Synthesis Of Transition Metal Catalysts And Their Catalytic Performance For CO₂ Methanation At Low Temperature

In the coking process,a large number of by-products coke oven gas are produced,which are rich in H2,CH4,CO,CO2 and N2,etc.Due to the shortage of natural gas and the low utilization rate of coke oven gas in our country,people are interested in using coke oven gas to synthesize natural gas.The main component of natural gas is methane.Coke oven gas methanation can not only produce high-quality energy methane,but also utilize CO and CO₂ in coke oven gas.In particular,the chemical properties of CO₂ are stable and difficult to activate.Thus,CO₂ methanation is the focus of current research.Currently,the challenges have been focused on the design of catalysts in CO₂ methanation to enhance the catalytic activity.According to previous reports,most catalysts have low activity at low temperature,but at high reaction temperature they are easy to deactivate and have side reactions.Therefore,it is urgent to break the monopoly of foreign catalytic technology by developing efficient catalyst for low-temperature CO₂ methanation.In this paper,a series of Ni based catalysts were designed and applied to CO₂ methanation at low temperature.The influence rules of the catalytic process were researched from the aspects of support property,catalyst preparation method,structure-activity relationship of catalysts.And the reaction mechanism and stability of the catalysts were also studied.The main work are summarized below:1)Diverse supports?ZSM-5,SBA-15,MCM-41,Al₂O₃ and SiO₂?with various mesoporous structures were introduced to fabricate Ni-based catalysts for the CO₂methanation by incipient wetness impregnation method.The influence of the interaction between the support and the active component on the catalystic activity was mainly studied.Ni/ZSM-5 catalyst displayed the most active catalytic properties.The excellent catalytic property of Ni/ZSM-5 catalyst was resulted from the basic property and the synergistic effect between nickel metal and support.2)A series of Ni_x Al-MO catalysts derived from Ni-Al hydrotalcite precursors were prepared to improve the low-temperature CO₂ methanation.By adjusting the Ni²⁺/Al³⁺ratios,the alkaline and reducibility of the catalysts were designed,and the catalysts showed efficient catalytic performance at low temperature.The superior catalytic property was related to the basic property,readily reducible NiO species,and the cooperation of metal nanoparticles and basic sites.The changes in the molar ratio of Ni²⁺/Al³⁺could induce the optimal tradeoff between H₂ activation and CO₂ activation.3)In order to further improve the catalytic performance for CO₂ methanation at low temperature,a new material prepared by integrating LDHs precursors with CeO₂ were developed.By optimizing the content of CeO₂ in the catalyst,the low temperature performance of the catalyst was improved.The NiAl-MO/CeO₂-5 catalyst exhibited the highest catalytic activity with CO₂ conversion of 91%at 250°C.The preparation of new materials by combining basic metal oxides with hydrotalcite precursors is a successful strategy for designing catalysts with excellent CO₂ methanation properties at low temperature.4)In order to improve the utilization rate of active components,catalytic performance,and shorten the preparation time of catalysts,a series of Ru-based catalysts for CO₂ methanation at low temperature were synthesized by chemical reduction method with ionic liquids as stabilizer reaction media.The effect of ionic liquids type and loading on the physicochemical property and catalytic activity were investigated.It is found that ionic liquids are not only used as a protectant to effectively prevent the aggregation and oxidation of the nanoparticles by space resistance and electrostatic protection,but also adsorbed on the surface of Ru nanoparticles as a modification layer with a strong adsorption to determine the size of nanoparticles and keep the high dispersion,and they were significantly affected the catalytic activity.