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

Abstract A new kind of SO 4 2− /TiO 2 /ZSM-5 catalysts were prepared by the sequential TiO 2 -CLD and sulfation of commercial HZSM-5 zeolite. Characterization results revealed that the external surface of ZSM-5 crystallite was wrapped by SO 4 2− /TiO 2 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 SO 4 2− /TiO 2 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 SO 4 2− /TiO 2 /ZSM-5 catalysts, which was probably due to the enhancement of sorption process for the gas-phase n-pentane molecules into HZSM-5 crystallite caused by the surface SO 4 2− /TiO 2 phase. Moreover, the SO 4 2− /TiO 2 /ZSM-5 catalysts with a suitable TiO 2 -loading exhibited excellent catalytic stability and coke-resistance ability in normal-paraffin cracking. A possible role of the surface SO 4 2− /TiO 2 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.