The Research Of Metal Catalysts Based Different Carriers For Dry Methane Reforming

Carbon dioxide and methane,two greenhouse gases,can be comprehensively used through dry methane reforming?DMR?.Furthermore,the synthesis gas produced by DMR can be used as a raw material in carbonyl synthesis and Fischer-Tropsch synthesis.In addition,the high reaction heat is a reversible process;therefore,it can be used as a medium to store and transport energy.Given the above,the effective measure,DMR,not only eliminates the harm to the environment but also relieves the energy crisis.The cheap,efficient and stable catalyst is the key to the implementation of DMR technology.Ni,as a non-noble metal,attracts widespread attention because of its low cost and high catalytic performance as exhibited in DMR.Nevertheless,Nickel-based catalysts tend to deactivate due to the sintering,oxidation and coke formation of nickel particles.Therefore,it is important to find suitable supports or methods to improve the resistance of the sintering and carbon deposition of Ni based catalysts.In addition,for catalyst supports,because of the low cost,stable structure at high temperature and large specific surface area,carbon materials have attracted much scholar's attention.The catalysts,with carbon fibers?CF?the support and Ni the reactive metal,was synthesized using impregnation and ultrasound-assisted methods for DMR.The catalyst with the best activity was prepared by the ultrasound-assisted method for15min.Compared with the catalyst prepared by traditional impregnation,CH₄conversion,CO₂ conversion,H₂ yield and CO yield are increased significantly.In addition,the activity of the nickel catalysts with different supports,Al₂O₃,La₂O₃,CF-Al₂O₃ and CF-La₂O₃,prepared by the ultrasound-assisted method is better than without ultrasound.Moreover,the BET,H₂-TPR and XRD characterization results can also be seen the ultrasound-assisted treatment generates small,uniform and well-dispersed metal particles.To further improve the catalytic performance of carbon based catalysts,the metal oxides and CF was combined to form the dual carrier system.The Ni/CF-U?Ni/Al₂O₃-U?Ni/La₂O₃-U?Ni/CF-Al₂O₃-U?Ni/CF-La₂O₃-U catalysts were synthesized using ultrasound-assisted methods for DMR.And,the Ni/CF-La₂O₃-U has the best catalytic performance.From the H₂-TPR,CO₂-TPD,XRD and TEM results,it was found that the activity of the Ni/CF could be enhanced by adding La₂O₃ due to the higher metal dispersion degree,the stronger metal-support interaction,the enhanced adsorption of CO₂ provided by the basic support and the removal of the deposited carbon.In addition,the effect of bimetallic structure on the catalytic performance was also studied.The reactive metal Co,Fe and Cu was introduced into the Ni/CF-La₂O₃-U catalyst,respectively.And their performance was evaluated by DMR.From the experimental results,the Ni-Co/CF-La₂O₃-U has the best catalytic performance.The preparation conditions of Ni-Co bimetallic catalyst were also studied.The experiments show that when Ni and Co impregnate at the same time and maintain Ni:Co=4:1,it has the best catalytic effect.The H₂-TPR results established that the addition of Co strengthens the interaction between the reactive metal and the support,resulting in a better dispersion and smaller particle size of the reduced reactive metal.Furthermore,it is also indicated the existence of Ni-Co phase in the reduced catalyst,which is proved by XRD.In addition,the synergistic effect between Ni and Co can effectively improve the carbon resistance of the catalyst and inhibit the migration and agglomeration of the active metal.The reaction process conditions also played an important role in the process of DMR.Therefore,this paper based on thermodynamic analysis used the ASPEN PLUS software to qualitative analysis and the experimental methods to evaluate quantitatively the effects of reaction temperature,air ratio of feed gas,reaction space velocity and reaction time on DMR.The results show that the DMR is promoted and is favorable for the synthesis of the product with the increase of temperature.Moreover,as the ratio of the intake ratio?CO₂:CH₄?increases,the ratio of H₂/CO decreases.With the increase of air velocity,the conversion rate of CH₄ and CO₂ and the yield of H₂ and CO are reduced continuously.In the catalytic life experiment of600min,the order of catalyst stability is Ni-Co/CF-La₂O₃-U>Ni/CF-La₂O₃-U>Ni/CF-U,and Ni-Co bimetallic catalyst has no obvious inactivation,showing good catalyst stability.Finally,the mechanism of DMR is simply explored,and an appropriate LH kinetic model is established for DMR reaction on Ni-Co/CF-La₂O₃-U catalyst.The equations of reaction rate constant K,CH₄ adsorption equilibrium constant K_CH4,CO₂adsorption equilibrium constant K_CO2 and temperature T are calculated respectively.The DMR reaction activation energy is 8.48kJ/mol,CH₄ adsorption activation energy is 15.879kJ/mol and CO₂ adsorption activation energy is 26.54kJ/mol at 700?⁸00?.Compared the kinetic calculation results based on the above LH mechanism and the experimental results,it is found that the LH models fit well.Therefore,this LH model can better react with the kinetic process of DMR reaction on Ni-Co/CF-La₂O₃-U catalyst.