Oxidative Dehydrogenation of Propane to Propylene with CO_2 over Cr/NaZSM-5 Catalysts

A series of Cr catalysts supported on submicro NaZSM-5 zeolite was prepared.The obtained samples were characterized by N2 adsorption,XRD,UV-Vis and H2-TPR,and tested as catalysts for dehydroge-nation of propane to propylene in the presence of CO2.The highest activity was achieved on the catalyst with a Cr content of 3% and a Si/Al molar ratio of 60.In this case,the propane conversion and propylene selectivity were 48.3%,86.0% and 30.1%,91.8%,respectively after the reaction at 550 ℃ for 10 min and 8 h.There is a good relationship between the initial activity and Cr6+ content of the catalysts,showing that a high content of Cr6+ species in the calcined catalyst is crucial for its high catalytic activity in dehydrogenation of propane to propylene with CO2.A higher propylene yield was obtained during propane dehydrogentaion in the presence of CO2 than N2.This can be attributed to a higher surface concentration of Cr6+ retained on the catalyst in the presence of CO2 as well as the elimination of hydrogen produced by propane dehydrogenation.