Preparation of hierarchical HZSM-5 based sulfated zirconium solid acid catalyst for catalytic upgrading of pyrolysis vapors from lignite pyrolysis

Abstract

H5 was developed to mesoporous system via alkali treatment, and sulfated zirconia (SZr) modified hierarchical HZSM-5 (AT0.2/H5) catalysts (named AT0.2/SZxH5) were successfully prepared by a series of post-treated method followed by Zr(NO3)4·5H2O and H2SO4 as active component. The innovative approach really enhanced acidity of AT0.2/H5 support, which results from the interaction of the sulfate groups attached to zirconia that doped on MFI framework with silanol groups. Adding active component can not only compensate for the loss of acid sites caused by NaOH treatment, but also re-develop more active sites owing to the formation of SZr. Meanwhile, NH3-TPD showed higher strong acid sites and weak acid sites in AT0.2/SZ6:1H5 than other prepared catalysts. The catalytic activity in converting lignite pyrolysis volatiles to light aromatics, including benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN), correlates well with the enhanced acidity. Compared with H5, the yield of light aromatics increased significantly from 15.2 to 19.3 mg/g over AT0.2/SZ6:1H5 at 600 °C. According to the characterization of N2 adsorption–desorption, SEM, and XRD, both the S species as SO42− and Z species as ZrO2 improved the textural properties of the support itself. Besides, the molar ratio of S/Zr was in direct proportion to the yield of BTEXN in a certain range, and 6:1 exhibited the optimal catalytic performance. The prepared solid acid catalyst provides a promising strategy to directional prepare light aromatics during lignite catalytic pyrolysis.