Effect of additives doping on catalytic properties of Mg ₃(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(VO ₄)₂ catalyst demonstrated a yield of cyclohexene of 8.2%, which was a promotion compared with 6.4% of Mg₃(VO₄) ₂.