SO42-/TiO2 promotion on HZSM-5 for catalytic cracking of paraffin

A new kind of SO42-/TiO2/ZSM-5 catalysts were prepared by the sequential TiO2-CLD and sulfation of commercial HZSM-5 zeolite. Characterization results revealed that the external surface of ZSM-5 crystallite was wrapped by SO42-/TiO2 phase; at the same time, the unique MFI-structure and pore properties were well preserved, and the new L acid sites were generated on the external surface. The surface SO42-/TiO2 phase promoted the paraffin saturation adsorption by 8%, and significantly enhanced the diffusion process in the ZSM-5 based catalysts. Compared to the parent HZSM-5 zeolite, a significant promotion of catalytic activity in n-pentane cracking was observed over the SO42-/TiO2/ZSM-5 catalysts, which was probably due to the enhancement of sorption process for the gas-phase n-pentane molecules into HZSM5 crystallite caused by the surface SO42-/TiO2 phase. Moreover, the SO42-/TiO2/ZSM-5 catalysts with a suitable TiO2-loading exhibited excellent catalytic stability and coke-resistance ability in normal-paraffin cracking. A possible role of the surface SO42-/TiO2 phase in coke formation was proposed that it effectively hindered the routes from olefins to aromatic hydrocarbons, and thus restrained the accumulation of coke deposit on the external surface. (C) 2017 Elsevier B.V. All rights reserved.