Effect of calcination on the structure and catalytic activities of titanium incorporated SBA-15

Well-ordered Ti-incorporated SBA-15 materials (shortly termed Ti-SBA-15) with Ti loading up to 10 mol% of Si were prepared by a one pot co-condensation method using tetraethyl orthosilicate (TEOS) as the silica source and titanium oxychloride as the Ti source in an acidic environment close to the isoelectric point of silanol groups (pH = 1.27-2.37). The Ti-SBA-15 materials with Ti/Si ratios smaller than 0.05 were curved solid tubes, while those with the Ti/Si ratios between 0.05-0.1 possessed platelet morphology and short mesochannels (ca. 150-500 nm). Titanium was homogeneously distributed in the silica framework of the as-made Ti-SBA-15 materials as isolated Ti species when the Ti/Si ratios were lower than 0.03. It formed small TiO2 nanocrystallites when the Ti loading was further increased or after the materials were calcined at temperatures higher than 500 degrees C. It is noteworthy that tetrahedrally coordinated Ti(IV) species were generated on the superficial areas of SBA-15 silica framework upon calcination at 600-1000 degrees C. These tetrahedrally coordinated Ti(IV) species not only stabilized the mesopore ordering up to 950-1000 degrees C, but also acted as effective catalytic sites in cyclohexene epoxidation.