(509u) CO2 Hydrogenation to Ethanol over Pd/Bi2O3 Catalysts: The Synergistic Effect of Pd Particle Size and Surface Oxygen Vacancy

Fossil fuel utilization leads to CO₂ emission in past decades, causing environmental concerns. Efficient conversion of CO₂ reduces its concentration in the atmosphere, additionally providing an alternative resource for the production of fuels and value-added chemicals. Heterogeneous catalysts are typically employed to overcome the kinetic and thermodynamic challenges for CO₂ conversion. Although CO₂ conversion has been broadly investigated, the products are generally C₁ species, including CO, CH₄ and CH₃OH. In the present contribution, we demonstrate that CO₂ is efficiently converted to ethanol over Pd/Bi₂O₃ catalysts. A mechanistic study shows that both Pd particle size and the oxygen vacancy synergistically promote ethanol formation from CO₂ hydrogenation. It was found that the products of CO₂ conversion over Pd/Bi₂O₃ depend on operating temperatures, Pd particle size and surface oxygen vacancy. The TOF (turnover frequency) values of ethanol formation are larger than those under other temperatures (160, 280 and 320 °C). This is likely because that 160 °C is not sufficiently high to activate CO and H₂ molecules, while when the temperature was elevated beyond 280 °C, CO₂ is over-converted to other species like CH₄ and CO. When Pd particle size is 1-1.5 nm, the TOF of ethanol at 200 and 240 °C is relatively high, while when the particle size is larger than 2 nm, the TOF decreases sharply. It indicates that ethanol formation relies on the particle size of Pd. Interestingly, the oxygen vacancy values and TOF are essentially linearly correlated. These experimental observations propose that CO₂ hydrogenation to ethanol over Pd/Bi₂O₃ catalysts are synergistically promoted by both Pd particle size and surface oxygen vacancy. In summary, CO₂ is efficiently converted to ethanol over Pd/Bi₂O₃ catalysts, where small Pd particle size and high oxygen vacancy synergistically promote ethanol formation rate under the investigated operating conditions.