Single Ir Atoms Anchored on Ordered Mesoporous WO3 Are Highly Efficient for the Selective Catalytic Reduction of NO with CO under Oxygen-rich Conditions

Graphical Single Ir atoms : In the CO+NO reaction, the catalyst with single-sited Ir atoms (0.28 wt %) anchored on a mesoporous WO 3 (Ir 1 /mesoporous-WO 3 ) showed much higher NO conversion and N 2 selectivity under oxygen-rich conditions than the catalysts supported with Ir nanoparticles on the same catalyst support (Ir NPs/mesoporous-WO 3 ) and on a non-mesoporous WO 3 (Ir/non-mesoporous-WO 3 ). Under oxygen-rich conditions, achieving a selective and efficient reduction of NO by CO is always challenging. Here, we report the synthesis of the catalyst consisting of single Ir atoms anchored on mesoporous WO 3 (denoted as Ir 1 /m-WO 3 ) using a facile template method followed by wet impregnation. X-ray diffraction and transmission electron microscope studies indicated that the Ir atoms were distributed uniformly on the internal surface of m-WO 3 . When tested for the reduction of NO by CO, the Ir 1 /m-WO 3 catalyst with a low Ir loading of 0.28 wt % exhibited excellent catalytic performance in the presence of 2 vol % O 2 (volume ratio of CO to O 2 being 1 : 10), achieving a NO conversion of 73 % and N 2 selectivity of 100 % at 350 °C. In particular, its turnover frequency (TOF) value reached 0.30 s −1 at 200 °C, which is six times higher than that of the catalyst with Ir nanoparticles supported on mesoporous WO 3 (0.05 s −1 ). The superior catalytic performance of Ir 1 /m-WO 3 is attributed to the formation of the isolated Ir atoms and the more newly generated Ir-WO 3 interfaces that can promote the adsorption and activation of NO, and the presence of accessible mesopores in m-WO 3 that facilitates the mass transfer of NO and CO. This study brings a new fundamental understanding of active sites in Ir-based catalysts for the CO+NO reaction and provides a new way to the design and synthesis of single-atom catalysts, especially precious metal catalysts for emissions control.