Features of Nb2O5 as a metal oxide support of Pt and Pd catalysts for selective catalytic oxidation of NH3 with high N2 selectivity

Selective catalytic oxidation of ammonia (NH3-SCO) to N2 and H2O was examined as one of the most efficient solutions for NH3 pollution because NH3 has potentially harmful effects on human health and the environment. The acidic metal oxide Nb2O5 that possesses both Brønsted and Lewis acid sites was chosen as the support of Pt and Pd catalysts for SCO of 50 ppm NH3. Both Pt/Nb2O5 and Pd/Nb2O5 showed extremely high levels of N2 selectivity (98% and 100%, respectively) at 100% NH3 conversion. The role of the acid sites of Pt/Nb2O5 and Pd/Nb2O5 in NH3-SCO was investigated by the NaOH treatment to neutralize the Brønsted acid sites. The selectivity to N2 decreased by the NaOH treatment of Pt/Nb2O5 and Pd/Nb2O5. These results suggested that the Brønsted acid sites were essentially important for improving N2 selectivity. This study provides a new concept for the design of a catalyst by using the acid sites of acidic metal oxide to improve the N2 selectivity of NH3-SCO.