Incorporation of titanium into H-ZSM-5 zeolite via chemical vapor deposition: Effect of steam treatment

Ti-ZSM-5 prepared by secondary synthesis, from the reaction of H-ZSM-5 with vapor phase TiCl₄, was characterized with several physicochemical techniques including FT-IR and UV/VIS-DRS. It was found that zeolite structure, surface area and pore volume did not change, and the framework aluminum could not be replaced by titanium atom during the secondary synthesis of Ti-ZSM-5. The incorporation of titanium into the framework might be due to reaction of TiCl₄ with the silanol groups associated with defects or surface sites. The formation of extra-framework titanium could not be avoided, unless the samples were further treated by water vapor at 550 °C or higher temperature. High temperature steam treatment of Ti-ZSM-5 prepared by chemical vapor deposition with TiCl₄ was efficient to prevent the formation of non-framework titanium species. Ti-ZSM-5 zeolites prepared in this work contained only framework titanium species and exhibited improved catalytic property close to TS-1 prepared by hydrothermal synthesis.