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

- High-pressure advantages are examined for stoichiometric CO2 hydrogenation to methanol.
- Reaction temperature and space velocity are systematically investigated under high-pressure conditions (46-442 bar).
- High-pressure facilitates the reaction to enter thermodynamically controlled regime with excellent catalytic performance.
- Strong interplay between kinetics and thermodynamics determines catalytic performance.
- A remarkable methanol yield of 15.3 gMeOH gcat−1 h−1 can be achieved at 442 bar at high space velocity.

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 gMeOH gcat−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 gMeOH gcat−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.

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