Highly Selective and Durable Photochemical CO2 Reduction by Molecular Mn(I) Catalyst Fixed on a Particular Dye-Sensitized TiO2 Platform

A Mn(I)-based hybrid system (OrgD-|TiO 2 |- MnP ) for photocatalytic CO 2 reduction is designed to be a coassembly of Mn(4,4′-Y 2 -bpy)(CO) 3 Br ( MnP; Y = CH 2 PO(OH) 2 ) and ( E )-3-[5-(4-(diphenylamino)phenyl)-2,2′-bithiophen-2′-yl]-2-cyanoacrylic acid (OrgD) on TiO 2 semiconductor particles. The OrgD-|TiO 2 |- MnP hybrid reveals persistent photocatalytic behavior, giving high turnover numbers and good product selectivity (HCOO – versus CO). As a typical run, visible-light irradiation of the hybrid catalyst in the presence of 0.1 M electron donor (ED) and 0.001 M LiClO 4 persistently produced HCOO – with a >99% selectivity accompanied by a trace amount of CO; the turnover number (TON formate ) reached ∼250 after 23 h of irradiation. The product selectivity (HCOO – /CO) was found to be controlled by changing the loading amount of MnP on the TiO 2 surface. In situ FTIR analysis of the hybrid during photocatalysis revealed that, at low Mn concentration, the Mn–H monomeric mechanism associated with HCOO – formation is dominant, whereas at high Mn concentration, CO is formed via a Mn–Mn dimer mechanism.