| 1. |
- Chaoquan, Hu, 1981, et al.
(författare)
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Methyl crotonate hydrogenation over Pt: Effects of support and metal dispersion
- 2016
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Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 511, s. 106-116
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Tidskriftsartikel (refereegranskat)abstract
- Gas-phase hydrogenation of methyl crotonate (MC) has been studied over Pt supported on Al2O3, C, SiO2,and TiO2. The physicochemical properties of the catalysts were characterized by use of N2 physisorption,transmission electron microscopy and CO chemisorption. The effects of Pt dispersion and nature of the support on the catalytic properties of the catalysts were determined by measurements of the kinetic parameters for MC hydrogenation. The results clearly display MC inhibition effects on the hydrogenation over the catalysts. However, the degree of MC-inhibition is found to depend on both the Pt dispersion and the support used. For alumina a high Pt dispersion can promote the resistance of the catalyst against MC-inhibition, and even allow hydrogen adsorption to become equilibrated on the Pt surface. Compared to SiO2 and C supports, Al2O3 improves the resistance of the Pt surface against MC inhibition, whereas TiO2reduces the resistance. Possible reasons are suggested to understand the positive effect of Al2O3 on Pt against MC inhibition.
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| 2. |
- Chaoquan, Hu, 1981, et al.
(författare)
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Selectivity and kinetics of methyl crotonate hydrogenation over Pt/Al2O3
- 2015
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Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 5:3, s. 1716-1730
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogenation of gas-phase methyl crotonate (MC) over Pt/Al2O3 was investigated with the aim to understand C=C hydrogenation in unsaturated methyl esters. Three Pt/Al2O3 catalysts with different Pt dispersions were prepared by varying calcination temperature and evaluated for MC hydrogenation. The main products were found to be methyl butyrate (MB) and methyl 3-butenoate (M3B), resulting from hydrogenation and shift of the C=C bond in MC, respectively. The measured activity for both hydrogenation and shift of the C=C in MC was found to depend on the Pt dispersion where higher Pt dispersion favors the C=C hydrogenation reaction. The effect of reactant concentrations on the activity and selectivity for MC hydrogenation over the Pt/Al2O3 catalyst was examined in detail. Under the investigated conditions, the C=C hydrogenation was found to have a negative reaction order with respect to MC concentration but a positive H2 order. Further understanding of the MC hydrogenation was provided from H2 chemisorption experiments over the catalyst with and without pre-adsorbed MC and from transient experiments using alternating MC and H2 feeds. Based on the present experimental results, a reaction pathway was proposed to describe gas-phase MC hydrogenation over Pt/Al2O3. In order to gain more insight into the reaction, a kinetic analysis of MC hydrogenation was performed by fitting a power-law model to the kinetic data, moreover, dissociative H2 adsorption on the catalyst was found to be the rate-determining step by comparing the power-law model with the overall rate expressions derived from mechanistic considerations.
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| 3. |
- Florén, Carl-Robert, 1988, et al.
(författare)
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Modelling complete methane oxidation over palladium oxide in a porous catalyst using first-principles surface kinetics
- 2018
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:2, s. 508-520
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive model is developed for complete methane oxidation over supported palladium. The model is based on first-principles microkinetics and accounts for mass and heat transport in a porous catalytic layer. The turnover frequency (TOF) is simulated for wet exhaust gas compositions, exploring the effects of temperature and total pressure on the TOF. Three different temperature regimes are identified each with different dependency on the total pressure. The regimes originate from temperature and pressure dependent coverages of carbon dioxide and water, which are the most abundant surface species hindering methane dissociation at low temperatures. The TOF is controlled by surface kinetics below 400 °C whereas above 500 °C and up to 8 atm, internal mass transport is controlling. A combination of kinetics, external and internal mass transport controls the TOF at other reaction conditions. The physically meaningful model paves the way for extrapolation and optimization of catalyst design parameters for high catalytic efficiency.
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| 4. |
- Florén, Carl-Robert, 1988, et al.
(författare)
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Multiscale reactor modelling of total pressure effects on complete methane oxidation over Pd/Al2O3
- 2019
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:12, s. 3055-3065
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Tidskriftsartikel (refereegranskat)abstract
- A two-dimensional multiscale model is developed for complete methane oxidation in a continuous flow reactor. The model considers mass and heat transfer for a porous alumina supported palladium catalyst coated on a ceramic monolith substrate and the surface kinetics are described by a first-principles microkinetic model for complete methane oxidation over PdO(101). The temperature dependent conversion for a synthetic exhaust gas composition shows a delayed ignition but a higher conversion at elevated temperatures when the total pressure is increased from 1 to 10 atm. The simulations reveal a temperature and total pressure dependent operating point where the methane conversion is maximized. Analysis of the kinetics shows that the reaction is suppressed by bicarbonates, hydroxyl species and water originating from adsorbed carbon dioxide and water from the gas phase. The reaction order with respect to water and carbon dioxide at 1 atm is -0.94 and -0.99, respectively, and decreases with increasing total pressure. The developed model paves the way for exploring how design parameters and reaction conditions influence the complete methane oxidation reaction.
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| 5. |
- Heard, Christopher, 1988, et al.
(författare)
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Kinetic Regimes in Ethylene Hydrogenation over Transition-Metal Surfaces
- 2016
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 6:5, s. 3277-3286
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Tidskriftsartikel (refereegranskat)abstract
- A first-principles microkinetic model has been developed and applied to ethylene hydrogenation over close-packed transition-metal surfaces of Ru, Rh, Pd, Os, Ir, and Pt. The model is based on density functional theory calculations, which have been used to determine the activation energies of the elementary steps of the reaction according to the Horuiti-Polanyi mechanism. A sensitivity analysis of the activity with respect to the kinetic parameters reveals distinctly different kinetic regimes across the periodic table. For Ru and Ir, the activity is controlled by the activation energy for ethylene to ethyl hydrogenation, whereas the other metals also have a sensitivity to the second hydrogenation step. The analysis shows, furthermore, that the activity could be enhanced considerably with minor reductions of the hydrogenation barriers.
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| 6. |
- Arora, Prakhar, 1987, et al.
(författare)
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Investigating the effect of Fe as a poison for catalytic HDO over sulfided NiMo alumina catalysts
- 2018
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 227, s. 240-251
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Tidskriftsartikel (refereegranskat)abstract
- The effect of iron (Fe) as poison present in renewable feeds was studied during hydrodeoxygenation (HDO) overmolybdenum based sulfided catalysts. The study was carried out at 6 MPa and 325 °C in batch reaction conditions. Different concentrations of Fe in the feed were tested over MoS2/Al2O3 and NiMoS/Al2O3. A notable drop in activity for the conversion of oxygenates was observed for both catalyst systems with an increased concentration of Fe in the feed. However, the changes in selectivity of products was opposite for unpromoted and Nipromoted catalysts. In the case of the NiMoS catalyst, at higher Fe concentration, the decarbonated product (C17 hydrocarbons) decreased while the direct hydrodeoxygenation product (C18 hydrocarbons)increased. On the contrary, for the base catalyst (MoS2), there was a decrease in the yield of direct hydrodeoxygenation (C18 hydrocarbons) products and an increase in yield of decarbonated products (C17 hydrocarbons). These sulfided catalysts have different sites for these two different reaction routes and they interacted differently with Fe during the deactivation process. With surface deposition of Fe, the ability of these catalysts to create active sites i.e. via sulfur vacancies deteriorated. TEM-EDX results suggested that the effect of Ni as a promoter for the decarbonation route was nullified and a resultant FeMo phase explains the drop in activity and change in selectivity.
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| 7. |
- Arora, Prakhar, 1987, et al.
(författare)
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Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils
- 2019
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 364, s. 376-389
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3catalyst. Intermediates like octadecanal (C18 O) and octadecanol (C18 OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.
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| 8. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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Evaluation of H2 effect on NO oxidation over a diesel oxidation catalyst
- 2015
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 179, s. 542-550
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Tidskriftsartikel (refereegranskat)abstract
- The influence of H2 on NO oxidation over Pt/Al2O3 as a model DOC catalyst was evaluated with various DOC feed mixtures. Discrimination of surface chemistry and exothermal effects due to addition of H2 was made based on differences in time scales of transient responses. H2 was proposed to retard Pt oxide formation mainly at low temperatures (ca.
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| 9. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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Kinetic modeling of C3H6 inhibition on NO Oxidation over Pt Catalyst
- 2016
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Ingår i: Bulletin of Chemical Reaction Engineering and Catalysis. - : Bulletin of Chemical Reaction Engineering and Catalysis. - 1978-2993. ; 11:1, s. 27-33
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Tidskriftsartikel (refereegranskat)abstract
- Exhaust after treatment for lean burn and diesel engine is a complex catalytic system that consists of a number of catalytic units. Pt/Al2O3is often used as a model Diesel Oxidation Catalyst (DOC) that plays an important role to facilitate oxidation of NO to NO2. In the present study, we proposed a detailed kinetic model of NO oxidation as well as low temperature C3H6 inhibition to simulate temperatureprogrammed reaction (TPR) data for NO oxidation over Pt/Al2O3. A steady-state microkinetic model based on Langmuir-Hinshelwood mechanism for NO oxidation was proposed. In addition, low temperature C3H6inhibition was proposed as a result of site blocking as well as surface nitrite consumption. The model can explain the experimental data well over the studied temperature range.
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| 10. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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Kinetic modeling of H2-assisted C3H6 selective catalytic reduction of NO over silver alumina catalyst
- 2015
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 278, s. 394-406
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Tidskriftsartikel (refereegranskat)abstract
- A global kinetic model was developed for C3H6-SCR consisting of NO oxidation, C3H6 oxidation and C3H6-SCR reactions with and without H-2 over Ag-Al2O3. The model is based on a dual role of H-2 to remove inhibiting nitrates from the active sites as well as to modify/form new active Ag sites. For model development, a range of temperature programmed reaction (TPR) and transient feed experimental conditions were used. The proposed model was eventually also validated with additional transient experimental data. The kinetic model proposed in this study predicts the experimental data well for a wide-range of feed conditions. Evaluation of mass transfer resistance in the washcoat indicated that during H-2-assisted C3H6-SCR, mild internal mass transfer resistance for NO was predicted to be important already at 250 degrees C.
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