Photocatalytic conversion of carbon dioxide into methanol using zinc-copper-M(III) (M = aluminum, gallium) layered double hydroxides

Ordered layered double hydroxides (LDHs) consisting of zinc and/or copper hydroxides were synthesized and combined with aluminum or gallium. These LDH compounds were then applied as photocatalysts to convert gaseous CO2 (2.3 kPa) to methanol or CO under UV-visible light using hydrogen. Zn-Al LDH was the most active for CO2 photoreduction and the major product was CO formed at a rate of 620 nmol h(-1) g(cat)(-1), whereas methanol was the major product formed by the inclusion of Cu in the LDH photocatalysts, e.g., at a formation rate of 170 nmol h(-1) g(cat)(-1), using Zn-Cu-Ga photocatalyst. The methanol selectivity improved by the inclusion of Cu from 5.9 to 26 mol% and 39 to 68 mol%, respectively, when Zn-Al (the conversion 0.16-0.11%) and Zn-Ga LDH catalysts were used (the conversion 0.02-0.03%). Specific interaction of Cu sites with CO2 was spectroscopically suggested to enable coupling with protons and photogenerated electrons to form methanol. (C) 2011 Elsevier Inc. All rights reserved.