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

摘要

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 WO3 (denoted as Ir-1/m-WO3) 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-WO3. When tested for the reduction of NO by CO, the Ir-1/m-WO3 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 degrees C. In particular, its turnover frequency (TOF) value reached 0.30 s(-1) at 200 degrees C, which is six times higher than that of the catalyst with Ir nanoparticles supported on mesoporous WO3 (0.05 s(-1)). The superior catalytic performance of Ir-1/m-WO3 is attributed to the formation of the isolated Ir atoms and the more newly generated Ir-WO3 interfaces that can promote the adsorption and activation of NO, and the presence of accessible mesopores in m-WO3 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.