A Straightforward Descriptor for the Deactivation of Zeolite Catalyst H-ZSM-5

ZSM-5 is a widely used zeolite catalyst and is employed industrially for the methanol to gasoline (MTG) process. Even so, deactivation of ZSM-5 by coke formation constitutes a major technical and also fundamental challenge. We investigate the deactivation of a range of ZSM-5 catalysts through catalytic testing, physicochemical characterization, and powder X-ray diffraction (XRD). It is demonstrated that the unit cell changes upon deactivation. Periodic density functional theory is used to show that the change is induced by certain methyl substituted benzenes in the channel intersection in ZSM-5. This finding is corroborated by Rietveld refinement of XRD data obtained for deactivated catalysts. We are able to establish a direct correlation between the difference in the length of the a- and b-unit cell vectors and the total amount of coke, the remaining acidity, and the remaining surface area of the catalysts. This a- minus b-parameter is a straightforward descriptor that carries the essential information regarding the degree of deactivation of a ZSM-5 catalyst, and a routine measurement of a diffractogram of the catalyst can be used to quantitatively assess the degree of deactivation.