Photocatalytic Conversion of CO₂ to CO by a Copper(II) Quaterpyridine Complex

Abstract

The invention of efficient systems for the photocatalytic reduction of CO comprising earth-abundant metal catalysts is a promising approach for the production of solar fuels. One bottleneck is to design highly selective and robust molecular complexes that are able to transform the CO gas. The Cu quaterpyridine complex [Cu(qpy)] (1) is found to be a highly efficient and selective catalyst for visible-light driven CO reduction in CH CN using [Ru(bpy) ] (bpy: bipyridine) as photosensitizer and BIH/TEOA (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole/triethanolamine) as sacrificial reductant. The photocatalytic reaction is greatly enhanced by the presence of H O (1-4 % v/v), and a turnover number of >12 400 for CO production can be achieved with 97 % selectivity, which is among the highest of molecular 3d CO reduction catalysts. Results from Hg poisoning and dynamic light scattering experiments suggest that this photocatalyst is homogenous. To the best of our knowledge, 1 is the first example of molecular Cu-based catalyst for the photoreduction of CO .

Dinuclear Metal Synergistic Catalysis Boosts Photochemical CO2‐to‐CO Conversion

“…[18][19][20][21][22][23][24][25] Thecritical bottleneck of this project is to develop cheap catalysts that can selectively and effectively reduce CO 2 into as ingle chemical fuel/feedstock. [28][29][30][31][32] Recently,w ereported ad inuclear molecular catalyst of [CoCo(OH)L 1 ](ClO 4 ) 3 (CoCo), [18] which displays much higher photocatalytic activity (TON = 16896) and selectivity (98 %) than the corresponding mononuclear complex of [CoL 2 (CH 3 CN)](ClO 4 ) 2 (Co,T ON = 1600 with 85 % selectivity) for the reduction of CO 2 to CO in H 2 O/CH 3 CN (L 1 = N[(CH 2 ) 2 NHCH 2 (m-C 6 H 4 )CH 2 NH (CH 2 ) 2 ] 3 N, L 2 = N,N',N''-tris(2-benzylaminoethyl)amine,F igure 1), probably aresult of the DMSC effect between two Co II ions,that is,one Co II serves as acatalytic center,and the other Co II acts as an assistant catalytic site to facilitate the cleavage of C À Obond of the O=CÀOH intermediate.A st he coordination environments of both Co II centers in CoCo are identical, it is not possible to identify the catalytic center and the assistant catalytic site in CoCo,thus the proposed DMSC effect within dinuclear CoCo need to be further investigated and confirmed. Particularly in water-containing catalytic systems,t he efficiency and selectivity are even lower due to the competitive reaction of proton reduction (Table S1).…”

A Copper(II) Molecular Catalyst for Efficient and Selective Photochemical Reduction of CO2 to CO in a Water‐Containing System

“…The more impressive fact is that the selectivity of 1 to CO was up to 98 % in a water‐containing photocatalytic system. This is also impressive among these reported catalysts because, except for several cases reported recently, most others show good selectivity for CO 2 reduction only in anhydrous system, yet the carbon‐neutral artificial photosynthesis cycle containing CO 2 reduction and water oxidation should proceed in water/water‐containing system.…”

“…According to the amount of CO and H 2 generated during the 10 h CO 2 photocatalysis by 1 , a TON of 9900 and a TOF of 0.275 s −1 were calculated with 0.05 μ m 1 , 0.4 m m [Ru(phen) 3 ](PF 6 ) 2 , and 0.3 m TEOA (Table , Entry 1; Table S3). These results suggest that 1 is a good catalyst towards photochemical CO 2 reduction, although not so excellent as the [Cu(qpy)] 2+ , which gives a TON above 12 000 at 1 m m of [Cu(qpy)] 2+ . It should be noted that when 1:1 ratio of 1 to [Ru(phen) 3 ](PF 6 ) 2 (0.05 m m each) was used, 0.9 μmol CO and 0.01 μmol H 2 were detected, giving a TON of 3.6 and a selectivity of 99 %.…”

“…Therefore, large amount of photosensitizer is needed to increase the electronic transmission from photosensitizer to catalyst, to sufficiently activate all the used catalyst. In fact, high ratio of photosensitizer to catalyst is commonly observed in reported photocatalytic systems, especially homogeneous photocatalytic systems for CO 2 reduction . The more impressive fact is that the selectivity of 1 to CO was up to 98 % in a water‐containing photocatalytic system.…”

“…The appearance of this complex is of guiding significance to the development of Cu‐based electrocatalysts for CO 2 reduction. However, in photocatalytic CO 2 reduction, there is only one copper complex of [Cu(qpy)] 2+ (qpy=2,2′:6′,2“:6”,2“′‐quaterpyridine) reported as an efficient catalyst for reduction of CO 2 to CO driven by visible‐light, exhibiting a TON of 12 400 and a selectivity of 97 % using 1 μ m of catalyst, which is among the top catalysts for photochemical CO 2 reduction among transition metal‐based catalysts reported so far …”