Preparation of supported Pt-M catalysts (M=Mo and W) from anion-exchanged hydrotalcites and their catalytic activity for low temperature NO-H2-O2 reaction

The NO-H2-O2 reaction was studied over supported bimetallic catalysts, Pt-Mo and Pt-W, which were prepared by coexchange of hydrotalcite-like Mg-Al double layered hydroxides by Pt(NO2)42−, MoO42−, and/or WO42− and subsequent heating at 600°C in H2. The Pt–Mo interaction could obviously be seen when the catalyst after reduction treatment was exposed to a mixture of NO and H2 in the absence of O2. The Pt-HT catalyst showed the almost complete NO conversion at 70°C, whereas the Pt-Mo-HT showed a negligible conversion. Upon exposure to O2, however, Pt-Mo-HT exhibited the NO conversion at the lowest temperature of ≥30°C, compared to ≥60°C required for Pt-HT. EXAFS/XANES, XPS and IR results suggested that the role of Mo is very sensitive to the oxidation state, i.e., oxidized Mo species residing in Pt particles are postulated to retard the oxidative adsorption of NO as NO3 and promote the catalytic conversion of NO to N2O at low temperatures.