A Raman and ultraviolet diffuse reflectance spectroscopic investigation of alumina-supported molybdenum oxide

Abstract

Summary A thorough calorimetric investigation of graphite-supported iridium particle chemistry was conducted. A careful determination of the particle size distribution assisted in the interpretation. The stoichiometry of oxygen, carbon monoxide, and hydrogen was determined: CO/Ir, = 0.50, O/h, = 1.0, H/h, = 1.0. The differential heats of adsorption of these molecules on the iridium surface was found to be very similar to those reported for alumina-supported iridium particles, suggesting support effects are minimal. Differential rate data were made available for the first time. It is clear that this basic information regarding adsorption stoichiometries, rates, and heats will be useful in future studies of the surface composition of multimetallic supported catalysts that contain iridium. The calorimeter allowed a study of the interaction between hydrogen and oxygen on an iridium surface. The rate, heat, stoichiometry, and sequence of steps that occur when differential hydrogen reduction of a preoxidized surface is carried out were all studied. It was found that the heat of reaction and the rate of reaction between dosed hydrogen and adsorbed oxygen progressively decreased. The measured integral heat, however, agreed with a simple thermodynamic model. The results of this study suggests that differential calorimeters can be valuable tools for providing information of the type required for detailed kinetic modeling of reactions taking place on catalyst surfaces. They also suggest that this type of calorimetry can provide detailed insight into the mechanism of surface reaction, an area of intense research at the present time.