Preparation Of Nickel-based Catalyst By Confinement Strategy And Its Performance In Methane Dry Reforming

The shortage of fossil fuels and the massive emissions of greenhouse gases are two major challenges.Methane dry reforming technology（DRM）is a promising technology that converts two greenhouse gases（CH₄ and CO₂）to produce syngas,which is conducive to providing new ideas for greenhouse gas governance and global low-carbon development.Meanwhile,syngas can be used directly as a feedstock for Fischer-Tropsch synthesis to produce liquid fuels and other high value-added chemicals.Ni-based catalysts have the advantages of low cost and high activity,which stand out among a series of DRM catalysts.However,Ni-based catalysts are prone to metal sintering and carbon deposition,and the catalyst is prone to deactivation over a short period of time,which is a key challenge to extend catalyst life and promote industrial applications.Therefore,it is urgent to develop a high performance catalyst for DRM,which can inhibit both metal sintering and carbon deposition.In this paper,two high-performance RhNi-MgAl₂O₄ and Ni@S-1@Si O₂catalysts have been developed from the perspective of confinement strategy.These two catalysts have high stability and high carbon accumulation resistance in DRM.A series of characterization methods have been used to investigate the physicochemical properties and reaction mechanism of the catalysts.Part Ⅰ:Preparation of Rh-MgAl₂O₄,Ni-MgAl₂O₄ and RhNi-MgAl₂O₄ catalysts by one-pot alcoholysis for low temperature DRM.An alloy-confined RhNi-MgAl₂O₄catalyst was designed to adjust the activation rates of methane and carbon dioxide.The experimental results show that RhNi-MgAl₂O₄ catalyst has excellent low temperature stability and coking-resistant compared with Ni-MgAl₂O₄ catalyst,and no carbon was detected at 600 ^oC for 20 h.At the same time,CO₂-TPD,XPS and in situ DRIFTS were used to further investigate the physicochemical properties and reaction mechanism of the catalyst.On the one hand,the presence of alloy promotes the reduction of oxides and the dispersion of metals.On the other hand,basic sites promote the activation of CO₂ into more O*,and CH_x*is more readily oxidized than C*.In addition,in situ DRIFTS results show that the DRM may follow the Langmuir-Hinshelwood（L-H）mechanism on the catalyst.Part Ⅱ:The single-shell confined Ni@S-1 and double shell confined Ni@S-1@Si O₂ catalysts were prepared for DRM.Ni@S-1@Si O₂ catalyst has good stability at a low temperature of 650 ^oC for 25 h and there is no carbon accumulation on the catalyst surface after the reaction.The physicochemical properties and mechanism of the catalysts were characterized by XRD,TEM,N₂-BET and in situ DRIFTS.The characterization further confirmed the successful synthesis of the double shell confined catalyst.The S-1 shell contained most of the metal confined in its interior,and a small part of the exposed active center was further confined by the outermost Si O₂ shell.The experimental results show that compared with the single-shell confined catalyst,the double shell confined catalyst inhibits the migration and aggregation of metal particles and the growth of carbon nanotubes,thus improving the low temperature stability and carbon accumulation resistance of the catalyst.In addition,in situ infrared results show that the DRM may follow the L-H mechanism on the catalyst.