Photocatalytic CO_2 Reduction by Periodic Mesoporous Organosilica (PMO) Containing Two Different Ruthenium Complexes as Photosensitizing and Catalytic Sites

摘要

A periodic mesoporous organosilica (PMO) containing 2,2'-bipyridine (bpy) ligands within the framework (BPy-PMO) has great potential for designing novel catalysts by modifying metal complexes. A photosensitizing site (Ru(PS)) was introduced by treating cis-[Ru(bpy)_2(dimethylsulfoxide)Cl]Cl with BPy-PMO. Then a catalytic site (Ru(Cat)) was brought in Ru(PS)x-BPy-PMO by reaction with a ruthenium polymer [Ru(CO)_2Cl_2]_n. The stepwise modification of BPy-PMO successfully affords a novel photocatalyst Ru(PS)x-Ru(Cat)y-BPy-PMO. The molar fractions (x, y) of Ru(PS) and Ru(Cat) were determined by energy dispersive Xray (EDX) measurement and quantification of the amount of CO emitted in the photo-decarbonylation of Ru(Cat), respectively. Photochemical CO_2 reduction (lex>430 nm) by Ru(PS)x-Ru(Cat)y-BPy-PMO in a CO_2-saturated N,N-dimethylacetamide/ water solution containing 1-benzyl-1,4-dihydronicotinamide catalytically produced CO and formate. The total turnover frequency of CO and formate reached more than 162 h~(-1) on x=0.11 and y=0.0055. The product selectivity (CO/formate) became large when the ratio of Ru(PS)-to-Ru(Cat) (x/y) was increased. The photocatalysts can be recycled at least three times without losing their catalytic activity, demonstrating that the Ru(PS) and Ru(Cat) units were strongly immobilized on the BPy-PMO framework.