The microporous and hierarchical ZSM-5 zeolites were studied with respect to their interaction with o-, m- and p-xylene molecules as well as the catalytic activity in xylenes isomerization process followed by 2D COS analysis of IR spectra. The aspects of mechanism of xylene isomerization reaction have been discussed in the light of the results of 2D COS analysis of IR spectra and catalytic performance of studied zeolites. The ZSM-5 zeolites were characterized by different Si/AI ratio and by various types of generated mesoporosity. This selection assured ability to follow properly the changes in the catalytic performance related not only to acidic properties but also to porosity of the samples. It was shown that the microporous character of zeolites was crucial for high selectivity to the most desired product i.e. p-xylene. In the case of hierarchical zeolites it was confirmed that the formation of by-products as mesitylene and toluene occurred during ortho-xylene isomerization. Furthermore, for hierarchical zeolites the high amount of silanols groups prompted to the coke formation on highly developed external surface. (C) 2016 Elsevier B.V. All rights reserved.