Nickel-based Spinel Catalyst For Selective CO Methanation In Hydrogen-rich Gas

Proton exchange membrane fuel cells?PEMFC?have attracted wide attention from countries around the world due to its high energy efficiency and zero emission.The on-board hydrogen production through steam reforming of fossil fuels can solve the problem of safe supply of hydrogen for vehicle fuel cells,however,it is inevitably to produce 0.5?2.0vol.%CO during the reforming process,which causes serious toxic effects for Pt-based anodes of PEMFC,thus leading to a sharp decline in battery performance.At present,selective CO methanation is the most effective purification method to achieve the acceptable ppm level of CO concentration in hydrogen-rich gas.The key lies in the development of a highly selective CO methanation catalyst with excellent low-temperature performanceIn this paper,Ni-ZrO₂/NiAl₂O₄ and Ru-Ni/NiAl₂O₄ catalysts have been prepared for selective CO methanation in hydrogen-rich gas.The supports as well as catalysts were characterized by various methods,such as XRD,BET,H2-TPR,H2-TPD,CO-TPD,XPS,TEM,SEM and TG.Combined with the results of catalytic activity test,the promotion effect of ZrO₂ promoter and precious metal Ru on Ni/NiAl₂O₄ catalyst were systematically investigated.The main research contents are as follows1.The nickel-rich NiAl₂O₄ support with various Ni/Al molar ratios were prepared by sol-gel method and Zr promoter was subsequently introduced by the co-impregnation method to prepare Ni-Zr/NiAl₂O₄ catalysts.The effects of nickel-rich support with various Ni/Al ratios,support calcination temperature,Zr/Al ratio,and Ni loading on the performance of the catalysts were studied.Moreover,the stability of the catalyst was also investigated.Experimental result shows that the appropriate Ni/Al ratio?0.65?of the nickel-rich support is helpful to promote the formation of ?-NiO and increase the number of Ni active sites in the catalyst.The low calcination temperature?600??leads to low crystallinity of NiAl₂O₄,while the high calcination temperature?800??will collapse the pore structure of the support,resulting in a decrease in BET specific surface area.At the same time,high calcination temperature will increase the content and crystallinity of NiAl₂O₄,which is not conducive to the reduction of NiO in the nickel-rich NiAl₂O₄ support.The addition of ZrO₂ promoter can significantly improve the low-temperature performance of Ni-ZrO₂/NiAl₂O₄ catalyst.The characterization results indicated that ZrO₂ promoter weakened the NiO-NiAl₂O₄ interaction and improved the reducibility of Ni oxides.In addition,Zr promoter reduced the Ni particle size.The highly dispersed small Ni particles led to enhanced exposure of Ni active sites,which increased the sorption capacities for both H2 and CO.Moreover,ZrO₂ could trigger electron transfer,increase the electron cloud density of Ni atoms,which facilitated the dissociation of CO via enhance Ni-C bond and weaken the C-O bond.Among the prepared catalysts,15Ni-0.05Zr/NA?0.65?catalyst showed excellent catalytic performance,which could reduce the CO concentration to a level of<10 ppm in the temperature range of 190?240? with a CH4 selectivity larger than 50%Furthermore,15Ni-0.05Zr/NA?0.65?showed a great stability during the 120h lifetime test2?Ru-Ni/NiAl₂O₄ catalysts were prepared by loading the active components Ni and Ru on the surface of the nickel-rich NiAl₂O₄ support via co-impregnation method.The effects of Ru loading,Ni loading and reduction temperature on catalyst performance were studied,and the stability of the catalyst was also investigated.The synergistic effect between Ru and Ni in Ru-Ni/NiAl₂O₄ catalyst is beneficial to improve the low temperature performance of the catalyst.The study found that the addition of Ru can significantly weaken the metal-support interaction between NiO and NiAl₂O₄.At the same time,the electron transfer from Ruo to Ni0 increases the electron cloud density of Ni0,which is beneficial to the dissociation and activation of CO.In addition,an appropriate amount of precious metal Ru reduces the size of Ni particles and increases the number of active sites,which increases the sorption capacities for H2.Among the catalysts,1.5Ru-15Ni/NA catalyst showed great catalytic performance,which could reduce the CO concentration to below 10 ppm over a wide temperature range of 190?230? with a CH4 selectivity larger than 50%,and under the reaction conditions of 200?,0.1MPa,WHSV=10800mL·g-1·h,the 1.5Ru-15Ni/NiAl₂O₄ catalyst displayed an excellent stability in 120h lifetime test.