TAP study on carbon monoxide oxidation over supported gold catalysts Au/Ti(OH)∗4 and Au/Fe(OH)*3: Moisture effect

The effect of moisture on the behavior of the active supported gold catalysts developed by us, Au/Ti(OH)∗4 (I) and Au/Fe(OH)∗3 (II), during CO activation and CO oxidation in the temperature range 298–473 K was investigated by the temporal analysis of products (TAP) technique. The oxidation reaction over the Au/Ti(OH)∗4 catalyst was totally suppressed by the presence of water, independent of the water content of 200 and 1000 ppm, the carbon monoxide-to-oxygen ratio, and the temperature. In contrast, the presence of water vapors showed no effect on CO oxidation over the Au/Fe(OH)∗3 catalyst. For both catalysts, the carbon monoxide adsorption feature was unalterable by the presence of water, namely CO molecules reversibly adsorbed on the catalyst surface, but the amount of CO adsorbed decreased by increasing water content. When a reaction mixture at a 1:1 ratio of CO to O2 was pulsed on the catalyst in the absence of water, the CO response curve showed two peaks, whereas in the presence of water, the TAP response curve showed only one peak. At a 1:3 CO-to-O2 ratio, the CO response curve showed only one peak, which shifted to a shorter time and narrowed in the absence of water. The shift was more pronounced on catalyst (II). The TAP experiments provided indirect evidence that CO and water adsorbed together (CO weakly and water strongly) and water blocked [irreversibly for Au/Ti(OH)∗4 and reversibly for Au/Fe(OH)∗3], the adsorption sites for oxygen.