Selective catalytic oxidation of NH3over noble metal-based catalysts: state of the art and future prospects

Selective catalytic oxidation of ammonia to nitrogen and water vapor (NH3-SCO) is considered to be an efficient technique to eliminate hazardous and pungent gaseous NH(3)is mainly emitted from selective catalytic reduction of NO(x)with NH(3)units using appropriate catalysts. Due to the satisfactory low-temperature ammonia oxidation activity, noble metal-based catalysts are the primary groups applied in the NH3-SCO reaction on account of their unique intrinsic properties. Meanwhile, it is essential that selectivity towards byproducts, including NO, NO(2)and N2O, is as low as possible so that the high N(2)selectivity meets the stringent environmental policies in practical scenarios. To provide an overview of the NH3-SCO reaction, this review starts with a general understanding of reaction mechanisms and catalyst promotion strategies. After that, the noble metal-based catalysts, namely Pt, Ag, Ru, Ir, Pd, Au and Rh-based catalysts, are discussed from the aspects of the regulation of active species, the adsorption and activation of reactants and intermediates, the formation of N-containing products and the coupling effects with NH3-SCR catalysts. Finally, a condensed summary of previous work as well as reasonable suggestions and perspectives on future trends in this field are presented. To the best of our knowledge, this is the first comprehensive review on the application of noble metal-based catalysts in the NH3-SCO reaction and we hope that this article will shed light on the rational catalyst design and in understanding the structure-property relationships of noble metal-based NH3-SCO catalysts.