Effect Of Cerium Addition And Oxygen Transfer On Methane Aromatization

In methane dehydroaromatization,the coke heavily formed during the reaction caused a severe deactivation of the catalysts.Addition of CO₂ and O₂ can inhibit coke formation and change the molybdenum species exists in the form of?MoO₃ ??? MoO_xC_y ??? Mo₂C?.However,MoOxCy is more sensitive to oxygen concentration,only in the case of adequate oxygen concentration.Cerium oxide can change the oxygen concentration by adsorption and release oxygen.If addition cerium oxide in Mo / Zeolite catalysts,it may prolong the MoO_xC_y species existence time by modulation of oxygen concentration,so as to improve the yield of aromatics.In this paper,the effect of the addition of O₂ and CO₂ for the methane conversion and the yield of benzene on the Mo/HZSM-5 catalyst were investigated.On this basis,we further studied the effect of different content of cerium oxide added in Mo /HZSM-5 catalyst and different oxidation of cerium filling method for the conversion of methane and benzene yield.In addition,the coke was characterized by TPO.The main conclusions were as follows:?1?The results showed that the conversion of methane and benzene yield were significantly increased when the oxygen content was maintained in 0.37%¹.1%.When the content of oxygen was 1.58%,the formation of benzene was inhibited.TPO results show that two kinds of coke exists on the catalyst,and add oxygen can inhibit coke formation.?2?.Adding different content of cerium oxide in Mo / HZSM-5 catalyst results showed that adding a small amount of cerium oxide can significantly inhibit the convresion of methane and the formation of benzene,but with the addition increased the inhibitory effect will be weakened.The TPO results showed that the catalyst produced a kind of new coke?3?.Different filling method of cerium oxide have the different results.Cerium oxide in the upper layer can increase the yield of benzene.Cerium oxide in the middle layer can also increase the yield of benzene only in the late reaction.Cerium oxide in the lower layer has little effect on the yield of benzene.