Insights into active sites and structure performance relationships for Beckmann Rearrangement over nanosphere sulfonic acid resins

The development of efficient and stable solid acid catalysts for the Beckmann Rearrangement is critical to advancing sustainable chemical synthesis. However, challenges persist in balancing active site density, structural stability, and mass transfer efficiency. To address these limitations, nanosphere sulfonic acid resins were synthesized through soap-free emulsion polymerization and evaluated in the liquid-phase Beckmann Rearrangement, achieving exceptional performance with 86.96 % conversion and 96.12 % selectivity. Density Functional Theory (DFT) calculations revealed distinct catalytic performance of terminal sulfonate groups versus paired sulfonate groups, with the latter found to be the dominant active sites. Three distinct reaction pathways for cyclohexanone oxime (COX) were proposed based on the spatially constrained distribution of the two different active sites within the catalyst architecture, supported by subsequent DFT calculations providing mechanistic insights into the differential characteristics. Characterization of the catalysts through BET, SEM, TEM, FT-IR, TG, and acid-base titration indicated that 20 % divinylbenzene (DVB) content yielded the highest acidic sites density, while 10 % DVB content produced the most uniform nanosphere morphology. Notably, turnover number (TON) analysis demonstrated that the catalyst with 10 % DVB content exhibited a TON 1.7 times higher than that of commercial resin, underscoring its superior efficiency.