Pub Date : 2015-07-03DOI: 10.1179/2055075815Y.0000000008
M. Bowker, R. Sharpe
Abstract. The effect of sputtering, annealing and oxidation on the surface properties of TiO2(110), and on the same surfaces with nanoparticles present, has been investigated. Sputtering the crystal clean gives a much reduced surface with Ti2+ as the dominant species. This,surface is mainly Ti3+,4+ after annealing in vacuum. Oxidation reduces the surface Ti3+ considerably. When Pd nanoparticles are annealed on any of the investigated titania surfaces the particles become encapsulated by a film of titanium oxide. This is particularly noticeable in ISS (ion scattering spectroscopy) where the Pd:Ti ratio drops by a factor of 300 after annealing to 750 K, indicating complete coverage of the Pd nanoparticles by the oxide film. This happens most easily for the nanoparticles deposited on the reduced surfaces (beginning at ~673K) but also occurs for the very oxidized surface at~773K. Thus reduced Ti from the subsurface region can migrate onto the Pd surface to form the sub-oxide, the sub-oxide being a thin TiO-like layer.
{"title":"Pd deposition on TiO2(110) and nanoparticle encapsulation","authors":"M. Bowker, R. Sharpe","doi":"10.1179/2055075815Y.0000000008","DOIUrl":"https://doi.org/10.1179/2055075815Y.0000000008","url":null,"abstract":"Abstract. The effect of sputtering, annealing and oxidation on the surface properties of TiO2(110), and on the same surfaces with nanoparticles present, has been investigated. Sputtering the crystal clean gives a much reduced surface with Ti2+ as the dominant species. This,surface is mainly Ti3+,4+ after annealing in vacuum. Oxidation reduces the surface Ti3+ considerably. When Pd nanoparticles are annealed on any of the investigated titania surfaces the particles become encapsulated by a film of titanium oxide. This is particularly noticeable in ISS (ion scattering spectroscopy) where the Pd:Ti ratio drops by a factor of 300 after annealing to 750 K, indicating complete coverage of the Pd nanoparticles by the oxide film. This happens most easily for the nanoparticles deposited on the reduced surfaces (beginning at ~673K) but also occurs for the very oxidized surface at~773K. Thus reduced Ti from the subsurface region can migrate onto the Pd surface to form the sub-oxide, the sub-oxide being a thin TiO-like layer.","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075815Y.0000000008","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65872309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-07-03DOI: 10.1179/2055075815Y.0000000006
Qifeng Yang, D. Joyce, S. Saranu, G. Hughes, A. Varambhia, Michael P. Moody, P. Bagot
The structure and composition of catalytic silver nanoparticles (Ag-NPs) fabricated through a novel gas condensation process has been characterized by Scanning Electron Microscopy (SEM) and Atom Probe Tomography (APT). SEM was used to confirm the number density and spatial distribution of Ag-NPs deposited directly onto standard silicon microposts used for APT experiments. Depositing nanoparticles (NPs) directly by this method eliminates the requirement for focussed ion beam (FIB) liftout, significantly decreasing APT specimen preparation time and enabling far more NPs to be examined. Furthermore, by encapsulating deposited particles before final FIB sharpening, the APT reconstruction methodologies have been improved over prior attempts, as demonstrated by comparison to the SEM data. Progress in these areas is vital to enable large-scale catalyst research efforts using APT, a technique, which offers significant potential to examine the detailed atomic-scale chemistry in a wide variety of catalytic NPs. Graphical Abstract
{"title":"A combined approach for deposition and characterization of atomically engineered catalyst nanoparticles","authors":"Qifeng Yang, D. Joyce, S. Saranu, G. Hughes, A. Varambhia, Michael P. Moody, P. Bagot","doi":"10.1179/2055075815Y.0000000006","DOIUrl":"https://doi.org/10.1179/2055075815Y.0000000006","url":null,"abstract":"The structure and composition of catalytic silver nanoparticles (Ag-NPs) fabricated through a novel gas condensation process has been characterized by Scanning Electron Microscopy (SEM) and Atom Probe Tomography (APT). SEM was used to confirm the number density and spatial distribution of Ag-NPs deposited directly onto standard silicon microposts used for APT experiments. Depositing nanoparticles (NPs) directly by this method eliminates the requirement for focussed ion beam (FIB) liftout, significantly decreasing APT specimen preparation time and enabling far more NPs to be examined. Furthermore, by encapsulating deposited particles before final FIB sharpening, the APT reconstruction methodologies have been improved over prior attempts, as demonstrated by comparison to the SEM data. Progress in these areas is vital to enable large-scale catalyst research efforts using APT, a technique, which offers significant potential to examine the detailed atomic-scale chemistry in a wide variety of catalytic NPs. Graphical Abstract","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075815Y.0000000006","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65872286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-07-03DOI: 10.1179/2055075815Y.0000000009
A. Torozova, P. Mäki-Arvela, N. Shcherban, N. Kumar, A. Aho, M. Štekrová, K. Maduna Valkaj, P. Sinitsyna, S. Filonenko, P. Yaremov, V. Ilyin, K. Volcho, N. Salakhutdinov, D. Murzin
Abstract Microporous, mesoporous and new hybrid materials were studied in verbenol oxide isomerization for the synthesis of biologically active substance with anti-Parkinson activity. H-Si-MCM-41, H-Al-MCM-41, H-Al-MCM-48, H-Beta-25 and H-Beta-300 were compared with hybrid materials. The latter with a zeolite-like micro-mesoporous structure were characterized and evaluated for their catalytic activity for the first time. The approach of dual templating for synthesis of new materials was applied in this work to combine properties of Beta-zeolites and mesoporous cellular foams. The selectivity to the target product was the highest over microporous mild acidic H-Beta-300 and hybrid ZF-100, with also mild acidity and even absence of strong acid sites. Selectivity at 97% and 99% of conversion was 61% and 59% for H-Beta-300 and hybrid ZF-100, respectively.
{"title":"Effect of acidity and texture of micro-, mesoporous and hybrid micromesoporous materials on the synthesis of paramenthanic diol exhibiting anti-Parkinson activity","authors":"A. Torozova, P. Mäki-Arvela, N. Shcherban, N. Kumar, A. Aho, M. Štekrová, K. Maduna Valkaj, P. Sinitsyna, S. Filonenko, P. Yaremov, V. Ilyin, K. Volcho, N. Salakhutdinov, D. Murzin","doi":"10.1179/2055075815Y.0000000009","DOIUrl":"https://doi.org/10.1179/2055075815Y.0000000009","url":null,"abstract":"Abstract Microporous, mesoporous and new hybrid materials were studied in verbenol oxide isomerization for the synthesis of biologically active substance with anti-Parkinson activity. H-Si-MCM-41, H-Al-MCM-41, H-Al-MCM-48, H-Beta-25 and H-Beta-300 were compared with hybrid materials. The latter with a zeolite-like micro-mesoporous structure were characterized and evaluated for their catalytic activity for the first time. The approach of dual templating for synthesis of new materials was applied in this work to combine properties of Beta-zeolites and mesoporous cellular foams. The selectivity to the target product was the highest over microporous mild acidic H-Beta-300 and hybrid ZF-100, with also mild acidity and even absence of strong acid sites. Selectivity at 97% and 99% of conversion was 61% and 59% for H-Beta-300 and hybrid ZF-100, respectively.","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075815Y.0000000009","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65872374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-05-05DOI: 10.1179/2055075815Y.0000000004
Tinku Baidya, P. Bera
Adsorption of CO as well as CO+O2 reaction over Cu2+ ion substituted Ce1 − xMxO2 (M = Zr, Hf and Th) supports have been studied by DRIFTS. Linear Cu+–CO bands are observed over all catalysts upon introduction of CO. But, Cu+–CO band positions are shifted to little higher frequencies in Ce0.68M0.25Cu0.07O2 − δ compared to Ce0.93Cu0.07O2 − δ. However, Cu+–CO bands are in same positions when CO and O2 are adsorbed simultaneously over all the catalysts. Ramping the temperature in the DRIFTS cell after simultaneous CO and O2 adsorption shows the formation of CO2 as well as decrease of CO. Comparison of intensities of CO2 bands of different catalysts as a function of temperature indicates that Ce0.68Th0.25Cu0.07O2 − δ shows lowest temperature CO oxidation among all the catalysts that is because of its more electron withdrawing power. Graphical Abstract
{"title":"Investigation of support effect on CO adsorption and CO + O2 reaction over Ce1 − x − yMxCuyO2 − δ (M = Zr, Hf and Th) catalysts by in situ DRIFTS","authors":"Tinku Baidya, P. Bera","doi":"10.1179/2055075815Y.0000000004","DOIUrl":"https://doi.org/10.1179/2055075815Y.0000000004","url":null,"abstract":"Adsorption of CO as well as CO+O2 reaction over Cu2+ ion substituted Ce1 − xMxO2 (M = Zr, Hf and Th) supports have been studied by DRIFTS. Linear Cu+–CO bands are observed over all catalysts upon introduction of CO. But, Cu+–CO band positions are shifted to little higher frequencies in Ce0.68M0.25Cu0.07O2 − δ compared to Ce0.93Cu0.07O2 − δ. However, Cu+–CO bands are in same positions when CO and O2 are adsorbed simultaneously over all the catalysts. Ramping the temperature in the DRIFTS cell after simultaneous CO and O2 adsorption shows the formation of CO2 as well as decrease of CO. Comparison of intensities of CO2 bands of different catalysts as a function of temperature indicates that Ce0.68Th0.25Cu0.07O2 − δ shows lowest temperature CO oxidation among all the catalysts that is because of its more electron withdrawing power. Graphical Abstract","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075815Y.0000000004","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65872097","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-04-28DOI: 10.1179/2055075815Y.0000000005
K. Morgan, R. Burch, M. Daous, J. Delgado, A. Goguet, C. Hardacre, L. Petrov, D. Rooney
The ability to reactivate, stabilize and increase the lifetime of gold catalysts by dispersing large, inactive gold nanoparticles to smaller nanoparticles provides an opportunity to make gold catalysts more practical for industrial applications. Previously it has been demonstrated that mild treatment with iodomethane (J. Am. Chem. Soc., 2009, 131, 6973; Angew. Chem. Int. Ed., 2011, 50, 8912) was able to re-disperse gold on carbon and metal oxide supports. In the current work, we show that this technique can be applied to re-disperse gold on a ‘mixed’ metal oxide, namely a mechanical mixture of ceria, zirconia and titania. Characterization was conducted to guage the impact of the iodomethane (CH3I) treatment on a previously sintered catalyst. Graphical Abstract
{"title":"Re-dispersion of gold supported on a ‘mixed’ oxide support","authors":"K. Morgan, R. Burch, M. Daous, J. Delgado, A. Goguet, C. Hardacre, L. Petrov, D. Rooney","doi":"10.1179/2055075815Y.0000000005","DOIUrl":"https://doi.org/10.1179/2055075815Y.0000000005","url":null,"abstract":"The ability to reactivate, stabilize and increase the lifetime of gold catalysts by dispersing large, inactive gold nanoparticles to smaller nanoparticles provides an opportunity to make gold catalysts more practical for industrial applications. Previously it has been demonstrated that mild treatment with iodomethane (J. Am. Chem. Soc., 2009, 131, 6973; Angew. Chem. Int. Ed., 2011, 50, 8912) was able to re-disperse gold on carbon and metal oxide supports. In the current work, we show that this technique can be applied to re-disperse gold on a ‘mixed’ metal oxide, namely a mechanical mixture of ceria, zirconia and titania. Characterization was conducted to guage the impact of the iodomethane (CH3I) treatment on a previously sintered catalyst. Graphical Abstract","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075815Y.0000000005","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65872187","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-04-01DOI: 10.1179/2055075815Y.0000000002
M. Bowker, M. House, Abdulmohsen A. Alshehri, C. Brookes, E. Gibson, P. Wells
Abstract Evolution of the IRAS spectrum with temperature after adsorbing methanol at room temperature. The bands at 2930 and 2820 cm− 1 are due to the methoxy species C–H stretches, while that at 2870 is due to the formate. Here, we report a simple, quantitative model to describe the behaviour of bi-cationic oxide catalysts, in terms of selectivity variation as a function of increased loading of one cation into a sample of the other. We consider its application to a particular catalytic system, namely the selective oxidation of methanol, which proceeds with three main C1 products, namely CO2, CO, and H2CO. The product selectivity varies in this order as Mo is added in increasing amounts to an iron oxide catalyst, and the product selectivity is determined by the distribution of dual sites and single sites of each species.
{"title":"Selectivity determinants for dual function catalysts: applied to methanol selective oxidation on iron molybdate","authors":"M. Bowker, M. House, Abdulmohsen A. Alshehri, C. Brookes, E. Gibson, P. Wells","doi":"10.1179/2055075815Y.0000000002","DOIUrl":"https://doi.org/10.1179/2055075815Y.0000000002","url":null,"abstract":"Abstract Evolution of the IRAS spectrum with temperature after adsorbing methanol at room temperature. The bands at 2930 and 2820 cm− 1 are due to the methoxy species C–H stretches, while that at 2870 is due to the formate. Here, we report a simple, quantitative model to describe the behaviour of bi-cationic oxide catalysts, in terms of selectivity variation as a function of increased loading of one cation into a sample of the other. We consider its application to a particular catalytic system, namely the selective oxidation of methanol, which proceeds with three main C1 products, namely CO2, CO, and H2CO. The product selectivity varies in this order as Mo is added in increasing amounts to an iron oxide catalyst, and the product selectivity is determined by the distribution of dual sites and single sites of each species.","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075815Y.0000000002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65872048","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-04-01DOI: 10.1179/2055075815Y.0000000001
P. Wells, E. Crabb, C. R. King, S. Fiddy, A. Amieiro-Fonseca, D. Thompsett, A. Russell
Abstract A controlled surface reaction (CSR) technique has been successfully employed to prepare a series of CeOx modified Pt/Al2O3 catalysts, offering a unique system to specifically probe the relationship between Ce and Pt without any bulk CeO2 present. Ce L3 edge X-ray absorption near edge structure (XANES) analysis was used to ascertain the oxidation state of the Ce in the catalyst materials in atmospheres of air, H2 (g), and CO (g) at room temperature. The XANES data showed that the Ce was present as both Ce3+ and Ce4+ oxidation states in an atmosphere of air, becoming predominantly present as Ce3+ in H2 and CO. The results indicate the role of Pt in the process, and show that with the absence of bulk CeO2, changes in Ce oxidation state can be observed at non-elevated temperatures. The CeOx/Pt/Al2O3 catalysts were tested for their performance toward the water gas shift (WGS) reaction and showed improved performance compared to the unmodified Pt/Al2O3, even at very low concentrations of Ce (∼0.35 wt-%).
{"title":"Reduction properties of Ce in CeOx/Pt/Al2O3 catalysts","authors":"P. Wells, E. Crabb, C. R. King, S. Fiddy, A. Amieiro-Fonseca, D. Thompsett, A. Russell","doi":"10.1179/2055075815Y.0000000001","DOIUrl":"https://doi.org/10.1179/2055075815Y.0000000001","url":null,"abstract":"Abstract A controlled surface reaction (CSR) technique has been successfully employed to prepare a series of CeOx modified Pt/Al2O3 catalysts, offering a unique system to specifically probe the relationship between Ce and Pt without any bulk CeO2 present. Ce L3 edge X-ray absorption near edge structure (XANES) analysis was used to ascertain the oxidation state of the Ce in the catalyst materials in atmospheres of air, H2 (g), and CO (g) at room temperature. The XANES data showed that the Ce was present as both Ce3+ and Ce4+ oxidation states in an atmosphere of air, becoming predominantly present as Ce3+ in H2 and CO. The results indicate the role of Pt in the process, and show that with the absence of bulk CeO2, changes in Ce oxidation state can be observed at non-elevated temperatures. The CeOx/Pt/Al2O3 catalysts were tested for their performance toward the water gas shift (WGS) reaction and showed improved performance compared to the unmodified Pt/Al2O3, even at very low concentrations of Ce (∼0.35 wt-%).","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075815Y.0000000001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65872484","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-04-01DOI: 10.1179/2055075815Y.0000000003
M. Dad, H. Fredriksson, J. van de Loosdrecht, P. Thüne, J. Niemantsverdriet
Abstract A systematic study was carried out to investigate the response of monodisperse supported Fe and FeMn nanoparticles to treatments in O2, H2 and H2/CO at temperatures between 270 and 400°C. Uniform size (7–14 nm), Fe and mixed FeMn nanoparticles were synthesised by applying thermal decomposition of Fe- and Mn-oleate complexes in a high boiling point solvent. By combining X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analysis, the phase composition and morphology of the model catalysts were studied. Energy-dispersive X-ray analysis shows that the catalyst particles have the expected composition of Fe and Mn. Well-defined crystallite phases [maghemite (γ-Fe2O3) and mixed FeMn-spinel] were observed after calcination at 350°C in Ar/O2 using XPS analysis. Upon subsequent treatments in H2 and H2/CO the crystal phases changed from maghemite (γ-Fe2O3) to metallic Fe, Fe carbide and graphitic C. Using Mn as a promoter influences the nanoparticle size achieved during the fabrication of Fe nanoparticles and improves their stability against morphological change and agglomeration during reduction and Fischer–Tropsch synthesis conditions.
{"title":"Stabilization of iron by manganese promoters in uniform bimetallic FeMn Fischer–Tropsch model catalysts prepared from colloidal nanoparticles","authors":"M. Dad, H. Fredriksson, J. van de Loosdrecht, P. Thüne, J. Niemantsverdriet","doi":"10.1179/2055075815Y.0000000003","DOIUrl":"https://doi.org/10.1179/2055075815Y.0000000003","url":null,"abstract":"Abstract A systematic study was carried out to investigate the response of monodisperse supported Fe and FeMn nanoparticles to treatments in O2, H2 and H2/CO at temperatures between 270 and 400°C. Uniform size (7–14 nm), Fe and mixed FeMn nanoparticles were synthesised by applying thermal decomposition of Fe- and Mn-oleate complexes in a high boiling point solvent. By combining X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analysis, the phase composition and morphology of the model catalysts were studied. Energy-dispersive X-ray analysis shows that the catalyst particles have the expected composition of Fe and Mn. Well-defined crystallite phases [maghemite (γ-Fe2O3) and mixed FeMn-spinel] were observed after calcination at 350°C in Ar/O2 using XPS analysis. Upon subsequent treatments in H2 and H2/CO the crystal phases changed from maghemite (γ-Fe2O3) to metallic Fe, Fe carbide and graphitic C. Using Mn as a promoter influences the nanoparticle size achieved during the fabrication of Fe nanoparticles and improves their stability against morphological change and agglomeration during reduction and Fischer–Tropsch synthesis conditions.","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075815Y.0000000003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65872080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-02-01DOI: 10.1179/2055075814Y.0000000007
Shu Zhao, Xingwu Liu, Chun-fang Huo, Yong-wang Li, Jianguo Wang, H. Jiao
Abstract The chemical–physical environment around iron based FTS catalysts under working conditions is used to estimate the influences of carbon containing gases on the surface structures and stability of ε-Fe2C, χ-Fe5C2, θ-Fe3C and Fe4C from combined density functional theory and atomistic–thermodynamic studies. Higher carbon content gas has higher carburization ability; while higher temperature and lower pressure as well as higher H2/CO ratio can suppress carburization ability. Under wide ranging gas environment, ε-Fe2C, χ-Fe5C2 and θ-Fe3C have different morphologies, and the most stable non-stoichiometric termination changes from carbon-poor to carbon-rich (varying surface Fe/C ratio) upon the increase in ΔμC. The most stable surfaces of these carbides have similar surface bonding pattern, and their surface properties are related to some common phenomena of iron based catalysts. For these facets, χ-Fe5C2-(100)-2.25 is most favored for CO adsorption and CH4 formation, followed by θ-Fe3C-(010)-2.33, ε-Fe2C-(121)-2.00 and Fe4C-(100)-3.00, in line with surface work function and the charge of the surface carbon atoms.
{"title":"Determining surface structure and stability of ε-Fe2C, χ-Fe5C2, θ-Fe3C and Fe4C phases under carburization environment from combined DFT and atomistic thermodynamic studies","authors":"Shu Zhao, Xingwu Liu, Chun-fang Huo, Yong-wang Li, Jianguo Wang, H. Jiao","doi":"10.1179/2055075814Y.0000000007","DOIUrl":"https://doi.org/10.1179/2055075814Y.0000000007","url":null,"abstract":"Abstract The chemical–physical environment around iron based FTS catalysts under working conditions is used to estimate the influences of carbon containing gases on the surface structures and stability of ε-Fe2C, χ-Fe5C2, θ-Fe3C and Fe4C from combined density functional theory and atomistic–thermodynamic studies. Higher carbon content gas has higher carburization ability; while higher temperature and lower pressure as well as higher H2/CO ratio can suppress carburization ability. Under wide ranging gas environment, ε-Fe2C, χ-Fe5C2 and θ-Fe3C have different morphologies, and the most stable non-stoichiometric termination changes from carbon-poor to carbon-rich (varying surface Fe/C ratio) upon the increase in ΔμC. The most stable surfaces of these carbides have similar surface bonding pattern, and their surface properties are related to some common phenomena of iron based catalysts. For these facets, χ-Fe5C2-(100)-2.25 is most favored for CO adsorption and CH4 formation, followed by θ-Fe3C-(010)-2.33, ε-Fe2C-(121)-2.00 and Fe4C-(100)-3.00, in line with surface work function and the charge of the surface carbon atoms.","PeriodicalId":43717,"journal":{"name":"Catalysis Structure & Reactivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1179/2055075814Y.0000000007","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65871785","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-02-01DOI: 10.1179/2055075814Y.0000000005
A. Beale, I. Lezcano‐González, T. Maunula, R. Palgrave
Abstract Vanadium based catalysts supported on a mixture of tungsten and titanium oxide (V2O5/WO3–TiO2) are known to be highly active for ammonia selective catalytic reduction (NH3–SCR) of NOx species for heavy-duty mobile applications. However they are also known to be sensitive to high temperatures which leads to both sintering of the anatase TiO2 support and a first order phase transition to rutile at temperatures >600°C. Here we report our attempts to use SiO2 to stabilize the TiO2 anatase phase and to compare its catalytic activity with that of a non-stabilized V2O5/WO3–TiO2 catalyst after thermal aging up to 800°C. Detailed characterization using spectroscopic (Raman, UV–vis, X-ray absorption spectroscopy), scattering and techniques providing information on the catalytic surface (Brunauer–Emmet–Teller, NH3 adsorption) have also been performed in order to understand the impact of high temperatures on component speciation and the catalytic interface. Results show that non-stabilized V2O5/WO3–TiO2 catalysts are initially stable after thermal aging at 600°C but on heating above this temperature a marked drop in catalytic activity is observed as a result of sintering and phase transformation of Anatase into Rutile TiO2 and phase segregation of initially highly dispersed WO3 and polymeric V2O5 into monoclinic WO3 and V2O3 crystallites. Similar behavior was observed for the 4–5 wt-% of SiO2-stabilised sample after aging above 700°C, importantly therefore, offset by some ∼100°C in comparison to the unstabilised sample.
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