Catalytic and noncatalytic CO oxidation on Au/TiO 2 catalysts

Abstract

The CO oxidation reaction has been studied on Au/TiO 2 catalysts prepared by incipient wetness (IW) and deposition–precipitation (DP) methods, with a range of metal loadings from 0.1 to 5 wt% for the former. We have found that there are three types of CO 2 production from fresh catalysts which have been calcined to only 120 °C, namely noncatalytic (types I and II) and catalytic (type III). The DP catalysts are far more active for type III reaction, showing activity at room temperature, whereas the IW catalysts generally do not show steady-state conversion until >120 °C. However, IW catalysts with low loadings produce type I CO 2 (that formed at room temperature), whereas higher loadings produce only type II (that formed when heating), with intermediate loadings showing both. We associate type I CO 2 production with monolayer Au catalysts, which have intimate contact with the TiO 2, and are probably already in some oxidic form. Type II behavior we associate with three-dimensional oxidic Au, the surface of which is no longer in direct contact with the support. The poor performance of IW catalysts compared with DP catalysts is ascribed to the presence of chloride in the former, which induces a larger average particle size, and vulnerability to extensive sintering.