Crystallinity effect in the textural properties of titania-TPA catalysts

Catalysts based in titania mixed with tungstophosphoric acid (TPA), H3PW12O40, in various proportions (L 15, 25 and 50 wt%) were obtained by the sol-gel method. The gels were prepared by hydrolysis and gellation of titanium n-butoxide with a TPA solution, using HNO3 as a catalyst to obtain a pH 3. Fresh samples were thermally treated from 100 to 800 degrees C, in a stepwise increment of 100 degrees C during 20 h per step. Specific surface areas were calculated by the BET method from the nitrogen adsorption isotherms; it was found that the surface area increased with TPA content. The crystallization behavior was followed by powder X-ray diffraction. Crystallite size measurements showed that anatase remains nanocrystalline in the studied temperature range. From the X-ray data, it was clear that below 700 degrees C TPA is highly dispersed in an amorphous state. (c) 2005 Elsevier B.V. All rights reserved.