Study On Preparation And Performance Of Spinel Supported Nickel-based Catalyst For Combined Steam And CO₂ Reforming Of Methane

The recycling of greenhouse gas CO2 and the conversion of clean fuel CH4 to produce high value-added chemicals are promising for addressing the issues of peaking carbon dioxide emissions and carbon neutral.Combined steam and CO2 reforming of methane(CSCRM)can simultaneously use CH4 and CO2 to efficiently produce clean syn-gas as raw materials for downstream chemical processes such as methanol synthesis or Fischer-Tropsch synthesis.At present,the industrial application of non-noble metal Ni-based catalysts for CSCRM is mainly limited by problems of sintering of Ni nanoparticles and carbon deposition on the catalyst under high temperature.Herein,the CSCRM reaction was performed under the condition of non-carbon deposition zone on thermodynamics to avoid the carbon deposition on the Ni catalysts.Furthermore,magnesium-aluminum spinel is used as the support for Ni catalysts to endow a strong metal-support interaction for anchoring Ni species and thus effectively hindering the sintering issues.First,a modified sol-gel method was proposed to prepare Ni/MgAl2O4 catalysts which shows better catalytic performance for CSCRM performed in the thermodynamic non-carbon deposition zone compared with the counterpart prepared by the traditional impregnation method.The effects of Ni loading of Ni/MgAl2O4 catalysts on the catalytic performances were further investigated.The results indicate that there is a volcanic trend between the catalytic activity and the nickel loading,and the optimal catalytic activity reaches the best at 10 wt%of nickel loading.Based on structural characterization such as H2-TPR,XRD and HAADF-STEM,it was found that the interaction between the active components of Ni and the support in the catalyst with 10 wt%of nickel loading(10Ni/MgAl2O4)is strong,which give rise to smaller Ni nanoparticles and anti-sintering ability,and thus better higher catalytic activity and stability.Subsequently,a ternary Ni/Mg/Al layer double hydroxides(LDH)was synthesized by a co-precipitation method to be employed as the precursor for Ni/MgAl2O4 catalysts.By reducing the LDH precursors under hydrogen,Ni/MgAl2O4 catalysts with uniform Ni nanoparticles distribution was prepared.By modulating the loading of Ni and the ratio of Mg/Ni in the precursor,a series of catalysts were prepared and comparatively investigated for CSCRM.The catalyst with 10 wt%of nickel loading and 0.5 of Mg/Ni ratio(0.5-LDH-10Ni-MgAl2O4)is demonstrated to show the best performances among these catalysts.Specifically,the catalyst shows 95%of CH4 conversion and 65%of CO2 conversion as well as 2.1 of H2/CO ratio in the product,which is suitable for downstream industrial production.Reaction kinetics studies reveal that the reaction rate over Ni-MgAl2O4 catalyst is the first order for CH4 and the zero order for both H2O and CO2.The activation energy of 0.5-LDH-10Ni-MgAl2O4 and 0.5-LDH-15Ni-MgAl2O4 catalysts are 83 kJ/mol and 96 kJ/mol,respectively.Comparative studies on the thermal stability for these Ni catalysts suggest that the Ni catalysts from the LDH precursors exhibit better anti-sintering ability than those ones prepared by the modified sol-gel method and the traditional impregnation method.These insights gained here could guide the design and optimization of Ni-based catalysts with high catalytic activity and stability for the CSCRM reaction.