CO₂ hydrogenation to methanol over bimetallic Pd-Cu catalysts supported on TiO₂-CeO₂ and TiO₂-ZrO₂

Binary supports TiO₂-CeO₂ and TiO₂-ZrO₂ improved CH₃OH formation and selectivity effectively, but with little effect on CO₂ conversion. Pd-Cu/Ti_0.8Ce_0.2O₂ enhanced CH₃OH formation by ca. 46 % comparing to Pd-Cu/TiO₂-C. Pd-Cu/Ti_0.1Zr_0.9O₂ exhibited the highest catalytic performance: CH₃OH formation rate was 0.62 μmol g-cat⁻¹s⁻¹, which was enhanced by 121 %, 51 %, and 51 % in comparison to Pd-Cu/TiO₂-C, Pd-Cu/ZrO₂-C, and Pd-Cu/Ti_0.8Ce_0.2O₂, respectively. More interestingly, lowering temperature from 523 K to 493 K further enhanced CH₃OH selectivity from 44.6%–58.8%. Binary supports significantly increased surface area. Unexpectedly, it did not improve H₂ reduction for Pd-Cu/Ti_xZr_1-xO₂ in H₂-TPR, but decreased H₂ uptake to stoichiometric level, implying SMSI was adjusted to moderate state. However, the excessive H₂ uptake further increased for Pd-Cu/Ti_xCe_1-xO₂, indicating unalleviated SMSI. Furthermore, Pd-Cu alloy formation was improved in Pd-Cu/Ti_xZr_1-xO₂, which was favorable for CH₃OH synthesis. Binary supports also improved CO₂ adsorptive behavior towards weakly-bonded species, contributing to better performance.