High-pressure advantages in stoichiometric hydrogenation of carbon dioxide to methanol

Interplay between three important reaction parameters (pressure, temperature, and space velocity) in stoichiometric hydrogenation of carbon dioxide (CO₂:H₂ = 1:3) was systematically investigated using a commercial Cu/ZnO/Al₂O₃ catalyst. Their impacts on reaction performance and important ranges of process conditions toward full one-pass conversion of CO₂ to methanol at high yield were rationalized based on the kinetics and thermodynamics of the reaction. Under high-pressure condition above a threshold temperature, the reaction overcomes kinetic control, entering thermodynamically controlled regime. Ca. 90% CO₂ conversion and >95% methanol selectivity were achieved with a very good yield (0.9–2.4 g_MeOH g_cat⁻¹ h⁻¹) at 442 bar. Such high-pressure condition induces the formation of highly dense phase and consequent mass transfer limitation. When this limitation is overcome, the advantage of high-pressure conditions can be fully exploited and weight time yield as high as 15.3 g_MeOH g_cat⁻¹ h⁻¹ could be achieved at 442 bar. Remarkable advantages of high-pressure conditions in terms of reaction kinetics, thermodynamics, and phase behavior in the aim to achieve better methanol yield are discussed.