Bimetallic Ni-Fe Catalysts Derived From A Layered Hydroxide Precursor For CO Methanation From Syngas

Natural gas as a clean and environmental-friendly energy substance,is being researched,developed and employed in the worldwide,and human demand for natural gas is growing.In recent years,coal as a raw material to generate synthetic natural gas by CO methanation is getting more and more attention.Methanation technology is one of the most important core technologies for coal generating natural gas,and methanation catalysts are of profound significance for methanation technology.Ni-based catalysts are often used as catalysts for the methanation reaction due to low cost and good activity,but Ni-based catalysts easily suffer sintering and carbon deposition,which results in deactivation of the catalyst.Therefore,the development of catalysts possessing the ability of anti-sintering and anti-carbon deposition is significant.Based on our previous work,Ni-based catalysts and Ni-Fe bimetallic nanoparticle catalysts derived from hydrotalcite precursors were prepared,and XRD,H₂-TPR,ICP,TG,BET,XPS and TEM characterization methods were used to study the structure of the catalyst.The effects of Ni loading,space velocity and iron content were discussed.At 600?,200h of the reaction time,the stability of the catalyst was investigated.The relationship between the structure and the performance of catalyst was obtained.The main research results of this paper are as follows:The xNi MgAlLDHs?x=15%,20%,25%,30%?with different nickel contents were prepared by coprecipitation method.The different contents of nickel had some influence on the structure of the catalyst,and the size of the reduced nickel nanoparticles is gradually increased with the increase of Ni content.Among them25Ni-CLDHs have the largest pore size and higher specific surface area.In the methanation reaction test,20Ni-red,25Ni-red and 30Ni-red catalysts showed high catalytic activity.But when the reaction conditions of the space velocity increased to60,000 mL·g^-1·h^-1,the 25Ni-red catalyst has higher performance than 20Ni-red catalyst,so the activity advantage of 25Ni-red catalyst is more obvious under the more severe conditions.NixFeLDHs?x=0,1%,2%,4%?precursors with good hydrotalcite structure were prepared by the same method.After calcination and reduction,Ni and Fe elements were reduced and formed highly dispersed nickel-iron alloy on the surface of the mixed oxide of magnesium oxide and alumina.The addition of iron made solid solution easier to reduce,decreased the catalyst reduction temperature and enhanced the degree of reduction.XRD,TEM analysis and XPS of the reduced catalyst proved the formation of the Ni-Fe alloy.In the methanation activity test,the addition of iron accelerated the reaction of CO methanation at low temperatures,and the Ni2Fe-red catalyst showed the highest CO conversion and methane selectivity,mainly due to the synergistic effect of nickel-iron alloys.The Ni2Fe-red catalyst showed the better ability of resisting carbon deposition and sintering than the Ni0Fe-red catalyst in the stability test,mainly due to the addition of iron to form a nickel-iron alloy and the iron element diluting nickel atoms on the surface,which inhibited the formation of nickel clusters and reduced carbon deposition and sintering.