Ambient temperature NO-H_2-O_2 reaction over supported Pt catalysts

摘要

Platinum catalysts supported on noncrystalline TiO_2 -ZrO_2 binary oxides were found to be highly active for the selective NO reduction in a stream of NO (0.08 vol percent) -H_2 (0.08-0.56 vol percent)-O_2 (10 vol percent) at low temperatures (<100 deg C). The NO conversion to N_2/N_2O occurred at >0.08 vol percent H_2 and the selectivity to N_2 increased with increasing H_2 concentration. in situ DRIFTS measurement suggested that the high selectivity in this temperature range is closely related to a stoichiometric reaction between H_2 and NO oxidatively adsorbed as nitrate (NO_3-). By comparison with the results from a parallel study of H_2-O_2 combustion, we propose that almost all of H_2 reacted is consumed by the reduction of nitrate species, which covered the Pt surface to inhibit H_2-O_2 combustion. The NO reduction activity was sensitive to the catalyst pretreatment; the catalyst reduced in H_2 allowed 89 percent NO conversion at 90 deg C, whereas the catalyst treated in O_2 required 175 deg C to attain the lower conversion of 50 percent. The effect of the pretreatment is closely related to the reactivity of nitrate adsorbates produced via different routes.