Co-Conversion Of Carbon Dioxide And Ethane On Modified Nanosized SSZ-13 Zeolite Catalyst

Thecatalytic transformation of carbon dioxide into chemicals can not only reduce theemission of greenhouse gases,but also solve the energy crisis.Ethane is abundant in natural gas,shale gas,coalbed methane,petroleum cracking gas,and coke oven gas.Ethane obtains high H/C ratio and be used as a low-cost hydrogen source to activate carbon dioxide.However,the carbon dioxide and ethane are stable and difficult to be activated at low temperature.Therefore,the construction of highly-efficient catalyst with low temperature activity is the key to realize the co-conversion of carbon dioxide and ethane.In this study,SSZ-13 zeolite with high adsorption capacity for ethane and carbon dioxide was chosen as support.The effect of Zn and alkali metals(Li,Na,K,Cs)modification was systematically studied.Obtained results are as follows:In the first place,the effect of crystal size on the co-conversion of carbon dioxide and ethane was systematically studied.The micro-sized SSZ-13 with grain size of 1?m and the nano-sized SSZ-13 with grain size of 20?50 nm were chosen as support.The structure-performance relationship between Zn species and catalytic performance was systematically studied.Results showed that the co-conversion of carbon dioxide and ethane over the Zn-modified nano-sized SSZ-13 was greathigher than that over the micro-sized SSZ-13 catalyst under the similar Zn loading.The better dispersion and accessibility of Zn species over nano-sized SSZ-13 resulting in lower reaction activation energy.However,the ethylene selectivity of nano-sized Zn_x/SSZ-13 is lower than that of micro-sized SSZ-13.In the second place,the feasibility of industrial application of Zn/nano-SSZ-13 zeolite catalyst was explored.The nano-sized SSZ-13 was extruded with alumina binder to form a shaped catalyst and then modified by Zn.Under the similar Zn loading,the powder catalyst obtained the analogical reactivity as the shaped catalyst,which has the prospect of commercial application.Finally,the effect of different alkali metal ions modification,such as Li,Na,K and Cs,on Zn_x/SSZ-13 catalyst were systematically studied.By means of carbon monoxide adsorption at nitrogen temperature by dual-beam Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,high resolution transmission electron microscopy and other characterization methods,combined with Density Functional Theory study.Results suggest that,the reaction rate of ethane dehygenation on(Zn-O-Zn)²⁺is controlled by the recombination desorption of the(Zn-OH)⁺and the hydrogen atoms on(Zn H)^-.If the surface hydrogen atoms are not desorbed immediately,the subsequent ethane will undergo hydrogenolysis and protolysis side reactions generating a large amount of methane.The acid content and carbon dioxide adsorption capacity of Zn modified nano-sized SSZ-13 catalyst were adjusted by potassium modification.The selectivity of ethylene was significantly improved,and the generation of coke was inhibited.Moreover,the presence of nearby K₂O made charge transfer to(Zn-OH)⁺oxygen,thus inhibiting proton transfer,reducing the acid strength of“Transient Br?nsted acid”in(Zn-OH)⁺,thus inhibiting protolysis side reaction thus improving ethylene selectivity.