Ni Based Catalysts From Layered Double Hydroxides For The Coke Oven Gas Methanation

With the rapid development of Chinese economy,the gap between social's demands and nature gas supply become more and more serious,production of synthetic nature gas?SNG?via coke oven gas methanation process can alleviate the shortage of nature gas.As an important composition of methanation process,how to preparation of catalyst with excellent properties for syngas methanation is a critical issue.In this paper,the preparation of catalyst by reduction of hydroxides directly,getting bimetallic catalyst and bi-support catalyst respectively,characterized the obtained catalyst through XRD,TPR,TG,BET,SEM,TEM and XPS.The catalytic performance was conducted with reaction gas mixture of 60%H₂,20%CO and 20%N2 in volume at a weight hourly space velocity of 15000 mL·gcat-1·h-1 under atmospheric pressure over fixed bed reactor.The thermal stability of catalyst was tested at 500 and 600? for 300 h simultaneously.Finally processed the profiles and then analyzed the relationship between catalytic structure and catalytic properties.The obtained information was listed below:Firstly,Ni-Co bimetallic catalyst has showed excellent lowly temperature performance,when temperature as lowly as 250?,the catalyst performed 100%CO conversion and 90%CH4 selectivity,we thought the synthetic energy effect between Ni and Co cause this phenomenon,which strengthened the Ni-C bond and weaken C-O bond,so the adsorbed CO on Ni atom can be activated easily.Secondly,Ni-Co bimetallic catalyst showed outstanding anti-sintering ability,when the stability test finished,particle size of the Ni-Co alloy stayed firmly,such advantage should attribute to:1.the catalyst possessed mesoporous structure which had confine effects for metal particles;2.the reduced metal particles were embedded in the amorphous Al₂O₃ matrix,as the TEM-EDS showed above results;3.As the XRD and TPR results suggested,interaction between cobalt species with Al₂O₃ is stronger than that of nickel species.In the high temperature reaction process,the interface between Ni-Co alloy and alumina would be reconstructed to lower the interface energy.Cobalt species were enriched to some extent between the interface,lowering the interface energy,strengthening the interaction between Ni-Co alloy and alumina,therefore,the active particles cannot move easily,resultantly elevating the anti-sintering ability of the Ni-Co alloy nanoparticles.Thirdly,the bimetallic catalyst also possessed highly carbon resistance which should attributed to:1.Ni-Co alloy stayed in a little size firmly which was unfavorable for coke formation;2.cobalt species is an excellent oxidation catalyst,water,a by-product of CO methanation,would be activated on cobalt species to eliminate the carbon deposited via oxidation reaction.Similarly,CO₂ in the reaction mixture might be activated to eliminate the deposited carbon;3.it is known that the graphite carbon generation is the combined actions of nickel atoms cluster.In Ni-Co alloy,the closely packed nickel atoms were diluted by cobalt atoms,thus the carbon formation was restrained.Finally,formation of layered double hydroxides-graphene compound through co-precipitation method,after reduction,Ni was supported on the graphene-Al₂O₃,which showed excellent anti-sintering ability due to the highly thermal conductivity of graphene,but the catalytic performance was poor attributed to the Ni was enveloped by the graphene.