Controlled dealumination of HY zeolite using mineral and organic acids: Linking acidity redistribution to isobutane alkylation behavior

Post-synthetic dealumination is an effective strategy for tailoring the acidity and pore architecture of Y-type zeolites for alkylation reactions. In this study, HY zeolite was modified using mineral acids (HCl and HNO3) and organic acids (oxalic and citric acid) to investigate the influence of acid type on framework stability, acidity redistribution, and catalytic behavior in isobutane/2-butene alkylation. The resulting Pt-loaded catalysts were systematically characterized by XRD, FTIR, FESEM–EDS, N2 adsorption–desorption, NH3-TPD, and thermogravimetric analysis. The results revealed that acid treatment induced significant changes in the Si/Al ratio, pore structure, and acid-site distribution while preserving the FAU framework to different extents. Among the investigated treatments, nitric acid generated the highest concentration of moderate-strength acid sites and an optimized balance between acidity and pore accessibility, resulting in superior catalytic performance. The Pt/ HNO3HY catalyst maintained butene conversion above 85%, achieved the highest C8 selectivity (88.5%), and exhibited enhanced trimethylpentane (TMP) formation with the lowest coke selectivity. In contrast, HCl treatment increased the proportion of strong acid sites, promoting heavier hydrocarbon formation and faster deactivation. Oxalic acid induced more selective dealumination but substantially reduced the overall acidity, leading to lower catalytic activity. Notably, citric acid treatment caused severe framework degradation and partial amorphization, indicating excessive dealumination and loss of structural integrity. These findings demonstrate that catalytic performance is governed primarily by acid-site redistribution rather than surface area alone, highlighting controlled nitric-acid dealumination as an efficient route for optimizing zeolite-based alkylation catalysts.