In-situ FTIR measurements of diffusion in coking zeolite catalysts Original Research Article

The effect of coke formed by conversion of ethylbenzene as well as ethene on the sorption capacity and diffusivity of benzene and ethylbenzene in H-ZSM-5 was investigated using the in-situ Fourier-transform infrared (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 HC ratios as determined ex-situ by analysis of the oxidation products of the coked zeolite. Both coke modifications, however, result in a similar and almost linear decrease of diffusivity and sorption capacity as a function of the amount of coke deposited. Only for higher loadings with low-temperature coke the decrease of the diffusivity of benzene becomes slightly more pronounced. In the case of coke formation via ethylbenzene conversion the diffusivity of ethylbenzene starts to decrease only after deposition of higher amounts of coke, while the sorption capacity is reduced almost linearily with the coke coverage.