Study On Preparation Of High Performance Co-based Catalysts And CH₄/CO₂ Reforming Technology

CH₄/CO₂reforming is a highly promising technology for CH₄and CO₂catalytic conversion,which can not only simultaneously convert two major greenhouse gases to mitigate the greenhouse effect,but also produce high-value syngas,achieving the efficient conversion and resourceful use of CH₄and CO₂.However,as both CH₄and CO₂molecules are highly stable and difficult to activate,the development of high-performance catalysts is a core issue in the development of CH₄/CO₂reforming technology.In this thesis,a series of CoCeO_2-δcomposite catalysts were prepared.The physicochemical properties of the prepared catalysts were investigated by H₂-temperature programmed reduction（H₂-TPR）,X-ray diffraction（XRD）,N₂adsorption-desorption,CO₂-temperature programmed desorption（CO₂-TPD）,inductively coupled plasma（ICP）and Quasi in-situ X-ray photoelectron spectroscopy（Quasi in-situ XPS）,and the relationship between the physicochemical properties of the catalysts and the CH₄/CO₂reforming performances was established.The main conclusions are as follows:1.The CoCeO_2-δcatalysts prepared by the hydrothermal-assisted soft template method have a high specific surface area（>100 m²/g）and well-developed pore structure,which is conducive to the dispersion of metallic Co and promotes the catalytic active centers to be formed.Meanwhile,the hydrothermal can promote strong electronic effects between Co and Cespecies of the porous CoCeO_2-δcatalysts to form electron-deficient CeO_2-δand electron-rich Co^δ-species,thus promoting the reactant molecules to be adsorbed and activated by the catalysts.The Co/Cemolar ratio has an important effect on the physicochemical properties of the CoCeO_2-δcatalysts.The 2CoCeO_2-δcatalyst prepared at a 2.0 Co/Cemolar ratio exhibited the best reforming catalytic performances,and the CH₄and CO₂conversions were 88.6%and 52.1%at atmospheric pressure and 700℃,respectively.In addition,the 2CoCeO_2-δcatalyst can maintain high cycle stability for CH₄/CO₂reforming.2.Despite the fact that the CoCeO_2-δcatalysts prepared by the co-precipitation method have a low specific surface area（<50 m²/g）and porosity,the introduction of glucose promoter to assist in-situ pre-reduction can effectively enhance the dispersion of metallic Co and promote the generation of active Co⁰species and oxygen vacancies on the catalyst surface.At the same time,the glucose promoter can enhance the electron effect between Co and Ceand promote the electron transfer between the active Co^δ-species and CO₂molecules,thus facilitating the CH₄/CO₂reforming reaction.A suitable Co/Cemolar ratio can promote a good interaction between Co and Cespecies,which is conducive to the reduction of the corresponding precursors and the generation of active Co⁰species and oxygen vacancies of the catalyst,and can also effectively inhibit the sintering of Co⁰species.The CoCeO_2-δcatalyst prepared with the introduction of a glucose promoter and a Co/Cemolar ratio of 3.0 showed the best reforming catalytic activity,and the CH₄and CO₂conversion was 87.2%and 54.0%at atmospheric pressure and 700℃,respectively.Meanwhile,the CoCeO_2-δcatalyst exhibited excellent reforming catalytic stability.3.The Co/Ce_xZr_1-xO_2-δcatalysts prepared by impregnation have good metal-support interactions.Cespecies can dissolve into the Zr O₂crystals to form a Ce-O-Zr solid solution,which promotes O atoms mobility in the lattice,thus facilitating the formation of oxygen vacancies on the catalyst surface and increasing the adsorbed oxygen species content on the catalyst surface.Meanwhile,the formation of Ce-O-Zr solid solution can enhance the interaction between metal Co and the support,and enhance the anchoring effect of the support on metal Co,thus promoting the dispersion of metal Co.The Ce/Zr molar ratio can effectively regulate the structure of the Ce-O-Zr solid solution,and a suitable Ce/Zr molar ratio can promote the reduction of precursors,which is conducive to the formation of more active Co⁰species and oxygen vacancies,and can also promote more basic centers to be formed on the catalyst surface,enhancing the CO₂adsorption performance of the catalyst.The Co/Ce_0.15Zr_0.85O_2-δcatalyst with a Ce/Zr molar ratio of 0.18 exhibited good reforming catalytic activity at atmospheric pressure and 700℃.