Engineering oxygen vacancies on Tb-doped ceria supported Pt catalyst for hydrogen production through steam reforming of long-chain hydrocarbon fuels

Steam reforming of long-chain hydrocarbon fuels for hydrogen production has received great attention for thermal management of the hypersonic vehicle and fuel-cell application.In this work,Pt catalysts supported on CeO_(2)and Tb-doped CeO_(2)were prepared by a precipitation method.The physical structure and chemical properties of the as-prepared catalysts were characterized by powder X-ray diffraction,scanning electron microscopy,transmission electron microscopy,Raman spectroscopy,H_(2)temperature programmed reduction,and X-ray photoelectron spectroscopy.The results show that Tb-doped CeO_(2)supported Pt possesses abundant surface oxygen vacancies,good inhibition of ceria sintering,and strong metal-support interaction compared with CeO_(2)supported Pt.The catalytic performance of hydrogen production via steam reforming of long-chain hydrocarbon fuels(n-dodecane)was tested.Compared with 2Pt/CeO_(2),2Pt/Ce_(0.9)Tb_(0.1)O_(2),and 2Pt/Ce_(0.5)Tb_(0.5)O_(2),the 2Pt/Ce_(0.7)Tb_(0.3)O_(2)has higher activity and stability for hydrogen production,on which the conversion of n-dodecane was maintained at about 53.2%after 600 min reaction under 700℃at liquid space velocity of 9 ml·g^(-1)·h^(-1).2Pt/CeO_(2)rapidly deactivated,the conversion of n-dodecane was reduced to only 41.6%after 600 min.

Low CO content hydrogen production from oxidative steam reforming of ethanol over CuO-CeO_2 catalysts at low-temperature

CuO-CeO2 catalysts were prepared by a urea precipitation method for the oxidative steam reforming of ethanol at low-temperature.The catalytic performance was evaluated and the catalysts were characterized by inductively coupled plasma atomic emission spectroscopy,X-ray diffraction,temperature-programmed reduction,field emission scanning electron microscopy and thermo-gravimetric analysis.Over CuOCeO2 catalysts,H2 with low CO content was produced in the whole tested temperature range of 250–450 C.The non-noble metal catalyst 20CuCe showed higher H2production rate than 1%Rh/CeO2 catalyst at 300–400 C and the advantage was more obvious after 20 h testing at400 C.These results further confirmed that CuO-CeO2 catalysts may be suitable candidates for low temperature hydrogen production from ethanol.

Silicon Nitride Supported Cobalt Catalyst for Enhanced Hydrogen Production from Ethanol Steam Reforming

Silicon nitride(Si_(3)N_(4))supported cobalt catalysts(Co/Si_(3)N_(4))were fabricated by using wetness impregnation procedure.The microscopic morphology,phase composition,and electronic states were characterized by XRD,TEM,SEM,and XPS,respectively.For comparison,cobalt catalyst supported on SiO_(2)(Co/SiO_(2))was also investigated.XPS studies and DFT calculations show that the cobalt species in Co/Si_(3)N_(4) have lower valence state than those in Co/SiO_(2).The catalytic ESR reactions demonstrate that Co/Si_(3)N_(4) exhibits distinctly higher catalytic activity and hydrogen selectivity than Si_(3)N_(4) support and Co/SiO_(2) catalyst with the identical cobalt loading,indicative of the favorable effect of Si_(3)N_(4) support on the catalytic performance of supported cobalt catalyst.Durability tests and TG-DSC studies show that Co/Si_(3)N_(4) catalyst exhibits better stability and resistance to coke during the same catalytic experiment period.

Improvement of low temperature activity and stability of Ni catalysts with addition of Pt for hydrogen production via steam reforming of ethylene glycol

Hydrogen production by steam reforming of ethylene glycol(EG) at 300℃ was investigated over SiO2 and CeO2 supported Pt–Ni bimetallic catalysts prepared by incipient wetness impregnation methods. It was observed that impregnation sequence of Pt and Ni can affect the performance of catalysts apparently. Catalyst with Pt first and then Ni addition showed higher EG conversion and H2 yield owing to the Ni enrichment on the surface and the proper interaction between Pt and Ni. It was observed that although SiO2 supported catalysts exhibited better activity and H2 selectivity, CeO2 supported ones had better stability. This is attributed to the less coke formation on CeO2. Increasing Pt/Ni ratio enhanced the reaction activity, and Pt3–Ni7 catalysts with 3 wt% Pt and 7 wt% Ni showed the highest activity and stability. Ni surficial enrichment facilitated the C-C bond rupture and water gas shift reactions;and Pt addition inhibited methanation reaction. Electron transfer and hydrogen spillover from Pt to Ni suppressed carbon deposition. These combined effects lead to the excellent performance of Pt3–Ni7 supported catalysts.

Ethanol steam reforming over Ni/ZSM-5 nanosheet for hydrogen production

Compared to reforming reactions using hydrocarbons,ethanol steam reforming(ESR)is a sustainable alternative for hydrogen(H_(2))production since ethanol can be produced sustainably using biomass.This work explores the catalyst design strategies for preparing the Ni supported on ZSM-5 zeolite catalysts to promote ESR.Specifically,two-dimensional ZSM-5 nanosheet and conventional ZSM-5 crystal were used as the catalyst carriers and two synthesis strategies,i.e.,in situ encapsulation and wet impregnation method,were employed to prepare the catalysts.Based on the comparative characterization of the catalysts and comparative catalytic assessments,it was found that the combination of the in situ encapsulation synthesis and the ZSM-5 nanosheet carrier was the effective strategy to develop catalysts for promoting H_(2) production via ESR due to the improved mass transfer(through the 2-D structure of ZSM-5 nanosheet)and formation of confined small Ni nanoparticles(resulted via the in situ encapsulation synthesis).In addition,the resulting ZSM-5 nanosheet supported Ni catalyst also showed high Ni dispersion and high accessibility to Ni sites by the reactants,being able to improve the activity and stability of catalysts and suppress metal sintering and coking during ESR at high reaction temperatures.Thus,the Ni supported on ZSM-5 nanosheet catalyst prepared by encapsulation showed the stable performance with~88% ethanol conversion and~65% H_(2) yield achieved during a 48-h longevity test at 550-C.

Brief review of hydrocarbon-reforming catalysts map for hydrogen production

Hydrogen energy,the cleanest fuel,presents extensive applications in renewable energy technologies such as fuel cells.However,the transition process from carbon-based(fossil fuel)energy to desired hydrogen energy is usually hindered by inevitable scientific,technological,and economic obstacles,which mainly involves complex hydrocarbon reforming reactions.Hence,this paper provides a systematic and comprehensive analysis focusing on the hydrocarbon reforming mechanism.Accordingly,recent related studies are summarized to clarify the intrinsic difference among the reforming mechanism.Aiming to objectively assess the activated catalyst and deactivation mechanism,the rate-determining steps of reforming process have been emphasized,summarized,and analyzed.Specifically,the effect of metals and supports on individual reaction processes is discussed followed by the metalsupport interaction.Current tendency and research map could be established to promote the technology development and expansion of hydrocarbon reforming field.This review could be considered as the guideline for academics and industry designing appropriate catalysts.

Steam Reforming of Dimethyl Ether over Coupled Catalysts of CuO-ZnO-Al2Oa-ZrO2 and Solid-acid Catalyst

Steam reforming （SR） of dimethyl ether （DME） was investigated for the production of hydrogen for fuel cells. The activity of a series of solid acids for DME hydrolysis was investigated. The solid acid catalysts were ZSM-5 [Si/A] = 25, 38 and 50： denoted Z（Si/Al）] and acidic alumina （γ-Al2O3） with an acid strength order that was Z（25）〉Z（38）〉Z（50）〉γ-Al2O3. Stronger acidity gave higher DME hydrolysis conversion. Physical mixtures containing a CuO-ZnO-Al2O3-ZrO2 catalyst and solid acid catalyst to couple DME hydrolysis and methanol SR were used to examine the acidity effects on DME SR. DME SR activity strongly depended on the activity for DME hydrolysis. Z（25） was the best solid acid catalyst for DME, SR and gave a DME conversion〉90% IT= 240℃,n（H20）/n（DME） = 3.5, space velocity = 1179 ml.（g cat）^-1.h^-1, and P= 0.1MPa]. The influences of the reaction temperature, space velocity and feed molar ratio were studied. Hydrogen production significantly depended on temperature and space velocity. A bifunctional catalyst of CuO-ZnO-Al2O3-ZrO2 catalyst and ZSM-5 gave a high H2 production rate and CO2 selectivity.

Ni/Y_2O_3-Al_2O_3 catalysts for hydrogen production from steam reforming of ethanol at low temperature

Y2O3-Al2O3 with different mole ratios of Y：Al were prepared by co-precipitation method. Catalysts Ni/Y2O3, Ni/Al2O3 and Ni/ Y2O3-Al2O3 were prepared by impregnation method. The result of BET showed that Al2O3 with relative high surface area was in favor of Ni distribution, whilst the TPR test demonstrated that composite support had appropriate synergistic effect between active constituent and sup-port, and NiO could be reduced more easily than loaded on the single support. H2-TPD test indicated that the catalyst NYA11 had lots of ac-tivity sites where H could be desorbed easily, which led to hydrogen-rich production over the catalyst. Composite support catalysts exhibited high activity for ethanol steam reforming （SRE）, and the supported catalyst with composite of 1：1 mole ratio of Y：Al exhibited the optimum catalytic properties for SRE. Ethanol could be completely converted over catalyst NYA11 even at 450 °C, and there had no inactivation after 60 h continuous reaction, hydrogen yield appeared maximum 35.9% at 400 ℃, and tended to increase with increasing H2O/EtOH molar ratio and feed flow rate.

Autothermal reforming of biogas over a monolithic catalyst

This study focused on measurement of the autothermal reforming of biogas over a Ni based monolithic catalyst. The effects of the steam/CH4 （S/C） ratio, O2/CH4 （O2/C） ratio and temperature were investigated. The CH4 conversions were higher under all examined temperatures than the equilibrium conversion calculated using the blank outlet temperature, because the catalyst layer was heated by the exothermic catalytic partial oxidation reaction. The CH 4conversion increased with increasing O2/C ratio. Moreover, the CH4 conversion was higher than the equilibrium conversion calculated using the blank outlet temperature for O2/C〉0.42 and reached about 100% at O2/C=0.55. However, the hydrogen concentration decreased for O2/C〉0.45 because hydrogen was combusted to steam in the presence of excess oxygen. On the other hand, the hydrogen and CO2 concentrations increased and the CO concentration decreased with increasing SIC ratio. As a result, it was found that the highest hydrogen concentrations and CH4 conversions were attained at the O2/C ratios of 0.45-0.55 and the SIC ratios of 1.5-2.5. Moreover, the H2/CO ratio could also be controlled in the range from about 2 to 3.5 to give at least 90% CH4 conversion, by regulating the O2/C or S/C ratios.

Improved catalytic performance of Ni catalysts for steam methane reforming in a micro-channel reactor

Milliseconds process to produce hydrogen by steam methane reforming （SMR） reaction, based on Ni catalyst rather than noble catalyst such as Pd, Rh or Ru, in micro-channel reactors has been paid more and more attentions in recent years. This work aimed to further improve the catalytic performance of nickel-based catalyst by the introduction of additives, i.e., MgO and FeO, prepared by impregnation method on the micro-channels made of metal-ceramic complex substrate. The prepared catalysts were tested in the same micro-channel reactor by switching the catalyst plates. The results showed that among the tested catalysts Ni-Mg catalyst had the highest activity, especially under harsh conditions, i.e., at high space velocity and/or low reaction temperature. Moreover, the catalyst activity and selectivity were stable during the 12 h on stream test even when the ratio of steam to carbon （SIC） was as low as 1.0. The addition of MgO promoted the active Ni species to have a good dispersion on the substrate, leading to a better catalytic performance for SMR reaction.

Methanol Steam Reforming over Na-Doped ZnO-Al2O3 Catalysts

In this study, the catalyst composition in binary ZnO-Al2O3 catalyst was initially evaluated and optimized for methanol steam reforming. Then different Na contents were loaded by an incipient wetness impregnation method onto the optimized ZnAl catalyst. It was found that the activity was greatly enhanced by the modification of Na, which depended on the Na content in the catalyst. The methanol conversion was 96% on a 0.1 Na/0.4 ZnAl catalyst (GHSV = 14,040 h-1, S/C = 1.4, 350°C), which was much higher with respect to a Na-free 0.4 ZnAl catalyst (74%). The remarkable improvement of activity was attributed to a weakening of the C-H bonds and clear of hydroxyl group by the Na dopant leading to an accelerated dehydrogenation of the reaction intermediates formed on ZnAl2O4 spinel surface and thus the overall reaction.

Study on Performance of Laminated Porous Metal Fiber Sintered Felt as Catalyst Support for Methanol Steam Reforming Microreactor

In this study, the laminated porous metal fiber sintered felt(PMFSF) functioning as catalyst support was used in a cylindrical methanol steam reforming(MSR) microreactor for hydrogen production. The PMFSF was fabricated by the low temperature solid-phase sintering method using metal fibers such as copper fibers and aluminum fibers which are obtained by the multi-tooth cutting method. The two-layer impregnation method was employed to coat Cu/Zn/Al/Zr catalyst on the PMFSF. The effect of fiber material, uniform porosity and gradient porosity on the performance of methano steam reforming microreactor was studied by varying the gas hourly space velocity(GHSV) and reaction temperature. Our results showed that the loading strength of porous copper fiber sintered felt(PCFSF) was better than porous aluminum fiber sintered felt(PAFSF). Under the same reaction conditions, the PCFSF showed higher methanol conversion and more H_2 output than PAFSF. Moreover, the gradient porosity(Type 5: 90%×80%×70%) of PMFSF used as the catalyst support in microreactor demonstrated a best reaction performance for hydrogen production.

Oxygen promoted hydrogen production from formaldehyde reforming with oxide-derived Cu nanowires at room temperature

This work demonstrates a two-step method to produce oxide-derived Cu nanowires on Cu mesh surface to offer a monolithic catalyst that outstandingly improves the hydrogen production from reforming formaldehyde and water under ambient conditions.Our results not only reveal that the special oxidederived nanostructure can significantly improve the formaldehyde reforming performance of Cu,but also display that the hydrogen production has a linear relationship with oxygen pressure.Specially,a maximum of 36 times increment in hydrogen generation rate is observed than that without oxygen during the reaction.Density functional theory calculations show that the formaldehyde molecule is adsorbed on Cu surface only when the adsorbed oxygen is in adjacency,and hydrogen release process is the ratedetermining step.This work highlights that the activity of deliberately synthesized catalyst can further be promoted by dynamic chemical modulation of surface states during working.

Hydrogen production by steam reforming of ethanol over copper doped Ni/CeO_2 catalysts

High surface area CeO2 was prepared by the surfactant-assisted route and was employed as catalyst support. The 0-3 at.% Cu doped Cu-Ni/CeO2 catalysts with 10 wt.% and 15 wt.% of total metal loading were prepared by an impregnation-coprecipitation method. The influence of Cu atomic content on the catalytic performance was investigated on the steam reforming of ethanol （SRE） for H2 production and the catalysts were characterized by N2 adsorption, inductively coupled plasma （ICP）, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, temperature-programmed rerduction （TPR） and H2-pulse chemisorption techniques. The activity and products distribution behaviors of the catalysts were significantly affected by the doped Cu molar content based on the promotion effect on the dispersion of NiO particles and the interactions between Cu-Ni metal and CeO2 support. Significant increase in the ethanol conversion and hydrogen selectivity were obtained when moderate Cu metal was doped into the Ni/CeO2 catalyst. Over both of the 10Ni98.5Cu1.5/CeO2 and 15Ni98.5Cu1.5/CeO2 catalysts, more than 80% of ethanol conversion and 60% of H2 selectivity were obtained in the ethanol steam-reforming when the reaction temperature was above 450 ℃.

Glycerol steam reforming over hydrothermal synthetic Ni-Ca/attapulgite for green hydrogen generation

Glycerol steam reforming(GSR)is one of the promising technologies that can realize renewable hydrogen production and efficient utilization of crude glycerol.To illuminate the functions of Ca content(3%,6%,9%,and 12%,by mass)and preparation method for Ni/ATP catalyst structure and its catalytic behaviors,the Ni-xCa/ATP(x=3%,6%,9%,and 12%,by mass)catalysts are prepared by co-impregnation(ci)and hydrothermal synthesis(hs)method and then tested in GSR.Characterization results of XRD,N_(2) adsorption–desorption,H_(2)-TPR,HRTEM,XPS,and NH_(3)/CO_(2)-TPD demonstrate that the combined effect between appropriate Ca additive(6%,by mass)and hs enhance catalyst reducibility,uniform distribution of Ca additive and nickel species over ATP,and adsorption for CO_(2).This attributes to hs method protects the ATP framework through suppressing the interaction of Ca with ATP and promotes the formation of NiCaOx interface sites.Therefore,Ni-6Ca/ATP-hs exhibits the highest conversion(86.77%)of glycerol to gas product and H_(2) yield(76.17%)and selectivity(58.56%)during GSR.Furthermore,XRD,HRTEM,TGDTG and Raman analyses confirm that Ni-6Ca/ATP-hs also reveals outstanding anti-sintering and coke resistance.In addition,the structural evolution process of Ni/ATP catalyst with Ca introduction and hs method is presented.Considering the high performance,simple preparation process and low cost,the as-prepared catalyst providing new opportunities for utilization of glycerol derived from biodiesel industry.

Production of Synthesis Gases from Ethanol Steam Reforming Process

In this study, the production of synthesis gases has been purposed under between 250oC - 700oC and 1 - 2 bars pressures. The research was conducted over a commercial BASF catalyst and a laboratory prepared catalyst. The catalyst has a content of different substances including basically NiO/Al2O3 and some additionals (Ca, Mg, Cr, Si). The experimental measurements were carried out within a recently developed experimental equipment which can be operated up to 1200o and 1 to 3 bars pressures. The study was conducted over a commercial BASF catalyst and a laboratory prepared catalyst under different ethanol/water ratios, temperatures, and catalyst loads. Under the condition when ethanol/water ratios were decreased from 1/2 to 1/10, it was observed that hydrogen ratios increased in exit gas composition of the reactor. With increments in catalyst loads from 1 to 5 grammes, hydrogen ratios in exit gas composition gradually increased. Reaction of ethanol-steam reforming started nearly at 300oC, and when temperature increments continued further up to 700oC, hydrogen yields in exit gas compositions of the reactor increased significantly to a range of 70% - 80%. In the case of using commercial BASF catalyst, hydrogen ratios in exit gas composition were found slightly higher than laboratory prepared catalyst. According to our observations, life time of laboratory prepared catalyst was found higher than the commercial BASF catalyst. In this study which kinetic measurements were applied, some kinetic parameters of ethanol-steam reaction were calculated. The mean activation energy of ethanol consumptions at 573oK - 973oK was found as 26.87 kJ/mol, approximately. All kinetic measurements were analyzed with a first order reaction rate model. In this study, some diffusion limitations existed, however, overall reaction was chemically controlled.

甲醇水蒸气重整制氢催化剂的研究进展

甲醇作为一种常温常压下稳定的液相储氢介质,具有高的氢碳比、价格低廉、储运方便等优势。通过甲醇重整制氢来替代传统碳氢化合物的催化重整过程是实现氢能绿色制取和高效储运的重要手段。本文首先介绍了甲醇重整制氢反应的机理及特点;然后从单金属、双金属以及金属价态调控方面综述了金属活性位点的结构优化策略;接着从载体元素掺杂、缺陷位点调控以及载体晶相控制方面阐述了金属-载体界面结构调控策略;进一步从载体诱导活化以及金属位点缓释方面论述了活性位点重构策略;最后对未来开发高性能催化剂的制备策略及其揭示构效关系所采用的表征技术和理论计算方法进行了展望。

Ni/ZrO_(2)-Al_(2)O_(3)催化剂催化沼气蒸汽重整制氢性能研究

沼气蒸汽重整是重要的制氢方式,开发高效稳定的催化剂是其规模化应用的重要环节。基于此,采用连续浸渍法制备了一系列基于ZrO_(2)-Al_(2)O_(3)复合载体的Ni基催化剂,对其进行了沼气蒸汽重整制氢催化性能测试。利用N_(2)吸/脱附、XRD等表征方法,分析了催化剂的织构性质、晶相组成等。探究了催化剂的物理结构和化学性质对沼气蒸汽重整制氢的影响机制,并探讨了焙烧温度与金属助剂Fe对催化剂催化性能的影响。结果表明,在700°C、空速12000 h^(-1)条件下,焙烧温度为550°C制得的Ni/ZrO_(2)-Al_(2)O_(3)表现出突出的催化性能,CH_(4)转化率和H_(2)产率分别稳定在89.94%和81.49%。ZrO_(2)-Al_(2)O_(3)复合载体相比于Al_(2)O_(3)载体增大了催化剂的比表面积,促进了平均粒径较小的Ni在载体表面的高度分散,进而提高了催化剂的催化沼气蒸汽重整制氢性能。焙烧温度可以调控催化剂的比表面积和孔体积,焙烧温度为550°C制得的Ni/ZrO_(2)-Al_(2)O_(3)的比表面积和孔体积比焙烧温度为700°C制得的Ni/ZrO_(2)-Al_(2)O_(3)大。Fe与ZrO_(2)的耦合改性提升了催化剂的还原性能,生成了更多高活性Ni^(0),有利于甲烷干重整制氢反应的发生,调控了气体产物中的n_(H_(2))/n_(CO)。

Ni-Pt/MgAl_(2)O_(4)双金属催化剂构筑及其对不同构型烃类蒸汽重整制氢性能的影响

航空煤油成分复杂,由上百种不同构型的烃类组成,然而正构烷烃、异构烷烃、环烷烃和芳香烃这几类主要组分的构型和性质差异甚大,导致其蒸汽重整反应特性存在较大差异。本论文在前期研发Ni/MgAl_(2)O_(4)基础上,引入Pt构建Ni-Pt双金属催化剂,系统考察了该催化剂对不同构型组分重整反应性能的差异,并对不同构型组分在该催化剂上的重整反应路径进行了阐述。结果表明:液相还原法引人Pt能够使双金属催化剂具有合适的酸性和良好的金属Ni分散性,Ni-Pt两种金属协同效应,不仅能够提高单Ni催化剂活性,同时能够减少Ni烧结,优化催化剂稳定性;另外,不同构型组分在双金属催化剂上的重整性能具有显著差异,其中正癸烷重整的产气率以及H,选择性较为优异。不同构型烃类燃料的反应活性为:甲基环已烷>正癸烷>乙苯。由于甲基环已烷在反应过程中C-C键键能弱,易开环形成链状自由基与水发生重整反应,乙苯具有芳香烃结构且不易开环,重整反应所需能量较高。

基于重整制氢技术的整体式催化剂研究进展

整体式催化剂具有高机械强度、高通量、低压降等特点,已成为重整制氢催化剂的研究热点。系统综述了整体式重整制氢催化剂的组成及其制备方法,分析了其结构特性,重点阐述了不同活性金属整体式催化剂在制氢领域的应用,展望了该领域未来可深入研究的方向。