Hydrodesulfurization of 4,6-dimethyldibenzothiophene over NiMo supported on Ga-modified Y zeolites catalysts

Abstract

Y zeolites modified by gallium (Ga) via three different modification methods (impregnation, post-synthesis and in situ synthesis) were synthesized, and the synthesized supports were impregnated by NiMo precursors. Characterization techniques such as XRD, N2 physical adsorption-desorption, ICP-OES, FT-IR, 71Ga MAS NMR, Py-FTIR, H2-TPR, HRTEM and XPS were performed to determine the effects of each modification of Y zeolite by Ga on the properties of the prepared supports and catalysts. Finally, 4,6-dimenthyldibenzothiophene (4,6-DMDBT) was used as a probe to evaluate the effects of the modification of Y zeolite by Ga on the catalytic performance of the prepared catalysts. The results show that the Modification of Y zeolite by Ga affected the position of the Ga species: in the impregnation modification method, Ga species deposited on the surface of Y zeolite mainly exist as non-framework Ga2O3; in the post-synthesis modification method, Ga species are introduced to the near-surface area and mainly exist as framework Ga species; and in the in situ synthesis modification method, Ga species are introduced throughout the whole framework and exist as framework Ga species. Ga species located at the surface and near-surface area effectively prevent the formation of strong Mo-O-Al bonds, which results in both modulated acidity and weakened interactions between active metals and the support (MSI). The hydrodesulfurization (HDS) results also show that the effects of Ga on NiMoS/Y-zeolite play a very important role in the catalytic performance of the corresponding catalysts. The superior HDS performance of the catalyst NiMo/GaHY (prepared via post-synthesis method) can be attributed to the better accessibility of active sites, the modulated acidity property, the proper MSI, the higher proportion of the NiMoS phase, the higher isomerization activity and the higher matching between hydrogenation activity and hydrolysis activity.