Preparation Of Ni/Mg_xAl_x-La_0.5-xZr_0.5-x?O?Catalyst And Performance Study On CO₂ Reforming Of Hydrocarbons

In recent decades,most energy consumption is relied on the fossil fuels,which would result in many serious problems such as environmental pollution and energy crisis.Shale gas,natural gas and other gas resources were considered as a promising low-carbon resource,and the amount of reserves is very abundant.But the proportion of natural gas to total energy consumption is very low.Therefore,the rational use of natural gas has become the main method to solve above-mentioned problems and also become research hotspot.It is well known that natural gas contains mainly methane,certain amount of ethane of mixed light alkanes and CO₂ etc.So the key issue to use natural gas was mainly focused on the efficient conversion of methane?CH₄?and ethane?C₂H₆?.The dry reforming of CH4?DRM?and mixed reforming of hydrocarbons?MRH?can not only provide a reasonable way to convert natural gas efficiently and rationally,but also produce chemical products with high added value.In the catalyst for hydrocarbon carbon dioxide reforming reaction,Ni-based catalyst has good catalytic performance and are inexpensive,which make it have a broad prospect of industrialization.However,the Ni-based catalyst also suffers from the coke deposition and sintering of NiO,which has seriously affected the large-scale use of Ni-based catalysts.In this paper we is aimed at the defects of Ni-based catalysts,designed and prepared a series of Ni/Mg_xAl_x-La_0.5-xZr_0.5-x?O?with different ratio of MgAl?O?/LaZr?O?by recombination sol-gel method.The effects of the ratio on the catalytic performances were investigated,the effects of reaction conditions?WHSV and temperature?on catalytic activity.At the same time,these catalysts were characterized by X-ray diffraction?XRD?,H2-temperature programmed reduction?H2-TPR?,N₂ isothermal adsorption-desorption?BET?,thermal gravimetric?TG?,scanning electron microscopy?SEM?,and the results were also analyzed.The main consequences are as follows:?1?The catalytic composite oxide supports were prepared by recombination sol-gel,traditional sol-gel,co-precpitation and physical mixing method,respectively.Then four different catalysts were prepared by loading 8wt%active component Ni with incipient wetness method.The effect of the preparation method on catalytic activity was investigated by the dry reforming reaction of methane,and the results showed that recombination sol-gel has high activity and good stability,which is due to the smaller size of the Ni testified by XRD.?2?The catalysts performances of Ni/Mg_xA_x-La_0.5-xZr_0.5-x?O??x=0,0.13,0.25,0.33,0.4,0.43,0.5?series catalysts prepared by recombination sol-gel on dry reforming of methane were investigated.Under the reaction condition of 800?,WHSV=27000mL/?h.g?,0.2g catalyst,Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1?O?behaved the highest reactivity,and the conversion of CH₄ and CO₂ were 96.1%and 95.9%.After 32h long-time activity test,no evident conversion decrease of CH₄ and CO₂ were observed,indicating the stability of the catalyst is better.?3?Characterization data of N₂ adsorption-desorption shown that Ni/Mg_xAl_x-La_0.5-xZr_0.5-x?O??x=0,0.13,0.25,0.33,0.4,0.43,0.5?catalysts had formed mesoporous structures.The different hysteresis loops were observed between single carrier Ni/Mg_0.5Al_0.5?O?and double carrier catalysts,indicating the mingle of LaZr?O?and MgAl?O?tends to change the pore structure.Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1?O?displayed bigger surface area and narrow pore size distribution.The results of XRD showed that different diffraction peaks of NiO and Ni were observed on fresh and spend catalysts,Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1?O?behaved the weakest and widest NiO and Ni peaks,which indicated small particle size,high dispersion of active metal NiO and strong resistance to sintering.At the same time,H2-TPR presented the interactions between the active components NiO and the support of each catalyst were different,the interaction of Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1?O?was the strongest,which may be the reason for strong resistance to sintering.Whisker carbon was clearly displayed on the spent Ni/Mg_0.5Al_0.5?O?and Mg_0.43Al_0.43-La_0.07Zr_0.07?O?by SEM analysis,the TGA result that the amount of carbon deposition on Ni/Mg_0.5Al_0.5?O?and Mg_0.43Al_0.43-La_0.07Zr_0.07?O?reached 7.70wt%and 5.03wt%,Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1?O?presented the least carbon deposition?1.56wt%?.?4?The catalytic performance of Ni/Mg_0.4Al_0.4-La_0.1Zr_0.1?O?catalyst prepared by four different methods on methane-ethane mixed hydrocarbon reforming reaction were studied.The results show that the recombination sol-gel method is also suitable for the reforming of mixed hydrocarbons.The C2H6 conversion was as high as 100%,and was mainly converted to syngas,less by-product,the selectivity is good.