Photocatalytic Reactions on the Single-Site Heterogeneous Catalysts

Single-site heterogeneous catalysts constructed with highly dispersed, spatially well-separated isolated species have attracted much attention due to their outstanding specific activity and selectivity attributable to the unsaturated surface coordination sites and unique local electronic structures. Furthermore, such single-site heterogeneous catalysts are considered to be attractive as models for the top surface of inorganic semiconducting materials. As catalysts and photocatalysts, they provide suitable reaction fields to investigate the relationship between the activity and local structure of the active sites. To obtain detailed information on the reaction mechanism at the molecular level, advanced characterization techniques such as X-ray absorption fine-structure spectroscopy (XAFS), FT-IR, UV-VIS, EPR, and photoluminescence spectroscopy were applied. Moreover, various solid materials such as silica, mesoporous materials including zeolites, and semiconducting materials offer applicable strategies to design unique single-site heterogeneous photocatalysts. In the present review, photocatalytic reactions on single-site heterogeneous catalysts constructed on semiconducting materials have been summarized. Special attention has been focused on photocatalytic reactions for clean energy such as the splitting of water, reduction of carbon dioxide with H2O, conversion of CH4, and fixation of nitrogen. Furthermore, the preparation of single-site heterogeneous catalysts, their characterizations, and the relationship between their local structures and photocatalytic activities are also discussed. The present review not only provides a systematic understanding of single-site heterogeneous photocatalysts but also an understanding of the reaction mechanisms of semiconducting photocatalysis at the atomic level as well as the design of high-performance catalytic and photocatalytic reaction systems. [GRAPHICS] .