Silica preparation via sol-gel method: a comparison with ammoximation activity

The influence of the synthesis parameters over the physico-chemical features of poroussilica gels derived from tetraethyl orthosilicate has been studied using nitrogen adsorption and FT-IR. Under acid conditions long shaped siloxane particles were produced and microporous amorphous silicas with high surface area were obtained. These samples showed a relatively high concentration of H-bonded and/or “internal” hydroxy groups. The base-catalyzed samples exhibited features of colloidal gel and mesoporous amorphous materials were obtained. The structure is characterized by relatively low surface area with a monomodal porosity. These silicas have an high concentration of the free surface silanol groups. The acid-catalyzed samples resulted completely inactive in the ammoximation reaction, while the base-catalyzed silicas were active in the same reaction.