| Hydrogen is known as the "21st Century" of energy, which is one of theideal low-carbon energy, and solved the rapid depletion of traditional energysources or excessive consumption of negative effects to the environment, morein line with the development trend of the future of energy. Ethanol streamreforming (ESR) have prospect application, and it is the current hot topic in thefield of new energy. The renewable biomass of ethanol provides a greendirection for sustainable energy development. The key of ethanol reforming isto develop novel reforming catalysts with high activity and high selectivity atlow temperature. Therefore, how to design and prepare catalysts, which ischeap, low energy consumption, high efficiency, long service life haveimportant theoretical and practical significance, and it is also a challengingsubject.Nickel-based catalysts for ESR has high activity and selectivity, and theprice is low, so it is a potential catalysts for ESR. But the stability of thenickel-based catalysts remain to be further improved. In this paper, the nickel catalyst and nickel as the active center, and the montmorillonite as the carrier,its structural and acidic properties of are tailored in large scales by differentmethods, i.e., impregnation method, interlayer cation exchange method andalkaline activation method. The activity and the selectivity of ESR wereqantitatively correlated with the structure, acidity, reduction behavior, and thesynergistic effect between different catalytic functions of the catalyst or MMT,which are characterized by XRD, physical/chemical adsorption, andmicroscopic techniques, etc. The mechanistic relationship between the thusmentioned factors and ESR performance of the catalyst, especially the keyfactor on selectively controlling the ESR product distribution was determined,and a reasonable model for the optimal multifunctional catalyst was proposed.The experiment and main conclusions are summarized as follows:（1）A series of Ni/MMT catalyst was prepared by incipient wetnessimpregnation, the preparation process and reaction conditions on thedispersion of nickel, the carrier structure, the influence of the catalytic activityand stability were studied. Results indicated that: Ni <10%, Ni adhere to thesurface of montmorillonite or insert the lamellar structure, which is amorphousmonolayer distribution, Ni is15%, exists with the form of NiO dispersed state.10Ni/MMT in the pretreatment temperature550℃, reduction temperature600℃, reaction temperature500℃condition, ethanol conversion rate close to100%, the H2selectivity~65.3%, other product gaseous CO2, CO, CH4selectivity~23.7%,~7.6%,~3.4%, and no liquid side-products were formed. When pretreatment temperature increased to600℃, with the impact of part ofNi and Al, montmorillonite layers structure order was damaged, the NiAl2O4spinel structure is difficult to restore. When reduction temperature increased to800℃, lead to Ni particles increases to16.9nm and decreaseing the H2production. According to the performance evaluation of the10Ni/MMTcatalytic stability,400℃low temperature reaction can produce a large numberof C2side-products. Combined with the carbon analysis, total amount ofcarbon deposition was28.5%, good resistance to carbon depositionperformance and total carbon amount to5.3%when temperature increased to500℃. The results of HRTEM indicate that, Ni (111) crystal face was the keyfactors to the ESR response performance, Effective fracture ethanol and C2product of C-C and C-H, Ni (111) crystal fully exposed, favorablefor the production of hydrogen.（2）On the basis of montmorillonite exchangeable cations，Al introducedinto the montmorillonite matrix.10%Ni load on Al-modified montmorilloniteby impregnation method, and study the structure of catalysts, acidity, catalyticactivity and stability. The results show that Ni is in amorphous and highlydispersed state; when the Al-exchange capacity increase from5CEC to20CEC,Ni to grow thin, and its specific surface area increase from26.6m2/g to132.8m2/g; Al>15CEC, Ni and Al form NiAl2O4, and generate a large number ofstrong acid sites; Ni/5Al-MMT at500℃, ethanol complete conversion,hydrogen is up to66.4%，no ethylene and acetaldehyde intermediate，but more Al>10CEC, the yield of hydrogen would decrease with the increase ofethylene. Ni/5Al-MMT at400℃is superior to10Ni/MMT, H2selectivitymaintain about60%, and intermediates C2was controlled below5%. Carbonanalysis and TEM results show that the coke in Ni/5Al-MMT was only4.5%,the average particle diameter was about10nm, not producing the reunionsintering phenomenon.（3） Using alkali-activated method to modify the structural ofNiAl-MMT. Study how NaOH influene the distance between layers, structurequalities, morphology and catalytic properties of catalyst. The results showthat NaOH destructs the order of montmorillonite lamellar structure, that theNi and Al enter into the zone of two-dimensional layer or are embedded inHouse-of-card space; the distance of layer space extended to1.5nm, thespecific surface area increased to168.2m2/g, and the pore diameter broadened(2-27nm); when reaction temperature is500℃, ratio of water/ethanol is8:1,space velocity is80,000h-1, NiAl-MMT/NaOH perform good catalyticproperties, ethanol conversion reach100%, the selectivity of H2is72.6%, CO2~18.4%, CO~6.3%, CH4~2.7%, no byproduct; the scheme ofNiAl-MMT/NaOH following: ethanol dehydrogenation'acetaldehydedecomposition'Methane reforming'WGSR, and NiAl-LDH catalystfollowing: ethanol dehydration'C2H4polymerise'Coke; HRTEM analysisshowed Ni0in NiAl-MMT/NaOH is a single crystal form after the reaction,there not obvious agglomeration and coke. （4）Deeply analysis the mechanism of modified alkali activation towardsmontmorillonite. Observe the NaOH concentration (5-15mol/L), treatmenttime (1-12h), treatment temperature (60-100℃) affect the morphology,structure and acidity of montmorillonite, load10%Ni on different alkaliactivated and study its performance in ESR reactions. The results show thatNaOH lead to the desilication and dealumination of montmorillonite, andcause the different damage to layer structure. The fallen Si and Al enter thezone of two-dimensional layer of montmorillonite and form an oxide pillaredstructure, and the active component Ni was placed on alkali-activatedmontmorillonite with a single amorphous distribution. Under the mildalkaline-modified conditions (MMT-5-3-80, MMT-10-3-80, MMT-15-3-60,MMT-15-1-80, MMT-15-3-80), its distance between layers broaden, thespecific surface area increase, pore diameters are almost2.1nm, and the porevolume exhibits a typical monotonically increasing structure called H4typeslit pore, which produce a large number of strong acid sites. Load Ni10%onmontmorillonite which was modified under mild conditions, the catalyticproperties tend to be similar with the reaction temperature of500℃, also theH2was selected less than35%that affected the hydrogen yield, while theselectivity of ethylene was close to40%. Under severer alkali-modifiedconditions (MMT-15-12-80, MMT-15-3-100), the structure of pore changesfrom H3to H4, develop into more mesoporous channels whose average porediameters is16nm. Because of the strong desiliconizing and dealumination, the severe acid sites are neutralized. Load10%Ni on modified alkalimontmorillonite, the ethanol conversion is100%and the selectivity is74.7at reaction temperature is500℃, no by-product of ethylene. The method ofalkali-activated montmorillonite provides a new strategy for the preparation ofintercalated layer materials. |
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