Incorporation of Titanium into Mesoporous Silica Molecular Sieve SBA-15

Abstract

Mesoporous silica molecular sieve SBA-15 has been synthesized and incorporated with variable amounts of titanium via incipient-wetness impregnation with titanium isopropoxide in ethanol followed by calcination. Characterization by powder X-ray diffraction, nitrogen adsorption, X-ray photoelectron, Raman, and diffuse reflectance ultraviolet spectroscopies has been carried out to understand the chemical nature of the titanium. The results suggest that titanium is present in two distinct chemical forms and that their relative amounts depend on the titanium loading. At low titanium loading of 1 atom % relative to silicon, the titanium ions are monatomically dispersed and the pore size of SBA-15 is not altered. This isolated titanium species reaches a maximum concentration around 6 atom % relative to silicon. At higher titanium loading, titanium dioxide (anatase) is also formed. The materials with significant titanium dioxide formation have reduced pore diameters, which suggests that the titanium dioxide exist...