Dry Reforming Of Methane Over Novel Nickel-based Catalysts

Syngas, a gas mixture that contains carbon monoxide and hydrogen, can be used asfuel or an intermediate in the production of other chemicals. Carbon dioxidereforming of methane can produce the low H2/CO ratio (1:1) syngas, which is moredesirable for the subsequent chemical synthesis. Besides, the comprehensiveutilization of carbon dioxide and methane can not only reduce greenhouse gases andprotect environment, but also bring considerable economic benefits. So the dryreforming of methane reaction has attracted much attention in recent years. Ni-basedcatalysts have been expected to be the extensively used catalysts in industry.However, the Ni-based catalysts tend to deactivate after a long-term catalytic processbecause of carbon deposition and sintering of nickel particles. Therefore, how toimprove the resistance of carbon deposition and prevent the sintering of nickelparticles is meaningful in both theory and practice.The dissertation is based on three influencing factors of the coking-resistance. Theinfluence of the catalytic activity and coking-resistance is investagated based onthree different kinds of catalysts. The purpose of the dissertation is to find therelationship between the morphologies and properties. The study includes threesections below.(1) The morphology dependence of catalytic properties of Ni/CeO2nanostructuresfor carbon dioxide reforming of methane is discussed. Compared with Ni/CeO2nanopolyhedra, Ni/CeO2nanorods expose the unusually reactive (110) and (100),which can provide more oxygen vacancies and higher oxygen mobility. The stronginteraction exists between the metal and supports on the Ni/CeO2nanorods catalysts.Therefore, the Ni/CeO2nanorods catalysts display more excellent catalytic activityand stability in30h. More importantly, the coke deposition on the used Ni/CeO2nanorods is less. The morphology dependence should response for the excellentcatalytic activity and coking-resistance. At last, a mechanism diagram for the dry reforming of methane over Ni/CeO2nanorods is given.(2) A kind of novel modual catalysts are investigated, which are designed via thecombination between the Ni-MgO-Al2O3mixed oxide nanoplates core andmesoporous SiO2coating shell. The modular design effectively combines theadvantages of both modules but prevents the defect of the individual modules. In thedry reforming of methane reaction, the modular catalysts show the high and stablecatalytic activity. Most importantly, they also display the enhanced capability ofcoke-and sintering-resistance. The excellent performance results from the dualconfinement: The first confinement is contributed to the mixed oxides nanoplatesderived from the LDH, which can generate the strong metal-support interactioneffect and enhance the chemisorption of CO2. The second confinement comes fromthe mesoporous SiO2shell, which also exhibit another “confinement effect”. Thedual confinement effects reinforce each other and make the novel modular catalystsshow significantly improved coking and sintering-resistant performance.(3) The novel monolithic catalysts derived from in-situ supported hydrotalcite-likefilms on aluminum wires are fabricated. The surface of aluminum substrate iscomposed of the interconnected mixed oxide nanoplate array. The hierarchicalstructure can increase the surface area, which is favorable for the dispersion of nickelparticles. After the calcination and reduction, the strong metal-support interactionexists on the catalysts derived from hydrotalcite-like compound precursors. Besides,the additation of Mg element can increace the amount of basic sites. Therefore, themonolithic catalysts show the higher coking-resistant properties than traditionalcatalysts via the impregnation method. The application of these monolithic catalystsprovides a novel insight on the coking-and sintering-resistance of catalysts forreforming reactions.