Catalytic behavior of manganese oxides for oxidative dehydrogenation of ethylbenzene with carbon dioxide.

Manganeses oxides (MnO x ) with different crystal and structural properties were prepared by the precipitation, the complex-decomposition, and the thermal decomposition methods, respectively. The materials were characterized by XRD, SEM, TEM, H 2 -TPR, TG-DSC, XPS, and N 2 adsorption/desorption at low temperatures. The samples were comparatively evaluated as catalysts for the oxidative dehydrogenation of ethylbenzene with carbon dioxide (CO 2 -ODEB). Results indicate that both Mn 2 O 3 and Mn 3 O 4 were active for CO 2 -ODEB and the Mn 3 O 4 prepared by the precipitation method showed the highest conversion of ethylbenzene over 60%. Moreover, the activity of MnO x for CO 2 -ODEB was significantly affected by the synthesis method and parameters of the oxides. The correlation between the reaction and characterization results indicates that the CO 2 -ODEB over MnO x may follow the redox mechanism involving the lattice oxygen, and the amount of the mobile oxygen species and the surface area were revealed to be key factors in determining the activity of the MnO x catalysts for the titled reaction. Together with the characterization results of XRD, TG-DSC, and H 2 -TPR, the irreversible reduction of MnOx to MnO under the conditions of CO 2 -ODEB was the main reason for the deactivation of the catalyst while the coke deposition had a less important impact on the stability of the catalyst. [ABSTRACT FROM AUTHOR]