Enhanced Catalytic Activity on Post-Synthesized Hollow Titanium Silicalite-1 with High Titanium Content on the External Surface

A titanium silicalite-1 (TS-1) extrudate with high content of titanium on the external surface was post-synthesized by using the mixed solution of tetrapropylammonium hydroxide and the hydrolysate of tetrabutyl titanate. The influence of Ti concentration in the post-synthesis solution on the physicochemical properties and catalytic performance of TS-1 was also studied. The amorphous silica support covering on the external surface of TS-1 was crystallized, and some hollows appeared in the samples that were post-synthesized. Most titanium introduced by this method are located at the external surface of the new generated TS-1 particles. The molar ratio of Si/Ti on the external surface decreases with the increase of the Ti concentration in the post-synthesis solution. The catalytic activity for phenol hydroxylation over the TS-1 samples is enhanced after the post-synthesis due to the new generated framework Ti on the external surface, providing the reactants more easily adsorbable active centers. A proper Ti concentration (10 vol%) in the post-synthesis solution leads to the highest catalytic activity by obtaining a proper ratio of tetrahedral and octahedral Ti to anatase TiO₂.