Article pubs.acs.org/JPCC
Nanoporous Gold-Supported Ceria for the Water−Gas Shift Reaction: UHV Inspired Design for Applied Catalysis Junjie Shi,‡ Andreas Schaefer,‡ Andre Wichmann,‡ M. Mangir Murshed,† Thorsten M. Gesing,† Arne Wittstock,*,‡ and Marcus Baü mer‡ ‡
Institute of Applied and Physical Chemistry and Center for Environmental Research and Sustainable Technology, University Bremen, Leobener Strasse NW 2, 28359 Bremen, Germany † Chemische Kristallographie fester Stoffe/FB02, Universität Bremen, Leobener Strasse NW 2, 28359 Bremen, Germany S Supporting Information *
ABSTRACT: Inspired by model studies under ultrahigh vacuum (UHV) conditions, inverse monolithic gold/ceria catalysts are prepared using thermal decomposition of a cerium nitrate precursor on a nanoporous gold (npAu) substrate. Cerium oxide deposits throughout the porous gold material (pores and ligaments 30−40 nm) are formed. npAu disks and coatings were prepared with loadings of about 3 to 10 atom % of ceria. The composite material was tested for the water−gas shift (WGS) reaction (H2O + CO → H2 + CO2) in a continuous flow reactor at ambient pressure conditions. Formation of CO2 was observed at temperatures as low as 135 °C with excellent stability and reproducibility up to temperatures of 535 °C. The considerably increased thermal stability of the material can be linked to the presence of metal oxide deposits on the nanosized gold ligaments. The loss of activity after about 15 h of catalytic conversion with heating to 535 °C was only about 10%. Photoemission spectroscopy indicates a defect (Ce3+) concentration of about 70% on the surface of the cerium oxide deposits, prior to and after WGS reaction. Raman spectroscopic characterization of the material revealed that the bulk of the oxide is reoxidized during reaction.
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INTRODUCTION During the last decades increasing demand for a novel type of water−gas shift (WGS) catalyst in the context of mobile and green energy harvesting such as in fuel cells surfaced.1,2 For either low-temperature fuel cells (polymer electrolyte membrane fuel cells, PEMFC) or high-temperature fuel cells in mobile applications such as in cars a novel type of WGS catalyst is required. These catalysts need to be highly active at low temperatures, shifting CO almost quantitatively to hydrogen (
