Effect of support of Co-Na-Mo catalysts on the direct conversion of CO₂ to hydrocarbons

This study of the effect of support of Co-Na-Mo based catalysts on the direct hydrogenation of CO₂ into hydrocarbons (HC) provides guidelines for the design of catalysts for CO₂ conversion. We demonstrate that the surface area of the support and the metal-support interaction have a key role determining the cobalt crystallite size and consequently the activity of the system. Cobalt particles with sizes <2 nm supported on MgO present low reverse water gas shift conversion with negligible Fischer-Tropsch activity. Increasing the cobalt particle size to ∼15 nm supported on SiO₂ and ZSM-5 supports not only substantially increases the CO₂ conversion but it also provides high HC selectivities. Further increase of the cobalt particle size to 25-30 nm has a detrimental effect on the global CO₂ conversion with HC:CO ratios below 1, however, lower methane selectivity and enhanced formation of unsaturated HC products are achieved. Additionally, the metal-support interaction potentially also has a strong effect on the growth chain probability of the formed hydrocarbons, increasing as the metal-support interaction increases. These evidences demonstrate that CO₂ conversion and hydrocarbon distribution can be tuned towards desired products by controlled catalyst design.