IN-SITU FTIR MEASUREMENTS OF DIFFUSION IN COKING ZEOLITE CATALYSTS

The effect of coke formed by conversion of ethylbenzene as well as eth ene on the sorption capacity and diffusivity of benzene and ethylbenze ne in H-ZSM-5 was investigated using the in-situ Fourier-transform inf rared (FTIR) technique. Conversion of ethene at T = 475 K and T = 575 K, respectively, results in the formation of different coke species as evidenced by clearly distinguishable IR spectra as well as different H/C ratios as determined ex-situ by analysis of the oxidation products of the coked zeolite. Both coke modifications, however, result in a s imilar and almost linear decrease of diffusivity and sorption capacity as a function of the amount of coke deposited. Only for higher loadin gs with low-temperature coke the decrease of the diffusivity of benzen e becomes slightly more pronounced. In the case of coke formation via ethylbenzene conversion the diffusivity of ethylbenzene starts to decr ease only after deposition of higher amounts of coke, while the sorpti on capacity is reduced almost linearily with the coke coverage.