Xylenes transformation over zeolites ZSM-5 ruled by acidic properties

Abstract The studies presented in this work offer an insight into xylene isomerization process, followed by 2D COS analysis, in the terms of different acidity of microporous zeolites ZSM-5. The isomerisation reaction proceeded effectively over zeolites ZSM-5 of Si/Al equal of 12 and 32. Among them, the Al-poorer zeolite (Si/Al = 32) was found to offer the highest conversion and selectivity to p -xylene with the lowest number of disproportionation products, both in ortho - and meta -xylene transformation. Further reduction of Bronsted acidity facilitated the disproportionation path (zeolites of Si/Al = 48 and 750). The formation of intermediate species induced by the diffusion constraints for m -xylene in 10-ring channels was rationalized in the terms of the methylbenzenium ions formation inside the rigid micropore environment. Finally, both microporous character of zeolite and the optimised acidity were found to be crucial for high selectivity to the most desired product i.e. p -xylene. The analysis of asynchronous maps allowed for concluding on the order of the appearance of the respective products on the zeolite surface.