Cr/SSZ-13催化二氧化碳氧化乙烷脱氢反应的研究

通过脱氢反应将低碳烷烃转化为同碳数的烯烃是烷烃高值化利用和烯烃原料多元化的重要途径。烷烃氧化脱氢制烯烃的反应具有不受反应平衡限制、积炭少、反应温度低等优点,一直是研究的热点。通过利用浸渍法制备不同铬（Cr）负载量的Cr_x/SSZ-13系列催化剂,采用氮气物理吸附、氨程序升温脱附（NH₃-TPD）、二氧化碳程序升温脱附（CO₂-TPD）、氢气程序升温还原（H₂-TPR）、紫外-可见吸收光谱（UV-Vis）以及高角度环形暗场-扫描透射电镜（HAADF-STEM）与耦合能谱分析（EDX-Mapping）等方法对催化剂进行了物性表征,并用微型固定床反应器评价催化剂对乙烷氧化脱氢制乙烯的催化性能,最终建立了Cr/SSZ-13催化剂的构效关系。研究发现,当n（二氧化硅）/n（氧化铝）=10时,Cr_1.5/SSZ-13-10催化剂上含有丰富的Cr³⁺物种,其中配位不饱和Cr³⁺是优异的脱氢活性位,有利于二氧化碳氧化乙烷脱氢反应的进行。因此,Cr_1.5/SSZ-13催化剂在650 ℃时表现出优异的催化性能,即二氧化碳转化率和乙烷转化率分别达到26.41%和53.2%,乙烯产率为38.83%。

Oxidative dehydrogenation of ethane with carbon dioxide to ethylene over Cr/SSZ-13 catalyst

The conversion of light alkanes into olefins with the same carbon number through dehydrogenation reaction is an important approach for high-value utilization of alkanes and diversification of olefin raw materials.Oxidative dehydrogenation of alkanes to olefins has been a hot issue due to its advantages such as no limit of reaction equilibrium,less carbon deposition and low reaction temperature.CRX/SSZ-13 series catalysts with different Cr loading were prepared by impregnation method.The physical properties of the catalysts were characterized by nitrogen physical adsorption,ammonia-temperature programmed desorption（NH₃-TPD）,carbon dioxide-temperature programmed desorption（CO₂-TPD）,hydrogen-temperature programmed reduction（H₂-TPR）,ultraviolet-visible spectroscopy（UV-Vis） and high-angle circular dark-field scanning transmission electron microscope（HAADF-STEM） coupled energy spectrum analysis（EDX-Mapping）.The catalytic performance of the catalysts for oxidative dehydrogenation of ethane to ethylene was evaluated in a micro fixed bed reactor.Finally,the structure-activity relationship of Cr/SSZ-13 catalyst was established.It was found that Cr_1.5/SSZ-13-10 catalystn（SiO₂）/n（Al₂O₃）=10] contained rich Cr³⁺ species,and the coordination unsaturated Cr³⁺ was an excellent dehydrogenation active site,which was co-nducive to the dehydrogenation of ethane by carbon dioxide oxidation.Therefore,Cr_1.5/SSZ-13-10 catalyst showed excellent catalytic performance at 650 ℃,the carbon dioxide conversion and ethane conversion reached 26.41% and 53.2%,respectively,and the ethylene yield was 38.83%.