Temperature-Programmed Desorption Mass Spectrometry (TPDMS) of Dispersed Oxides

Abstract

Temperature-programmed desorption mass spectrometry (TPDMS) is discussed with reference to studies of modified pyrogenic oxides. Simple theoretical models are presented in order to allow an approximate analytical treatment of TPDMS data. The ‘unimolecular’ decomposition of alkoxide groups was studied. The rate constants of the reactions were derived from TPDMS measurements. The kinetics of thermal transformations of phosphorous and phosphoric acids on a pyrogenic silica surface were investigated by TPDMS. Oxidation–reduction reactions in samples containing phosphorous acid resulted in the removal of molecular phosphorus (P4). Two stages of phosphorus evolution were observed which were attributed to the disproportion of phosphorus in the surface monolayer (high-temperature stage) and in the bulk layers (low-temperature stage). The biologically active samples obtained by adsorption of cyanocobalamine, glucose and raffinose on ultrafine oxide surfaces were studied via a combination of temperature-programmed desorption and solid-state thermal analysis mass spectrometry (TPD/TA MS). The role of the charged cobalt atom and of the propionamide and benzimide groups in the adsorption mechanism is discussed. It was shown that the adsorption of cyanocobalamine on the silica surface transformed the propionamide group to a weakly bound form. TPD/TA MS data were obtained confirming the stable adsorption of glucose and raffinose on an ultrafine pyrogenic silica surface modified by amino groups.