Low-Temperature CO2 Hydrogenation to Liquid Products via a Heterogeneous Cascade Catalytic System

Research described in this paper targeted a cascade system for the hydrogenation of CO2 to methanol via formic acid and/or formate intermediates, a reaction sequence that has been accomplished previously using homogeneous catalysts. On the basis of results for the hydrogenation of CO2, formic acid, and ethyl formate over a series of Cu- and Mo2C-based catalysts, we selected a Cu chromite catalyst for CO2 hydrogenation to the formate and a Cu/Mo2C catalyst to convert the formate to methanol. These catalysts worked cooperatively in the presence of ethanol, yielding a methanol turnover frequency of 4.7 × 10–4 s–1 at 135 °C, 10 bar of CO2, and 30 bar of H2 in 1,4-dioxane. The performance for this Cu chromite:Cu/Mo2C cascade system surpassed the additive production of the individual catalysts by ∼60%. The results also allowed an investigation of the reaction pathways. The hydrogenation of CO2 to formic acid appeared to be the rate-limiting step for most of the catalysts. This is not surprising given the thermo...