Adsorption and Photochemical Properties of a Molecular CO2 Reduction Catalyst in Hierarchical Mesoporous ZSM-5: An In Situ FTIR Study.

As part of our recent effort to attach well-defined molecular photocatalysts to solid-state surfaces, this present study investigates adsorption and photochemical properties of a tricarbonyl rhenium(I) compound, Re(bpy)(CO)3Cl (bpy = 2,2'-bipyridine), in hierarchical mesoporous ZSM-5. The molecular Re(I) catalyst, a Ru(bpy)3(2+) photosensitizer, and an amine-based electron donor were coadsorbed in the mesopores of the hierarchical ZSM-5 through simple liquid-phase adsorption. The functionalized ZSM-5 was then characterized with infrared and UV-visible spectroscopies and was tested in CO2 reduction photocatalysis at the gas-surface interface. In the mesoporous ZSM-5, CO2 molecules were adsorbed on the amine electron-donor molecules as bicarbonate, which would release CO2 upon light irradiation to react with the Re(I) catalyst. The formation of important reaction intermediates, particularly a Re-carboxylato species, was revealed with in situ Fourier transform infrared spectroscopy in combination with isotopic labeling. The experimental results indicate that hierarchical mesoporous zeolites are promising host materials for molecular photocatalysts and that zeolite mesopores are potential "reaction vessels" for CO2 reduction photocatalysis at the gas-solid interface.