Abstract: Thermodynamic calculations were performed for both the main reaction of aniline to diphenylamine and its side reactions under gas-phase and liquid-phase conditions. The results indicate that the equilibrium constant for the liquid-phase reaction is significantly higher than that for the gas-phase reaction, and the liquid-phase environment effectively suppresses side reactions. The suitable temperature range for the liquid-phase reaction was determined to be 200-350℃. Based on the thermodynamic findings, a series of La/Ce-modified H-β and HY zeolite catalysts were prepared. These catalysts were thoroughly characterized using techniques such as XRD, N? physisorption, NH3-TPD, and Py-IR, and their catalytic performance was evaluated in a fixed-bed reactor. The results indicated that the H-β zeolite subjected to alkaline treatment and metal modification exhibited the best performance, attributed to its abundant Br?nsted acid sites and suitable medium-strength acid sites in the 250-400℃ range, as well as a favorable pore structure.When using the BA-4 catalyst under a reaction pressure of 2.0 MPa, the optimal temperature range to maximize diphenylamine yield was identified as 300-350℃. This result not only confirms the practical effectiveness of the BA-4 catalyst,but also validates the crucial role of thermodynamic analysis in guiding rational catalyst design.

Key words: aniline, diphenylamine, thermodynamics, equilibrium constant, zeolite catalyst