The Preparation And Performance Research Of Ni-based Catalyst In Steam Reforming Of Methane

Hydrogen is an ideal clean energy,which has no pollution to the environment,in recent years,the development of hydrogen energy has aroused widespread concern.That the study of methane steam reforming（SMR）in the traditional process of enriching hydrogen is very important.SMR is a relatively mature hydrogen production process in the industry,but the methane water vapor reforming reaction is a strong endothermic reaction.Increasing the methane conversion rate must be carried out at high temperatures（800～900℃）,but high temperatures mean higher energy consumption and reactors that require better material,both economically and economically produce.Therefore,the hot research of methane steam reforming hydrogen production technology is to develop a catalyst which can effectively reduce the energy consumption and low temperature and high activity and good anti-carbon deposition performance.In this study,RZrO_x（R=Tb,Er,Dy,Y,Pr）composite oxide carrier was prepared with ammonium bicarbonate as precipitant,Ni/RZrO_xseries catalysts were prepared by impregnation of active component Ni on RZrO_xcomposite oxide carrier by impregnation method.Then the paper investigated the effects of praseodymium and zirconium ratio on Pr_xZr_1-xO_y（x=0.1,0.2,0.3,0.4,0.5）composite oxide carrier and the structure and properties of Ni/Pr_xZr_1-xO_yseries catalyst in detail.Series catalysts were prepared by Ni impregnation method and study the effect of Ni content to the a Ni/PrZr₄O_x（Whose a was mass fraction of active component of Ni,the molar ratio of Pr/Zr was 1:4）catalysts.It was also compared the oxidation and catalytic activity of the Ni-R-Zr series catalysts（R=Tb,Er,Dy,Y,Pr）,which were prepared by coprecipitation method.That the Er_{（1-x）}Pr_xFeO₃（x=0,0.1,0.3,0.5,0.7,0.9）series carriers prepared by coprecipitation method and Ni/Er_{（1-x）}Pr_xFeO₃series catalysts prepared by the method of impregnation with Ni were studyed.The technology was used to characterize the catalyst such as X-ray diffraction（XRD）,temperature programmed reduction（TPR）and temperature programmed oxidation（TPO）.The steam reforming of methane reacted in micro fixed bed,that the activity and selectivity of the catalysts to catalyze the steam reforming of methane reaction were evaluated.In the study of Ni/RZrO_x series catalysts,it was found that the doping of rare earth ions made the composite oxide with zirconium ions with cubic lattice structure,and the rare earth ions entered the ZrO₂ lattice and caused the lattice expansion of ZrO₂.The rare earth was not easily reduced by hydrogen in the ZrO₂ lattice.The catalyst had high catalytic activity,high temperature stability and good carbon deposition resistance in SMR reaction,which was prepared by the combination oxide carrier of rare earth and zirconium.The results show that the catalytic activity of the catalyst in the Ni/RZrO_x series catalyst is the best in the SMR reaction.At the reaction temperature of 650℃,the conversion of CH₄ reached 94%,the molar percentage of hydrogen in the mixed gas after reaction reached 78.4%.In the study of Ni/Pr_xZr_1-xO_yseries catalysts,it was found that the praseodymium zirconium composite oxide was prepared by coprecipitation method,which had cubic lattice structure,and praseodymium ion entered the zirconia lattice to cause lattice expansion.The doping of praseodymium in zirconium dioxide contributes to the dispersion of the active nickel component of the catalyst,which prevented the catalyst from sintering inactivation during the high temperature reaction and could improve the anti-carbon deposition ability of the catalyst.In addition,the activity and selectivity of the catalyst in the methane steam reforming reaction and the redox nature of the catalyst were affected by the ratio of praseodymium zirconium.When the molar fractionof Pr/Zr was 2/8,the activity of the catalyst and the selectivity of hydrogen were the highest.In the study of a Ni/PrZr₄O_x series catalysts,it was found that the half-peak width of the characteristic diffraction peak of nickel oxide in a Ni/PrZr₄O_x series catalyst decreased with the increase of Ni content,and the average grain size of Ni increased.In the reaction temperature range of 400～800℃,the activity of 20Ni/PrZr₄O_x catalyst was the best,the conversion of CH₄was 99.19%,and the molar percentage of H₂in the mixed gas after reaction was 81.94%.The main diffraction peak of ZrO₂carrier over 20Ni/PrZr₄O_x catalyst changed with the increase of calcination temperature,the activity and the molar percentage of H₂ over The 20Ni/PrZr₄O_x catalyst were the highest at 100℃c alcination.The methane conversion and the molar percentage of H₂in the mixed gas after reaction reached 99.93%and 88.47%respectively.Under the condition of water/carbon ratio=5,the 20Ni/PrZr₄O_xcatalyst was the most selective hydrogen in the steam reforming of methane,which reached 92.1%and the high water/carbon ratio was beneficial to suppress the formation of carbon deposition.In the study of Ni-R-ZrO_x series catalysts,it was found that the non-dopant catalyst was prepared by coprecipitation method,which had no monoclinic ZrO₂.The catalytic activity of the catalyst doped with Er was the highest at the same reaction temperature.When the reaction temperature was 650℃,the methane conversion rate reached 98.94%,and the molar percentage of hydrogen in the mixed gas after reaction was 85.9%.Under the same reaction temperature,the Ni/RZrO_xseries catalyst blend the activity of the Pr adjuvant and the molar percentage of hydrogen in the mixed gas after reaction was the highest,which reached 94%and 78.4%respectively.At the same time,the catalytic performance of the catalyst was not prepared by coprecipitation method about N-E-Z,it indicated that the activity of catalysts was largely influenced by the preparation method.In the study of Ni/Er_{（1-x）}Pr_xFeO₃ series catalysts,it was found that the unit cell structure of the catalyst may change with the increase of the amount of praseodymium,which lead to the decrease of the crystallization degree of the catalyst,the easy reduction of the catalyst and reduced the phenomenon of reduction temperature.When the optimum ratio of Er/Pr was 1:1,the catalytic effect was the best,the catalyst activity of Ni/Er_0.5Pr_0.5FeO₃ was the highest in the temperature range of750～800℃,and the methane conversion rate was 87.91%,The grain size of the catalyst increased with the increase of the calcination temperature,the diffraction peak of the catalyst gradually became sharp and the grain size of the catalyst increased as the calcination temperature increased,the crystallinity of the catalyst increased too.When the calcination temperature of the catalyst of Ni/Er_0.5Pr_0.5FeO₃was 700℃,The conversion of methane and the molar percentage of hydrogen in the mixed gas after reaction were the largest,reaching 90.68%and 86.27%respectively.