Cobalt ferrite aerogels by epoxide sol-gel addition: Efficient catalysts for the hydrolysis of 4-nitrophenyl phosphate

Porous cobalt ferrite aerogel catalysts were obtained by 1,2-epoxide sol-gel process and investigated in the hydrolysis of 4-nitrophenyl phosphate. These materials were synthesized by reacting cobalt andiron salts with propylene oxide in methanol, dried by supercritical carbon dioxide, and calcined between 200 and 800 degrees C. The catalysts were characterized using Fourier Transform Infrared (FTIR) spectroscopy, nitrogen adsorption-desorption technique, and powder X-ray diffraction (XRD). The "as-prepared aerogel" surface exhibits M-OH groups that disappear after annealing, which enhances the spinel structure. This was coupled with a better crystallinity revealed by XRD peaks sharpness. The crystallite sizes were found to be between 6.3 and 28.1 nm. In addition, the catalysts revealed high porosities that decrease as the annealing temperature increases. The catalysis showed that the catalytic activity significantly rely on the synthesis procedure and mainly the calcination temperature. Samples calcined at 600 degrees C and above did not show any catalytic activity, however, the highest catalytic efficiency was for those calcined at 200 degrees C with 100% selectivity for the 4-nitrophenol. The correlation of the characterization techniques and the catalysis tests revealed that the catalytic properties of these sol-gel materials are due to the existence of residual surface OH groups. (C) 2009 Elsevier B.V. All rights reserved.