Synthesis Of Nano-CoCe Catalyst And Study For CH₄/CO₂ Reforming Technology

CO₂ and CH₄ are the main components of greenhouse gases,which have caused great harm and threat to human.It is imperative to reduce greenhouse gas emissions.CH₄ is also the main component of natural gas,rational utilization of natural gas has become one of the effective ways to reduce energy pressure.CH₄/CO₂ reforming reaction uses CH₄ and CO₂ as reactants,and produces syngas（H₂/CO）which with high added value.It provides an effective way for rational and effective utilization of CH₄and CO₂,and has important environmental and energy benefits.In this paper,CoCe catalysts were prepared to explore the relationship between the physicochemical properties of CoCe catalysts and CH₄/CO₂ reforming reaction.The reducibility of the precursors,phase structure,pore structure,surface chemical composition and alkaline site properties of the prepared catalysts were studied by H₂-temperature programmed reduction（H₂-TPR）,X-ray diffraction（XRD）,N₂adsorption-desorption,Quasi in-situ X-ray photoelectron spectroscopy（Quasi in-situ XPS）and CO₂-temperature programmed desorption（CO₂-TPD）.The prepared catalysts were used in CH₄/CO₂ reforming reaction,and to establish the relationship between the physical and chemical properties of the catalysts and its catalytic performance.The main conclusions are as follows:1.The synergistic effect of Co and Ce species in CoCe catalyst improves the activation rate of CH₄ and CO₂,thus showing superior catalytic activity for CH₄/CO₂reforming reaction.The oxygen vacancies of CoCe catalyst prepared by grinding method are inherent defects which are thermal instability,and the Co species on the catalyst surface are agglomerated crystalline state.Some Co species in the CoCe catalysts prepared by impregnation method dissolve into Ce O₂ lattice to form oxygen vacancies with good thermal stability,and the Co species on the catalyst surface are highly dispersed.Therefore,it shows superior CH₄/CO₂ reforming performance.When the reaction temperature is 600℃,the CH₄ and CO₂ reforming conversion can reach43.4%and 29.0%,respectively.2.The preparation method has a significant effect on the catalytic performance of CoCe catalyst.The CoCe-HT catalyst prepared by hard template method has the largest specific surface area and developed pore structure,and shows good catalytic activity and stability for CH₄/CO₂ reforming reaction.The pore size of CoCe-ST catalyst prepared by soft template method is small,which is not conducive to the diffusion of reaction gas molecules in the pore at low temperature.So it has poor low-temperature CH₄/CO₂ reforming performance.CoCe-CP and CoCe-HY catalysts prepared by coprecipitation and hydrothermal methods have small specific surface area,low porosity and large metal Co particles,and their CH₄/CO₂ reforming performance is poor.The CoCe-CA catalyst prepared by complexing method has the smallest specific surface area,but its Co and Ce species are evenly mixed and have good interaction.It shows the best catalytic activity and stability of CH₄/CO₂ reforming reaction.When the reaction temperature is 700℃,the conversion of CH₄ and CO₂ can reach 96.7%and 55.4%respectively.3.The Co/Ce molar ratio has a significant effect on the performance of CoCe catalyst prepared by complexing method.The specific surface area,alkali number and CH₄/CO₂ reforming activity of CoCe catalyst show a volcanic trend with the increase of Co/Ce molar ratio.The CoCe11 catalyst with Co/Ce molar ratio of 1,has good interaction between Co and Ce species,and it shows the best catalytic activity and use stability.When the reaction temperature is 700℃,the conversion of CH₄ and CO₂ can reach 96.7%and 55.4%respectively.