Role of the Acid Site for Selective Catalytic Oxidation of NH3 over Au/Nb2O5

Selective catalytic oxidation (SCO) of NH3 to harmless N-2 and H2O is an ideal technology for its removal. To develop air purification systems for a living environment, catalysts that can work at room temperature with high selectivities to N-2 are required. However, it has been a technical challenge because the reported catalysts either needed high operating temperatures or showed low selectivities to N-2. In this study, we first demonstrated that acidic metal-oxide-supported gold catalysts showed good N-2 selectivities compared with that of other metal-oxide-supported gold catalysts. A gold catalyst with niobium oxide synthesized by the hydrothermal method as a support showed high catalytic activity and high selectivity to N-2 at low temperatures (18% NH3 conversion with 100% N-2 selectivity at 25 degrees C) and at high temperatures (100% NH3 conversion with 95% N-2 selectivity at 245 degrees C). Important roles of Bronsted acid sites and formation of active oxygen sites in improving N-2 selectivity were revealed in this study. To the best of our knowledge, this is the first report of efficient catalysts that presented high NH3 conversion with high N-2 selectivity at 25 degrees C which will offer great scopes for commercial applications related to control of odors. In addition, this breakthrough finding that acid sites would greatly affect N-2 selectivity and catalytic activity will provide a new trend in designing efficient catalysts not only for SCO of NH3 but also for the other selective catalytic oxidation.