Selective catalytic oxidation (SCO) of NH3 to harmless N2 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 N2 are required. However, it has been a technical challenge because the reported catalysts either needed high operating temperatures or showed low selectivities to N2. In this study, we first demonstrated that acidic metal-oxide-supported gold catalysts showed good N2 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 N2 at low temperatures (18% NH3 conversion with 100% N2 selectivity at 25 °C) and at high temperatures (100% NH3 conversion with 95% N2 selectivity at 245 °C). Important roles of Brønsted acid sites and formation of active oxygen sites in improving N2 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 N2 selectivity at 25 °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 N2 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.

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Gold nanoparticles of small sizes with a highly uniform dispersion were successfully deposited on several crystalline forms of Ta 2 O 5 (pseudohexagonal, orthorhombic, and pyrochlore) by the sol immobilization method. The pseudohexagonal Ta 2 O 5 (TT-Ta 2 O 5 ) synthesized by a hydrothermal method showed the highest catalytic activity for CO oxidation as a support for gold catalysts. The temperature at 50% CO conversion was −11 °C for 1 wt % Au/ TT-Ta 2 O 5 , and the temperature was 23 °C at 100% CO conversion (space velocity of 20000 mL h −1 g cat −1). To investigate the reaction mechanism, in situ diffuse reflectance infrared Fourier transform spectroscopy for Au/TT-Ta 2 O 5 was performed, and the sequential delivery of adsorbed CO on Ta 2 O 5 sites and Au sites to the active sites was observed at −120 °C. The results of temperatureprogrammed CO reduction suggested that the oxygen adsorbed at −100 °C contributed mainly to the high catalytic activity of CO oxidation, while the lattice oxygen played a minor role for CO oxidation from −60 to 100 °C, which was the same temperature range with the actual reaction condition.

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