Selective CO2 reduction into formate using Ln–Ta oxynitrides combined with a binuclear Ru(II) complex under visible light

Abstract

Ln–Ta oxynitrides with defect fluorite structure were found to serve as effective semiconductor components in visible-light-driven Z-scheme CO 2 reduction with a binuclear Ru(II) complex, giving high selectivity to formate (>99%). • Ln–Ta oxynitrides LnTaO x N y (Ln = Nd, Sm, Gd, Tb, Dy and Ho) were synthesized. • Some of LnTaO x N y loaded with Ag and a Ru(II) complex photocatalyzed CO 2 reduction. • The highest activity was obtained with TbTaO x N y . • High formate selectivity (>99%) was accomplished. Hybrid materials constructed from a visible-light-absorbing semiconductor and a functional metal complex have attracted attention as efficient photocatalysts for CO 2 reduction with high selectivity to a desired product. In this work, defect fluorite-type Ln–Ta oxynitrides LnTaO x N y (Ln = Nd, Sm, Gd, Tb, Dy and Ho) were examined as the semiconductor component in a hybrid photocatalyst system combined with known Ag nanoparticle promoter and binuclear ruthenium(II) complex ( RuRu′ ). Among the LnTaO x N y examined, TbTaO x N y gave the highest performance for CO 2 reduction under visible light ( λ > 400 nm), with a RuRu′ -based turnover number of 18 and high selectivity to formate (>99%). Physicochemical analyses indicated that high crystallinity and more negative conduction band potential of LnTaO x N y with the absence of Ln-4f states in the band gap structure contributed to higher activity of the hybrid photocatalyst.