Two-Stage Conversion of Carbon Dioxide to Methanol on Co-Pd-Containing Catalysts Based on Aluminosilicates at Atmospheric Pressure

Abstract

A two-stage process for CO₂ conversion into methanol under continuous flow and atmospheric pressure conditions is proposed, using a bimetallic cobalt–palladium catalyst supported on a Siral-type aluminosilicate (Co-Pd/Siral). In the first stage, CO₂ is hydrogenated to methane at 473–523 K according to the reaction: CO₂ + 4H₂ → CH₄ + 2H₂O, carried out in the first reactor. After removing the water formed, the second stage involves the conversion of methane, unreacted CO₂, and H₂ into methanol in a second reactor at 573 K. The introduction of 0.5 wt.% palladium into the 10 wt.% Co/Siral catalyst was shown to promote methanol formation, with a maximum yield of 3.3% observed at 573 K. It is suggested that the catalytically active sites for CO₂ hydrogenation to methane are nanosized Co, CoO_x particles, while methanol is formed through the oxidation of methane over nanosized PdO particles, following the reaction: PdO + CH₄ → Pd + CH₃OH. Methane is oxidized by PdO, and the Pd–PdO redox cycle is sustained by carbon dioxide through the reaction: Pd + CO₂ → PdO + CO. In addition, cobalt oxides (CoO_x) contribute to CO₂ activation, significantly facilitating the catalytic cycle.