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Effect of Thickness of Chromium Hydroxide Layer on Ag Cocatalyst Surface for Highly Selective Photocatalytic Conversion of CO₂ by H₂O

Pang, Rui, Teramura, Kentaro, Asakura, Hiroyuki, Hosokawa, Saburo, Tanaka, Tsunehiro
ACS sustainable chemistry & engineering 2018 v.7 no.2 pp. 2083-2090
carbon dioxide, carbon monoxide, carbonates, chromium, copper, gold, hydrogen, hydrogen production, palladium, photocatalysis, photocatalysts, platinum, silver
In this study, we developed a Ag–Cr core–shell-structured (Ag@Cr) cocatalyst that modified the surface of the Ga₂O₃ photocatalyst. Compared to results provided by modifications with Ag cocatalysts and M–Cr dual cocatalysts (M = Au, Cu, Pd, and Pt), this change significantly improved the formation rate of CO and selectivity toward CO evolution in the photocatalytic conversion of CO₂ by the electron donor H₂O. As a result of this modification, the Cr(OH)₃·xH₂O shell changed to Cr(OH)ₓ(CO₃)y during the photocatalytic conversion. Furthermore, the thickness of the Cr(OH)₃·xH₂O shell was found to influence the photocatalytic performance. More specifically, Cr(OH)₃·xH₂O shells that were too thick or too thin were not beneficial to the CO evolution and suppression of H₂ evolution. Notably, the highest photocatalytic activity (525.3 μmol h–¹), selectivity toward CO evolution (85.2%), and turnover number of CO to Ag (167) was achieved over 0.25 mol % (Ag@Cr)/Ga₂O₃. In addition to Ga₂O₃, the Ag@Cr cocatalyst modification strategy can also be applied to other photocatalyst materials such as NaTaO₃, ZnGa₂O₄, and ZnGa₂O₄/Ga₂O₃ for the highly effective photocatalytic conversion of CO₂ to CO when using H₂O as an electron donor.