Electron Transfer from Support/Promotor to Metal Catalyst: Requirements for Effective Support

Electron transfer from transition metal (TM) catalysts deposited on support to reaction molecules adsorbed is a key step in many catalysis reactions. Electron donation from a certain type of support and/or a promotor much enhances this electron transfer. In this paper the author considers requirements for efficient support materials based on a contact resistance between support and metal catalyst, showing metallic nature of the support is much favorable for this purpose. The origin of high performance in cesium promotors is suggested to be electride nature of their suboxides derived from the salts under the reaction conditions. TM-loaded alkali(A)/alkaline earth (AE) hydrides work as efficient catalysts. Since TM forms stronger or comparable bonding with H − compared with A/AE-H bonding, the formation of H-vacancy is much enhanced by TM-deposition. Thus, their high activity may be understood by the formation of surface electride, which serves as an electronic promotor, by deposition of TM on these hydrides. Improvement of electron transfer may be expected for insulating supports if Fermi-level pinning occurs at surface defects created by TM-deposition. Graphic Abstract