Improving the photocatalytic reduction of CO2 to CO through immobilisation of a molecular Re catalyst on TiO2.

The photocatalytic activity of phosphonated Re complexes, [Re(2,2′-bipyridine-4,4′-bisphosphonic acid) (CO)3(L)] (ReP; L=3-picoline or bromide) immobilised on TiO2 nanoparticles is reported. The heterogenised Re catalyst on the semiconductor, ReP–TiO2 hybrid, displays an improvement in CO2 reduction photocatalysis. A high turnover number (TON) of 48 molCO molRe−1 is observed in DMF with the electron donor triethanolamine at λ>420 nm. ReP–TiO2 compares favourably to previously reported homogeneous systems and is the highest TON reported to date for a CO2-reducing Re photocatalyst under visible light irradiation. Photocatalytic CO2 reduction is even observed with ReP–TiO2 at wavelengths of λ>495 nm. Infrared and X-ray photoelectron spectroscopies confirm that an intact ReP catalyst is present on the TiO2 surface before and during catalysis. Transient absorption spectroscopy suggests that the high activity upon heterogenisation is due to an increase in the lifetime of the immobilised anionic Re intermediate (t50 %>1 s for ReP–TiO2 compared with t50 %=60 ms for ReP in solution) and immobilisation might also reduce the formation of inactive Re dimers. This study demonstrates that the activity of a homogeneous photocatalyst can be improved through immobilisation on a metal oxide surface by favourably modifying its photochemical kinetics.

报道了固定在二氧化钛纳米粒子上的膦酸化铼配合物[Re(2,2′ - 联吡啶 - 4,4′ - 双膦酸)(CO)₃(L)]（ReP；L = 3 - 甲基吡啶或溴离子）的光催化活性。半导体上的异相化铼催化剂，即ReP - TiO₂杂化物，在二氧化碳还原光催化方面有所改进。在二甲基甲酰胺（DMF）中，以三乙醇胺为电子给体，在λ>420 nm处观察到高达48 molCO·molRe⁻¹的周转数（TON）。ReP - TiO₂与先前报道的均相体系相比具有优势，并且是迄今为止在可见光照射下用于二氧化碳还原的铼光催化剂所报道的最高周转数。在λ>495 nm的波长下，甚至观察到ReP - TiO₂对二氧化碳的光催化还原。红外光谱和X射线光电子能谱证实，在催化之前和催化过程中，完整的ReP催化剂存在于TiO₂表面。瞬态吸收光谱表明，异相化后的高活性是由于固定化的阴离子铼中间体的寿命增加（ReP - TiO₂的t₅₀%>1 s，而溶液中ReP的t₅₀% = 60 ms），并且固定化可能还会减少无活性铼二聚体的形成。这项研究表明，通过有利地改变其光化学动力学，将均相光催化剂固定在金属氧化物表面可以提高其活性。