Intermediate-crystallization promoted catalytic activity of titanosilicate zeolites

Abstract

The exploration of highly efficient catalysts based on nano-sized hierarchical titanosilicate zeolites with controllable active titanium species is of great importance in promoting the oxidative desulfurization of bulky organosulfur compounds. Here we report the anatase-free nano-sized hierarchical TS-1 (MFI) zeolite prepared via a seed-assisted hydrothermal method. Interestingly, it is found that the intermediately crystallized zeolite phase exhibits better performance in oxidative desulfurization of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), with a turnover number up to 17.9 and 18.0 at 30 min of the reaction, respectively, almost two fold higher than those of the final completely crystallized zeolite phase (8.8 and 6.7, respectively). This superior activity is attributed to the existence of abundant inter- and intracrystalline mesopores, and the surface enriched active titanium species, as well as the absence of anatase species within the nano-sized intermediate phase, which is beneficial for exposing more accessible active sites, enhancing the mass transfer efficiency, as well as avoiding the inefficient decomposition of oxidants. This intermediate crystallization method provides a useful strategy in exploring highly efficient zeolite catalysts.