A core-shell structured Zn/ZSM-5@MCM-41 catalyst: Preparation and enhanced catalytic properties in propane aromatization

The core-shell ZSM-5@MCM-41 catalysts with various MCM-41 shell thickness were successfully synthesized by the epitaxial recrystallization method using hexadecyltrimethylammonium bromide (CTAB) as a template, and the corresponding Zn/ZSM-5@MCM-41 synthesized by the incipient wetness impregnation were tested in propane aromatization. Multitechniques including XRD, N2 adsorption–desorption, ICP, TEM, EDS-mapping, IR, NH3-TPD and IG were employed to investigate the physicochemical properties of Zn/ZSM-5@MCM-41 and the deactivation of carbon deposits. Results revealed that the diffusion capacities of Zn/ZSM-5@MCM-41 have been dramatically improved after the epitaxial growth of mesoporous MCM-41 shell. In addition, the non-acidic MCM-41 layer covering on ZSM-5 core could decrease Brønsted acid sites, preventing the formation of carbon deposits. Applying the protective MCM-41 shell increased the lifetime of the catalyst in comparison to Zn/ZSM-5 catalyst without the MCM-41 shell. However, the overgrowth of the MCM-41 shell with the formation of amorphous silica particles extended the diffusion path of reactants and products, which blocked the pore structure of the catalyst and reduced the catalytic properties in propane aromatization. In this sense, the controlled formation of appropriate thickness of MCM-41 shell around ZSM-5 core accounted for the enhanced catalytic properties.