DIFFERENTIAL CALORIMETRIC CHARACTERIZATION OF THE OXYGEN HYDROGEN INTERACTION ON GRAPHITE-SUPPORTED IRIDIUM CATALYST PARTICLES

The differential kinetics and heat of reaction between oxygen and hydrogen on graphite-supported iridium particles was studied by using heat flow calorimetry. Hydrogen was used to gradually titrate a surface that was initially covered by a monolayer of oxygen. It was found that there was a gradual decline in the heat of reaction and rate of reaction with decreasing coverage but that the integral heat of reaction was close to that predicted by a simple thermodynamic model. To understand the results, it was necessary to fully characterize the particle size distribution and surface area. This was done by using X-ray diffraction, transmission electron microscopy, and differential calorimetric studies of oxygen, carbon monoxide, and hydrogen adsorption.