Pre-reduction of Au/iron oxide catalyst for low-temperature water-gas shift reaction below 150 °C

Low-temperature water-gas shift reaction (WGS) using gold catalyst is expected to be an attractive technique to realize an efficient on-site hydrogen production process. In this paper, Au/Fe₃O₄ catalysts for promoting the WGS below 150 °C were developed by a preliminary reduction of Au/iron oxide (Fe³⁺) catalyst utilizing high reactivity of Au nano-particles. The reduction was conducted under a CO, H₂, or CO/H₂O stream at either 140 or 200 °C, and the effect of reduction conditions on the characteristics of the Au/Fe₃O₄ catalyst and on the catalytic activity in WGS at 80 °C was investigated. The reaction progress during the pre-reduction treatment was qualitatively analyzed, and it was found that the iron oxide in Au/Fe₂O₃ calcined at 200 °C was easily reduced to Fe₃O₄ phase in all reduction conditions. The reduction conditions affected the characteristics of both Au and iron oxide, but all of the reduced catalysts had small Fe₃O₄ particles of less than 20 nm with Au particles on the surface. The surface area and content of cationic Au were high in the order of CO, H₂, CO/H₂O, and 140, 200 °C. In the WGS test at 80 °C using the developed catalysts, the activities of the catalysts pre-reduced by CO at 140 or 200 °C and by H₂ at 140 °C were very high with 100% CO conversion even at such a low temperature. These results indicated that factors such as higher surface area, crystallized Fe₃O₄, and cationic Au content contributed to the catalytic activity.