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.