Alumina-Supported Alpha-Iron(III) Oxyhydroxide as a Recyclable Solid Catalyst for CO₂ Photoreduction under Visible Light

Photocatalytic conversion of CO₂ into transportable fuels such as formic acid (HCOOH) under sunlight is an attractive solution to the shortage of energy and carbon resources as well as to the increase in Earth's atmospheric CO₂ concentration. The use of abundant elements as the components of a photocatalytic CO₂ reduction system is important, and a solid catalyst that is active, recyclable, nontoxic, and inexpensive is strongly demanded. Here, we show that a widespread soil mineral, alpha-iron(III) oxyhydroxide (α-FeOOH; goethite), loaded onto an Al₂O₃ support, functions as a recyclable catalyst for a photocatalytic CO₂ reduction system under visible light (λ>400 nm) in the presence of a Ru^II photosensitizer and an electron donor. This system gave HCOOH as the main product with 80–90 % selectivity and an apparent quantum yield of 4.3 % at 460 nm, as confirmed by isotope tracer experiments with ¹³CO₂. The present work shows that the use of a proper support material is another method of catalyst activation toward the selective reduction of CO₂.