Synthesis of bifunctional CuO–ZnO@Cu-MOR catalytic membrane reactor for efficient CO₂ hydrogenation to methanol

The catalytic membrane reactor (CMR) effectively integrates chemical reaction with separation by a permselective membrane, leading to a significant enhancement of the conversion due to the removal of products during chemical processes. In the previous work, the removal of by-product water through the hydrophilic zeolite LTA membranes has substantially enhanced the conversion of carbon dioxide (CO₂) hydrogenation to methanol. However, it is necessary to further improve the stability of the membrane reactor under elevated temperature and pressure conditions. In this study, we have synthesized a novel CuO–ZnO@Cu-MOR CMR for CO₂ hydrogenation to methanol. With a higher Si/Al ratio than zeolite LTA, zeolite mordenite (MOR) contributes to the structural stability of the membrane reactor under elevated temperature, enabling stable operation at at 250 °C over 200 h. Simultaneously, the copper exchange of MOR effectively balances the hydrophilicity and stability of the separation membrane, which not only enhances the hydrophilicity of the MOR membrane, but also narrows the pore size of the MOR membrane due to the distinctive shrinkage effect. The limitation of thermodynamic equilibrium is broken attributing to the removal of the by-product steam by the hydrophilic Cu-MOR membrane. As a result, a CO₂ conversion of 35.2 % and a methanol selectivity of 96.7 % has been achieved at 250 °C and 3.0 MPa, which higher than those obtained in the catalytic fixed-bed reactor (CFBR).