Preparation, Characterization And Catalytic Performance Of Nickel-based Catalysts Supported On MgO For Carbon Dioxide Reforming Of Methane

With the development of modern science and human social activities, theadjustment of energy structure and environmental protection has become an importantissue in the strategy of sustainable development. Presently, carbon dioxide reformingof methane has attracted much attention because this reaction can effectivelytransform these two greenhouse gases （methane and carbon dioxide） into valuablesynthesis gas. Great efforts have been made on the development of highly active andstable catalysts for carbon dioxide reforming of methane. This article focused on theNi/MgO catalysts system. Some factors such as the exposed facet of crystallinematerials, specific surface area and morphology which have important influence oncatalyst activity and stability were investigated systematically, and some propertiessuch as physicochemical properties of supports, metal-support interaction and thedispersion degree of active metal were analyzed in detail.MgO nanosheets with （111） facet as the major surface were successfullysynthesized and employed as a support for nickel catalysts in the carbon dioxidereforming of methane. It was found that Ni/MgO（111） catalysts showed bettercatalytic activity and stability than Ni/MgO（CM） catalysts. The TOF of CH₄and CO₂over Ni/MgO（CM） catalyst were0.47S^-1and0.53S^-1, and the TOF of CH₄and CO₂over Ni/MgO（111） catalyst were0.63S^-1and0.72S^-1, respectively，under the reactionconditions of650°C, atmospheric pressure,36SL h^-1g^-1. After100hours reaction,the conversion of CH₄only decreased8.8%under Ni/MgO （111） catalyst. However，after10h of reaction, the Ni/MgO（CM） catalyst underwent an obvious decrease ofabout16%for methane conversion.In this thesis, we further studied the effects of different nickel loadings on theperformance of nickel-based catalysts supported on MgO （111）. The results showedthat the activity and stability were increased with Ni loadings increasing from2to10wt.%, but the stability of catalyst was decreased with the increasing of Ni loadingfrom10to20wt.%. At the same time, it was also found that different Ni loadings ofNi/MgO（111） deactivated differently: Deactivation of2%Ni/MgO（111） catalyst couldbe mainly attributed to the oxidation of Ni particles, while for the catalysts with Niloadings more than2wt.%, the deactivation was attributed to the sintering of nickelparticles and carbon deposition. In addition, MgO with different specific surface area were prepared in order tostudy the effect of specific surface area on the performance of catalyst. The resultsshowed that: as for MgO, the higher the specific surface area of the support, the largerthe dispersion of active metal, which may lead to high initial activity. The ability toactivate CO₂of the support was also an important factor of the catalysts.In this paper, mesoporous MgO （named as MgO（H）） was also successfullyprepared.6%NiO-MgO and Ni/MgO（H） were prepared by one step synthesis methodand impregnation method, respectively. It was found that mesoporous pore structureof MgO（H） could effectively limit the growth of the activity metal, which led to thehigh dispersion degree of active metal and high activity, with the conversion of CH₄only decreasing5%after100h reaction. The influence of Ni loadings on theperformance of Ni/MgO （H） catalysts was similar to that of Ni/MgO（111） catalyst. Itwas found that NiO-MgO catalyst had the higher initial activity compared to Ni/MgO（H） catalyst because of the higher nickel dispersion of NiO-MgO catalyst. But thestability of NiO-MgO catalyst was worse than that of Ni/MgO（H） catalyst because ofthe weak ability to activate CO₂and the introduction of Na during the preparation.After100hours reaction, the conversion of CH₄decreased11.5%over NiO-MgOcatalyst.