Preparation And Performance Of Stable Nickel-based Catalysts With High Activity For Dry Reforming Of Methane

Dry reforming of methane(DRM)reaction is an important way to synthesize chemical raw material syngas.DRM process can not only consume CH4 and CO2,but also produce syngas with a product ratio of H2/CO of 1:1,which is convenient for efficient Fischer-Tropsch synthesis and the production of important chemical products.However,since there is no cheap and easily available catalyst with high activity and stability,it is still difficult to industrialize DRM reaction.The key technical problem is the catalyst deactivation caused by carbon deposition and agglomeration of active metal atoms at high temperature.To solve above two problems,this work regulated the oxygen vacancy(Ov)concentration of the CeO2 and the Ov was cooperated with Ni single atoms(SAC)to construct the Ov-SAC model catalyst,and this led to the efficient removal of carbon deposition in the DRM process.In addition,this work utilized a new support MXene and the active metal atoms were stabilized on it.The agglomeration of metal atoms in the DRM process was effectively inhibited due to the MXene.The main contents are as follows:(1)Ni/CeO2 single atom catalyst was prepared by precipitation-hydrothermal method.The second metal M(M=Mg,Co,and Zn)was doped to precisely regulate the Ov concentration of CeO2(from 21.9%to 30.8%).Ni single atoms act as the active sites for CH4 activation and Ov act as the active sites of CO2 activation.The Ov-SAC catalytic model was constructed.Compared with the Ni/CeO2 nanoparticle catalyst prepared by impregnation method,the Ni/CeO2 SAC showed higher initial catalytic activity in the DRM process,and achieved 90%CH4 conversion under the temperature of 800℃ and space velocity of 30000 mL g-1 h-1.During the continuous reaction of 150 h,the prepared single atom catalysts with higher oxygen vacancy concentration showed better catalytic stability.Along with the Ov concentration increased from 21.9%to 30.8%,the carbon deposition of the catalyst decreased by 50%.This synergistic effect between Ni single atom and oxygen vacancy realizes the continuous high catalytic activity of DRM reaction.(2)Based on the successful study of efficient carbon removal in the first work,this work focuses on the suppression of metal atoms agglomeration in the DRM process.A series of Ni-based catalysts were prepared by equal volume impregnation method.The used catalyst supports were Ti3C2 two-dimensional material(MXene),kintercalated MXene,Ti3C2 paper,TiO2,and TiC,respectively.Among them,Ti3C2 paper is difficult to load Ni atoms because of the small number of layers.The intercalation of K will occupy the interlayer of MXene,which makes Ni difficult to load and exhibited little catalytic activity.On the contrary,the Ni@MXene catalyst performed the best DRM activity(CH4 conversion up to 75%)and stability under the temperature of 800 ℃ and space velocity of 30000 mL g-1 h-1.Compared with other supports,Ti3C2 MXene with multilayer structure can effectively promote the dispersion of Ni atoms and inhibit the agglomeration of Ni atoms in the DRM process.