Understanding Elementary Steps of Transport of Xylene Mixtures in ZSM-5 Zeolites

The transport of p-xylene in purely siliceous MFI was investigated in the presence of coadsorbed m-xylene by combining fast time-resolved IR spectroscopy and frequency response methods. p-Xylene transport rates are dominated by diffusion in the straight channels of MFI, which is 8 times faster than transport in the sinusoidal channels. m-Xylene adsorbed on the outer surface lowers the sorption rate of p-xylene significantly by blocking pore entrances, whereas m-xylene adsorbed in the MFI pores hardly influences the p-xylene transport rates. If the pore entrance is the rate-determining step of the transport process, as for the MFI samples investigated, m-xylene sorption on the outer surface selectively impedes faster transport through the straight pore openings