An FTIR study of surface ceria hydroxy groups during a redox process with H2

Badri, Ahmed; Binet, Claude; Lavalley, Jean‐Claude

doi:10.1039/ft9969204669

Cited by 225 publications

(198 citation statements)

References 11 publications

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“…Exposure to the CO+O 2 gas mixture at T=523 K resulted in spectra very similar to that observed at T=383 DRIFT spectra in the region 3800-3100 cm was assigned to triply bridging OH (III) species [35]. Increase of the temperature resulted in a slight (~10 cm (accordingly to the corresponding ν(CO 3 ) bands in Figure 5) through reaction of CO with terminal (OH-I) hydroxyl groups.…”

Section: In-situ Driftsmentioning

confidence: 74%

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part II: Oxidation states and surface species on Pd/CeO2 under reaction conditions, suggested reaction mechanism

Pozdnyakova

Teschner

Wootsch

et al. 2006

Journal of Catalysis

199

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The aim of the PROX reaction is to reduce the CO content of hydrogen feed to proton exchange membrane fuel cells (PEMFC) by selective oxidation of CO in the presence of excess hydrogen. Both Pt and Pd on ceria are active in CO oxidation (without hydrogen) while Pd is poorly active in the presence of hydrogen. In this paper we aimed at finding the reasons of such behavior, using the same techniques for Pd/CeO 2 as for Pt/CeO 2 in Part I: catalytic tests, in-situ DRIFTS, high-pressure XPS, HRTEM and TDS. The reaction mechanism of CO oxidation (without hydrogen) was also examined. It does not occur via the exactly same mechanism on Pt and Pd/CeO 2 catalyst. In the presence of hydrogen (PROX) at low temperature (T=350-380 K), the formation of Pd β-hydride was confirmed by high-pressure in-situ XPS. Its formation greatly suppressed the possibility of CO oxidation, because oxygen both from gas phase and support sites reacted fast with hydride H to form water, and this water desorbed from Pd easily. Nevertheless, CO adsorption was not hampered here. These entities transformed mainly to surface formate and formyl (-CHO) species instead of oxidation as observed by DRIFTS. The participation of a low-temperature water-gas-shift type reaction proposed for the platinum system [Part I] was hindered. Increasing temperature led to decomposition of the hydride phase and a parallel increase in the selectivity towards CO oxidation was observed. However, it remained still lower on Pd/CeO 2 than on Pt/CeO 2 .

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Section: In-situ Driftsmentioning

confidence: 74%

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part II: Oxidation states and surface species on Pd/CeO2 under reaction conditions, suggested reaction mechanism

Pozdnyakova

Teschner

Wootsch

et al. 2006

Journal of Catalysis

199

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“…A small shoulder at 3565 cm À1 may be attributable to triply bridging OH species. [33] Exposing the catalyst to dry CH 4 -oxidation conditions for 1 h (Figure 9 d) caused minimal changes; however, heating the sample to 800 8C (Figure 9 e) greatly reduced the intensity of the n(OH) stretching band. The fact that this feature is significantly less evident in the case of Pd/Si-Al 2 O 3 ( Figure 9 e-f) aged under wet conditions suggests that the stable hydroxyls are somehow linked to the defective -nanostructured ceria.…”

mentioning

confidence: 96%

Methane Catalytic Combustion over Hierarchical Pd@CeO₂/Si‐Al₂O₃: Effect of the Presence of Water

et al. 2014

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The influence of water vapor on methane catalytic combustion was studied over a Pd@CeO2/Si‐Al2O3 catalyst, carefully designed to maximize Pd‐CeO2 interaction and prevent metal sintering and compared to a conventional impregnated catalyst with identical chemical composition. Although the nanostructured Pd@CeO2/Si‐Al2O3 catalyst is thermally stable, the addition of water to the reaction feed leads to a transient deactivation at low temperatures, consistent with the well documented competitive adsorption. In addition to this, the hierarchically structured catalyst exhibits an additional severe deactivation after methane oxidation in the presence of water vapor at 600 °C that can be reversed only by heating the catalyst above 700 °C. The presence of water in the reaction feed deactivates the conventional impregnated catalyst less severely and the activity largely returns upon water removal. Catalytic FTIR and CO‐chemisorption data indicate that this severe deactivation process in the hierarchical catalyst is due to the formation of stable OH groups on the surface of the ceria nanoparticles. These hydroxyl groups are suggested to significantly inhibit the oxygen spillover from the CeO2 nanoparticles to Pd, preventing its efficient re‐oxidation, as observed by operando X‐ray absorption near edge spectroscopy (XANES) experiments. At the same time, their presence can contribute to limit the gas phase accessibility of Pd, as indicated by the decrease of CO chemisorption capability. The presence of hydroxyls plays a minor role on the deactivation of the conventional catalyst at 600 °C.

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“…The first zone displays bands corresponding mainly to hydroxyl species (isolated ones of various types giving sharp bands in the 3720-3600 cm −1 range and associated species giving a broad band extending from ca. 3800 to 3000 cm −1 ) [54,55]. A second spectral zone below 1700 cm −1 exhibits most intense bands of carbonate or related species [56][57][58].…”

Section: Nature Of Active Sites/entities and Further Hints On Catalytmentioning

confidence: 99%

Characterization of Active Sites/Entities and Redox/Catalytic Correlations in Copper-Ceria-Based Catalysts for Preferential Oxidation of CO in H2-Rich Streams

et al. 2013

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This article reviews work done at authors' laboratories about catalysts based on combinations between copper and ceria for preferential oxidation of CO in H 2 -rich streams (CO-PROX). The main focus of this review is the characterization of active sites for the process on the basis of spectroscopic analysis of the systems under reaction conditions (operando techniques). On such a basis, it is exposed the state of the art in this field in connection with results obtained in other laboratories. OPEN ACCESSCatalysts 2013, 3 379 Keywords: copper-ceria catalysts; CO preferential oxidation (CO-PROX); diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS); X-ray absorption near edge spectroscopy (XANES); Raman; X-ray diffraction (XRD); X-ray photoelectron spectroscopy (XPS)

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An FTIR study of surface ceria hydroxy groups during a redox process with H2

Cited by 225 publications

References 11 publications

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part II: Oxidation states and surface species on Pd/CeO2 under reaction conditions, suggested reaction mechanism

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part II: Oxidation states and surface species on Pd/CeO2 under reaction conditions, suggested reaction mechanism

Methane Catalytic Combustion over Hierarchical Pd@CeO₂/Si‐Al₂O₃: Effect of the Presence of Water

Characterization of Active Sites/Entities and Redox/Catalytic Correlations in Copper-Ceria-Based Catalysts for Preferential Oxidation of CO in H2-Rich Streams

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An FTIR study of surface ceria hydroxy groups during a redox process with H2

Cited by 225 publications

References 11 publications

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part II: Oxidation states and surface species on Pd/CeO2 under reaction conditions, suggested reaction mechanism

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part II: Oxidation states and surface species on Pd/CeO2 under reaction conditions, suggested reaction mechanism

Methane Catalytic Combustion over Hierarchical Pd@CeO2/Si‐Al2O3: Effect of the Presence of Water

Characterization of Active Sites/Entities and Redox/Catalytic Correlations in Copper-Ceria-Based Catalysts for Preferential Oxidation of CO in H2-Rich Streams

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Methane Catalytic Combustion over Hierarchical Pd@CeO₂/Si‐Al₂O₃: Effect of the Presence of Water