Structure Analysis of Al-Modified TiO2 Nanocatalyst Supports

The structures of Al-modified anatase TiO2 supports were analyzed using traditional analysis techniques of X-ray diffraction, transmission electron microscopy, and N-2 sorption as well as X-ray absorption near-edge spectroscopy, Al-27 magic-angle spinning NMR, and low-temperature heat capacity. The combined results from these characterizations reveal that the Al dopant is incorporated either on the surface or in vacancies depending on the details of the synthetic method used. Alumina incorporated on the surface stabilizes TiO2 by lowering the surface energy of anatase and stabilizing planes with high surface energy that would otherwise join to achieve a reduced surface energy. On the other hand, Al incorporated in TiO2 vacancies stabilizes the structure through increasing lattice strain and limiting mass transport necessary for grain growth. The 22 mol % Al-modified TiO2 with Al on the surface had average crystallite diameter of 6 nm, surface area of 184 m(2)g(-1), pore volume of 0.34 cm(3)g(-1), and pore diameter of 6.4 nm compared with the 22 mol % Al-modified TiO2 with Al incorporated in vacancies and on the surface which had average crystallite diameter of 2 3 nm, surface area of 471 m(2) g(-1), pore volume of 0.44 cm(3) g(-1), and pore diameter of 4.4 nm. This work demonstrates the importance of structure analysis of doped nanomaterials in the development of stabilized catalysts and catalyst supports.