Preparation Of Ni/SiO₂ Catalyst In CO Methanation Via Coordination Impregnation

Nickel based catalysts has been widely used in methane steam reforming,carbon dioxide reforming of methane,partial oxidation of methane,catalytic reaction system of CO methanation etc for the abundant resources,high catalytic activity,good selectivity,simple preparation canditions,easy control of reaction conditions and other advantages.However,Nickel based catalysts also have some drawbacks.For example,Nickel based catalysts easily accumulate carbon during the reaction process,resulting in catalyst deactivation,and nickel based catalysts are easy to sinter at high temperature resulting in poor stability.Therefore,we need to find a suitable preparation method to avoid the drawbacks and improve the catalytic performance of nickel based catalysts.Compared with water impregnation,coordination impregnation is a simple and effective way to adjust the Ni species absorbed on the surface of the carrier by adding coordination agent in the aqueous solution of the precursor salt.Based on this,this work used ammonia as complexing agent to prepare Ni/SiO₂,and the catalytic performance were evaluated with CO methanation as model reaction.the influence of coordination impregnation on the structure of Ni/Si O₂ catalyst was also studied.As a reference,Ni/SiO₂ catalyst was also prepared via water impregnation.The results showed two kinds of Ni species with less water formed after dried:Ni-containing phyllosilicates（PS）and the anchored Ni²⁺on the surface of SiO₂ derived from adsorption of[Ni（NH₃）₆]²⁺.Compared with the reference catalyst,the water content of these two special structures was lower,and the interaction between Ni species with Si O₂ was enhanced,which improves the dispersion of the catalyst effectively.thus this process improved the activity and stability of the catalyst,and enhanced its sinter resistance.In addition,the influence of the calcination temperature on the structure and properties of Ni/SiO₂ catalyst during the ammonia impregnation was investigated.The interaction between Ni species and carriered was enhanced when calcination temperature was increases from 400℃ to 500℃,and the dispersion of catalyst was increased,resulting in the increase of activity.When the calcination temperature is further increased,the aggragation of NiO increases,which results in the formation of larger Ni particles.Thus the activity of catalyst decreased.The activity enhancement of the catalyst calcined at800℃ could be attributed to the formation of amorphous nickel silicate.Finally,the effect of different ligands on the catalytic performance was preliminarily investigated.It was found that the catalyst prepared with ethylenadiamine as the ligand had the best catalytic performance,followed by ammonia,but it was better than that of reference catalyst prepared via water impregnation.While EDTA was the worst.It could be seen that the coordination impregnation with suitable ligand is an effective mathod to improve the catalytic performance of Ni based catalysts.