| 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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