Carbon Dioxide to Methanol: The Aqueous Catalytic Way at Room Temperature

Carbon dioxide may constitute a source of chemicals and fuels if efficient and renewable processes are developed that directly utilize it as feedstock. Two of its reduction products are formic acid and methanol, which have also been proposed as liquid organic chemical carriers in sustainable hydrogen storage. Here we report that both the hydrogenation of carbon dioxide to formic acid and the disproportionation of formic acid into methanol can be realized at ambient temperature and in aqueous, acidic solution, with an iridium catalyst. The formic acid yield is maximized in water without additives, while acidification results in complete (98 %) and selective (96 %) formic acid disproportionation into methanol. These promising features in combination with the low reaction temperatures and the absence of organic solvents and additives are relevant for a sustainable hydrogen/methanol economy. An iridium complex was successfully employed in the direct, homogeneous transformation of carbon dioxide to formic acid and methanol, through formic acid disproportionation, in aqueous solution and at ambient temperature. Unprecedented methanol selectivities of 96 % were obtained for complete formic acid conversion in the presence of sulfuric acid under optimized conditions. The reactions reported here might be beneficial in the fields of CO2 valorization, sustainable H2 storage, and alternative formic acid/methanol production.