| 1. |
- Andersson, Arne, et al.
(författare)
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Direct Propane Ammoxidation to Acrylonitrile: Kinetics and Nature of the Active Phase
- 1993
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Ingår i: New Frontiers in Catalysis (Studies in Surface Science and Catalysis ). - 0167-2991. ; 75, s. 691-705
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Konferensbidrag (refereegranskat)abstract
- The kinetics of the direct synthesis of acrylonitrile from propane on V-Sb-Al-(W) mixed oxides indicate that acrylonitrile (ACN) forms by two parallel pathways, one directly from propane and the second, which is the prevalent path, through the intermediate formation of propylene (C3=). The limiting factor in the formation of ACN is the relative slowness of the step of allylic oxidation to ACN of the intermediate C3=, and the higher rate of C3= oxidation to carbon oxides as compared to that of ACN to COx. The step of C3= oxidation to ACN is controlled by the surface availability of NH3 which, in turn, depends considerably on the side reaction of NH3 oxidation to N2. The catalytic behavior of different modified V-Sb-(Al)-O systems and their characterization by X-ray diffraction analysis and Raman, Infrared and X-ray Photoelectron spectroscopies indicate that i) a reduction of both V and Sb occurs during the catalytic reaction, ii) the presence of vanadium not stabilized in the rutile-like phase is responsible for the side reaction of NH3 oxidation and lowering of the selectivity, iii) alumina reacts with antimony forming an AlSbO4 rutile phase which could be epitaxially intergrown or in solid solution with the VSbO4/Sb2O4 system, which, in turn, limits the presence of not stabilized (unselective) vanadium species, and iv) antimony oxide supported on alumina is also selective in propane ammoxidation, but forming acetonitrile as the main product. The doping with vanadium of this sample increases slightly the activity, but especially gives rise to the formation of acrylonitrile instead of acetonitrile.
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| 2. |
- Andersson, Arne, et al.
(författare)
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Structure-Activity Relationships in the Oxidation of Alkylaromatics over Metal Oxides
- 1991
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 67, s. 43-55
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Tidskriftsartikel (refereegranskat)abstract
- In order to accomplish oxidation of alkylaromatic compounds, both cations, which serve as adsorption centers, and oxygen species of suitable bond strength are needed. When compared to partial oxidation, relatively weakly bonded oxygen species are involved in combustion. On the basis of these criteria, using a simple model of the active ensemble, a relationship between reaction rate and bond strength is derived for partial and total oxidation. Its applicability is demonstrated using data for the oxidation of toluene over a large number of binary metal oxides. Some characteristic features following from the model are discussed, considering catalytic results on the structure sensitivity of oxidation and ammoxidation reactions over crystalline V,O and MOO,. Furthermore, kinetic results on the oxidation of toluene to benzaldehyde and carbon oxides in presence of ammonia, which serves as an electron donor to the catalyst surface, demonstrate that the oxygen species taking part in partial oxidation and combustion are nucleophilic and electrophilic in character, respectively.
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| 3. |
- Andersson, Sven-Ingvar, 1943, et al.
(författare)
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Discrepancies in FCC Catalyst Evaluation of Atmospheric Residues
- 2007
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. - 0444530606 ; 166, s. 13-29
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Tidskriftsartikel (refereegranskat)abstract
- Processing of atmospheric residues in fluid catalytic crackers (FCC) is a field of considerable interest today. When this application was new, around 1984, Statoil initiated a test program related to fluid catalytic cracking of North Sea atmospheric residues. Within this program catalysts and feeds are tested in a Micro Activity Test (MAT) reactor at Statoil and in a circulating Arco Pilot Unit at Chalmers.The catalysts are tested with the same atmospheric residue feed that is used in the commercial FCC unit at the Statoil Mongstad refinery in Norway. This is essential because erroneous ranking of the catalysts might otherwise occur. The equilibrium catalyst in a commercial residue FCC unit has normally high metals content. This is simulated by testing the catalysts impregnated by nickel and vanadium and deactivated by the cyclic propene steaming (CPS) method.New catalysts are tested together with a reference catalyst in both the MAT and Pilot Unit reactors. Usually the catalysts show the same ranking in both the MAT and Pilot Unit reactors but there are exceptions. If the matrix properties for two catalysts are different, the ranking of the two catalysts might be different in the MAT and PIlot Unit reactors.
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| 4. |
- Nilsson, Jerker, et al.
(författare)
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Formation of active phases in the Sb-V-, Al-Sb-V-, and Al-Sb-V-W-oxide systems for propane ammoxidation
- 1997
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 110, s. 413-422
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Tidskriftsartikel (refereegranskat)abstract
- The Sb-V-O, Al-Sb-V-O and Al-Sb-V-W-O systems were investigated for the ammoxidation of propane to acrylonitrile. Compared with pure approximate to SbVO4, the approximate to SbVO4 that was obtained by co-calcination of pure approximate to SbVO4 with alpha-Sb2O4 at 800 degrees C and subsequent sieving was found to be much more selective to acrylonitrile. XRD data showed no variation of the rutile unit cell for synthesis ratios Sb:V greater than or equal to 1, indicating that the active phase is approximate to SbVO4 with a surface enriched with Sb. Characterisation of syntheses in the Al-Sb-V-O system allowed the identification of a trirutile-like phase with the composition Al1-xSbVxO4 (0 < x < 0.5). The synthesis of this phase, which is active and selective to acrylonitrile, requires excess of aluminium. Over a fresh preparation with Al, Sb, V and W the activity and the selectivity to acrylonitrile increased considerably with time-on-stream. This behaviour shows that the active rutile phase is formed in situ, and EDX analyses gave the average composition Al0.1Sb0.8V0.7W0.4O4. The highest yield to acrylonitrile that was observed for the three systems was 37 % and was obtained over the Al-Sb-V-W-oxide.
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| 5. |
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| 6. |
- Sanati, Mehri, et al.
(författare)
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A Study of Spreading of Vanadia on Titania Polymorphs Using Mechanical Mixtures
- 1993
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Ingår i: New Frontiers in Catalysis (Studies in Surface Science and Catalysis ). - 0167-2991. ; 75, s. 1755-1758
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Konferensbidrag (refereegranskat)abstract
- Mechanical mixtures of V2O5 and each of the three titania polymorphs TiO2(B), anatase and rutile were heated in air at 450°C. Spreading of vanadia was found to occur on all three polymorphs. After 36 hours of heating, coverage with interacting vanadia (the part that is insoluble in aq. NH3) on TiO2(B), anatase and rutile, respectively, was 54, 48 and 38 % of a theoretical monolayer. Raman spectra confirmed spreading and interaction. HREM images revealed no formation of multilayers of vanadia on titania. Use of the monolayer catalysts for toluene ammoxidation indicated their activity for benzonitrile formation to vary with respect to support in the order TiO2(B) > anatase > rutile.
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| 7. |
- Westerberg, B, et al.
(författare)
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Kinetic study of the selective catalytic reduction of nitric oxides with hydrocarbon in diesel exhausts
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 317-326
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of the selective catalytic reduction of nitric oxides (NOx) on a proprietary high temperature catalyst with diesel as the reductant have been studied. The objective was to derive a kinetic model that can be used for real time simulation of the catalyst. In the extension, the real time simulation will be used when controlling the injection of reductant. This is a requirement for achieving a high efficiency and a low fuel penalty. The response time and the NOx conversion level upon transient diesel injection was found to be dependent on the temperature. At temperatures below 570 K very low or no NOx conversion was observed. Above 570 K a small conversion was observed. No direct response upon diesel injection could be distinguished and the NOx conversion was independent on the hydrocarbon concentration. As the temperature was increased the response became apparent and then faster and the conversion level gradually became more dependent on the hydrocarbon concentration. Above 700 K the response was immediate (response time less than 15 s) and the conversion level was directly dependent on the hydrocarbon concentration. It was concluded that the NOx reduction proceeds via the formation of a hydrocarbon intermediate and the successive reaction between the hydrocarbon intermediate and NOx. When this reaction mechanism was modeled many features of the catalyst behaviour were reproduced.
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| 8. |
- Grahn, Mattias, et al.
(författare)
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A novel experimental technique for estimation of molecular orientation in zeolite
- 2007
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 170, s. 724-731
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Tidskriftsartikel (refereegranskat)abstract
- FTIR spectroscopy in combination with polarized light and an ATR probe coated with a b-oriented ZSM-5 film was for the first time used to determine the orientation of adsorbed molecules in the ZSM-5 structure. Two adsorbates were studied, n-hexane and p-xylene and the results agreed with previously reported results obtained by other experimental techniques.
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| 9. |
- Li, Qinghua, et al.
(författare)
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The synthesis of small colloidal crystals of TPA-silicalite-1 with short synthesis times and high yields
- 1999
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 125, s. 133-140
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Tidskriftsartikel (refereegranskat)abstract
- A two-stage varying-temperature crystallization procedure can be used to synthesize particularly small colloidal crystals of TPA-silicalite-1 with reduced synthesis times and high yields. Using this procedure involves starting a synthesis at a reduced temperature which favours the nucleation of a large crystal population. The reduced temperature is maintained throughout the nucleation stage, after which an elevated temperature is used to accelerate the crystal growth and reach higher equilibrium yields favoured by higher temperatures
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| 10. |
- Tang, Liqiu, et al.
(författare)
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Synthesis and structures of new silicogermanates
- 2004
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Ingår i: Studies in Surface Science and Catalysis. - : Elsevier B.V.. - 0167-2991. ; 154:1, s. 739-745
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Tidskriftsartikel (refereegranskat)abstract
- Three new micro-porous silicogermanates, (NH4)F[(Ge3.14Si6.86)O20] (SU-9), (NH4F[(Ge6.78Si3.22)O20] (SU-10) and [(Ge2.40Si9.60)O24] (SU-11) were synthesized under hydrothermal conditions with the presence of structure directing agents and the structures were solved by single crystal X-ray diffraction. SU-9 and SU-10 are built up by the double T4-rings (D4Rs) and they have the zeolite structure types of AST and ASV, respectively. SU-11 is built up by the T12-units and has the zeolite structure type of MFI. In three compounds, both silicon and germanium atoms are tetrahedrally coordinated with oxygen atoms and share the same tetrahedral sites.
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| 11. |
- Tosheva, Lubomira, et al.
(författare)
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A method for the preparation of silicalite-1 microspheres
- 1999
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 125, s. 21-28
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Tidskriftsartikel (refereegranskat)abstract
- Silicalite-1 containing microspheres were prepared by a new method based on the use of anion exchange resins as shape directing templates. The resins were hydrothermally treated in a synthesis solution yielding silicalite-1 at 100°C and finally removed by calcination. The resultant material consists of hard, solid and white spherical particles with a shape and size identical to the ion exchange resin used. Characterization of samples taken out after different times of treatment showed that an amorphous silica is formed at the beginning of the treatment. This amorphous silica shows structural changes with time parallel to which silicalite-1 starts to form. The crystallization reaction discontinues after a treatment time of about 48 h. A calcined sample obtained after 48 h contains a large amount of amorphous matter and the additional hydrothermal treatment does not substantially improve the crystallinity of the product. Silicalite-1 microspheres of a very high crystallinity were obtained by a two-step procedure using an initial treatment at 100°C followed by a secondary treatment at a higher temperature.
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| 12. |
- Zsigmond, A, et al.
(författare)
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Aerobic oxidations on metal macrocycles encapsulated in zeolites
- 1995
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 94, s. 728-735
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Tidskriftsartikel (refereegranskat)abstract
- Zeolite-encapsulated Fe-phthalocyanine and Co-salophen catalysts were used in the palladium-catalyzed aerobic oxidation of hydroquinone to benzoquinone, in the oxidation of l-octene to 2-octanone and in the allylic oxidation of cyclohexene to 3-acetoxycyclohexene. These catalysts proved to be active in the above reactions and they were stable towards self-oxidation and it was possible to reuse them in subsequent runs. The specific activity of the encapsulated Fe-phthalocyanine catalyst was about four times higher than those of the free complex.
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| 13. |
- Zsigmond, A, et al.
(författare)
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Selective oxidation of benzyl alcohol on a zeolite ship-in-a-bottle complex
- 1997
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 108, s. 453-459
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Tidskriftsartikel (refereegranskat)abstract
- A Co(salophen)/zeolite catalyst was prepared by the template synthesis method. This catalyst proved to be active in the ruthenium catalyzed oxidation of benzyl alcohol. The heterogenized Co(salophen), having the same amount of complex produced a higher rate in the oxidation reactions than the free complex. It can be explained by the sites isolation theory. In the case of the heterogenized catalyst it was not necessary to use an extra axial ligand such as triphenylphosphine. It was also found that in the case of Co(salophen)/zeolite catalyst the choice of the solvent was not so critical, as in the case of the free complex.
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| 14. |
- Acke, Filip, 1968, et al.
(författare)
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Influence of the platinum-support interaction on the direct reduction of NOx under lean conditions
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 285-294
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts containing Pt supported on SiC, Al2O3 and ZSM-5 were prepared and studied for NOx reduction by C3H6 in Oz excess under transient (temperature ramps) and steady-state conditions. The maximum NOx reduction activity in the heating ramp experiments was similar for Pt/SiC and Pt/ZSM-5, while Pt/Al2O3 showed higher maximum activity. Both N-2 and N2O formation was observed for all catalysts, although the respective amounts varied with the investigated system. Highest Nz selectivity was observed for Pt/Al2O3. When the NOx reduction activity was studied under steady-state conditions the activity of Pt/Al2O3 decreased substantially (mainly due to a loss in N-2 production). Pt/ZSM-5 became somewhat more selective towards Na production whereas the activity and selectivity of Pt/SiC remained at about the same values as far the heating ramp experiments. Adsorbed species on the surface of the different catalysts were investigated using in-situ FTIR in order to obtain information about the reaction mechanisms. The adsorption of species on Pt/SiC was negligible, while a number of absorption bands were observed for Pt/Al2O3 (N and C containing species, and -NCO) and Pt/ZSM-5 (HC).
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| 15. |
- Alfredsson, Viveka, et al.
(författare)
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Formation mechanism of mesoporous silica formed with triblock copolymers; effect of salt addition
- 2005
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 158, s. 97-104
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Tidskriftsartikel (refereegranskat)abstract
- SBA-15 was synthesised with Pluronic P104 ((EO)(27)-(PO)(61)-(EO)(27))) its Structure promoter at 45 degrees C, with and without NaCl (1.0 M) added to the Synthesis Mixture. TEOS (tetraethyl orthosilicate) was used as silica source. The formation process was studied by in-situ SAXS/SAXD using synchrotron light. Addition of salt affects the micellar size, initial cell-parameter of the 2-D hexagonal phase (p6mm) as well as the kinetics of the aggregation of the polymer-silica composite. The effects caused by the salt are explained by a general ionic effect. The salt makes the aqueous Solution more polar and hence a worse solvent for the polymer. The ethylene oxide chains of the polymer will be more solvophobic. This leads to a larger aggregation number ofthe micelles as well as to a stronger interaction between them.
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| 16. |
- Alfredsson, Viveka, et al.
(författare)
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In-situ studies of the formation mechanism of SBA-15
- 2005
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Ingår i: Nanoporous Materials IV, 156. - 0444517480 ; 156, s. 69-74
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Konferensbidrag (refereegranskat)abstract
- The formation process of SBA-15 has been investigated by time resolved TEM, in-situ SAXS/SAXD and in-situ NMR. The synthesis was done at 35 degrees in acidic solution with tetramethylorthosilicate as the silica source and Pluronic P123 as the structure directing amphiphile. The initially formed silica-polymer composite consists of flocs of spherical micelles in a silica matrix. The micelles then coalesce forming rods that eventually pack into the ordered array of which SBA-15 consists.
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| 17. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Sulphur dioxide deactivation of NOx storage catalysts
- 1999
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 126, s. 317-324
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Tidskriftsartikel (refereegranskat)abstract
- The influence of sulphur dioxide on the NOx storage performance of a Pt-Rh/BaO/Al2O3 model catalyst has been investigated. Addition of 2.5-25 vol.-ppm SO2 to a synthetic lean-burn exhaust, containing NO, C3H6, O2 and Ar, caused deactivation of the NOx storage function of the catalyst. The rate of deactivation was found to be proportional to the exposure of SO2. This effect is seen for temperatures between 250 and 450 degrees C. Together with in situ FTIR measurements, this leads to the conclusion that sulphur accumulates in the NOx storage component of the catalyst during the exposure. Furthermore, SO2 also inhibits the oxidation capacity of the catalyst during lean periods as is observed by a decreased NO oxidation activity. The presence of SO2 also reduces the reduction capacity of the catalyst under rich periods, which leads to an increased N2O formation and a decreased NO conversion.
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| 18. |
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| 19. |
- Erkfeldt, Sara U, 1974, et al.
(författare)
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Poisoning and regeneration of NOx adsorbing catalysts for automotive applications
- 1999
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 126, s. 211-218
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency and product formation as a function of temperature, time and gas stoichiometry, in the regeneration of an SO2 poisoned NOx storage and reduction (NSR) catalyst has been studied. Using these results a simple model for sulphur poisoning and regeneration of this type of catalyst is proposed. SO2 poisons the catalyst, which results in a decrease of the NOx conversion with increasing SO2 exposure time. The NOx storage capacity can be regained after regeneration of the catalyst. The regeneration is most effective using long regeneration time, high temperature and low lambda value. A measure of the regeneration efficiency, activity based sulphur removal (ASR), is defined. ASR is used to model the regeneration efficiency with the independent variables; regeneration time, temperature and lambda value. The model describes the experimental results well. The amounts of released SO2, H2S and COS, during the regeneration differ depending on regeneration conditions. Low lambda values give high amounts of H2S and low amounts of SO2, whereas the reverse is true for high lambda values. The production of COS is low in all cases. The results can schematically be described with a model where sulphur can migrate between deactivating and non-deactivating positions on the catalyst surface.
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| 20. |
- Fridell, Erik, 1963, et al.
(författare)
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Investigations of NOx storage catalysts
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 537-547
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Tidskriftsartikel (refereegranskat)abstract
- NOx storage catalysts are used to reduce nitrogen oxides from lean-burn vehicles. The nitrogen oxides are stored in the catalyst during lean conditions and subsequently released and reduced during short periods of rich conditions. In the present study, we systematically investigate the sequence of elementary steps in the NOx reduction cycle, and the extent to which these steps influence the maximum NOx, reduction potential of the catalyst. As a model system, we use barium oxide as the NOx, storing compound in a Pt/Rh/Al2O3 system. Kinetics of NO oxidation, NO and NO2 adsorption, NO and NO2 release and reduction are studied under controlled conditions with systematic variations of temperature, gas composition, and storing/release times. The transient experiments comprise a storing phase using a lean NO/C3H6/O2/N2 gas mixture, and a regenerating phase where the O2 now is turned off. Experimentally, a significant amount of NOx is found to be stored in the Ba-containing material. A maximum in NOx storage is observed around 380 degrees C. For most of the experiments, there are clear NO and NO2 desorption peaks upon switching from the storing to the regeneration phase. TPD studies of NO and NO2 reveal a significant difference between prereduced and pre-oxidised samples where the former produce predominantly N2 and N2O at around 200 degrees C while NO and O2 desorb from the latter around 500 degrees C. In situ FTIR spectra show nitrate peaks in the region 1300-1400 cm(-1) when NOx is stored under lean conditions.
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- Skoglundh, Magnus, 1965, et al.
(författare)
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Light-off performance over cobalt oxide- and ceria-promoted platinum and palladium catalysts
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 113-122
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Tidskriftsartikel (refereegranskat)abstract
- Monolith catalysts containing Co, Ce, Pt and Pd supported on alumina were prepared and tested with respect to low-temperature activity for oxidation of CO and propene. The catalysts were either pre-oxidised or pre-reduced prior to evaluation with respect to light-off performance, using net oxidising and net reducing CO/C3H6/O2/N2 gas mixtures. Promotion of Pt and Pd with cobalt or cerium oxide, favoured the low temperature activity significantly. Pre-reduction of Co- and Ce-promoted noble metals shifted the conversion starts of CO and propene toward lower temperatures compared with pre-oxidised samples. Pre-reduction of cobalt oxide, without Pt or Pd, yielded a dramatic improvement of the low-temperature catalytic performance compared with pre-oxidation of the said oxide. The catalysts were characterised by temperature programmed desorption of CO and specific surface area measurements. The high activity over the pre-reduced cobalt containing catalysts is suggested to be due to the presence of reduced cobalt oxide sites on those samples.
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| 25. |
- Van den Hark,, et al.
(författare)
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Production of fatty alcohols by heterogeneous catalysis at supercritical single-phase conditions
- 2000
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 130 A, s. 539-544
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Tidskriftsartikel (refereegranskat)abstract
- Fatty alcohols can be produced by catalytic hydrogenation of fatty acid methyl esters. This heterogeneous catalytic reaction, traditionally performed in a multi-phase system, is limited by the mass transport of hydrogen to the catalyst. 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 we have created supercritical single-phase conditions. These single-phase conditions eliminate the transport resistance for hydrogen and create the possibility to control the concentration of all the reactants at the catalyst surface independently of the other process settings. In this way, extremely rapid hydrogenation can be combined with a high product selectivity. In our lab-scale experiments the catalyst activity was studied as a function of hydrogen pressure, substrate concentration and temperature. The catalyst activity was extremely high compared to the multi-phase hydrogenation. Complete conversion of the liquid substrate was reached in a few seconds. The high catalyst activity results in reaction rates which are comparable with similar gas-phase hydrogenation reactions of much smaller molecules (e.g. methylacetate). As long as single-phase conditions remain -in our experiments we have tested up to 15 wt.% substrate- the gas-phase-like activity can be maintained. Our results prove that performing hydrogenation at supercritical single-phase conditions is beneficial for this and other heterogeneous catalytic processes which are limited by mass transfer. © 2000 Elsevier Science B.V. All rights reserved.
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