Insights into the role of silanols in methanol to propene reaction over silicalite-2 zeolite through post-treatments

Abstract As an efficient catalyst in methanol to propene (MTP), silicalite-2 zeolite was subjected to acidization and desilication. Changes in the properties of modified zeolites were investigated by XRD, FTIR, SEM, TPD, and sorption techniques. It was shown that the samples through post-treatments all showed a similar initial catalytic activity, while the deactivation behaviors were distinct. Samples through desilication exhibited a 2-fold improvement in catalytic lifetime (methanol conversion falling to 95%), while acidization accelerated the deactivation apparently. The results from in-situ FTIR and OH-FTIR revealed that the accessibility of acid sites (mainly H-bonded silanols) determines the initial activity and the location of isolated silanols is crucial for deactivation. The isolated silanols in the pore can impact the formation and diffusion of the intermediate species and subsequently affects the coke capacity and mobility. The external surface is indicated to be responsible for the tolerance of external coke. Thus, less internal isolated silanols and larger external surface area can jointly contribute to a long catalytic lifetime over silicalite zeolite.