Unimolecular reactions on silica surface. I. Thermal decomposition of methoxysilyl groups

The breakdown of CH3O groups of methoxysilylated silica has been investigated by means of temperature-programmed desorption in the 370-1170 K interval with mass spectrometric analysis of the decomposition products in the interval of masses from 2 to 32 amu. It has been established that the principal channel of decomposition is the reaction of formaldehyde evolution with the formation of an Si-H bond. The rate constants of this process have been calculated. The MNDO method in the cluster approximation has been used to calculate sections of the potential energy surface with respect to the reaction coordinate, and also the vibrational frequencies in the ground and transition states.