This review systematically analyses recent studies on CO₂ hydrogenation to methanol with a focus put on primary and secondary reactions. Thermodynamic aspects, active sites and reaction mechanisms are discussed. We also provide personal views on possible developments in this area and recommendations for catalytic tests and their evaluation to properly compare different catalysts.

Abstract

Carbon dioxide (CO₂) hydrogenation to methanol (CH₃OH) is one of the most promising approaches to provide this platform chemical and to close carbon cycles. In this minireview, we systematically analyze primary and secondary reactions which can take place in this reaction over Cu-based catalysts. In addition to repeatedly discussed reverse water gas shift reaction (RWGS) and CH₃OH production directly from CO₂, we consider decomposition, dehydration, dehydrogenation, and steam reforming of the desired alcohol. These reactions are usually ignored in the studies dealing with CO₂ hydrogenation to CH₃OH but can worsen the catalyst efficiency. Apart from the corresponding thermodynamic analysis, proposed reaction mechanisms and active sites are described and discussed. The effects of co-fed water, CH₃OH and methyl formate on catalyst performance are critically scrutinized, too. We also provide several criteria for unambiguous comparison of different catalysts in terms of CH₃OH selectivity and their activity.