Cu/ZnO/CeO₂ Supported on MOF-5 as a Novel Catalyst for the CO₂ Hydrogenation to Methanol: A Mechanistic Study on the Effect of CeO₂ and MOF-5 on Active Sites

Cu/ZnO/CeO₂ nanocomposite was supported on metal organic framework (MOF-5) to enhance active sites dispersion and control the nanoparticles agglomeration during synthesis through strong metal-support interactions. The incorporation of MOF-5 alleviated the obstacle facing the commercial ternary Cu/ZnO/Al₂O₃ regarding low surface area due to nanoparticles agglomeration. In addition, Cu/ZnO/CeO₂@MOF-5 gave higher methanol selectivity than the commercial catalyst which can be accounted for by the interfacial sites generated between MOF-5 and Cu/ZnO which favour methanol synthesis over carbon monoxide through regulating the intermediates bonding energies. CeO₂ as support for Cu/ZnO nanoparticles was also compared with commercial support and showed to have led to smaller particle size and superior dispersion of Cu active sites as well. Cu/ZnO/CeO₂@MOF-5 resulted in methanol STY of 23.3 mg g_cat h⁻¹ and selectivity of 79% at mild reaction temperature (260 °C) and pressure (10 bar). Two different MOFs including cerium based MOF and ZIF-8 demonstrated inferior performance compared to MOF-5.