Correlation between CO surface coverage and selectivity/kinetics for the preferential CO oxidation over Pt/γ-Al2O3 and Au/α-Fe2O3: an in-situ DRIFTS study

Schubert, Markus M.; Kahlich, M.J.; Gasteiger, Hubert A.; Behm, R. Jürgen

doi:10.1016/s0378-7753(99)00314-6

Cited by 160 publications

(105 citation statements)

References 30 publications

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“…To comprehend this behavior, the fact that cerium oxide has a strong tendency to provide active oxygens with strong oxidation power [6,12,25,26], which are however reactive towards both CO and H 2 , must be taken into account. This causes a drop of selectivity at higher temperature due to the higher activation energy of H 2 oxidation compared to that of CO [27][28][29][30].…”

Section: Catalytic Activitymentioning

confidence: 99%

Ru–Pd Bimetallic Catalysts Supported on CeO2-MnOX Oxides as Efficient Systems for H2 Purification through CO Preferential Oxidation

et al. 2018

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Abstract:The catalytic performances of Ru/ceria-based catalysts in the CO preferential oxidation (CO-PROX) reaction are discussed here. Specifically, the effect of the addition of different oxides to Ru/CeO 2 has been assessed. The Ru/CeO 2 -MnO x system showed the best performance in the 80-120 • C temperature range, advantageous for polymer-electrolyte membrane fuel cell (PEMFC) applications. Furthermore, the influence of the addition of different metals to this mixed oxide system has been evaluated. The bimetallic Ru-Pd/CeO 2 -MnO x catalyst exhibited the highest yield to CO 2 (75%) at 120 • C whereas the monometallic Ru/CeO 2 -MnO x sample was that one with the highest CO 2 yield (60%) at 100 • C. The characterization data (H 2 -temperature programmed reduction (H 2 -TPR), X-ray diffraction (XRD), N 2 adsorption-desorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS)) pointed out that the co-presence of manganese oxide and ruthenium enhances the mobility/reactivity of surface ceria oxygens accounting for the good CO-PROX performance of this system. Reducible oxides as CeO 2 and MnO x , in fact, play two important functions, namely weakening the CO adsorption on the metal active sites and providing additional sites for adsorption/activation of O 2 , thus changing the mechanism from competitive Langmuir-Hinshelwood into non-competitive one-step dual site Langmuir-Hinshelwood/Mars-van Krevelen. As confirmed by H 2 -TPR and XPS measurements, these features are boosted by the simultaneous presence of ruthenium and palladium. The strong reciprocal interaction of these metals between them and with the CeO 2 -MnO x support was assumed to be responsible of the promoted reducibility/reactivity of CeO 2 oxygens, thus resulting in the best CO-PROX efficiency at low temperature of the Ru-Pd/CeO 2 -MnO x catalyst. The higher selectivity to CO 2 found on the Ru-Pd system, which reduces the undesired H 2 consumption, represents a promising result of this research, being one of the key aims of the design of CO-PROX catalysts.

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Section: Catalytic Activitymentioning

confidence: 99%

Ru–Pd Bimetallic Catalysts Supported on CeO2-MnOX Oxides as Efficient Systems for H2 Purification through CO Preferential Oxidation

et al. 2018

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“…Thus, the knowledge of the surface coverage at meaningful catalytic turnover is critical and has always been the motivation of extensive experimental efforts. 1,2,3 Unfortunately, only a very few number of experimental techniques are capable of deriving such information, the most important ones being the various forms of vibrational spectroscopies. In this manuscript we will experimentally assess the coverage of surface species under catalytic turnover and correlate these with the reactivity.…”

Section: Introductionmentioning

confidence: 99%

Do observations on surface coverage-reactivity correlations always describe the true catalytic process? A case study on ceria

Farra

Eichelbaum

Schlögl

et al. 2013

Journal of Catalysis

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In situ (operando) investigations aim at establishing structure-function and/or coverage-reactivity correlations. Herein, we investigated the HCl oxidation reaction (4HCl + O 2 → 2Cl 2 + 2H 2 O) over ceria. In spite of its remarkable performance, under low oxygen over-stoichiometry this oxide is prone to a certain extent to subsurface/bulk chlorination, which leads to deactivation. In situ Prompt Gamma Activation Analysis (PGAA) studies evidenced that the chlorination rate is independent of the pre-chlorination degree but increases at lower oxygen over-stoichiometry, while dechlorination is effective in oxygen-rich feeds and its rate is higher for a more extensively pre-chlorinated ceria. Even bulk CeCl 3 could be transformed into CeO 2 under oxygen excess. Electron Paramagnetic Resonance experiments strongly suggested that oxygen activation is inhibited by a high surface chlorination degree.The coverages of most abundant surface intermediates, OH and Cl, were monitored by in situ infrared spectroscopy and PGAA under various conditions. Higher temperature and p(O 2 ) led to enhanced OH coverage, reduced Cl coverage, and increasing reactivity. Variation of p(HCl) gave rise to opposite correlations, while raising p(Cl 2 ) did not induce any measurable increase in the Cl coverage despite the strong inhibition of the reaction rate. The results indicate that only a small fraction of surface sites are actively involved in the reaction and most of the surface species probed in the in situ observation are spectator. Therefore, when performing in situ steady-state experiments, a large set of variables should be considered to obtain accurate conclusions.

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“…Recently, the preferential oxidation of CO in H 2 has been studied for applications in polymer electrolyte-type fuel cells (PEFCs) to reduce the CO con-centration in the produced fuel gases down to 10 ppm to prevent the fuel cell electrodes from being poisoned [4,5]. The outstanding catalytic activities of Pt, Rh, and Au are widely recognized [6][7][8][9][10][11]. A high activity for CO oxidation at higher reaction temperatures (150-250 • C) can be obtained on Pt catalysts; however, the competitive adsorption of CO and O 2 decreases the low-temperature activity of the catalysts [8,10].…”

Section: Introductionmentioning

confidence: 99%

“…The outstanding catalytic activities of Pt, Rh, and Au are widely recognized [6][7][8][9][10][11]. A high activity for CO oxidation at higher reaction temperatures (150-250 • C) can be obtained on Pt catalysts; however, the competitive adsorption of CO and O 2 decreases the low-temperature activity of the catalysts [8,10]. The reaction mechanism has also been extensively investigated over these catalysts [10,11].…”

Section: Introductionmentioning

confidence: 99%

Formation of subsurface oxygen species and its high activity toward CO oxidation over silver catalysts

Cheng

Huang

et al. 2005

Journal of Catalysis

177

126

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Correlation between CO surface coverage and selectivity/kinetics for the preferential CO oxidation over Pt/γ-Al2O3 and Au/α-Fe2O3: an in-situ DRIFTS study

Cited by 160 publications

References 30 publications

Ru–Pd Bimetallic Catalysts Supported on CeO2-MnOX Oxides as Efficient Systems for H2 Purification through CO Preferential Oxidation

Ru–Pd Bimetallic Catalysts Supported on CeO2-MnOX Oxides as Efficient Systems for H2 Purification through CO Preferential Oxidation

Do observations on surface coverage-reactivity correlations always describe the true catalytic process? A case study on ceria

Formation of subsurface oxygen species and its high activity toward CO oxidation over silver catalysts

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