The selective oxidation of methanol to formaldehyde, the oxidative dehydrogenation of ethane and the oxidative dehydrogenation of propane have been investigated using niobium based catalysts. It has been shown that niobium oxides prepared by different methods show in general a low conversion of reactant in all probe reactions investigated. However, high selectivity to the desired products are maintained (i.e. formaldehyde, ethylene and propene) at elevated temperatures. The introduction of phosphorus into niobium based catalysts enhanced the catalytic performance of the catalyst The aim was to maintain a high selectivity of desirable products whilst increasing conversion. Two sets on niobium and phosphorus based catalysts were investigated. The first set of catalyst was niobium oxide phosphates, NbOPC>4, prepared from a method which was analogous to VPO work. Catalytic testing of the niobium oxide phosphates showed an increased conversion in both methanol oxidation and ethane oxidative dehydrogenation. However, there was little effect in using niobium oxide phosphates for the oxidative dehydrogenation of propane. Comparing niobium oxide phosphates to niobium oxides, the conversion doubled with respect to oxidative dehydrogenation of ethane and increased 18-fold with respect to methanol oxidation. The second set of niobium and phosphorus based catalysts were niobium phosphates, NbPOs. These were prepared from the reduction of niobium oxide phosphates. Catalytic testing showed an increased conversion in both methanol oxidation and ethane oxidative dehydrogenation. This is the first time that niobium phosphates and oxyphosphates have been investigated as catalysts and they demonstrate appreciable activity for a range of selective oxidation reactions.
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