Low temperature catalytic NOx–H2 reactions over Pt/TiO2-ZrO2 in an excess oxygen

Platinum catalysts supported on noncrystalline TiO2-ZrO2 binary oxides were found to be highly active for the selective NO reduction in a stream of NO (0.08 vol.%)–H2 (0.08–0.56 vol.%)–O2 (10 vol.%) at low temperatures (<100°C). The NO conversion to N2/N2O occurred at >0.08 vol.% H2 and the selectivity to N2 increased with increasing H2 concentration. In situ DRIFTS measurement suggested that the high selectivity in this temperature range is closely related to a stoichiometric reaction between H2 and NO oxidatively adsorbed as nitrate (NO3−). By comparison with the results from a parallel study of H2–O2 combustion, we propose that almost all of H2 reacted is consumed by the reduction of nitrate species, which covered the Pt surface to inhibit H2–O2 combustion. The NO reduction activity was sensitive to the catalyst pretreatment; the catalyst reduced in H2 allowed 89% NO conversion at 90°C, whereas the catalyst treated in O2 required 175°C to attain the lower conversion of 50%. The effect of the pretreatment is closely related to the reactivity of nitrate adsorbates produced via different routes.