A review on the computational studies of the reaction mechanisms of CO₂ conversion on pure and bimetals of late 3d metals

Despite series of experimental studies that reveal unique activities of late 3d transition metals and their role in microorganisms known for CO₂ conversion, these surfaces are not industrially viable yet. An insight into the elementary steps of surface catalytic processes is crucial for effective surface modification and design. The mechanisms of CO₂ transformation into CO, through the reverse water gas shift and methane reforming, are being studied. Mechanisms of CO₂ methanation is also being explored by the Sabatier reaction into methane. This review covers both experimental and theoretical studies into the mechanisms of CO₂ reduction into CO and methane, on single metals and bimetals of late 3d transition metals, i.e. Fe, Co, Ni, Cu and Zn. This paper highlights progress and gaps still existing in our knowledge of the reaction mechanisms. These mechanistic studies reveal CO₂ activation and reduction mechanisms are specific to both composition and surface facet. Surfaces with least CO₂ binding potential are seen to favour CO and O binding and provide higher barriers to dissociation. No direct correlation has been seen between binding strength of CO₂ and its degree of activation. Hydrogen-assisted dissociation is seen to be generally favoured kinetically on Cu and Ni surfaces over direct dissociation except on the Ni (211) surface. Methane production on Cu and Ni surfaces is seen to occur via the non-formate pathway. Hydrogenation reactions have focused on Cu and Ni, and more needs to be done on other surfaces, i.e. Co, Fe and Zn.