Co-conversion Of CO₂ And Ethane Over Metal Modified SSZ-13 Zeolite Catalysts

Ethane production has increased dramatically as the massive exploration of shale gas resources in recent years.The transformation of ethane to value-added ethylene is of great significance to the chemical industry.Most of commercial ethylene is produced by steam cracking of ethane or naphtha at high temperatures?higher than 850??.The thermal cracking is an energy consuming process which also requires high demand of reactor quality.Carbon dioxide with oxidation ability could be applied to activate ethane under mild reaction conditions.Ethylene and syngas could be simultaneously produced in this co-conversion.The target of alleviating carbon dioxide pollution and saving energy could be fulfilled together.In this work,transition metal such as Zn and Cr were used as active components.Zn or Cr impregnated zeolites with different topology structure were prepared and characterized by XRD,Physisorption,TPD,FTIR and DTG-TGA-MS.The catalytic performance of these catalysts during the co-conversion of CO₂ and ethane were investigated in fixed bed,aiming to explore the relationship between the structural and physicochemical properties of catalysts and their catalytic performance.Zn modified zeolites with different pore structure were investigated and the influence of supports on the catalytic performance was studied.It was found that Zn modified SSZ-13zeolite with similar pore size as CO₂ and ethane showed the best conversion activity.Structural and physicochemical properties as well as catalytic performance of Zn/SSZ-13 and Zn/ZSM-5 zeolites were compared.The transformation rate of CO₂ and ethane over Zn modified SSZ-13 catalysts equals to 1.0 which is great higher than that over Zn modified ZSM-5.In addition,CO₂ and ethane conversion increased linearly with the increase of Zn loading.CO₂ physisorption and CO₂-TPD-MS showed Zn improved the adsorption capacity of SSZ-13 zeolite for CO₂.The hydrothermal stability of Zn_2.92/SSZ-13 was compared with that of Zn_2.50/ZSM-5 catalysts.After 10 h continuous steaming at 650?,most of the Zn active centers and pore structure were maintained over Zn_2.92/SSZ-13,while the active centers and pore structure of Zn_2.50/ZSM-5 catalyst were severely destroyed.Abovementioned results indicate that Zn_2.92/SSZ-13 catalyst obtains high hydrothermal stability.Moreover,the activity of Zn_2.92/SSZ-13 catalyst can be recovered sufficiently after burning carbon deposition and the catalytic performance wasn't obviously influenced after 4 times of reaction-regeneration suggesting the excellent regeneration stability.The effects of reaction conditions on the catalytic performance of CO₂ and ethane co-conversion over Zn/SSZ-13 catalysts was systematically investigated.Following conclusions are made:?1?CO₂ and ethane conversion rises with temperature.The selectivity of ethylene was high?84-94%?under low temperature?550-600??and decreased with the increase of temperature.Large amounts of methane?24-36%CH₄ selectivity?by-product was produced under high temperature?625-650??.?2?The ethane conversion and ethylene yield markedly increased with the ratio of CO₂/C₂H₆ increasing.The co-feeding of CO₂ into ethane could suppress the formation of carbon deposition.According to literature,Cr modified SSZ-13 catalysts were well recognized as the optimal catalyst for ethane dehydrogenation with CO₂ as oxidant.Thus,the catalytic performance of Zn/SSZ-13 was systematically compared with Cr/SSZ-13.Results showed that the catalytic activity to convert CO₂ and ethane and hydrothermal stability of Zn/SSZ-13catalyst were great better than those of Cr/SSZ-13.Besides,the Zn/SSZ-13 catalyst was environmental benign with excellent regeneration performance.Based on this study,the Zn/SSZ-13 catalysts exhibit promising future in the commercial application.