title: Temperature dependence of photocatalytic CO2reduction by trans(Cl)-Ru(bpy)(CO)2Cl2: activation energy difference between CO and formate production.
abstract: The temperature dependence of photocatalytic CO2reduction by trans(Cl)-Ru(bpy)(CO)2Cl2(bpy: 2,2'-bipyridine) has been researched in ethanol (EtOH)/N,N-dimethylacetamide (DMA) solutions containing [Ru(bpy)3]2+(a photosensitizer) and 1-benzyl-1,4-dihydronicotinamide (BNAH, an electron donor). The catalytic system efficiently reduces CO2to carbon monoxide (CO) with formate (HCOO-) as a minor product. The mechanism of the catalysis consists of the electron-relay cycle and the catalytic cycle: in the former cycle the photochemically generated reduced species of the photosensitizer injects an electron to the catalyst, and in the latter the catalyst reduces CO2. At a low concentration of the catalyst (5.0 μM), where the catalytic cycle is rate-determining, the temperature dependence of CO/HCOO-is also dependent on the EtOH contents: the selectivity of CO/HCOO-decreases in 20% and 40%-EtOH/DMA with increasing temperature, while it increases in 60%-EtOH/DMA. The temperature dependence of the CO/HCOO-selectivity indicates that the difference in activation energy (ΔΔG‡) between CO and HCOO-production is estimated as ca. 3.06 kJ mol-1in 40%-EtOH/DMA at 298 K.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan. ishida@sci.kitasato-u.ac.jp.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ishida
authors.forename: Akihiko
authors.initials: A
authors.lastname: Sakaba