Photocatalysis of CO₂ Reduction by a Ru(II)–Ru(II) Supramolecular Catalyst Adsorbed on Al₂O₃

Abstract

Various hybrid systems consisting of metal-complex photocatalysts and semiconductor materials have been developed for photocatalytic CO 2 reduction via the Z-scheme mechanism. Such systems are often composed of a supramolecular photocatalyst with Ru(II) photosensitizer and Ru(II) catalyst (RuRu). In this study, RuRu was adsorbed on Al 2 O 3 particles, and the photocatalytic activity of RuRu/Al 2 O 3 in CO 2 reduction was investigated in detail, especially by changing the adsorption density of RuRu. The production of HCOOH, which is the main product of CO 2 reduction, decreased upon increasing the adsorption density of RuRu owing to the formation of Ru polymers through the reductive coupling of the Ru catalyst units of RuRu moieties at high adsorption densities. This behavior contrasts with the previously reported behavior of RuRe/Al 2 O 3 with the same Ru(II) photosensitizer and a Re(I) catalyst unit. Moreover, the coadsorption of mononuclear Ru(II)-complex photosensitizers (Ru) close to RuRu on Al 2 O 3 substantially improved the photocatalytic activity of RuRu (turnover number of HCOOH formation increased more than 10 times) because Ru photochemically supplies electrons to the intermediate formed from the reduced Ru species to suppress the decomposition of RuRu.

Photoinduced morphological transformation of a self-assembled iron(ii) coordination polymer: high-performance, non-precious metal, and self-enhancing photocatalytic CO2 reduction

“…1,2 A variety of catalysts have therefore been developed to promote efficient conversion of CO 2 into value-added products such as CO, HCOOH, CH 3 OH, and CH 4 under light irradiation. 3–11 Among numerous homogeneous and heterogeneous catalysts, transition metal coordination polymers are emerging as superior catalysts for CO 2 photoreduction owing to versatile metal centers, tunable organic ligands, and rich structural morphologies. 12–15 Coordination polymers are commonly heterogeneous and recyclable through facile separation after catalysis, making them potentially attractive in industrial applications.…”

Identification of Crucial Photosensitizing Factors to Promote CO2‐to‐CO Conversion

“…[21][22][23] In order to boost electron transfer between the PSs and catalysts, Ishitani et al developed a series of RuÀ Re and RuÀ Ru bimetallic supramolecular catalysts by anchoring them on the surface of g-C 3 N 4 and Al 2 O 3 for efficient CO 2 photoreduction. [24][25] Ouyang et al synthesized two pyrenylmodified Ir(III)-and Co(II)-based molecules to elucidate the co-facial π-π interaction for accelerating electron transfer from excited-state PSs to catalyst. [26] In addition, we have coupled efficient Ir(III)-and Ru(II)-based PSs and catalysts through co-coordination mode in the metal-organic framework platform to facilitate the transfer of photogenerated electrons for boosting photocatalysis.…”

A Molecular Z‐Scheme Artificial Photosynthetic System Under the Bias‐Free Condition for CO2 Reduction Coupled with Two‐electron Water Oxidation: Photocatalytic Production of CO/HCOOH and H2O2

“…Following the Re‐complexes, various other metal‐complexes, such as Ru II ‐, [5] Ir III ‐ [6] Cu I ‐, [7] Co II ‐, [8] Ni II ‐, [9] Mn I ‐, [10] and Fe II ‐complexes, [11] have been reported to electrochemically/photochemically catalyze CO 2 reduction. Because of their superior properties, such as photo‐ and thermal stability, high reduction ability, and extremely low absorption in the visible region without interfering with light harvesting by a redox photosensitizer, trans (Cl)‐[Ru(diimine)(CO) 2 Cl 2 ]‐type catalysts have been widely used in various photocatalytic systems for CO 2 reduction [5b,12] . Many photocatalytic CO 2 reduction systems, consisting of metal‐complex catalysts and redox photosensitizers that initiate a single photochemical electron transfer from the reductant to the catalyst, exhibit high photocatalytic properties such as high quantum yield, durability, and product selectivity [2b,5b,13] .…”