CO₂ Hydrogenation to Methanol and Methane over Carbon-Supported Catalysts

Abstract

Methanol and methane are among the important products obtained during the hydrogenation (HYD) of CO2. The distribution of products and their yields can be influenced by operating conditions. In this case, the type of catalyst has a dominant effect. Gradual transformation of CO2 involves several surface intermediates. Special geometry of active site is required for maximizing the yield of methanol and for minimizing the reaction run-away to methane. Such a state can be attained over catalysts that contain CuO-ZnO components. Catalysts containing other transition metals and noble metals are less suitable, while the same catalysts exhibit good performance during the HYD of CO2 to methane. In industrial applications, catalysts supported on oxidic supports, i.e., Al2O3, SiO2, TiO2, etc., have been used. During HYD of CO2, 1 and 2 mol of water are generated for every mole of methanol and methane, respectively. The stability of catalysts used for HYD of CO2 can be enhanced by replacing oxidic supports with carbon supports. Amorphous carbons, such as activated carbon, and carbon nanomaterials, such as carbon nanotubes, carbon nanofibers, and graphene-derived solids, have been tested both as catalysts and supports. For methanol synthesis, CuO-ZnO catalysts supported on these carbons have been evaluated. Similar carbon supports have been used for the preparation and testing of methanation catalysts consisting of a wide range of transition and noble metals as active metals. Both monometallic and bimetallic catalysts were evaluated.