism there are two parallel routes originating from the same active site, which is suggested to be an ensemble exposing vanadium ions and electrophilic oxygen species. One of the routes proceeds without participation of ammonia, while in the other route ammonia is adsorbed. In both routes, the rate-determining step can be considered to be one of the steps in a stepwise reoxidation process. The rates for formation of carbon oxides decrease strongly with increasing partial pressure of ammonia, which is due to a combined effect of introduction of a new reaction pathway and competitive adsorption between oxygen and ammonia.
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14.
  • Sanati, Mehri, et al. (författare)
  • Kinetic Study on Propane Ammoxidation to Acrylonitrile over V-Sb-O/TiO2(B)
  • 1998
  • Ingår i: Catalysis Today. - 0920-5861. ; 42:3, s. 325-332
  • Tidskriftsartikel (refereegranskat)abstract
    • Kinetic study on propane ammoxidation to acrylonitrile over V–Sb–O/TiO2(B) was undertaken by a strict mathematical analysis of experimental rate dependencies on reactant pressure in order to obtain expression describing completely the data.
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15.
  • Berg, M., et al. (författare)
  • Catalytic combustion of low heating value gas mixtures : comparison between laboratory and pilot scale tests
  • 2000
  • Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 59:02-jan, s. 117-130
  • Tidskriftsartikel (refereegranskat)abstract
    • Catalytic combustion of low heating value fuels is a promising method for electricity production combining the use of a renewable fuel with ultra-low emissions. In the present work, catalytic combustion of a low heating value gas has been studied over monolithic catalysts in an atmospheric 30 kW pilot catalytic combustor connected to a wood pellet gasifier. The results have been compared to similar tests with a model gas mixture and a series of test in a laboratory scale reactor for monolithic samples. Various catalyst configurations have been tested, such as precious metal-based catalyst impregnated on modified alumina washcoats and hexaaluminate washcoats. Cordierite monoliths with various cells per square inch were used as supports, but hexaaluminate extruded monoliths were also used. The catalysts were combined in different segment series. The results show that it is possible to ignite the low heating value gas at compressor outlet temperatures without the use of pre-burners over precious metal catalysts. Generally, trends and phenomena obtained in laboratory reactor operating close to isothermal could be confirmed in the pilot operating at close to adiabatic conditions. Further results, such as deactivation by sulphur compounds, fuel-NOx conversion and emissions of carbon monoxide and total hydrocarbons, are addressed in the paper.
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16.
  • Ersson, A., et al. (författare)
  • Catalytic combustion of methane over bimetallic catalysts a comparison between a novel annular reactor and a high-pressure reactor
  • 2003
  • Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 83:04-jan, s. 265-277
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of adding a co-metal, Pt or Rh, to Pd/-gamma-Al2O3 catalysts were studied with respect to the catalytic activity for methane combustion and compared to a Pd/gamma-Al2O3 catalyst, using both a pressurized pilot-scale and a lab-scale annular reactor. Temperature programmed oxidation (TPO) experiments were also carried out to investigate the oxygen release/uptake of the catalyst materials. Palladium showed an unstable behavior both in the pilot and lab-scale experiments at temperatures well below the PdO to Pd transformation. An addition of Pt to Pd stabilized, and in some cases increased, the catalytic activity for methane combustion. The TPO experiments showed that the oxygen release peak was shifted to lower temperatures even for low additions of Pt, i.e. Pd:Pt = 2:1. For additions of rhodium only small beneficial effects were seen. The steady-state behavior of the lab-scale annular reactor correspond well to the pressurized pilot-scale tests.
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17.
  • Högberg, Hans-Erik, et al. (författare)
  • Biocatalysis as a useful tool in pheromone synthesis. Enantiomerically pure building blocks from baker's yeast reductions and enzyme catalysed resoluti
  • 1994
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 22:3, s. 591-606
  • Tidskriftsartikel (refereegranskat)abstract
    • Biocatalytical methods are presented which provide useful building blocks for pheromone synthesis. Examples of the utility of this approach are the preparation of building blocks for the synthesis of stereochemically pure isomers of pine sawfly pheromones and some other pheromones. Enantiom- erically pure ( 98% ee) 2-methyl-1-alkanols 2 were obtained via baker's yeast reduction of suitable α,β-unsaturated aldehydes, and by using lipases from Pseudomonas to effect resolution by transesterification of suitable racemic precursors to 2-methyl-1-alkanols 2 which gave high enantiomeric ratios E > 100. The resolution by esterification mediated by lipase from Candida rugosa of racemic 2-methylalkanoic acids also gave high enantiomeric ratios E> 100 after having improved the reaction conditions by regulating water activity, by choice of the appropriate complimentary substrate alcohol and by adjusting the initial equivalents of the latter present at the start. Also discussed is the separation of diastereomers of diprionol 1, which is naturally occurring in the pine sawfly Neodiprion sertifer, where it is the direct precursor of its pheromone.
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18.
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19.
  • Lassinantti, Magdalena, et al. (författare)
  • Preparation and evaluation of thin ZSM-5 membranes synthesized in the absence of organic template molecules
  • 2001
  • Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 67:1-3, s. 109-119
  • Tidskriftsartikel (refereegranskat)abstract
    • Porous α-alumina supports with a pore size of 100 nm were seeded with colloidal TPA-silicalite-1 crystals with a size of 120 nm. The seeded supports were calcined and treated in a synthesis solution free from organic template molecules to form ZSM-5 films on the supports. According to SEM images, the films were about 2 μm thick and no defects could be found on the as-synthesized membranes. Single gas permeation data was collected and good quality membranes (defined as having a non-detectable permeance of SF6 after drying at 100°C) were further evaluated using binary/ternary gas mixtures. The selectivity for n-butane/i-butane had a maximum value of 17.8 at 220°C. Water was selectively separated from a helium-diluted vaporized water/ethanol azeotrope with a maximum selectivity of 12.4.
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20.
  • Pocoroba, E., et al. (författare)
  • Ageing of palladium, platinum and manganese-based combustion catalysts for biogas applications
  • 2000
  • Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 59:02-jan, s. 179-189
  • Tidskriftsartikel (refereegranskat)abstract
    • During recent years, catalytic combustion of low heating value gases has received increased attention. The purpose of the present work was to study the effect of ageing for 30 days at 1000 degrees C in air saturated with 12% steam on Pd- and Pt-impregnated as well as Mn-substituted lanthanum hexaaluminate materials. Both hexaaluminate powders and 400 cpsi cordierite monoliths, washcoated with hexaaluminate powder, were aged. Powders were characterised by BET and XRD, whereas the catalytic activity of the washcoated monoliths was evaluated in a bench-scale rig for conversion of synthetic gasified biomass. The surface areas decreased significantly during the first day of ageing, whereas further ageing had only a minor influence. The pure lanthanum-alumina sample was a mixture of the hexaaluminate LaAl11O18 phase and the less preferable perovskite LaAlO3 phase, which increased after ageing. The Mn-substituted lanthanum-alumina mainly showed pure hexaaluminate phase both before and after ageing. The catalytic activity tests showed that Pd-impregnated lanthanum hexaaluminate was the most active catalyst for combustion of carbon monoxide and hydrogen, retaining low light-off temperatures also after 30 days of ageing. However, the ignition temperature for 50% conversion (T-50) of methane was approximately 300 degrees C higher than for the fresh sample. Pt-impregnated samples were less active than the Pd ones. The Pt-loading decreased after ageing, whereas the Pd-loading remained fairly constant. However, the amount of Pd oxide decreased after ageing. Further, the Mn-substituted samples were less active than the precious metal ones. Here, the activity for the combustion of carbon monoxide was substantially affected by ageing. The formation of nitrogen oxides from ammonia was lower over the aged samples than over fresh ones; the Mn-substituted sample aged 30 days showed the lowest yield, only 30% of ammonia was converted to nitrogen oxides.
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21.
  • Pradier, C.M., et al. (författare)
  • NO reduction by isobutene, in the presence of oxygen, on platinum and copper : a comparative study
  • 1996
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 29:1-4, s. 59-65
  • Tidskriftsartikel (refereegranskat)abstract
    • The reaction of NO, oxygen and isobutene was studied under conditions close to stoichiometric, on a platinum and on a copper disk in order to better understand the role of each metal, free of any support and dispersion effects. The products of the reaction were analysed by mass spectrometry and an XPS characterization of the surface was carried out at different stages of the reaction. A correlation between the catalytic activity for NO conversion and the presence of adsorbed intermediates has been clearly demonstrated on platinum. On copper, a redox cycle of the metal is necessary to activate the catalyst. On platinum, oxygen is necessary to initiate the reaction, clean the surface and form reactive intermediates; the reaction is strongly sensitive to oxygen concentration, whereas on copper, oxygen does not directly participate in the reaction mechanism.
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22.
  • Rymes, J., et al. (författare)
  • Microemulsions in the preparation of highly active combustion catalysts
  • 2002
  • Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 75:1-4, s. 297-303
  • Konferensbidrag (refereegranskat)abstract
    • Catalytic activity in combustion of toluene in toluene-air mixtures and physical-chemical properties of platinum catalysts prepared from reverse microemulsions (water-in-oil) and by classical impregnation from water solutions of H2PtCl6 were studied. Microemulsion catalysts were more active than those prepared classically from water solutions. Size of Pt in classically impregnated catalysts was three times higher than that of catalysts prepared from microemulsions. In case of microemulsion preparation method, platinum is located near the pellet surface or its position in the pellet can be optimised. The effect of oil used in microemulsion system seems to be negligible for the activity of the catalysts with 0.1 wt.% Pt.
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23.
  • Sterte, Johan, et al. (författare)
  • Application of the seed-film method for the preparation of structured molecular sieve catalysts
  • 2001
  • Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 69:1-4, s. 323-329
  • Tidskriftsartikel (refereegranskat)abstract
    • The seed-film method has been applied for the preparation of various materials of potential interest as structured molecular sieve catalysts. The method has proven to be very flexible and allows for the reproducible preparation of a number of molecular sieve–substrate combinations as well as the control of the materials’ properties of importance in catalytic applications such as zeolite loading, film thickness, film density and crystal orientation. The preparation of thin molecular sieve films on ceramic foams, α-alumina pellets and porous alumina supports as well as various metal surfaces is described. The preparation of zoned coatings with a compositional gradient is also discussed.
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24.
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25.
  • Adams, Emma, 1989, et al. (författare)
  • Ammonia formation over Pd/Al2O3 modified with cerium and barium
  • 2016
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 267, s. 210-216
  • Tidskriftsartikel (refereegranskat)abstract
    • We report experimental results for ammonia formation from nitric oxide and either a direct source of hydrogen or from a mixture of carbon monoxide and water over palladium based catalysts. Specifically, the addition of barium or cerium into an alumina supported palladium sample was studied. Static and transient flow reactor experiments were performed in order to identify the effects of temperature and the presence of oxygen on the activity for ammonia formation. Modification of Pd/Al2O3 with cerium proved to be beneficial for the activity due mainly to its enhancement of the water-gas-shift reaction, thus providing a higher availability of hydrogen for ammonia formation, but also because it remains active in the presence of slightly oxidizing global conditions when hydrogen is provided directly to the feed. Although the modification of Pd/Al2O3 with barium did not affect the ammonia formation during static conditions, the activity during lean/rich cycling increased. This is important for applications of passive selective catalytic reduction.
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26.
  • Adams, Emma, 1989, et al. (författare)
  • Water–gas-shift assisted ammonia formation over Pd/Ce/alumina
  • 2018
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 307, s. 169-174
  • Tidskriftsartikel (refereegranskat)abstract
    • We report experimental results for the water–gas-shift assisted formation of ammonia from nitric oxide over alumina supported palladium, modified with various amounts (0–38 wt.%) of cerium. Static and transient flow reactor experiments were performed in order to identify the effects of temperature and the presence of oxygen on the activity for ammonia formation over the catalysts. The water–gas-shift reaction is enhanced with increasing cerium content, thus providing more hydrogen for ammonia formation. During transient operation at temperatures above 350 °C, a slight delay in ammonia formation is observed over the sample containing the highest cerium loading due to its (relatively) high dynamic oxygen storage capacity. At temperatures below 175 °C, N2O formation is preferred over NH3 formation. This work highlights the importance of balancing the effects that ceria influences when choosing the ceria loading for ammonia formation in passive-SCR applications.
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27.
  • Ahmadi, Mozhgan, et al. (författare)
  • Development of an on-line tar measurement method based on photo ionization technique
  • 2011
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 176:1, s. 250-252
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents work in progress for development of an on-line method based on PID (Photo Ionization Detector) for quantitative measurement of tar from biomass gasification. To calibrate the method the PID signals are compared to quantitative data of individual tar compounds obtained by an established reference method. The measured response factors for the model tar compounds demonstrated very good linearity. The PID approach was tested on-line with real producer gases from an atmospheric fluidized bed gasifier operated at 800-900 °C. The results suggest that PID can be used for continuous on-line tar measurement of product gases from biomass gasification.
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28.
  • Albertazzi, S, et al. (författare)
  • The technical feasibility of biomass gasification for hydrogen production
  • 2005
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 106:1-4, s. 297-300
  • Tidskriftsartikel (refereegranskat)abstract
    • Biomass gasification for energy or hydrogen production is a field in continuous evolution, due to the fact that biomass is a renewable and CO2 neutral source. The ability to produce biomass-derived vehicle fuel on a large scale will help to reduce greenhouse gas and pollution, increase the security of European energy supplies, and enhance the use of renewable energy. The Varnamo, Biomass Gassification Centre in Sweden is a unique plant and an important site for the development of innovative technologies for biomass transformation. At the moment, the Varnamo plant is the heart of the CHRISGAS European project, that aims to convert the produced gas for further upgrading to liquid fuels as dimethyl ether (DME), methanol or Fischer-Tropsch (F-T) derived diesel. The present work is an attempt to highlight the conditions for the reforming unit and the problems related to working with streams having high contents of sulphur and alkali metals.
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29.
  • Andersson, Arne, et al. (författare)
  • A study of the ageing and deactivation phenomena occurring during operation of an iron molybdate catalyst in formaldehyde production
  • 2006
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 112:1-4, s. 40-44
  • Tidskriftsartikel (refereegranskat)abstract
    • Catalyst from a Perstorp Formox formaldehyde plant, operating with high inlet concentration of methanol (10.2 vol.%), was discharged from single tubes of a multi-tube reactor after half the expected lifetime of the catalyst and again after termination of the load. Each tube was filled with two different layers of catalyst. From the inlet of the reactor the first layer was a catalyst mixed with inert rings, which was followed by a second layer of pure catalyst extending from the middle to the outlet of the reactor. Catalyst fractions from the two layers were characterized with various techniques including BET, Fourier transform Raman (FT-Raman) spectroscopy, X-ray diffraction (XRD), elemental analysis with atomic absorption spectroscopy (AAS) and activity measurements. It was found that the surface area of the catalyst in the mixed layer increases during operation while a small decrease is noticeable for the catalyst below in the pure layer. Elemental analysis, XRD and FT-Raman show that during operation of the catalyst there is migration of Mo species from the upper part of the reactor towards the outlet. Activity measurements reveal severe deactivation of the catalyst in the mixed layer. It is concluded that the deactivation primarily is due to formation of volatile species formed by the MoO3 surface reacting methanol, causing a decrease of the MoO3/Fe-2(MoO4)(3) mole ratio in the catalyst. Concerning the catalyst in the pure layer, the condensation of needle-like crystals of MoO3 mainly occurs on the external surface of the catalyst ring.
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30.
  • Andersson, Ronnie, 1975, et al. (författare)
  • Enhanced mass and heat transfer in catalytic reactors
  • 2013
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 216, s. 117-120
  • Tidskriftsartikel (refereegranskat)abstract
    • Mass and heat transfer in square ducts with one side containing a porous wall were simulated using large eddy simulation (LES). Increased wall normal turbulent intensity was observed along the porous wall compared to the smooth wall. Depending on the wall permeability the fluid elements penetrated to different depth resulting in enhanced mass and heat transfer rates. The larges effect was obtained for mass transfer in liquids with up to 20 times larger mass transfer rate, compared to smooth surfaces. An increased penetration into the porous wall was obtained with more open porous structure and with fluids having high density and low viscosity. Most benefit of the porous walls is obtained for fluids with high rho/mu ratio and high Pr or Sc numbers i.e. for mass transfer in liquids.
  •  
31.
  • Arora, Prakhar, 1987, et al. (författare)
  • The role of catalyst poisons during hydrodeoxygenation of renewable oils
  • 2021
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 367, s. 28-42
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrodeoxygenation (HDO) activity of NiMo catalysts have been evaluated in the presence of catalyst poisons in bio-based feedstocks. An in-house synthesized NiMo/Al2O3 catalyst was placed in a refinery unit for biofuel production. Iron (Fe), phosphorus (P) and metals were identified as major contaminants. Calcination treatment was explored to recover the activity of spent catalysts. The effect of Fe, K and phospholipid containing P and Na on catalyst deactivation during hydrodeoxygenation of stearic acid was simulated at lab-scale. Fe caused the most deactivation where the highest feed concentration of the Fe compound resulted in 1480 ppm Fe deposited on the catalyst. Elemental distribution along the radial axis of spent catalysts indicated: Fe deposited only to a depth of 100 μm irrespective of concentration while P and Na from phospholipid and K penetrated deeper in catalyst particles with a distribution profile that was found to be concentration dependent.
  •  
32.
  • Auvray, Xavier, 1986, et al. (författare)
  • The addition of alkali and alkaline earth metals to Pd/Al2O3 to promote methane combustion. Effect of Pd and Ca loading
  • 2018
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 299, s. 212-218
  • Tidskriftsartikel (refereegranskat)abstract
    • Methane catalytic combustion was studied on Pd/Al2O3 catalysts modified with alkali and alkaline earth metals (K, Na, Ca and Ba). Temperature-programmed reactions were performed in flow reactor on washcoated monolithic samples. CO chemisorption was carried out and BET surface area was measured in order to characterize the catalysts. Addition of alkaline metals was either beneficial or detrimental for methane oxidation, depending on the catalyst composition and pretreatment. High loading of alkaline modifiers and cooling in reaction mixture increased the light-off temperature of methane oxidation. However, promotion was achieved by doping with calcium after cooling in inert atmosphere. Furthermore, calcium doping was more beneficial in presence of NO, which inhibits the methane oxidation. Higher Pd loading enhanced CH4 oxidation, whereas the effect of calcium depends on Ca and Pd loading. Indeed, the promotion by calcium was more pronounced on catalysts with 5% Pd than with 2.5% Pd. On 2.5% Pd catalyst, high Ca loading was detrimental for CH4 oxidation. In contrary, on 5% Pd catalyst, even 1.51 wt% calcium (the highest loading used) induced promotion, which demonstrates a correlation between Ca: Pd ratio and promotion/inhibition effect. Samples with a mass ratio of 0.15 showed the best activity.
  •  
33.
  • Barrientos, Javier, et al. (författare)
  • Further insights into the effect of sulfur on the activity and selectivity of cobalt-based Fischer–Tropsch catalysts
  • 2016
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 275, s. 119-126
  • Tidskriftsartikel (refereegranskat)abstract
    •  A sulfur poisoning study was performed by ex situ poisoning of a platinum-promoted cobalt/alumina catalyst with different sulfur amounts. The poisoned catalyst samples were tested at relevant Fischer–Tropsch reaction conditions and at the same CO conversion in order to evaluate the effect of sulfur on catalyst activity and product selectivity. It was found that the activity and the selectivity to long-chain hydrocarbons decrease with increasing sulfur content. Moreover, it was found that sulfur has no significant effect on the CO2 selectivity. It was also shown that sulfur significantly enhances olefin hydrogenation. Finally, a deactivation model relating the catalyst activity and the sulfur to cobalt active site ratio was proposed and used to describe the experimental results.
  •  
34.
  • Bernardini, A., et al. (författare)
  • Direct synthesis of H2O2 over Pd supported on rare earths promoted zirconia
  • 2015
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 256, s. 294-301
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work Pd (0.3 or 0.6 wt.%) was supported on both ZrxM1-xO2 (M = La, Y, Ce) and on mechanical mixtures of CeO2 and ZrO2. The synthesized catalysts were characterized by XRD, TPR, AAS and CO chemisorption and tested for the direct synthesis of hydrogen peroxide in a high pressure semibatch apparatus. The reactants conversion was limited in order to avoid mass-transfer limitations. No selectivity enhancers of any kind were used and the all the materials were halide free. Small metal particles were obtained (1-2.6 nm). Supports with smaller pore diameters leaded to larger Pd particles, which in turn were found to preferentially support the formation of the peroxide. Moreover, supports with higher reducibility favored the production of H2O2, probably due to an easier reduction of the active metal, essential to achieve high selectivity. Notwithstanding the absence of enhancers, the specific activity and selectivity recorded were very high.
  •  
35.
  • Biasi, Pierdomenico, et al. (författare)
  • Application of the Catalyst Wet Pretreatment Method (CWPM) for catalytic direct synthesis of H2O2
  • 2015
  • Ingår i: Catalysis Today. - : Elsevier. - 0920-5861 .- 1873-4308. ; 246:Special Issue, s. 207-215
  • Tidskriftsartikel (refereegranskat)abstract
    • This work concerns a new technique to post-modify the catalytic material intended for use in H2O2 direct synthesis. The catalyst chosen was a commercially available 1 wt.% Pd/C. The catalyst was modified with the so-called Catalyst Wet Pretreatment Method (CWPM) that is used to post-modify prepared catalysts with aqueous solutions of NaBr, in different concentrations. The performance of pristine and the pretreated materials were then compared in the H2O2 direct synthesis and characterized before and after the catalytic tests in order to understand the role of the different concentrations of bromide in the CWPM procedure. The surface features of the different catalysts were analyzed with CO chemisorption (metal dispersion and mean particle size), Transmission Electron Microscopy (TEM, for Pd morphology and Pd particle size distributions), Inductive Coupled Plasma (ICP, for Pd content) and Ion Chromatography (IC, for bromide content). Various features of the materials prepared with the CWPM were correlated with the catalytic performance. It was found that the bromide has an active role in the reconstruction of metal phase and it does not only act as a poison for the most active catalytic sites as often reported in literature. By using this new protocol, the production H2O2 was almost doubled compared to the non-modified material when no direct promoters were added to the reaction environment.
  •  
36.
  • Bora, Tanujjal, et al. (författare)
  • Defect engineered visible light active ZnO nanorods for photocatalytic treatment of water
  • 2017
  • Ingår i: Catalysis Today. - : ELSEVIER SCIENCE BV. - 0920-5861 .- 1873-4308. ; 284, s. 11-18
  • Tidskriftsartikel (refereegranskat)abstract
    • Photocatalytic degradation of organic wastes and microbes in water using solar light is a green technology that requires the design of visible light active photocatalysts. Here we report the fabrication of visible light active zinc oxide nanorods (ZnO NRs), wherein the visible light absorption is enhanced by modulating the surface defects on the NRs. Oxygen vacancies in the NRs as characterized by photoluminescence and X-ray photoelectron spectroscopy are controlled by annealing at different temperatures in the ambient. The role of surface defects on the visible light photocatalytic degradation of an organic dye, industrial waste, bacterial culture and inland brackish water is studied. Results presented here provide a simple strategy to make the wide bandgap ZnO NRs visible light active, enabling their use for the photocatalytic decontamination of water.
  •  
37.
  • Boutonnet, Magali, et al. (författare)
  • Microemulsion droplets to catalytically active nanoparticles : How the application of colloidal tools in catalysis aims to well designed and efficient catalysts
  • 2017
  • Ingår i: Catalysis Today. - : Elsevier. - 0920-5861 .- 1873-4308. ; 285, s. 89-103
  • Tidskriftsartikel (refereegranskat)abstract
    • In this review, we report the successful application of a colloidal tool, namely microemulsions (ME) in the design of catalysts for various applications. First, a brief introduction to MEs and the water-in-oil (w/o) ME reaction method is given. The first ME formulations used for catalyst synthesis are discussed. Catalytic activity of the materials obtained from those initial studies, both as particles deposited onto a support as well as directly as nanoparticles in ME suspension is described. Then various application examples which highlight several important properties of the catalysts obtained from w/o ME are given. For example, particle size control achieved with ME is very relevant to surface sensitive reactions, whose selectivity depends greatly on metal particle size. Another important aspect is related to the unique microenvironment of MEs which results in specific interactions within the formed materials; this is particularly important for certain catalysts such as mixed oxide particles, conferring them with special properties and enhanced performance. Comparison of activity and selectivity of impregnation-prepared versus ME-prepared materials is given for several catalytic reactions. Finally, the more recently developed oil-in-water (o/w) ME method is described, along with examples of materials obtained by this method as catalysts, including photocatalysis. The different aspects discussed in this review demonstrate the importance of the ME reaction method for the design of nanocatalysts with enhanced activity and selectivity.
  •  
38.
  • Broqvist, Peter, 1975, et al. (författare)
  • NOx storage on BaO: theory and experiment
  • 2004
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 96:1-2, s. 71-78
  • Tidskriftsartikel (refereegranskat)abstract
    • We review our understanding of the NO2 interaction with BaO. The presented picture has evolved from calculations using the density functional theory, reactor measurements and vibrational spectroscopy of surface species during NO2 storage on a BaO/Al2O3 catalyst and BaO powder. The DFT calculations predict nitrite formation on the BaO(1 0 0) surface upon NO2 adsorption. A particular stable adsorption configuration is a nitrate-nitrite pair geometry, with the nitrate bonded to a barium cation and the nitrite involving a surface oxygen anion. This configuration is supported by vibrational spectroscopy. Only nitrite formation is observed for NO exposure to BaO powder at low temperatures, whereas signatures at similar to250degreesC reveal the formation of surface nitrates. Continuous NO2 adsorption at this temperature results in surface Ba(NO3)(2), as well as bulk Ba(NO3)(2), formation.
  •  
39.
  • Busch, Michael, 1983, et al. (författare)
  • Validation of binuclear descriptor for mixed transition metal oxide supported electrocatalytic water oxidation
  • 2013
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 202:1, s. 114-119
  • Tidskriftsartikel (refereegranskat)abstract
    • The energy profiles of the di-hydroxo – di-oxo – peroxo pathway are discussed for a set of 3d transition metal oxides comprising V(III–V), Cr(III–V), Mn(II–IV, Mn(III–V), Fe(II–IV), Co(II–IV) and Ni(II–IV) using density functional theory (DFT). Two classes of oxides were identified. The first class, comprising V(III–V), Cr(III–V) and Fe(II–IV), displays exothermicity for the oxidation of di-hydroxo to di-oxo versus the tyrosine/tyrosyl-radical (TyrOH/TyrO) couple and endothermicity for the subsequent O-O bond formation ([−/+] class), while the second class, comprising Mn(III–V), Co(II–IV) and Ni(II–IV), shows endothermicity with respect to the oxidation step and exothermicity for the O-O bond formation ([+/−] class). The energetics of the endothermicity (exothermicity) for the oxidation step is reflected in the exothermicity (endothermicity) of the subsequent O-O bond formation step. Mn(II–IV) is not part of any of the two classes. Instead it shows zero exothermicity with respect to TyrOH/TyrO for the oxidation step and a small endothermicity for the O-O bond formation step. Despite the promising energy profile Mn(II–IV) is argued to be inactive due to a large activation barrier. A set of improved hetero-nuclear candidate catalysts is predicted by mixing [−/+] with [+/−] transition metal oxides. A simple and efficient method to estimate the energy profile of mixed transition metal oxides from the homo-nuclear systems is demonstrated. The validity of this procedure is checked and agreement with the explicitly calculated values is found. All considered heteronuclear candidate catalysts display enhanced performance compared to the pure homonuclear systems.
  •  
40.
  • Creci, Simone, 1992, et al. (författare)
  • Methoxy ad-species in MFI zeotypes during methane exposure and methanol desorption followed by in situ IR spectroscopy
  • 2021
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 369, s. 123-128
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation and evolution of methoxy ad-species in MFI zeotypes after CH4 exposure, and during temperature programmed desorption of CH3OH have been investigated in situ with diffuse reflectance Fourier transform infrared spectroscopy. Fe and/or Al atoms have been incorporated in framework position prior to crystallization and the influence of the resulting acidity on CH4 activation and CH3OH desorption has been examined. The results show that the presence of Fe promotes CH4 activation and that methanol is more strongly bound to the zeotype in the presence of Al. Because CH4 activation and CH3OH extraction are two of the key steps in the direct conversion of methane to methanol, our results indicate that Al-free zeotypes containing Fe atoms pinpoint important catalyst design parameters needed for this reaction.
  •  
41.
  • Csendes, Z., et al. (författare)
  • Synthesis, structural characterisation, and catalytic activity of Mn(II)-protected amino acid complexes covalently immobilised on chloropropylated silica gel
  • 2015
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 241, s. 264-269
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work the syntheses, structure, superoxide dismutase (SOD) activity and the catalytic use in the oxidative transformations of cyclohexene of covalently grafted Mn(II)-complexes formed with various C-protected amino acid (L-histidine, L-cysteine and L-cystine) ligands are presented. The structural features of the surface complexes were studied by EPR, X-ray absorption, and mid/far IR spectroscopies. The superoxide dismutase activities of the materials were determined in a biochemical test reaction. The obtained materials were used as catalysts for the oxidation of cyclohexene with peracetic acid in acetone. Covalent grafting and building the complex onto the surface of the chloropropylated silica gel were successful in all cases. It was found that in many instances the structures obtained and the coordinating groups substantially varied upon changing the conditions of the syntheses. All the covalently immobilised Mn(II)-complexes displayed superoxide dismutase activity and could catalyse the oxidation of cyclohexene. (C) 2014 Elsevier B.V. All rights reserved.
  •  
42.
  • Dahlin, Sandra, et al. (författare)
  • Chemical aging of Cu-SSZ-13 SCR catalysts for heavy-duty vehicles –Influence of sulfur dioxide
  • 2018
  • Ingår i: Catalysis Today. - Amsterdam : Elsevier. - 0920-5861 .- 1873-4308. ; 320, s. 72-83
  • Tidskriftsartikel (refereegranskat)abstract
    • Selective catalytic reduction of nitrogen oxides is an efficient technique for emission abatement in heavy-dutyvehicles. Cu-SSZ-13 SCR catalysts are more active than vanadium-based catalysts at low temperatures, but aremore sensitive to deactivation by sulfur. Consequently, there is a need to study poisoning by sulfur for thiscatalyst material. This experimental investigation focuses on the effect of sulfur on the low-temperature per-formance of Cu-SSZ-13 SCR catalysts. The effect of sulfur exposure temperature, and the influence of the NO 2 /NO x ratio, are considered and two different regeneration temperatures are compared. In addition, catalystsamples from an engine-aged catalyst are evaluated. The SO 2 exposure temperature is shown to have an im-portant impact on the deactivation of the Cu-SSZ-13 catalyst. The lowest sulfur exposure temperature (220 °C)results in the most severe deactivation, while the highest temperature during sulfur exposure (400 °C) results inthe lowest degree of deactivation. This was found to be related to the amount of sulfur on the catalyst.Additionally, SO 2 exposure was shown to decrease the N 2 O selectivity. The engine-aged catalyst has a decreasedperformance in terms of both decreased activity and increased N 2 O selectivity. For this catalyst, impurities fromfuel and engine-oil can play a role in the deactivation. Different deactivation mechanisms are seen for the lab-and engine-aged catalysts.
  •  
43.
  • Dahlin, Sandra, et al. (författare)
  • Effect of biofuel- and lube oil-originated sulfur and phosphorus on the performance of Cu-SSZ-13 and V2O5-WO3/TiO2 SCR catalysts
  • 2021
  • Ingår i: Catalysis Today. - : Elsevier B.V.. - 0920-5861 .- 1873-4308. ; 360, s. 326-339
  • Tidskriftsartikel (refereegranskat)abstract
    • Two different SCR catalysts, V2O5-WO3/TiO2 and Cu-SSZ-13, were exposed to biodiesel exhausts generated by a diesel burner. The effect of phosphorus and sulfur on the SCR performance of these catalysts was investigated by doping the fuel with P-, S-, or P + S-containing compounds. Elemental analyses showed that both catalysts captured phosphorus while only Cu-SSZ-13 captured sulfur. High molar P/V ratios, up to almost 3, were observed for V2O5-WO3/TiO2, while the highest P/Cu ratios observed were slightly above 1 for the Cu-SSZ-13 catalyst. Although the V2O5-WO3/TiO2 catalyst captured more P than did the Cu-SSZ-13 catalyst, a higher degree of deactivation was observed for the latter, especially at low temperatures. For both catalysts, phosphorus exposure resulted in suppression of the SCR performance over the entire temperature range. Sulfur exposure, on the other hand, resulted in deactivation of the Cu-SSZ-13 catalyst mainly at temperatures below 300-350 °C. The use of an oxidation catalyst upstream of the SCR catalyst during the exhaust-exposure protects the SCR catalyst from phosphorus poisoning by capturing phosphorus. The results in this work will improve the understanding of chemical deactivation of SCR catalysts and aid in developing durable aftertreatment systems. 
  •  
44.
  • Das, T., et al. (författare)
  • Charge transfer driven interaction of CH4, CO2 and NH3 with TiS2 monolayer : Influence of vacancy defect
  • 2021
  • Ingår i: Catalysis Today. - : Elsevier B.V.. - 0920-5861 .- 1873-4308. ; 370, s. 189-195
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we have investigated the dissociation of hydrogen rich CH4 and NH3 molecules along with CO2 on the surface of pristine and various defect induced TiS2 monolayer. The aim is to see whether the monolayer surfaces are able to produce H2 by decomposing the feedstock adsorbates and also to examine whether it can be a sorbent for CO2. We have tried to explore a monolayer surface which can simultaneously act as a catalyst to dissociate CH4, as well as to adsorb CO2 which is the only harmful by-product in steam reforming method for hydrogen production from CH4. The hydrogen generation has been predicted from the nature of gas adsorption, and the adsorption energies have been estimated to see whether it falls under chemisorption or physisorption range. Both S and Ti vacancy defects have been studied and the first-principles electronic structure calculation helps to envisage the charge redistribution of the three adsorbates on both pristine and defective TiS2 surfaces.
  •  
45.
  • Di, Mengqiao, 1994, et al. (författare)
  • Why nitrogen oxide inhibits CO oxidation over highly dispersed platinum ceria catalysts
  • 2024
  • Ingår i: Catalysis Today. - 0920-5861. ; 426
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of nitrogen oxide on the lean CO oxidation activity of highly dispersed Pt/ceria and reference Pt/alumina catalysts has been studied by kinetic measurements and infrared spectroscopic characterization. Co-feeding of nitrogen oxide leads to the formation of nitrates on the supports that induce a highly oxidized character of the Pt sites and in the case of Pt/ceria, inhibit ceria lattice oxygens to react with CO adsorbed on Pt rim sites via a Mars-van Krevelen mechanism below the ignition temperature. The build-up of nitrates below the light-off temperatures is faster when CO is present in the feed. Above the light-off temperatures, carbonates replace the nitrates while the catalytic activity remains high.
  •  
46.
  • Elm Svensson, Erik, et al. (författare)
  • Microemulsion synthesis of MgO-supported LaMnO3 for catalytic combustion of methane
  • 2006
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 117:4, s. 484-490
  • Tidskriftsartikel (refereegranskat)abstract
    • Catalysts with 20% LaMnO3 supported on MgO have been prepared via CTAB-1-butanol-iso-octane-nitrate salt microemulsion. The preparation method was successfully varied in order to obtain different degrees of interaction between LaMnO3 and MgO as shown by TPR and activity tests after calcination at 900 degrees C. Activity was tested on structured catalysts with 1.5% CH4 in air as test gas giving a GHSV of 100,000 h(-1). The activity was greatly enhanced by supporting LaMnO3 on MgO compared with the bulk LaMnO3. After calcination at 1100 degrees C both the surface area and TPR profiles were similar, indicating that the preparation method is of little importance at this high temperature due to interaction between the phases. Pure LaMmO(3) and MgO were prepared using the same microemulsion method for comparison purposes. Pure MgO showed an impressive thermal stability with a BET surface area exceeding 30 m(2)/g after calcination at 1300 degrees C. The method used to prepare pure LaMnO3 appeared not to be suitable since the surface area dropped to 1.1 m(2)/g already after calcination in 900 degrees C.
  •  
47.
  • Eriksson, Sara, et al. (författare)
  • Fuel-rich catalytic combustion of methane in zero emissions power generation processes
  • 2006
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 117:4, s. 447-453
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel catalytic combustion concept for zero emissions power generation has been investigated. Catalysts consisting of Rh supported on ZrO2, Ce-ZrO2 or alpha-Al2O3 were prepared and tested under fuel-rich conditions, i.e. for catalytic partial oxidation (CPO) of methane. The experiments were performed in a subscale gas-turbine reactor operating at 5 bar with exhaust gas-diluted feed mixtures.The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order Rh/Ce-ZrO2 < Rh/ZrO2 < Rh/alpha-Al2O3. The Rh loading, however, only had a minor influence. The high activity of Rh/Ce-ZrO2 is probably related to the high dispersion of Rh on Ce-ZrO2 and the high oxygen mobility of this support compared to pure ZrO2. The formation of hydrogen was also found to increase over the catalyst containing ceria in the support material.
  •  
48.
  • Eriksson, Sara, et al. (författare)
  • Partial oxidation of methane over rhodium catalysts for power generation applications
  • 2005
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 100, s. 447-451
  • Tidskriftsartikel (refereegranskat)abstract
    • The partial oxidation of methane (POM) to syngas, i.e. H-2 and CO, over supported Rh catalysts was investigated at atmospheric pressure. The influence of support material, Rh loading and the presence of water vapor on the methane conversion efficiency and the product gas composition was studied. The catalysts containing ceria in the support material showed the highest activity and formation of H2 and CO. By increasing the Rh loading, a decrease of the ignition temperature was obtained. The addition of water vapor to the reactant gas mixture was found to increase the ignition temperature and the formation of hydrogen, which is favorable for combustion applications where the catalytic POM stage is followed by H-2-stabilized homogeneous combustion.
  •  
49.
  • Ersson, Anders, et al. (författare)
  • A comparison between hexaaluminates and perovskites for catalytic combustion applications
  • 2006
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 112:04-jan, s. 157-160
  • Tidskriftsartikel (refereegranskat)abstract
    • Hexaaluminates and perovskites are two promising candidates for use in catalytic combustion applications. In the present study two hexaaluminates, LaMnAl11O19 and LaCoAl11O19, were compared with two perovskites, LaMnO3 and LaCoO3, with respect to their thermal stability and catalytic activity for combustion of methane and gasified biomass. The results showed that the hexaaluminates retained a much higher surface area even after calcination at 1200 degrees C compared to the perovskites. LaMnAl11O19 showed the highest catalytic activity of all catalysts. LaCoAl11O19 generally showed low activity. Of the two perovskites, LaCoO3 was the most active, and the initial test run the activity for biomass combustion were close to that one of LaMnAl11O19 even though its surface area was only one tenth of the hexaaluminate's. However, it was severely deactivated in the second test run. Similar deactivation but less severe was also found for the other catalyst.
  •  
50.
  • Friberg, Ida, 1990, et al. (författare)
  • Structure and performance of zeolite supported Pd for complete methane oxidation
  • 2021
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 382, s. 3-12
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of zeolite support materials and their impact on CH oxidation activity was studied utilizing Pd supported on H-beta and H-SSZ-13. A correlation between CH oxidation activity, Si/Al ratio (SAR), the type of zeolite framework, reduction-oxidation behaviour, and Pd species present was found by combining catalytic activity measurements with a variety of characterization methods (operando XAS, NH -TPD, SAXS, STEM and NaCl titration). Operando XAS analysis indicated that catalysts with high CH oxidation activity experienced rapid transitions between metallic- and oxidized-Pd states when switching between rich and lean conditions. This behaviour was exhibited by catalysts with dispersed Pd particles. By contrast, the formation of ion-exchanged Pd and large Pd particles appeared to have a detrimental effect on the oxidation-reduction behaviour and the conversion of CH . The formation of ion-exchanged Pd and large Pd particles was limited by using a highly siliceous beta zeolite support with a low capacity for cation exchange. The same effect was also found using a small-pore SSZ-13 zeolite due to the lower mobility of Pd species. It was found that the zeolite support material should be carefully selected so that the well-dispersed Pd particles remain, and the formation of ion-exchanged Pd is minimized. 4 4 3 4 4 2+ 2+ 2+
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