Preparation And Reaction Performance Of Catalysts For Oxidative Dehydrogenation Of Ethane Based On CO₂ Weak Oxidation

CO₂ is a suitable oxidant for the dehydrogenation of C₂H₆ to C₂H₄,and It provides a new way for the production of ethylene.CO₂ can be used to remove H₂ that is one of the C₂H₆ dehydrogenation by-products and reduce the aggregation of carbon deposit and promote the thermodynamic equilibrium of C₂H₆ dehydrogenation to C₂H₄.This method can not only provide new methods for natural gas utilization,but also reduce CO₂ emissions,so it has both the significance of environmental protection and energy improvement.To achieve this reaction,a better catalyst should be developed to achieve higher conversion and C₂H₄ selectivity of C₂H₆.A variety of transition metals and rare earth metal catalysts were prepared by equal volume impregnation method.The catalytic performance of different transition metal catalysts and rare earth metal catalysts in the catalytic oxidation of C₂H₆ with CO₂ in a fixed bed reactor was investigated.The reaction properties of transition metal oxides represented by Cr and rare-earth metal oxides represented by La on different supported catalysts were investigated.The catalytic performance of transition metal and rare earth metal catalysts represented by Cr/SiO₂ and La/SiO₂ under different loading conditions were studied.The characteristics of the non catalytic reaction of CO₂ and C₂H₆ with the change of temperature.The influence of CO₂ and C₂H₆ inlet ratio M_CO2/M_C2H6 on gas-solid catalytic reaction and the effect of CO₂ on the catalytic performance of catalysts with different supports were investigated.The effects of the structure and composition of the catalysts on the catalytic performance of the catalysts were studied by means of XRD,BET,TPR and SEM/EDS.The results show that,when the temperature reaches 650?,the non catalytic reaction of CO₂ and C₂H₆ begins to occur under the condition of no catalyst,and CO₂does not participate in the reaction.The reaction substance is the coupling of the dehydrogenation of ethane and the hydrosolution of ethane.The conversion rate of C₂H₆increases with the increase of reaction gas inlet ratio M_CO2/M_C2H6,and the selectivity of ethylene increases first and then decreases.The best M_CO2/M_C2H6 ratio is 2.By comparing the experimental results of catalytic oxidative dehydrogenation of C₂H₆ to ethylene with and without CO₂,it is found that the presence of CO₂ can increase the conversion rate of C₂H₆ and the yield of C₂H₄.In the three transition metals of Cr,Co and Fe,metal Cr has the best catalytic activity and the highest C₂H₄ yield.The Co based catalyst has a high conversion rate of C₂H₆ and CO₂ in the reaction system,but the selectivity of Co for CO is far higher than that of C₂H₄,which makes the C₂H₄ yield of the Co based catalyst low.In the three rare earth metal oxides of La,Sm and Ce,the three have good selectivity for C₂H₄.Ce has the best selectivity for C₂H₄,even at high temperature,with high C₂H₄ selectivity.Metal Sm has the best catalytic activity and the highest C₂H₄ selectivity,but its C₂H₄selectivity is low.Overall,transition metals have better catalytic activity for C2H6 and CO₂ than rare earth metals,but rare earth metals have higher C₂H₄ selectivity than transition metals.For SiO₂,?-Al₂O₃ and TiO₂ three catalysts carrier,the same amount of Cr and La exhibited the best C₂H₆ conversion and C₂H₄ yield on the?-Al₂O₃ carrier.The catalyst activity and C₂H₄ yield of catalyst with TiO₂ carrier are the smallest.The dispersion of metal oxides is an important factor affecting the catalytic activity.?-Al₂O₃ has the best specific surface area,so that the active components of the catalyst can be dispersed uniformly on the carrier,which is beneficial to the activity of the catalyst.The TiO₂carrier has the smallest specific surface area,and the surface of the carrier has large metal oxide crystalline phase,which reduces the activity of the catalyst.According to the experimental results,the high temperature??29?700??is very unfavorable to the C₂H₄selectivity of the catalyst with?-Al₂O₃ carrier.Based on Cr/SiO₂ and La/SiO₂,the catalytic performances of various catalysts with three different loading conditions were discussed.The catalytic activity of Cr/SiO₂ first increased and then decreased with the increase of loading capacity,and reached the best catalytic activity and the highest C₂H₄ yield at 10%loading.The catalytic activity and C₂H₄ selectivity of La/SiO₂ increased with the increase of loading and reached the best at 15%.The rare earth metal La has better dispersion than the transition metal Cr.The catalytic properties of transition metals and rare earth metals in CO₂-C₂H₆catalytic oxidation to C₂H₄ reaction system were systematically studied in this paper.The influence of multiple variables on the catalytic activity of catalyst and the selection rate of C₂H₄ was discussed,and the theoretical support was provided for the research and preparation of the catalyst for the catalytic oxidation of CO₂-C₂H₆ to C₂H₄.