Study of low temperature water gas shift reaction on promoted Au/Al2O3 catalysts

Abstract

The goal of this research was to test the activity of the promoted Au/Al2O3 catalyst for the low temperature water gas shift (LT-WGS) reaction. First, a series of 1.25 wt.% Au/MOx/γ-Al2O3 (M= Ce, Mg, Fe, Mn, Co, Ni) catalysts were prepared by impregnation of the metal oxide promoter on alumina support followed by the homogeneous deposition precipitation of Au on the promoter-alumina complex. The catalysts were tested in a microflow reaction system. It was found that these promoted catalysts were non-active for the WGS reaction under 5% CO, 15% H2O, 60% H2 and balance He. Considering that previously reported studies had mainly focused on CeO2 promoted/supported catalyst due to its significant positive effects on WGS activity, the study was continued only with the Ce containing catalyst. The activity of the catalyst increased with increasing Ce loading from 1.25 wt.% to 10 wt.% significantly while the increase in the activity was minor with the further increase of the ceria content to 20 wt.%. The effect of Au loading was also investigated for x%Au/20wt.%Ce/γ-Al2O3 catalyst and the CO conversion decreased first with the increasing Au content from 1 wt.% to 3 wt.% but it increased with further increase of Au to 5 wt.%. On the best performing catalyst (5wt.%Au/20wt.%Ce/γ-Al2O3) three different (1, 2, 3) H2O/CO ratios were studied and it was observed that the activity increased with the increasing water vapor pressure. Moreover, activity of 5wt.%Au/20wt.%Ce/γ-Al2O3 catalyst was evaluated for the WGS reaction under different reaction conditions including without H2 and CO2 (only 5% CO, 15% H2O and balance He), with 15% CO2 but without H2, with 60% H2 but without CO2 and with both 15% CO2 and 60% H2. Although the negative effect of the presence of 15% CO2 in the feed was quite small, the conversion decreased dramatically with the addition of 60% H2. The presence of CO2 and H2 in the feed together resulted the lowest conversion as expected.