Coke Resistant La₂O₃ Supported Ni Catalysts With High Efficiency For Methane Dry Reforming For Hydrogen Production

With the continuous optimization of energy consumption construction,the proportion of fossil energyconsumption has gradually decreased in recent years.However,the consumption of petroleum,coal and natural gas still accounted for 85%in global energy consumption in 2017.It can be seen that fossil energy is still dominant in the main energy consumption today.As a consequence of exploitation and use of fossil energy,a large amount of industrial pollution are discharged.Therefore,the clean development and effective utilization of fossil energy has been widely concerned.The abundant reserves,mature mining technology and cleaner to use of Shale gas?unconventional natural gas?makes it is an inevitable trend for energy consumption structure inclines from oil and coal to natural gas.Methane as the main component of natural gas,how to use it cleanly and efficiently is an urgent problem to be solved.Dry reforming of methane?DRM?has become one of the research hotspots recently because it can use CH₄ and CO₂ as raw materials to produce more valuable chemicals?H₂ and CO?,which can not only alleviate the greenhouse effect,but also convert low-value chemicals into high-value chemicals.Nickel-based catalysts are the most promising catalysts for DRM reaction because of their high initial activity and low cost.However,carbon deposition and sintering of active components in the DRM reaction will lead to deactivation of the catalysts.Therefore,it's urgent for nickel-based catalysts to solve the carbon deposition and aggregation of active sites problem.In this study,we designed and synthesized Nickel-based catalysts with better carbon deposition resistance on the basis of a thorough understanding of the DRM reaction mechanism,as well as catalyst structures,surface properties and the interaction between Ni and supports.Part 1:La₂O₃ supports were synthesized by glycine nitrate combustion?GNC?,precipitation?PP?and thermal decomposition?TD?methods,respectively.Ni/La₂O₃catalysts were prepared by impregnation of active component Ni for DRM reaction.The experimental results showed that the surface properties,activity,stability and carbon deposition resistance of the catalysts prepared by different methods are different.The Ni/La₂O₃-GNC catalyst has the highest specific surface area of Ni,the most surface alkaline sites and the largest amount of active oxygen,and shows the highest activity,stability and the best carbon deposition resistance among all the catalysts.DRM Ni/La₂O₃ catalyst with high activity,good stability and strong carbon deposition resistance can be obtained by optimizing the synthesis method of La₂O₃support.Part 2:Based on the results of part1,Ni/La₂O₃ catalyst with good catalytic performance can be obtained by GNC method,but there is still a certain amount of carbon deposition in the spent catalyst after DRM stability test.In this part,we focuse on the optimization of coke resistance ability of Ni/La₂O₃ catalysts by Fe doping modification.La₂O₃ support was synthesized by GNC method,Ni and Fe were loading by impregnation method,and a series of Ni/La₂O₃ catalysts with the same Ni content and different Fe content were obtained.XRD,XPS and STEM-EDX Mapping results confirm that Ni-Fe alloy phase exists in the reduced Ni-Fe/La₂O₃ catalyst,TGA-DSC and Raman results show that the addition of Fe can significantly improve the coke resistance ability of the Ni/La₂O₃ catalyst.However,the addition of Fe tends to agglomerate the active Ni particles,which is not conducive to the dispersion of the active metal Ni.When Fe doping content is more than 0.5%,DRM reaction activity will decrease significantly.There were no significant carbon deposition on6Ni-0.5Fe/La₂O₃ and 6Ni-1Fe/La₂O₃ catalysts after 50 h DRM reaction.