Improved Supported Metal Oxides for the Oxidative Dehydrogenation of Propane

Abstract

The oxidative dehydrogenation of propane (ODHP) is an attractive reaction for the on-purpose production of propylene. Unfortunately, rapid consecutive over-oxidation of the desired olefin limits the selectivity and hampers the industrial feasibility. Supported metal oxides, and in particular dispersed vanadium-containing materials, have shown promising results. Yet one has to improve both the selectivity and activity (space–time–yield) to make this reaction attractive. In this contribution we build upon our previous work that allowed us to increase the dispersion of group V metal oxides on silica using a sodium promoter. Using Raman spectroscopy and 51V MAS NMR, we postulate that the minor decrease in our observed turnover frequency (TOF) for ODHP using sodium-promoted materials may be due to Na+ ions weakly interacting with the V=O site, responsible for the initial H-atom abstraction. While our observed TOF is well within the range of literature reported TOF for these materials, such a large deviation in reported TOF (varying almost three orders of magnitude) may be due to various impurities used in the silica of these previously reported studies. Subsequently, we prepared a ternary metal oxide catalyst based on vanadium and tantalum that shows superior selectivity and productivity. Indeed, productivity of a combined V- and Ta-oxide catalyst supported on silica doubles the productivity of catalysts with low loadings of vanadium oxide supported on silica. The reasons for the significant improvement are currently under investigation.