Single-site photocatalytic solids for the decomposition of undesirable molecules

Photocatalytic solids, in which the absorption occurs at isolated, spatially well-separated centres, are particularly useful catalysts for effecting reactions that are of prime importance in both remedial and preparative contexts. These are qualities that they share with single-site (thermally-activated) heterogeneous catalysts; but they have the added advantage of being more readily probed during the actual processes of catalytic turnover, since they generally function under ambient conditions, unlike most conventional solid catalysts which usually operate at elevated pressures and temperatures. Thus, they are amenable to investigation by ( in situ) X-ray absorption (XAFS), FT-IR, UV-Vis, and EPR spectroscopic studies as well as to photoluminescence measurement. This affords greater insight into the mechanisms of the photocatalytic reactions as we illustrate in this short review. Open-structure solids such as mesoporous silica and zeolitic aluminosilicates offer a generally applicable strategy to design new single-site photocatalysts such as those described here for the decomposition of NO to N-2 and O-2 and for the selective oxidation of CO in the presence of H-2.