Influence of water steam and copper oxidation state on the CO2 hydrogenation to ethanol over copper catalysts

Abstract

CO2 is a greenhouse gas, whose emissions into the atmosphere has intensified in recent decades. Mitigating approaches have been studied in several countries around the world, such as the catalytic hydrogenation of CO2 via heterogeneous catalysis at gas-phase to produce chemical compounds with high added value. Typically, in this process, H2 gas is used as a hydrogen source, and copper-based catalysts, temperatures of 200–300 ºC and pressures of 2–7 MPa are employed to obtain, mainly, products containing one-carbon atom chain. Thus, the investigation of more favorable conditions for the hydrogenation of CO2 at gas-phase, utilizing copper-based materials, for the efficient and selective production of high energy density compounds, such as ethanol, is necessary. In this context, the present work provides information about the influence of the water steam and copper oxidation state on the CO2 hydrogenation to ethanol. Our data show that the presence of water steam during the reaction generated a mixture of oxidized and metallic Cu species on the copper catalyst, which resulted in an 80-fold increase in the ethanol productivity at 200 °C and atmospheric pressure. When water steam is not used, the oxidized Cu species are reduced during the reaction and the ethanol productivity decreases drastically, indicating that water plays an important role in the conversion of CO2 to ethanol.