Activity of molybdenum oxide catalyst in the dehydrogenation n-butane

The catalytic properties of molybdenum oxide on alumina for the dehydrogenation of n-butane were studied at 560 degrees C under atmospheric pressure. The rapidity of the technique used to analyze the reaction product (Fourier transform infra red gas analysis) made it possible to measure the activity in dehydrogenation and the changes in the reduction level of the catalyst during the first minutes on stream. The highest activity was obtained with a molybdenum content of 13%, which corresponds to a theoretical monolayer coverage on the gamma-alumina. The oxidation state of the molybdenum active in the dehydrogenation was either Mo5+ or MO4+. Some catalyst samples were modified with magnesium to improve the selectivity to n-butenes. The highest yield of n-butenes achieved, 8%, was obtained with a Mg:Mo molar ratio of 1:1. The best selectivity to C-4 alkenes, 80%, was obtained with the highest content of magnesium, and was partly attributable to the formation of C-4 alkenes via the oxidative dehydrogenation reaction. The active oxidation state of molybdenum for dehydrogenation was not stable under the conditions used for testing, but was reduced to lower oxidation states, resulting in an increased selectivity to n-butane cracking and coke formation. (C) 1999 Academic Press.