Mo loading effects over Mo/Si: Ti catalysts in the oxidative dehydrogenation of ethane

A series of molybdena catalysts (0-20 wt% loadings) were studied with regard to their activity for the oxidative dehydrogenation (ODH) of ethane. Catalysts with single oxide supports of silica and titania were also examined. X-ray diffraction, Raman spectroscopy (ambient and dehydrated conditions), and X-ray photoelectron spectroscopy were used to determine the nature of the molybdena phases supported over the mixed oxide support, Initially, MoOx preferentially supports on titania. However, interaction with silica is present even at the lowest wt% loading. With increased wt% loading, MoOx increasingly interacts with the silica phase of the support as titania increasingly segregates into larger anatase domains. Since MoOx species may share several types of support ligands with differing electronegativity, one cannot adequately describe MoOx species as being supported exclusively on SiO2 or TiO2 domains but rather, as indicated by the Raman results, as being supported on a mix of both species. The structural differences are reflected in ODH reaction performance. The ethylene yield increases with Mo loading over Si:Ti 1: 1 to a maximum at 10% Mo/Si: Ti 1: 1, where there may exist an optimum coverage of MoOx that shares several types of support ligands from both silica and titania domains of the support. The desorption behavior of products formed following ethane adsorption was studied with Mo wt% loading using temperature-programmed desorption. (C) 2002 Elsevier Science (USA).