Effect of additives doping on catalytic properties of Mg3(VO4)2 catalysts in oxidative dehydrogenation of cyclohexane

Effects of additives comprising alkali and alkaline earth metals (Li, Na, K and Ca) introduced to Mg3(VO4)2 on their structures, physicochemical properties and the catalytic behaviors in the oxidative dehydrogenation of cyclohexane were investigated. The characterization and the experimental results showed that the additive does not affect markedly the structure of the catalyst, but blocks the active sites and hinders the reducibility of the active species thus decreasing the catalytic activity. Moreover, the additive could enhance the selectivity to cyclohexene by enhancing the nucleophilicity, the redox property as well as the type and number of the oxygen species on the catalyst surface. The doped catalysts could give the catalytic activity and selectivity to cyclohexene in the orders of K- < Na- ≈ Ca- < Li- < non-doped and non-doped < Li- < Na- < K- < Ca-, respectively. Among the doped catalysts, Ca–Mg3(VO4)2 catalyst demonstrated a yield of cyclohexene of 8.2%, which was a promotion compared with 6.4% of Mg3(VO4)2.

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► The additives give a positive effect on the selectivity to cyclohexene obtained from cyclohexane oxidative dehydrogenation.
► The additive blocks the active sites and hinders the reducibility of active species to decrease the catalytic activity.
► The additive changes the acid-basic nature, the type and number of the oxygen species to improve cyclohexene selectivity.
► Ca-catalyst could give a relatively higher yield of cyclohexene than the other doped-catalysts.