Characterization of Mo-MnO catalyst for propane oxidative dehydrogenation

Abstract

Manganese oxide catalysts impregnated with molybdenum have been examined for the propane oxidative dehydrogenation. These catalysts exhibit catalytic activity and yield to propane at temperatures as low as 623 K. The catalysts were characterized by S BET, XRD, Laser Raman, TPR, EPR and XPS. Independently of molybdenum loading, none of the impregnated catalysts shows the patterns corresponding to molybdenum oxide by XRD. The reaction of molybdenum with manganese would probably occur starting from OH centers as reacting nuclei and it continued from there. Thus, the OH of manganese oxide surface would restrain the dispersion of the formed molybdate. However, the results of Raman spectroscopy analysis of catalysts before and after the catalytic test indicate that the reaction test could be responsible for modifications in the surface composition. Characterization before and after catalytic test corroborates the concept of the existence of a “dynamic feature” in which the reaction of the adsorbed phase plays a key role in the surface reconstruction. EPR results as well as XPS ones for catalysts after test have shown that independently of molybdenum loading, at a superficial level, all of them have similar characteristics. Evidently, the reaction test promote a surface reconstruction. XPS data together with those obtained by XRD which show that the greater the load, the more intense the MnMoO 4 signal indicate that MnMoO 4 accumulates in a definite place being the XRD signal more intense by localized mass growth. These evidences and the consequent description of the resulting surface architecture allow to understand the results of catalytic evaluation tests.