Nanoporous Gold-Supported Ceria for the Water-Gas Shift Reaction: UHV Inspired Design for Applied Catalysis

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 watergas shift (WGS) reaction (H2O + CO + H-2 + CO2) in a continuous flow reactor at ambient pressure conditions. Formation of CO2 was observed at temperatures as low as 135 degrees C with excellent stability and reproducibility up to temperatures of 535 degrees 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 degrees 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.