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The important variables in the synthesis of stable, high surface area, aluminum-modified anatase TiO2 catalyst supports were identified and optimized using statistically designed experiments (DOEs). The first DOE examined ten variables at two levels and a second DOE studied eight variables at three levels. Equations were developed to predict the conditions to obtain the highest surface area and pore volume at the desired pore diameter and predict the pore diameter range that may be obtained. Confirmation trials closely matched predicted surface areas, pore volumes, and pore diameters in all but one trial. Rinsing order (before or after calcination) was the most significant factor. Other important factors were calcination temperature, mol% aluminum, and water addition speed. The results of this study demonstrate (a) the power of DOEs in identifying and controlling synthesis variables in relatively few experiments and (b) how analysis of factor effects can provide insight into the formation mechanism.

The structures of Al-modified anatase TiO2 supports were analyzed using traditional analysis techniques of X-ray diffraction, transmission electron microscopy, and N2 sorption as well as X-ray absorption near-edge spectroscopy, 27Al 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 m2 g–1, pore volume of 0.34 cm3 g–1, and pore diamete...

The effects of dopants Al, La, Si, and Zr on the stability, surface area, and porosity of anatase were investigated. Anatase materials stabilized with 0–14 mol% La, Si, Zr, or 0–85 mol% Al were studied. Materials were characterized using XRD, TEM and N 2 adsorption. Results show that (1) dopants increased the surface area and thermal stability of anatase through structural modifications and grain growth inhibition, (2) due to structural modifications it was important to select the appropriate hysteresis branch for pore diameter calculations, and (3) a thorough analysis of N 2 adsorption and TEM data provided additional insight into how stabilizing agents affected the mesoporous structure. Stabilized titanias produced by this method demonstrated equivalent or higher thermal stability and surface area compared with pure anatase and previously reported materials after treatment at 400 °C and 700 °C including 22 mol% Al–TiO 2 calcined at 400 °C which had a surface area of 479 ± 39 m 2 /g, a pore volume of 0.46 ± 0.04 cm 3 /g, and a pore diameter of 2.9 ± 0.2 nm.