Design And Catalytic Performance Studies Of Two-Dimensional Nickel-based Catalysts For Dry Reforming Of Methane

The dry reforming of methane（DRM）reaction comprehensively utilize CH₄ and CO₂ to produce the syngas（H₂/CO）,which can mitigate the influence of greenhouse effect in some degree.Meanwhile,the ratio of the produced H₂/CO is 1/1,which is more desirable for the Fischer-Tropsch process.Therefore,DRM has attracted more and more attention.Due to the excellent catalytic activity and low-cost,the Ni-based catalysts have been widely used in the DRM reaction.However,catalyst deactivation by sintering of Ni species and carbon deposition are the major problems over the Ni-based catalysts.Therefore,it is quite urgent to develop high-performance Ni-based catalysts.Recently,the fast development of two-dimensional（2D）materials has provided new opportunities for catalysts design with the high catalytic activity,selectivity and stability.In this dissertation,with the combinative use of materials design,in situ techniques and the performance evaluation of the DRM reaction,the deep insight of the structure-activity and the catalysis mechanism of the2D Ni-based catalysts have been studied.The catalytic performance can be enhanced through the addition of promoter and design of core-shell structure.The main results can be summarized as follows:（1）The promotional effects of rare earth elements（Sc,Y,Ce,and Pr）on NiMgAl catalysts derived from layered double hydroxides were investigated for dry reforming of methane.The study mainly investigate how these additives affect the behavior of the catalysts surface and interface,thus,identifying the catalytic mechanism via the elucidation of the promotional effects of these properties on the catalytic performance.It was found that the modified catalysts showed the improved catalytic stability and coke resistance,which may result from the following favorable properties:enhanced surface basicity,abundant oxygen vacancies,superior redox properties and highly dispersed Ni particles.Notably,the Ce or Pr modified catalysts showed the higher performance than the others due to the coexistence of redox pairs,like Ce³⁺/Ce⁴⁺,which can contribute to the enhancement of redox properties and formation of oxygen vacancies simultaneously.Furthermore,in situ DRFITS analysis illustrated the details of carbonate species formation and transformation during catalysis processes for getting deep insight into the catalytic mechanism.（2）In this work,based on the highe chemical and thermal stability of 2D h-BN material,we present the design and synthesis of two-dimensional Ni/BN@SiO₂catalyst with stable architecture and well defined metal-support interface.The conjugated mesoporous silica is considered as an excellent host to disperse and confine Ni nanoparticles.As-prepared catalysts with the highly dispersed and nano-sized Ni species showed the excellent catalytic activity,stability and enhanced coke-and sintering-resistance.The synergistic effect between the Ni-BN interface and confinement of mesoporous silica constitute the key advantage of the DRM reaction.Importantly,the catalysts exhibit excellent catalytic stability and coke-resistance,which may result from a combined effect of both the Ni-BN interface and nano-sized Ni species,including the strong metal-support interaction,synergistic effects of nano-sized Ni species and h-BN interface in the activation of CH₄ and CO₂ and the high coke resistance of h-BN support.Combining the catalytic performance and the in situ DRIFTs studies,a full length researchs of the adsorption and activation mechanism of the reactants over the catalysts were clarified.Meanwhile,the coke-and sintering-resistance mechanisms of the catalysts were illustrated.（3）h-BN nanomaterial with abundant defective sites can be used as support to load Ni species（Ni/BN）.This study is aimed to illustrate the promotional effects of the Ni/BN catalysts with different defective sites on the catalytic performance during the DRM reaction.It is found that a simple,one-step mechano-chemical process can effectively exfoliate and functionalize h-BN.the experimental research illustrate that the defective sites can be benefit to the highly dispersion Ni species,which can effectively inhibit the metal sintering under the high temperature reaction.Therefore,the abundant active sites can participate the DRM reaction,leading to the enhanced catalytic activity.Furthermore,in situ DRIFTs studies and density functional theory calculations reveals that the abundant defective sites can promote the activation of CH₄ and CO₂,clarifying the reaction pathways over the Ni/BN catalysts with defective sites.As a result,these advantageous properties result in the remarkably catalytic stability and coke-resistance.