Nanoporous Gold-Supported Ceria for the Water–Gas Shift Reaction

Jul 22, 2014 - Photoemission spectroscopy indicates a defect (Ce3+) concentration of about 70% on the surface of the cerium oxide deposits, prior to a...
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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.



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 (