P-modified deactivated TS-1: A benign catalyst for the MTP reaction

Highly efficient catalyst is the core for the conversion of methanol to propylene (MTP). The deactivated TS-1 zeolite (De-TS-1) derived from the industrial ammoximation process has been successfully applied in the MTP reaction. After a series of systematic characterizations, the Si-OH groups adjacent to open Ti species (Si-OH(Ti) groups) were identified to be the active centers for the MTP reaction. Through further P modification on the acid-washed H-De-TS-1 zeolite, the obtained H-De-TS-1–0.4 P zeolite showed a better performance in the reaction. The total olefins selectivity and the single-run lifetime reached 87.9% and 91 h respectively and the hydrogen transfer index was as low as 0.11. This improvement could be attributed to the attenuated acid properties of H-De-TS-1–0.4 P zeolite, which suppressed the hydrogen transfer reactions, aromatization reactions and promoted the formation of olefins. During the process of P modification, phosphoric acid not only reacted with the Si-OH(Ti) groups to decrease the amount and strength of Brønsted acid sites, but also interacted with Ti-OH groups to transform the tetrahedral Ti species into octahedral ones and meanwhile decreased the amount and strength of Lewis acid sites.