Selective oxidation of methanol to hydrogen over gold catalysts promoted by alkaline-earth-metal and lanthanum oxides

Abstract

A series of alumina-supported gold catalysts was investigated for the CO-free production of hydrogen by partial oxidation of methanol. The addition of alkaline-earth metal oxide promoters resulted in a significant improvement of the catalytic performance. The methanol conversion was ca. 85 % with all studied catalyst materials, however, the selectivity for hydrogen increased from 15 % to 51 % when going from the unpromoted to a BaO-promoted catalyst. The formation of the undesired byproducts CO, methane, and dimethyl ether was considerably reduced as well. The observed trend in catalyst performance follows the trend in increasing basicity of the studied promoter elements, indicating a chemical effect of the promoter material. Superior catalytic performance, in terms of H2 and CO selectivity, was obtained with a Au/La2O3 catalyst. At 300 °C the hydrogen selectivity reached 80 % with only 2 % CO formation, and the catalyst displayed a stable performance over at least 24 h on-stream. Furthermore, the formation of CO was found to be independent of the oxygen concentration in the feed. The commercial lanthanum oxide used in this study had a low specific surface area, which led to the formation of relative large gold particles. Therefore, the catalytic activity could be enhanced by decreasing the gold particle size through deposition on lanthanum oxide supported on high-surface-area alumina.