| 1. |
- Becker, Elin, 1981, et al.
(författare)
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Methane oxidation over alumina and ceria supported platinum
- 2009
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1957-1961
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of methane over Pt/Al(2)O(3) and Pt/CeO(2) catalysts was studied by transient gas-flow reactor and in situ FTIR spectroscopy experiments. The Pt/CeO(2) catalyst is generally more active, indicating more efficient CH(4) dissociation, especially during oxygen pulsing, which likely is connected to the higher oxygen storage capacity/mobility of ceria.
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| 2. |
- Carlsson, Per-Anders, 1972, et al.
(författare)
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Virtual control for high conversion of methane over supported Pt
- 2009
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1962-1966
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Tidskriftsartikel (refereegranskat)abstract
- A transient model for oxidation of methane over Pt/Al2O3 monolith catalysts has been developed by rigorous consideration of mass- and heat transport and mean-field treatment of the reaction kinetics. By coupling a virtual regulator using the reactant slip, methane or oxygen partial pressures, or oxygen surface coverage as feedback variable(s) as such or in combinations for control of feed composition, the influence of gas composition changes on the methane conversion has been investigated.
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| 3. |
- Grasselli, Robert K., et al.
(författare)
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Active centers, catalytic behavior, symbiosis and redox properties of MoV(Nb,Ta)TeO ammoxidation catalysts
- 2006
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 38:1-3, s. 7-16
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Tidskriftsartikel (refereegranskat)abstract
- Selective as well as waste forming active centers were defined for MoVNbTeO and MoVTaTeO catalysts in the ammoxidation of propane to acrylonitrile and all catalytic functionalities were assigned to specific elements at the respective active centers. Symbiosis between M1 and M2 phases of these catalysts was observed, with phase cooperation being more extensive in the Nb than Ta containing compositions. The difference in catalytic effectiveness arises most likely because contact and surface area exposure of the two respective, cooperating phase pairs are not equal. The M1 phase of the catalysts is reducible by propane and ammonia in the absence of dioxygen and is regenerable to its original, fully oxidized state by dioxygen (air). No structural collapse is observed even after 120 C3H8 + NH3 reduction pulses. The so induced reduction of the catalyst extends up to 70 layers deep. The product distribution over the first few pulses is very similar to that under catalytic conditions, supporting the concept that lattice oxygen is involved in the catalytic ammoxidation process. Therefore, the ammoxidation of paraffins is a redox process, as is of course the well-known olefin ammoxidation process.
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| 4. |
- Guimond, S., et al.
(författare)
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Vanadium oxide surfaces and supported vanadium oxide nanoparticles
- 2006
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Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 38:1-3, s. 117-125
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Tidskriftsartikel (refereegranskat)abstract
- The information obtained from the characterization of vanadium oxide single crystal surfaces is related to the study of vanadia nanoparticles supported on silica and alumina thin films, model systems for the so-called “supported monolayer vanadia catalysts”. It is found that these particles have properties similar to V2O3 surfaces, where the topmost V ions are involved in vanadyl groups and have a 5+ oxidation state. A vibrational spectroscopy investigation combined with DFT calculations show that the accepted interpretation of vibrational spectra from vanadia catalysts must be revised.
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| 5. |
- Holmberg, Johan, et al.
(författare)
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Catalytic effects in propene ammoxidation achieved through substitutions in the M2 phase of the Mo-V-Nb-Te-oxide system
- 2006
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 38:1-3, s. 17-29
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Tidskriftsartikel (refereegranskat)abstract
- M2-type phases M3TeO10 (M = Mo and V), belonging to the Mo-V-Nb-Te-oxide system, were prepared by substituting to various degrees the M-metal with W, Ti, Nb or Fe, and Te with Ce. The compositions were characterized by BET, XRD and XPS and were studied for propene ammoxidation. The variations of the unit cell parameters with substitution reveal that the orthorhombic, pseudo-hexagonal M2 structure is preserved to different degrees depending on the substituent and its amount. It is noted that partial substitution with W, Ti, Ce and Fe all increase the activity of the base composition and that Ce, and especially W, improve the selectivity to acrylonitrile at the expense of acrolein. The results of the activity measurements and the XPS investigation indicate that the site, activating propene and ammonia on the unsubstituted M2 phase is a surface ensemble of Mo and Te. W and Ce were found to be able to mimic the role of Mo and Te, respectively; W mainly via site isolation and electronic effects, Ce via redox effects. V- and Ti-sites are shown to be inactive, having merely the role of structure adjusting elements, and serving as templates to complex the excess Te on the surface.
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| 6. |
- Häggblad, Robert, et al.
(författare)
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Substituted Mo-V(Ti)-Te(Ce)-oxide M2 catalysts for propene ammoxidation
- 2008
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 50:1-4, s. 52-65
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Tidskriftsartikel (refereegranskat)abstract
- One of the most effective propane to acrylonitrile ammoxidation catalyst is comprised of the two phases M1 (orthorhombic) Mo7.5V1.5NbTeO29 and M2 (pseudo-hexagonal) Mo4V2Te2O20. Under reaction conditions, the two phases work in symbiosis with each other where M1 is the paraffin activating component and M2 is the olefin activating component. Since the catalytic improvement of either phase should result in an enhancement of the overall acrylonitrile yield, controlled substitution of certain elements in either or both phases might result in the desired improvement. Our current study concentrates on the partial substitutions of V with Ti and Te with Ce in the M2 phase. Ti substitution results in a considerable propene activity improvement, whereas the selectivity to acrylonitrile is unaffected. Substitution with Ce, on the contrary, substantially improves the selectivity to acrylonitrile. Also, a minor improvement of the activity is notable. The acrylonitrile selectivity improvement is a result of better NH3 utilization and comes at the expense of reduced acrolein make. XRD reveals that all of the substituted compositions retain the M2 structure and essentially are monophasic. XANES recordings show for the bulk that the Mo is 6+, the V is 4+, or 4+ and 5+ when Ce is present, the Ti is 4+, the Ce is 3+, and the Te 4+ with some 6+ also present. According to the ESR data, in the M2 with Ce (7Te/3Ce) only 21% of the V is 4+, the remainder being 5+, which tentatively can be explained by the existence of some cation vacancies in the hexagonal channels. HRTEM imaging reveals little if any differences between the materials, all have the typical pseudo-hexagonal habit of the M2 phase and expose a 1-2 nm thick surface layer without any apparent long-range ordering. XPS data show that all catalysts, including the base, are highly enriched at the surface with Te at the expense of other metals. The 7Te/3Ce composition exhibits also substantial Ce surface enrichment. Moreover, the valences of the cations at the surface differ from the bulk in that for all fresh catalysts V is 5+ and Te is 6+ on the surface. Characterization by XPS of catalysts used in propene ammoxidation, reveals reduction of Te and, except when Ce is present, also Mo. Therefore, it might be inferred that the surfaces of the catalysts studied here are comprised essentially of one or a few monolayers of TeMoO or TeCeMoO on an interacting M2 crystalline base.
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| 7. |
- Härelind Ingelsten, Hanna, 1973, et al.
(författare)
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Mechanistic aspects of lean NO2 reduction by propane over H-ZSM-5
- 2007
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 42-43:1-4, s. 105-107
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the mechanism of lean NO2 reduction by propane. In particular the role of isocyanate- and amine species has been studied in transient experiments by in situ Fourier Transform Infrared (FTIR) spectroscopy. The results imply that these species are possible reaction intermediates over acidic HZSM-5.
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| 8. |
- Härelind Ingelsten, Hanna, 1973, et al.
(författare)
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Mechanistic Considerations of the NOx Source and the Reducing Agent for Lean NOx Reduction over H-ZSM-5
- 2009
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1921-1924
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the reaction mechanism for lean NOx reduction by propane. In particular the role of the NOx-source, i.e. NO or NO2, for the SCR mechanism has been studied by transient experiments using in-situ FTIR spectroscopy and the results are discussed in relation to isopropylamine and ammonia as reducing agents.
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| 9. |
- Kamp, Carl Justin, 1982, et al.
(författare)
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The Role of Active Sites in the Non-Catalytic Oxidation of Carbon Particulate Matter: A Theoretical Approach
- 2009
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1951-1956
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of carbon particulate matter is a complex process involving many different surface compounds; however, it is clear that there is a direct relationship between the inherent structure of the carbon and the oxidation reaction rate. This reaction occurs on surface sites which are on the periphery of the crystallites that make up carbon particles. These surface sites can be described as active sites where the reaction occurs and spectator sites that do not participate in the reaction. A model has been constructed that calculates the distribution of these types of surface sites during oxidation to show their dynamic behavior, and is compared to experimental data.
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| 10. |
- Kannisto, Hannes, 1979, et al.
(författare)
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Aspects of the Role of Hydrogen in H-2-Assisted HC-SCR Over Ag-Al2O3
- 2009
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1817-1820
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Tidskriftsartikel (refereegranskat)abstract
- The role of hydrogen in H-2-assisted HC-SCR of NOx over Ag-Al2O3 is investigated by XPS and in situ DRIFT spectroscopy. Hydrogen does not reduce the surface silver species to metallic silver, however direct reduction of surface nitrates by hydrogen is observed. It is proposed that one important role of hydrogen is the removal of nitrates from the Ag-Al2O3 surface.
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