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Article Abstract
The catalytic efficacy of the monobipyridyl (η--Cymene)Ru(II) half-metallocene, [(-Cym)Ru(bpy)Cl] was evaluated in both mixed homogeneous (dye + catalyst) and heterogeneous hybrid systems (dye/TiO/Catalyst) for photochemical CO reduction. A series of homogeneous photolysis experiments revealed that the (-Cym)Ru(II) catalyst engages in two competitive routes for CO reduction (CO to formate conversion via Ru-hydride vs CO to CO conversion through a Ru-COOH intermediate). The conversion activity and product selectivity were notably impacted by the p value and the concentration of the proton source added. When a more acidic TEOA additive was introduced, the half-metallocene Ru(II) catalyst leaned toward producing formate through the Ru-H mechanism, with a formate selectivity of 86%. On the other hand, in homogeneous catalysis with TFE additive, the CO-to-formate conversion through Ru-H was less effective, yielding a more efficient CO-to-CO conversion with a selectivity of >80% (TON of 140 and TON of 626 over 48 h). The preference between the two pathways was elucidated through an electrochemical mechanistic study, monitoring the fate of the metal-hydride intermediate. Compared to the homogeneous system, the TiO-heterogenized (-Cym)Ru(II) catalyst demonstrated enhanced and enduring performance, attaining TONs of 1000 for CO-to-CO and 665 for CO-to-formate.
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Photocatalytic Conversion of CO to Formate/CO by an (η--Cymene)Ru(II) Half-Metallocene Catalyst: Influence of Additives and TiO Immobilization on the Catalytic Mechanism and Product Selectivity.
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