Preparation Of Highly Stable Nickel-based Catalysts By Surface Space Confinement Strategy And Performance In Methane Dry Reforming

With the increase of population and the rapid development of economy,people’s demand for fossil energy is increasing.The burning of fossil energy will bring a series of ecological and environmental problems,among which the carbon dioxide produced by the burning of coal and oil will cause the greenhouse effect such as glacier melting,climate warming and sea level rise.Methane,the main component of natural gas and shale gas,has 25-30 times the greenhouse effect of carbon dioxide.In order to improve the ecological environment,methane dry reforming technology uses methane and carbon dioxide,which can effectively convert methane and carbon dioxide into carbon monoxide and clean energy hydrogen at the same time.The core problem of this technology is the selection of catalysts,which are generally divided into noble metal catalysts and non-noble metal catalysts.Nickel-based catalysts are generally used in methane dry reforming because of their high initial activity,low price and abundant resources.However,as dry reforming of methane is a strong endothermic reaction,the reaction conditions are generally in the range of 800-1000℃,which will lead to the problem of catalyst sintering and aggregation.In addition,there is a large amount of carbon deposition due to the imbalance of methane cracking and carbon dioxide activation in low temperature dry reforming of methane,resulting in the deactivation of the catalyst.Therefore,the preparation of catalysts with high stability and high resistance to carbon accumulation is the most important.A batch of nickel-based catalysts modified by basic metal oxides and ultrafine nano-particle nickel-based catalysts were prepared and applied to methane dry gas reforming reaction to explore the catalytic performance of catalysts at low temperature and high temperature respectively.The first part of this paper adopts wet impregnation to prepare nickel-based catalysts modified by MgO and La₂O₃ for low-temperature methane dry reforming.In order to improve the problem of methane cracking and carbon dioxide activation imbalance in low temperature process,the alkaline site of the catalyst was added to promote carbon dioxide adsorption and activation,inhibit carbon deposition,and improve the anti-carbon deposition performance of the catalyst.The experimental results showed that,compared with Ni@DMS and Ni-MgO@DMS catalyst,trace carbon was generated after the reaction at 550℃for 8 h,Ni-La₂O₃@DMS catalyst did not detect the carbon generation after the reaction at 550℃for 8 h,and Ni-La₂O₃@DMS catalyst was reacted at 550℃again for 50 h.Only a small amount of carbon accumulates.By in situ infrared and CO₂-TPD characterization,it is confirmed that adding basic metal oxides can effectively improve the adsorption and activation of carbon dioxide.In the second part of this paper,highly dispersed nickel-based catalysts were prepared by staging calcination under different atmospheres,which showed excellent catalytic activity and anti-carbon accumulation performance when applied to methane dry reforming reaction.Ni_0.5@DMS catalyst remained stable after 50 h reaction at800℃and showed excellent anti-carbon accumulation performance.Oxidation state Ni_0.5@DMS catalyst was applied to dry reforming of methane reaction,oxidation catalyst and also found square one similar to the catalytic activity of catalyst performance,the two catalysts spherical aberration electron microscopy test,found also in the types of catalyst activity center in the form of single atoms and clusters,and oxidation catalyst exists in the form of atomic clusters.The experimental results show that the catalysts with clusters of atoms as active centers are favorable for the reaction and the catalysts with single atoms or clusters of atoms as active centers can improve the stability and anti-carbon accumulation performance of the catalysts.