Selective formation of propylene from methanol over high-silica nanosheets of MFI zeolite

Abstract

A high-silica nanosheet MFI zeolite was successfully assembled by low-cost raw materials and a special bifunctional organic surfactant. It showed high propylene selectivity (51.0%) and high propylene/ethylene (P/E) ratio (12.1), as well as long catalytic lifetime in methanol to propylene (MTP) reaction under the operating condition of T=450°C, P=0.1MPa (PMeOH=20kPa) and WHSV=1.5h−1. The excellent catalytic performance of MFI nanosheets could mainly be ascribed to its unique morphology and textural properties. The ultrathin nanosheets enormously shorten the diffusion path length and thus remarkably improve the molecular diffusion. As a result, the product molecules could easily escape from zeolite channels, and the secondary reactions like aromatization and hydrogen transfer are inhibited dramatically, leading to a high propylene selectivity and a low deactivation rate. Moreover, the considerably large specific surface area and high mesoporosity of the nanosheet MFI zeolite enable it to accommodate a lot more coke deposition, which also gives a good contribution to the notable improvement in the catalytic lifetime.