Temperature-programmed desorption mass spectrometry of carbonized silica surface

Thermally stimulated desorption of phenylethanol bound by partial carbonization to a silica gel surface was studied. The different pathways of uni- and bimolecular desorption were investigated by temperature-programmed desorption processes mass spectrometry (TPD MS). A simple approach for describing the desorption process is proposed. Approximations are introduced which allow the derivation of non-isothermal kinetic and temperature dependencies in analytical form. The formulae for rate constants are presented for first-, second- and third-order reactions in the case of rectangular activation energy distribution. Products of thermal decomposition of the carbonized surface layer were observed and identified. Broadening of TPD spectra is observed due to both superposition of a few decomposition pathways and surface heterogeneity magnified by the previous carbonization of the samples.