Gold–ceria catalysts for low-temperature water-gas shift reaction

Abstract

Nanostructured Au–ceria is a promising new catalyst for low-temperature water-gas shift (LTS). Preparation, characterization, and catalytic properties of this material are reported in this paper. Gold–ceria was prepared by deposition–precipitation (DP), coprecipitation (CP), and gelation methods. The gold loading was varied between 1 and 8.3 at.%, while lanthanum used as a dopant in ceria, was 4 or 10 at.%. Most gold is in metallic state, but ionic gold was also present as identified by XPS. The average ceria crystallite size in samples prepared by gelation was 4.5 and 7 nm, respectively, after calcination at 400 or 650 °C. The gold particle size in samples prepared by DP was <5 nm after 10 h long heating in air at 400 °C. The gold particle size did not increase with gold loading in these samples. A dramatic effect of gold on the reducibility of the surface oxygen of ceria was found by H 2-temperature-programmed reduction (TPR). All of the available surface oxygen was reduced, while there was no effect on the bulk oxygen of ceria. The enhancement of cerium oxide reducibility by gold is independent of the method of catalyst preparation. Oxygen storage capacity (OSC) measurements using step pulses of CO were in agreement with the TPR results; the presence of gold greatly enhances the OSC of ceria. Similar tests with copper-containing ceria were conduced for comparison. Carbon-containing species left on the surface after the CO step, can be fully removed with O 2 or partially removed with H 2O. The high catalytic activity of Au–ceria for LTS reaction correlates well with the ceria structure and oxygen transfer properties.