Preparation Of Bi-promoters Modified Ni/SiO₂ Catalysts And Their Catalytic Performance For CO Methanation

In recent years,natural gas has aroused increasing attention and research as a clean and environment-friendly energy source.Based on the China's energy structure characteristics of rich coal,lean oil,and low gas,the process of using coal as raw material to produce synthesis gas and further to prepare natural gas through CO methanation reaction has received great attention.During this process,the design of the catalyst for the methanation of syngas is the critical step.But mono-additives added catalysts prone to sintering and carbon deposition serious during long-term reaction.Therefore,it is of great significance to develop catalysts with strong anti-sintering and anti-carbon deposition properties.In this paper,bi-promoted Ni/SiO₂ catalysts were prepared to reisistance the sintering and carbon deposition of catalyst.Considering the function of Ni,CeO₂,La₂O₃ and SiO₂ in the CO methanation reaction,the catalyst precusors of silica supported La_1-xCe_xNiO₃?x=0.05,0.10,0.15,0.20,0.25,0.30,1.00?were prepared by the incipient wetness impregnation combined with citrate complexing method.During activation,the catalyst precursors was reduced to Ni-La₂O₃-CeO₂/SiO₂ where Ni nanoparticles were modified by bi-promoters of CeO₂and La₂O₃ and the effects of La and Ce on methanation performance were discussed.The activity test showed that all the catalysts established higher catalytic activity.With the increase of Ce content,the activity for CO methanation increases first and then decreases,and the catalyst of La_0.75Ce_0.25NiO₃/SiO₂ eatablished the best activity.The catalysts were characterized by using XRD,TEM,BET,H₂-TPD,XPS,TG and Raman techniques.Compared with the mono-promoted catalysts,the bi-promoted La_0.75Ce_0.25NiO₃/SiO₂ showed much better resistance to carbon deposition,higher resistance to sintering and higher activity for CO methanation,which might be due to co-eliminating effect of the two promoters for the deposited carbon,the confinement of the interacted two promoters for Ni and the higher dispersion of Ni nanoparticles derived from the smaller size of La_0.75Ce_0.25NiO₃.A series of 30%La_xM_1-xNi_yN_1-yO₃/SiO₂?M:K,Ca,Y,Sr;N:Fe,Co?catalysts were prepared.The influence of different element doping of the catalyst on the methanation performance was investigated.In detail,the effect of B-site doped Fe on the methanation activity was studied deeply.The precusors of 30%LaNi_yFe_1-yO₃/SiO₂?y=0.8,0.9,1.0?was prepared firstly,after reduction,La₂O₃-modified Ni-Fe/SiO₂catalyst?La₂O₃-Ni-Fe/SiO₂?can be obtained.This catalysts were characterized by XRD,TPR,TEM etc.,indicating that Ni-Fe alloy has been formed.In the perovskite LaNi_1-yFe_yO₃,the Ni³⁺and Fe³⁺are uniformly dispersed and can be simultaneously reduced from the perovskite when treated in a reducing atmosphere,which is favorable for the formation of Ni-Fe alloy,thereby increasing the activity of the CO methanation reaction.