Kinetic studies and mechanism of the reaction of propylene with nitric oxide for acrylonitrile synthesis in the presence of nickel oxide on alumina catalysts

Abstract

The reaction of propylene with nitric oxide for the synthesis of acrylonitrile has been studied over nickel oxide supported on alumina as catalyst. A xerogel catalyst of composition 2NiO, Al 2O 3 was prepared by thermal decomposition, under vacuum at 400 °C, of a nickel hydroaluminate, 2NiO, Al 2O 3, 8H 2O. Aerogel catalysts NiOAl 2O 3 and NiOAl 2O 3SiO 2 of variable compositions were prepared by the autoclave method (hypercritical conditions). All these solids are selective (80%) in the formation of acrylonitrile at 410 °C. The best catalytic activity and selectivity are observed after a previous activation of the catalyst by oxygen at 410 °C for 48 hr. The kinetic studies reveal that the mechanism of the reaction is of the “redox” type. First there is reduction of the catalyst by propylene with formation of dehydrogenated radicals; these then form acrylonitrile with atomic nitrogen released by the dissociation of nitric oxide which reoxidizes the catalyst. The behavior of xerogel catalyst ( Ni Al = 1 ) and of aerogel catalysts ( Ni Al varying between 0.2 and 1) is similar for the same composition. The formation of acetonitrile is attributed to the oxidation of acrylonitrile over a fresh catalyst (barley reduced). The formation of carbon dioxide devolves from the oxidation of acrolein.