Photocatalytic CO₂ Reduction in N,N-Dimethylacetamide/Water as an Alternative Solvent System

Abstract

N,N-Dimethylacetamide (DMA) was used for the first time as the reaction solvent in the photocatalytic reduction of CO2. DMA is highly stable against hydrolysis and does not produce formate even if it is hydrolyzed. We report the catalytic activities of [Ru(bpy)2(CO)2](PF6)2 (bpy = 2,2'-bipyridine) in the presence of [Ru(bpy)3](PF6)2 as a photosensitizer and 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor in DMA/water. In the photochemical CO2 reduction, carbon monoxide (CO) and formate are catalytically produced, while dihydrogen (H2) from the reduction of water is scarcely evolved. We verified that BNAH is oxidized to afford BNA dimers during the photocatalyses in DMA/water. The plots of the production for the CO2 reduction versus the water content in DMA/water show that the 10 vol % water content gives the highest amount of the reduction products, whose reaction quantum yields (Φ') are determined to be 11.6% and 3.2% for CO and formate, respectively. The results are compared with those in the N,N-dimethylformamide (DMF)/water system, which has been typically used as the solvent system for the CO2 reduction.

Unexpected effect of catalyst concentration on photochemical CO2 reduction by trans(Cl)–Ru(bpy)(CO)2Cl2: new mechanistic insight into the CO/HCOO− selectivity

“…We further showed that the oxidized form of BNAH was the BNA dimer, e.g. , 1,1′-dibenzyl-1,1′,4,4′-tetrahydro-4,4′-binicotinamide (4,4′-BNA 2 ), 47,49 indicating that the reduced species of the photosensitizer ([Ru(bpy) 3 ] + ), which was generated by the reductive quenching of the excited [Ru(bpy) 3 ] 2+ with BNAH, supplied the electrons to the catalyst.…”

“…1–4 Until now, many metal complexes have been investigated for CO 2 reduction catalysis. 5–15 As metal complexes for the catalysts, manganese mono(bipyridyl) tricarbonyl, 16–18 cobalt and iron porphyrin, 19–21 cobalt tris(bipyridyl) 22 and macrocycle, 23,24 nickel cyclam, 25–27 molybdenum and tungsten mono(bipyridyl) tetracarbonyl, 28 rhodium bis(bipyridyl), 29,30 palladium phosphine, 31–33 rhenium mono(bipyridyl) tricarbonyl, 34–42 osmium mono(bipyridyl) dicarbonyl, 43,44 iridium poly(pyridyl) and dihydride pincer, 45,46 ruthenium mono(bipyridyl) and bis(bipyridyl) dicarbonyl complexes 47–70 have been investigated. Most of these yield CO and/or formate as the two-electron reduction products of CO 2 .…”

“…In the catalyses, the product selectivity depends on the reaction conditions: acidic conditions enhance CO production while basic conditions cause formate production. 51–56,69 Photochemical reductions have mostly resulted in formate production 47–49,51–53,57–62,70 while electrochemical reductions have achieved the selective formation of CO. 55,63–69 The reaction mechanisms of Ru( ii ) complexes have been proposed as shown in Scheme 1. 50–56,69 The widely accepted mechanism of CO production is as follows: (1) the Ru( ii ) complex accepts one electron to release CO, (2) the one-electron-reduced complex accepts another electron, and (3) the two-electron-reduced complex undergoes an electrophilic attack by CO 2 along with protonation and dehydration to regenerate the starting Ru( ii ) complex.…”

“…47 DMA is used as an alternative solvent for N , N -dimethylformamide (DMF), which is the most frequently used solvent in photochemical CO 2 reduction, but has been indicated to cause contamination of HCOO – by hydrolysis. 74 In the DMA/water systems using BNAH as the electron donor, the black precipitate scarcely formed, and the photocatalytic CO 2 reduction proceeded smoothly.…”

A importância do estado excitado 3MLCT de compostos de Ru(II), Re(I) e Ir(III) no desenvolvimento de fotossensores, OLEDS e fotorredução de CO2

“…O CO 2 pode ser reduzido diretamente em superfícies metálicas, entretanto, o sobrepotencial ainda é extremamente alto e ocorre o envenenamento da superfície do metal. [198][199][200] Desta maneira, o uso de compostos de coordenação como fotocatalisadores ou eletrocatalisadores é a vanguarda destas reações, [201][202][203][204][205][206] pois nestes compostos pode-se ajustar seus potenciais formais de redução de maneira a corresponder aos potenciais necessários para redução de CO 2 , assim como também podem favorecer a cinética e aumentar a estabilidade do estado de transição, o que torna a catálise altamente modulável. 207 O mecanismo genérico para a redução de CO 2 fotoassistida por complexos metálicos inicia-se em um composto de coordenação atuando como fotossensibilizador, F, que é excitado, F*, após absorver luz, Equação 4.…”