Design Of Nanoconfined Nickel Catalysts For CO₂ Reforming Of Methane

CH4-CO2 reforming process,an important way for CH4 utilization,can convert CH4 and CO2 into synthesis gas with great industrial value.Baesd on its tantalizing economic prospects and remarkable environmental values,the process has become a research hotspot in recent years.However,the process has not been industrialized due to the restriction of catalyst.The purpose of this study is to prepare a highly efficient and stable Ni-based catalyst.In this project,a layer of mesoporous material was coated on nanocatalyst in order to prepare the nanoconfined catalyst.The experimental results proved that the nanoconfined catalyst combines the high efficiency of nanocatalyst with the stability of core-shell structure.Firstly,in this project,the factors affecting catalytic performance such as zirconia crystalline phases,Ni introduction methods,silica coating methods and shell content were optimized.Subsequently,the morphologies of nano-CeO2 encapsulated by Si02 were studied.In addition,the effects of Al2O3 introduction methods including deposition-prcipataiton(DP)and evaporation-induced self-assembly(EISA)on catalytic performance in Ni-m-ZrO2-Al2O3 system were investigated.In other words,the preparation methods,such as deposition-prcipataiton evaporation-induced self-assembly(DP-EISA)and sequential deposition-prcipataiton(S-DP),were studied.Finally,the modern characterization technologies such as XRD,N2 sorption,H2-TPR,CO2-TPD,XPS,TEM and TGA were chosen to characterize catalyst samples.Based on above characterization results,the differences in the performance of the catalyst samples investigated were reasonably explained.The primary research results obtained from this dissertation are generalized as below:1.Among the three Ni/nano-Ce02 confined by Si02,Ni/Ce02 nanorod@Si02 showed excellent catalytic performance.XRD and N2 sorption results indicated that the rod based catalyst had smaller Ni particle size,higher proportion of initial Ni(111)crystal facet and advantages in pore structure,which contributed to its higher catalytic activity;The typical core-shell structure was observed on the rod sample by TEM results.Based on H2-TPR results,amone the three type nanoconfined catalysts,the rod sample had the highest propotion of NiO species strongly interacted with the support.XPS results showed that the highest oxygen vacancy concentration was formed on the rod sample.The three points above accounted for the rod sample’s excellent stability.2.Compared with the Ni/m-Zr02 catalyst,the activity and stability of the catalyst were improved with the aid of Al2O3 introduced by EISA and DP methods.Specificly,the advantages of DP and EISA methods were in enhancing its activitity and stability,respectively.DP-EISA method was the better preparation method in Ni-m-Zr02-Al2O3 catalytic system.The DP-EISA catalyst was relatively stable in activity within 24 h of reaction.Unfortunately,although the S-DP catalyst had a higher initial activity,it deactivated rapidly.N2 adsorption,XRD and TGA results indicated that the S-DP sample had a larger specific surface area,a smaller Ni particle size and serious carbon deposition after reaction.The three points above led to its higher initial activity and poorer stability;TEM,H2-TPR and C02-TPD results showed that the DP-EISA sample had the typical core-shell structure,stronger metal-support interaction and advantages in the number of alkaline sites,which undoubtedly resulted in its better stability.