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 (alpha-FeOOH; goethite), loaded onto an Al2O3 support, functions as a recyclable catalyst for a photocatalytic CO2 reduction system under visible light (lambda>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 (CO2)-C-13. The present work shows that the use of a proper support material is another method of catalyst activation toward the selective reduction of CO2.

Automated summary

This study demonstrates the use of a widespread soil mineral as a solid catalyst for the photocatalytic conversion of CO2 into formic acid under visible light. This finding has significant implications for addressing energy and carbon resource shortages, as well as reducing atmospheric CO2 concentration.