Study of Residual Oxygen Species over Molybdenum Carbide Prepared During In Situ DRIFTS Experiments

Abstract

In situ diffuse reflectance infrared Fourier transform spectroscopy was applied to monitor the temperature-programmed carburization of molybdenum trioxide. This technique indicated the existence of surface residual oxygen species on Mo₂C synthesized even up to 973 K, indicating incomplete carburization. The presence of residual oxygen species on the carbide was deduced from the IR band at 790 cm^-1. It was observed that the Mo₂C sample, prepared with a final temperature of 1023 K, presented a higher density of sites titrated by carbon monoxide and a higher activity in benzene hydrogenation than the samples prepared at 923 or 973 K. This higher density of sites and activity were interpreted in terms of improved degrees of carburization at the surface of the carbide. The temperature-programmed desorption of benzene over those three Mo₂C samples showed that the higher the activity in benzene hydrogenation, the lower the maximum desorption temperature: the tendency also observed going from Mo to Ru. This desorption temperature evolution could be explained in terms of an increased degree of carburization, which conferred to Mo₂C a reactivity toward benzene closer to that of Ru.