CO₂-selective methanol steam reforming on In-doped Pd studied by in situ X-ray photoelectron spectroscopy

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• 作者：Christoph Rameshan ; Harald Lorenz ; Lukas Mayr ; Simon Penner ; Dmitry Zemlyanov ; Rosa Arrigo ; Michael Haevecker ; Raoul Blume ; Axel Knop-Gericke ; Robert Schl?gl ; Bernhard Kl?tzer
• 关键词：PdIn near-surface alloy ; Pd foil ; Methanol dehydrogenation ; Methanol steam reforming ; Water activation ; In situ X-ray photoelectron spectroscopy (AP-XPS)
• 刊名：Journal of Catalysis
• 出版年：2012
• 出版时间：November, 2012
• 年：2012
• 卷：295
• 期：Complete
• 页码：186-194
• 全文大小：894 K

文摘

In situ X-ray photoelectron spectroscopy (in situ XPS) was used to study the structural and catalytic properties of Pd-In near-surface intermetallic phases in correlation with previously studied PdZn and PdGa.

Room temperature deposition of ¡«4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453 K in vacuum yields a ¡«1:1 Pd/In near-surface multilayer intermetallic phase. This Pd₁In₁ phase exhibits a similar ¡°Cu-like¡± electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd₁Zn₁ counterpart.

Catalytic characterization of the multilayer Pd₁In₁ phase in MSR yielded a CO₂-selectivity of almost 100 % between 493 and 550 K. In contrast to previously studied In₂O₃-supported PdIn nanoparticles and pure In₂O₃, intermediate formaldehyde is only partially converted to CO₂ using this Pd₁In₁ phase. Strongly correlated with PdZn, on an In-diluted PdIn intermetallic phase with ¡°Pd-like¡± electronic structure, prepared by thermal annealing at 623 K, methanol steam reforming is suppressed and enhanced CO formation via full methanol dehydrogenation is observed.

To achieve CO₂-TOF values on the isolated Pd₁In₁ intermetallic phase as high as on supported PdIn/In₂O₃, at least 593 K reaction temperature is required. A bimetal-oxide synergism, with both bimetallic and oxide synergistically contributing to the observed catalytic activity and selectivity, manifests itself by accelerated formaldehyde-to-CO₂ conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd₁In₁ inhibited inverse water-gas-shift reaction on In₂O₃ and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO₂-selectivity of the supported catalyst.