Synthesis and catalytic performance of hierarchical MCM-22 zeolite aggregates with the assistance of carbon particles and fluoride ions

Abstract

Hierarchical MCM-22 zeolite aggregates (MCM-22-FC) were prepared by one-pot hydrothermal synthesis with the assistance of carbon particles and fluoride ions. The effects of carbon particles and fluoride ions on the morphology and catalytic properties of the MCM-22 zeolite were investigated. The hierarchical MCM-22-FC zeolite aggregates were constructed by intergrown and stacked thin MCM-22 lamellas and possessed macro-/mesopores and inherent micropores. The MCM-22-FC zeolite was modified to form the Mo/MCM-22-FC catalyst, which exhibited an improved benzene yield and aromatic selectivity as well as catalyst life in the methane dehydroaromatization (MDA) reaction. Based on NH 3 -TPD and pyridine-Fourier transform infrared spectroscopy measurements together with thermogravimetric analysis, we found that the improved MDA catalytic performance of Mo/MCM-22-FC resulted from the formation of more active MoC x or MoO x C y species that evolved from increased amounts of Brönsted acids with the assistance of fluoride ions. This promoted the diffusion of large molecule products because of the thin MCM-22 lamellas. Less excess Brönsted acid sites were retained in the Mo/HMCM-22-FC catalyst because the formation of active centers inhibited the formation of coke, which contributed to its improved aromatic selectivity Hierarchical MCM-22 zeolite aggregates constructed by intergrown and stacked thin MCM-22 lamellas were prepared by one-pot hydrothermal synthesis with the assistance of carbon particles and fluoride ions. The Mo/MCM-22-FC catalyst exhibited an improved benzene yield and aromatic selectivity as well as catalyst life in the methane dehydroaromatization reaction.