Carbon dioxide (an abundant, inexpensive, and renewable carbon resource) is one of the most significant greenhouse gases that cause global warming and climate changes. Carbon dioxide can be used to synthesize useful chemical products such as linear carbonates like dimethyl and diethyl carbonate and methane. Carbon dioxide valorisation (from biomass or industrial flue gases, for instance) using catalytic processes is an excellent alternative to reduce greenhouse gas emissions. As the use of catalyst as a powder imply the need for a large amount of catalyst in the catalytic bed and the consequent problems with pressure drop, the use of carbon powders processed into pellets (cylindrically-shaped pieces) is mandatory to reduce the total catalyst volume, the pressure drop in the catalytic bed, and the formation of hotspots.
In this work, Cu, Ni, Cu-Ni, Ru, Fe, and Ru-Fe monometallic and bimetallic catalysts were synthesized by the wetness impregnation over pellets of activated carbon and evaluated in the production of dimethyl carbonate and diethyl carbonate (Cu, Ni, Cu-Ni) and methane (Ru, Fe, Ru-Fe). The highest catalytic activity (in terms of turnover frequency) was obtained over bimetallic catalysts with Cu: Ni, 2:1, 3:1 molar ratio in dimethyl and diethyl carbonate, respectively and Ru in methane formation. The increased activity was attributed to the synergetic interaction between metals in the alloy formed on the surface of the catalyst. Results suggest that the synthesized catalysts could potentially be used for carbon dioxide fixation processes.