The Application Of Ni-based Catalyst For Syngas Methanation

The methanation reaction is an effective route to produce synthetic nature gas(SNG),and the Ni-based catalysts are extensively used for this reaction.However,due to the high CO concentration,high reaction temperature and the presence of sulfur-containing compounds in syngas,the Ni-based catalysts suffer from the sintering,carbon deposition and sulfur poisoning during the methanation reaction,and resulting catalyst deactivation.How to improve the sulfur-tolerant,anti-sintering and anti-carbon deposition abilities of the Ni-based catalysts remains a great challenge.This work is carried out from two aspects:active sites modification and reaction-diffusion coupling.The main contents are listed below:(1)The presence of promoter is a efficient method to mediate the property of the active sites.Ru is one of the noble metal promoters for the supported Ni-based catalysts for methanation.Our previous study had developed a new way to synthesize Ru-additive Ni catalyst via a polyethylene glycol(PEG)-assisted impregnation method.This method facilitated the formation of bimetallic Ni-Ru particles with smaller size and more defects and higher reducibility.On the basis of study above,in situ XRD,XPS and CO chemisorbed infrared spectroscopy(CO-IR)were used to further investigate the crystalline structure and the surface composition of bimetallic Ni-Ru particles formed and their effects on the intrinsic activity and stability of methanation.It was evidenced that the sizes of metallic Ni-Ru particles keep unchanged,but their interfacial properties(e.g.surface compositions,chemical states and the microstructures)changed as increasing the reduction temperature from 573 K to 793 K.The particles formed at 693K own more surface defects and the one formed at 573K had more surface Ru atoms.Combining with CO methanation test results,it was found that the activity of Ni-Ru bimetallic catalyst was decided by the amount of defect sites;and increasing surface Ru atoms in Ni-Ru particles could promote the anti-coking property in CO methanation.(2)In addition to metal promoter,N-doped carbon species can also be used as promoter owing to its special electron property.In this paper,we used DCDA-additive impregnation method to synthesize SiO2 supported Ni catalyst.The addition of DCDA was favorable to deposit trace pyrrolic nitrogen containing carbon on Ni(111)planes.Such carbon deposition allowed the electron transfer ffor the reaction on this Ni(111).This effect facilitated the WGSR happened on Ni(111)and significantly rom pyrrolic nitrogen atoms to Ni(111)planes,leading to more active sites available reduced the deposition of carboxyl and carbonyl species,and resulting better long-term stability(3)In addition to the active sites modification,the change of support pore structure can vary the concentration of each gas due to different internal diffusion effects,which leading better catalytic performance.Based on the above reason,we used SiO2 aerogel with large pore size and high surface area as support to prepare supported Ni-based catalyst in this paper.And the resultant catalyst was applied in H2S-containing methanation to study the effect of internal diffusion.The results showed the SiO2 aerogel supported Ni-based catalyst had better sulfur-tolerant ability.