Preparation of Pd/Al2O3 Catalyst and Its Toluene Catalytic Decomposition: Optimization of Preparation Conditions and Performance

Palladium-containing catalysts are widely applied in VOCs treatment. However, the pH value of the impregnation solution significantly affects the size and form of palladium particles on the catalyst surface, restricting its catalytic performance. To clarify the influence of pH value on the micro-structure and value state of palladium species, this study systematically investigated alkaline pH values (8, 9, 10) on the physicochemical properties and toluene oxidation performance of Pd/Al ₂ O ₃ catalysts. Characterization results indicated that the catalyst prepared under pH = 9 (N-9) exhibited the best Pd dispersion (29.45%) and the smallest average Pd particle size (3.78 nm, significantly smaller than 7.92 nm of N-8 and 7.29 nm of N-10), with the active palladium species mainly existing in the form of PdO, and had a moderate distribution of surface basic sites. In the toluene oxidation reaction, N-9 demonstrated outstanding low-temperature activity (T ₅₀  = 237.9℃, T ₉₈  = 247.3℃) and the lowest apparent activation energy (9.9 kJ·mol ^-1 ), significantly outperforming the catalysts prepared under pH = 8 (N-8) and pH = 10 (N-10) conditions. Moreover, after continuous operation at 250℃ for 16 hours, the activity retention rate of N-9 exceeded 99%, demonstrating excellent stability. This superior performance was mainly attributed to the highly dispersed and small-sized PdO nanoparticles formed under pH = 9 conditions and their optimized interaction with the Al ₂ O ₃ support. This study provides an optimized strategy based on precise pH regulation of the impregnation solution for the development of efficient and stable industrial VOCs purification catalysts.