Differential thermal analysis of PtO2/carbon

The reactions between Pt oxides and carbon black in helium and air were examined by DTA. The thermograms were dependent on the mode of sample preparation. 20 wt.% PtO₂ supported on carbon catalyst heated in He at 10°C min^?1 produced an exotherm at approximately 400°C. Physical mixtures of PtO₂ and carbon only reacted at a higher temperature (approximately 550°C) in He where PtO₂ is thermally decomposed to Pt and O₂. In air, Pt catalyzed the oxidation of cabon in the 20 wt.%Pt supported on carbon sample. On the other hand, PtO₂ in the physical mixture did not appear to catalyze the oxidation of carbon in air. This difference in behavior is explained by assuming that atomic oxygen is produced in the supported catalyst sample which reacts at low temperature with carbon. In the physical mixture, thermal decomposition of PtO₂ yields molecular oxygen which reacts with carbon at a higher temperature than does atomic oxygen.