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

Christoph Rameshan, University of Innsbruck; Max Planck Society
Harald Lorenz, University of Innsbruck
Lukas Mayr, University of Innsbruck
Simon Penner, University of Innsbruck
Dmitry Zemlyanov, Birck Nanotechnology Center, Purdue University
Rosa Arrigo, Max Planck Society
Michael Haevecker, Max Planck Society
Raoul Blume, Max Planck Society
Axel Knop-Gericke, Max Planck Society
Robert Schloegl, Max Planck Society
Bernhard Kloetzer, University of Innsbruck

Abstract

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 similar to 4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453 K in vacuum yields a similar to 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. (C) 2012 Elsevier Inc. All rights reserved.

Discipline(s)

Nanoscience and Nanotechnology