Atomic-scale insights into the nature of active sites in Fe2O3-supported submonolayer WO3 catalysts for selective catalytic reduction of NO with NH3

The high activity of a catalyst can be attributed to structural and electronic effects (including particle shape, thickness, and charge transfer). Downsizing the active component of a catalyst from its bulk phase to a monolayer-thick entity will eliminate the particle shape effect and simplify the interpretation of the nature of the active sites. Here, the catalyst architecture of submonolayer (an atomic surface coverage less than one monolayer) WO3 supported over well-defined ferric oxide nanoplates was successfully synthesized by a facile impregnation method. Because the supported WO3 surface layers and Fe2O3 nanoplates used here were substantially uniform, our work also shows how the determination of the nature of active sites is possible at the nanoscale level. The as-prepared 0.05 monolayers WO3/Fe2O3, i.e., 0.05 monolayers of WO3 supported on Fe2O3, exhibited a high catalytic activity and wide operating temperature window for the selective catalytic reduction of NOx with NH3 (NH3-SCR) in NOx pollution abatement. The surface ammonia species on both Lewis acid sites and Bronsted acid sites were found to participate in the reaction. The kinetic study demonstrated that the interface of W-O-Fe of 0.05 monolayer WO3/Fe2O3 was associated with the active sites, and that the formation of bulk WO3 does not increase the density of the active sites for the reaction. These findings provide a basis for enhancing the NH3-SCR catalytic performance by establishing active site at the Fe-W interface, which gives an effective approach for the design and synthesis of new and cost-efficient catalysts.