Thermodynamics Calculation of Reaction Synthesis Pathways for Ag-Al₂O₃ Powder By First-Principles Calculations

Ag/Al₂O₃ powders are highly effective catalytic materials utilized in the epoxidation of ethylene to produce ethylene oxide. One of the critical challenges in this catalytic process is the stability of nano-sized Ag particles, especially during high-temperature catalysis. However, this issue can be effectively addressed through in-situ reaction synthesis. To gain a deeper understanding of the underlying mechanisms, the phase transformation process and the thermodynamic mechanism of the oxidation reaction in the Ag/Al₂O₃ system have been investigated using first-principles thermodynamic calculations in conjunction with traditional thermodynamic data. These calculations, whose accuracy has been verified, provide valuable insights into the behavior of Ag and Al under different conditions. The results indicate that, during AgAl solid-solution oxidation, Ag-containing Al preferentially forms the stable intermediate phase Ag₂Al instead of undergoing direct oxidation; this pathway becomes thermodynamically more favorable at higher Ag concentrations. With increasing temperature, Ag₂Al is further oxidized to yield Ag and Al₂O₃. It is also found that above 237°C, Ag₂O and AgAlO₂ become unstable. The overall reaction pathway is solid solution→Ag₂Al→Ag + Al₂O₃. This comprehensive study provides a robust theoretical calculation basis for the development and optimization of in-situ reaction-synthesized Ag/Al₂O₃ powder composite materials, which have significant potential for practical applications in catalysis.