Effect of surface Na+ or K+ ion exchange on hydrodesulfurization performance of MCM-41-supported Ni-W catalysts

摘要

Ni-W hydrodesulfurization (HDS) catalysts supported on MCM-41 synthesized from two different silica sources (sodium silicate hydrate and tetraethylorthosilicate) as well as on Na+ or K+ ion exchanged MCM-41 were prepared. These catalysts were used to investigate the influence of the surface properties of MCM-41 on the performance of HDS catalysts with DBT as the model molecule. The XRD and N-2 adsorption results indicated that the MCM-41 prepared from tetraethylorthosilicate (MCM-41(T)) exhibited the best structural properties. The mesostructure of MCM-41 synthesized from sodium silicate (MCM-41(S)) remained after ion exchange with Na2C2O2 and K2C2O2. Both pyridine FT-IR and Hammett indicators showed that only MCM-41(S) possessed some Bronsted and Lewis acid sites. Ni-W/MCM-41(S) showed the highest HDS and hydrogenation activities. The introduction of Na+ and K+ strongly inhibited the hydrogenation activity of Ni-W/MCM-41(S) but enhanced its hydrogenolysis activity. UV-vis and TPR studies indicated that the introduction of Na+ and K+ into MCM-41(S) may lead to the segregation of surface Ni species and may hinder the reducibility of the supported Ni-W oxides. Spillover hydrogen, which is "trapped" by Na+ and K+, may play an important role in the HDS activity and selectivity of Ni-W catalysts. (c) 2006 Elsevier B.V. All rights reserved.