Kinetic study of alkoxylation and rehydroxylation reactions on silica surfaces

The rates of alkoxylation and rehydroxylation reactions were investigated on silica surfaces preheated at various temperatures. The effect of preheating temperature was examined for both reactions. The initial rate of reaction was analyzed and discussed as a representative reactivity of the silica surface. For the alkoxylation reaction, the apparent rate of reactions on the total active sites was analyzed by measuring the alkoxyl groups formed on the surface. The rate of the alkoxylation reaction increased with the preheating temperature, which could be attributed to the increase in the number of reactive siloxane bridges. It was shown that the preheating treatment caused the compensation effect for the surface alkoxylation reactions. An analysis for the state of the activated complex in the reaction was proposed to discuss the kinetic characteristics. For the rehydroxylation reaction, the rate of reaction forming hydroxyls from siloxane bridges was measured. The rate of rehydroxylation decreased with increasing the preheating temperature. For both the alkoxylation and rehydroxylation, the reactivity of siloxane bridges decreased with increasing the preheating temperature.