MICROCALORIMETRIC STUDY OF THE INTERACTION OF CO, O-2 AND CO + O-2 WITH PT/SNO2 AND SNO2 CATALYSTS

The heat evolved in the interaction of CO, O2, and CO + O2 with SnO2 and Pt/SnO2 catalysts was evaluated at different temperatures in the range 300-475 K using microcalorimetry. The effect of oxygen and hydrogen pretreatments of the samples on the heat evolved shows that in the case of Pt/SnO2, the values were higher for the oxidized sample as compared to the reduced sample, whereas the trend was reversed for metal-free SnO2. The thermochemical data reveal heterogeneity of CO or O2 adsorption/reaction sites and show that the heat evolved in interaction of a gas is considerably influenced by the chemical nature of the catalyst surface and by the presence of preadsorbed species. The data support the view that the lattice oxygen abstraction from SnO2 plays an important role in CO oxidation at all the catalyst temperatures under study. The presence of platinum is found to augment Sn4+ → Sn2+ conversion. It is suggested that the energy released in the chemisorption of carbon monoxide or oxygen over Pt gives rise to a localized temperature surge in the vicinity of metal sites and this additional source of energy leads to enhanced CO oxidation activity of Pt/SnO2 via accelerated lattice oxygen abstraction. © 1990.