Efficient Catalysts for Diphenylamine Alkylation: Citric Acid-Induced Highly Dispersed Ce on MCM-22

Alkylated diphenylamine antioxidants offer excellent oxidative stability and environmental benefits. The incorporation of rare earth elements is believed to enhance the performance of molecular sieve catalysts in alkylation reactions; however, traditional cerium-modified catalysts often experience cerium aggregation, leading to a reduced catalytic performance. This study explores a citric acid-assisted complexation–impregnation method to incorporate cerium species into MCM-22, overcoming the aggregation issues of traditional cerium-modified catalysts. Optimizing the citric acid to cerium (CA/Ce) ratio resulted in highly dispersed cerium species and enhanced catalyst acidity. Characterization confirmed that the CeM-3 catalyst with a CA/Ce ratio of 3 maintained structural integrity, minimized pore blockage, and improved cerium utilization. The CeM-3 catalyst achieved a DNDPA yield of 55.14% after optimization. DFT calculations revealed that the cerium modification stabilized the molecular sieve and improved substrate adsorption. This work offers an efficient strategy for the design of high-performance zeolite catalysts for sustainable alkylation processes.