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%)-H-2 (0.08-0.56 vol-%)-O-2 (10 vol.%) at low temperatures (< 100<degrees>C). The NO conversion to N-2/N2O occurred at >0.08 vol% 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 (NO3-). 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% NO conversion at 90 degreesC, whereas the catalyst treated in O-2 required 175 degreesC 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. (C) 2001 Elsevier Science B.V. All rights reserved.