Gold Catalyst for Low Temperature Water-Gas Shift Reaction

The main goal of this reseach is to prepare a gold catalyst with good activity and stability for low temperature water-gas shift reaction (WGS). The following effects on reaction activity were studied: (1) catalyst preparation methods; (2) choice of supports (CeO2 or TiO2); (3) catalyst pretreatment before WGS; (4) water amount during WGS. Moreover, the properties of the catalysts were investigated by using HRTEM, FTIR, XPS, TPR, AA and BET. For nano-gold supported on CeO2 (i.e., Au/CeO2), the catalyst pretreated with reductive gas possessed much higher WGS activity than that with non-reductive gas, among which activity under CO is better than that under H2. Reductive pretreatments lead to larger amounts of metallic gold on the catalysts and oxygen vacancies in CeO2, which can be the reason for better activity preformances. Research work concerning the effect of water amounts revealed that the discrapencies in water amounts would affect both the activity and stability for WGSR. When the reactant gas with highest H2/CO ratio, derived from steam-methane reforming, was introduced into the reactor, the amount of water should be higher than 20 mol% to prevent the oscillation of activity. For the study of variables in deposition-precipitation method to prepare Au/CeO2, pH value of gold solutions and a prior modification of CeO2 caused little differences on the activity of gold catalysts. Desorption of surface oxygen from CeO2 became more difficult after the prior modification, thus lowered the activity. However, the presence of nanogold causes CeO2 to be reduced under low temperature, which could compensate the poor performance of modified CeO2. For nano-gold supported on TiO2 (i.e., Au/TiO2), difference between pretreatments was less significant than that seen in Au/CeO2, but Au/TiO2 had much better activity than Au/CeO2 at 200 oC based on same gold amounts. The catalyst prepared at pH 9 had activity similar to that prepared at pH 6 per weight of gold, but possessed lower gold loading. Therefore, higher activity was obtained for Au/TiO2 prepared at pH 6 based on the same weight of total catalysts. Finally, by testing in different reaction conditions, it was found that Au/TiO2(pH6) possessed higher activity than other catalysts reported in the literature. Moreover, it was stable in long-term activity test. In summary, Au/TiO2(pH6) is the most suitable one for practical uses and future study on this catalyst is required for better activity performances.