Metal-ion-planted MCM-41. Part 3. Incorporation of titanium species by atom-planting method

Abstract

Titanium-containing MCM-41, Ti-MCM-41, has been prepared by a solid–gas reaction between siliceous MCM-41 and TiCl₄ vapor at elevated temperatures (303–1073 K), i.e. by the atom-planting method. The optimum preparation conditions, the coordination states of the Ti species incorporated, and the mechanism of Ti incorporation have been investigated. Ti ions were readily incorporated into MCM-41 by TiCl₄ treatment with only a trace amount of Si released. The amount of Ti incorporated decreased with increasing treatment temperature. Ti incorporation was accomplished more rapidly at higher temperatures. The amount of Ti loaded was reduced with increasing temperature in the pretreatment of the parent MCM-41. Ti species thus incorporated were exclusively highly dispersed within the MCM-41 structure in tetrahedral coordination, but a small number of them gave anatase TiO₂ upon TiCl₄ treatment at or above 773 K. The characterization of Ti ions and ²⁹Si MAS NMR suggest that Ti ions are incorporated through the reaction of TiCl₄ with the surface silanols.