Preparation Of Highly Stable Ni/ZrO₂ Catalysts For CO Methanation

Recently,the demand for natural gas has increased sharply.Beside the imports of natural gas,the process of methane production through coal-derived syngas methanation is becoming more and more mature in China.However,the design of stable and efficient catalysts are the fundamental restriction of this technology.Nickel-based catalysts are usually chosen for methanation because of their plentiful sources,low cost and similar catalytic activity to noble metal catalysts.Meanwhile,nickel-based catalysts suffer from deactivation because of carbon deposition and sintering of Ni nanoparticles.Therefore,it is extremely important to design and develop nickel-based catalysts with both anti-coke and anti-sintering properties.The strong exothermic reaction of CO methanation causes migration,agglomeration and sintering of Ni nanoparticles.In addition,CO disproportionation produces carbon and the large amount of carbon deposits and encapsulates the active Ni nanoparticles during methanation reaction,leading to the deactivation of the catalysts.The regeneration of the deactivated catalysts is costly.Therefore,the design and synthesis of Ni catalyst with high anti-coke and anti-sintering properties is the keypoint to the application of CO methanation.Considering the two problems of sintering of Ni nanoparticles and carbon deposition in the practical application of nickel-based catalysts for CO methanation,we developed an effective method to produce novel Ni/ZrO₂ catalysts by using confinement effect for CO methanation.The carbon intermediate species could be converted effectively,which is originated from the confined interface between Ni and ZrO₂ along with the defective sites on ZrO₂.Furthermore,we established the intrinsic relationship between the structure of the catalyst and its anti-coke and anti-sintering properties by theoretical basis and modern technical characterizations.Typically,metal-organic framework（MOF）containing metallic Ni was prepared with different nickel salts onto zirconium-based MOF materials（UiO-66）.In the process of synthesizing UiO-66,different nickel sources[Ni（NO₃）₂.6H₂O,NiCl₂.6H₂O,Ni（CH₃COO）₂.4H₂O]were introduced into the catalyst precursor by"one pot method".Nickel-based catalysts with abundant pore structure were obtained by thermal calcination.The active Ni nanoparticles were confined between ZrO₂,forming strong Ni and support interaction.Modern instrumental characterizations show that the catalysts synthesized by one-pot method have developed porous structure.In addition,the confined Ni/ZrO₂catalysts forms more metal support interface,which is benefit to the conversion of carboneous species by hydrogenation to CH₄.Also,the strong interaction between Ni and ZrO₂ with confinement effects is able to effectively prevent the sintering of Ni nanopartilces in CO methanation.This porous architecture on Ni/ZrO₂ facilitates mass transfer and heat transfer during CO methanation,minimizing the heat effect for sintering of Ni nanoparticles.