A Hybrid Ru(II)/TiO₂ Catalyst for Steadfast Photocatalytic CO₂ to CO/Formate Conversion Following a Molecular Catalytic Route

Herein, we employed a molecular Ru­(II) catalyst immobilized onto TiO₂ particulates of (4,4′-Y₂-bpy)­Ru^II(CO)₂Cl₂ (<b>RuP</b>; Y = CH₂PO­(OH)₂), as a hybrid catalyst system to secure the efficient and steady catalytic activity of a molecular bipyridyl Ru­(II)-complex-based photocatalytic system for CO₂ reduction. From a series of operando FTIR spectrochemical analyses, it was found that the TiO₂-fixed molecular Ru­(II) complex leads to efficient stabilization of the key monomeric intermediate, Ru^II-hydride (LRu^II(H)­(CO)₂Cl), and suppresses the formation of polymeric Ru­(II) complex (−(L­(CO)₂Ru–Ru­(CO)₂L)_<i>n</i>−), which is a major deactivation product produced during photoreaction via the Ru–Ru dimeric route. Active promotion of the monomeric catalytic route in a hetero-binary system (IrPS + TiO₂/<b>RuP</b>) that uses TiO₂-bound Ru­(II) complex as reduction catalyst led to highly increased activity as well as durability of photocatalytic behavior with respect to the homogeneous catalysis of free Ru­(II) catalyst (IrPS + Ru­(II) catalyst). This catalytic strategy produced maximal turnover numbers (TONs) of >4816 and >2228, respectively, for CO and HCOO^– production in CO₂-saturated <i>N</i>,<i>N</i>-dimethylformamide (DMF)/TEOA (16.7 vol % TEOA) solution containing a 0.1 M sacrificial electron donor.