Coke formation in zeolite ZSM-5

Abstract

The coke contents and sorption capacities of three ZSM-5 zeolites with different Al Si ratios were followed during methanol conversion until the zeolites were completely deactivated. For two of the zeolites the volume of coke exceeded the concomitant decrease in void volume, so that some coke must have been sited on the external surfaces of the zeolite crystals. An estimate was made of the ratio of external to internal coke for these zeolites. For the third zeolite the assumption that there was some external coke implies that there was also some topological blocking of parts of the channel system by coke. The presence of internal coke in the third zeolite was deduced by selective removal of coke by oxidation in an oxygen plasma and was confirmed by X-ray diffraction.