A study of nickel molybdenum oxide catalysts for the oxidative dehydrogenation of n-hexane.

Abstract

Nickel molybdenum oxide catalysts with different chemical compositions have been synthesized and tested for the oxidative dehydrogenation of n-hexane. The co-precipitation method was used for the synthesis and several methods were used to characterize these catalysts. These include inductively-coupled plasma optical emission spectroscopy, Raman spectroscopy, infrared spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, temperature programmed reduction, temperature programmed desorption, X-ray photo-electron spectroscopy and X-ray diffraction spectroscopy techniques as well as the Brauner-Emmet-Teller technique for surface area determination. The phase composition of the catalysts was largely dependent on the chemical composition. Catalyst testing on n-hexane feed was done with a fixed bed continuous flow reactor and experiments were performed with feed/air ratios above and below the flammability limit. Varied reaction conditions were used for the catalytic testing. Prior to the catalytic testing, blank experiments were performed. Analysis of the products were done both online and offline in conjunction with gas chromatography employing FID and TCD detectors. The influence of the catalyst on the conversion of n-hexane and selectivity to dehydrogenation products is reported. Products observed were the carbon oxides (CO and CO2), isomers of hexene (1-hexene, 2-hexene and 3-hexene), cyclic C6 products (cyclohexene and benzene), cracked products: alkanes/alkenes (propane/ene, butane/ene) and oxygenates (ethanal, acetic acid and propanoic acid). B-NiMoO4 was most selective to the hexenes, especially, 1-hexene and a reaction scheme is proposed.