Hydrogen production from ethanol steam reforming over Rh/CeO2 catalyst

Hydrogen production from ethanol steam reforming over an Rh/CeO₂ catalyst was investigated with a stoichiometric feed composition. Ethanol was entirely converted to hydrogen and C₁ products (CO, CO₂, CH₄) at 400 °C due to the remarkable C–C bond cleavage capacity of Rh species. The Rh/CeO₂ catalyst exhibited stable activity and selectivity without the obvious deactivation during 70 h on stream test. Structural analysis of the aged catalysts indicated that the strong interaction between Rh and ceria support efficiently inhibited Rh particles sintering (stable at around 2 nm) and coke formation to guarantee catalyst stability.     

镍基乙醇水汽重整催化剂:机理、失活与构效关系

为了应对潜在的氢能利用需求,乙醇水汽重整反应受到了越来越多的关注。镍基催化剂因其高活性、高选择性以及成本优势而极具应用前景,同时在提高催化剂稳定性、降低反应温度、提高氢气收率等方面仍然有进一步发展的空间。更深入认识反应机理、失活机制和催化剂的构效关系是开发高效催化剂的关键。本文对近年来镍基乙醇重整催化剂的研究进展进行了整理总结,首先介绍了通过原位光谱、动力学以及理论计算等手段取得对反应中间物种与反应机理的新认识,分析了催化剂失活的主要原因,并且讨论了镍基催化剂的活性相、尺寸效应、助剂效应,双金属效应等问题,最后简单介绍了得益于基础研究进展的催化剂合成方面的成果,并提出对镍基乙醇水蒸气重整（ESR）剂未来发展的看法：在线/原位表征技术和理论计算将有助于真正理解镍基ESR催化剂的构效关系和反应机理,而新材料,如碳化钼的应用可能在提高催化剂反应性能方面起到作用。     

Ni-Fe/Al_2O_3催化剂催化乙醇水蒸气重整制氢研究

利用浸渍法制备了不同组成的Ni-Fe/Al2O3催化剂,对催化剂进行了X射线衍射(XRD)表征。以乙醇水蒸气重整(SRE)反应为探针,采用固定床反应器考察了催化剂组成、反应温度对活性和选择性的影响。实验结果表明,Ni-Fe/Al2O3较Ni,Fe单独担载的Ni/Al2O3,Fe/Al2O3选择性高,低温活性好,Ni是主要活性组分,Ni,Fe配比影响活性和选择性,其中Ni10Fe5性能最佳。400℃时,乙醇转化率可达100%,H2,CO和CO2选择性分别55.4%,0.86%和82.18%;450℃时,乙醇转化率为100%,H2,CO和CO2选择性分别67.18%,4.30%和91.01%,且反应温度影响SRE反应系统中各相关反应在系统中的权重。     

Hydrogen production by oxidative steam reforming of ethanol over an Ir/CeO2 catalyst

Oxidative steam reforming of ethanol over an Ir/CeO₂ catalyst was investigated. Ethanol dehydrogenation to acetaldehyde and decomposition to methane and carbon monoxide were the primary reactions at low temperatures, and complete reforming of ethanol was achieved at 773 K with hydrogen, carbon oxides and methane as the only products in the outlet stream. More importantly, stability test revealed that the Ir/CeO₂ catalyst could show rather stable catalytic performance for 60 h time-on-stream without deactivation. The improvement was attributed to the effective prevention of the sintering of the highly dispersed Ir particles through the strong interaction between Ir and CeO₂ and to the significant resistance to coke deposition due to the higher oxygen storage-release capacity of ceria.     

Co/ZrO2催化乙醇水蒸汽重整制氢反应的研究

采用浸渍-热分解-氢还原法制备Co/ZrO2催化剂,并用XRD、BET比表面、TPR、差热-热重等测试分析手段对该催化剂进行表征。采用固定床反应器考察了催化剂对乙醇水蒸汽重整制氢反应的催化性能。结果表明:700℃焙烧的ZrO2以单斜和四方相形式共存,负载Co后观察不到有四方相。3%Co/ZrO2催化剂对乙醇水蒸汽重整制氢反应表现出较高的活性。在500℃、水醇比为3∶1时,乙醇的转化率达到76.6%,H2的产率和选择性为0.57mol/mol和81.8%。反应温度升高,提高了乙醇的转化率和H2产率,同时也促进了催化剂表面的积炭。     

乙醇水蒸气重整制氢反应机理的研究进展

总结了乙醇水蒸气重整反应研究中给出的有关反应中间体存在的实验证据,就文献中有关机理的讨论作了较为详细的介绍,综述了乙醇水蒸气重整制氢过程中可能存在的反应路径。指出催化剂的组成、晶格结构、表面酸碱性、氧化还原性等因素对催化反应机理有显著影响,原料水醇比、温度、压力等反应工艺条件也会影响反应产物的选择性和平衡浓度。指出量化计算催化剂表面性质和晶格结构参数,深入研究催化反应机理,是乙醇水蒸气重整制氢的研究趋势。     

AgCl/H-ZSM-5催化分解NO反应及失活机理

采用水热分散法制备了AgCl/H-ZSM-5催化剂，并对其催化分解NO的反应进行了研究。运用X-射线衍射（XRD）、固体魔角旋转核磁共振（MASNMR）和能量色散X-射线微区分析（EDAX）对Ag-Cl/H-ZSM-5催化剂进行表征，着重阐明AgCl/H-ZSM-5催化剂在NO分解反应过程中活性相、载体的结构变化与催化分解NO反应活性的关系。     

Kinetics of steam reforming over a Ni/alumina catalyst

Steam reforming of methane over a commercially available, nickel/alumina catalyst was experimentally studied. The reactor employed for the study was made of 7 mm i.d. quartz tube and catalyst particles were 0.84-1 mm in size. The amount of catalyst charge in the reactor was around 0.3 gram. Experiments were carried out varying the steam to methane ratio in the feed gas from 1 to 10 and reaction temperature from 823 to 1073 K. Nitrogen gas was used to control partial pressure of methane and steam. Using Marquardt method reaction rate derived from the experiments was fitted to $$reaction rate = 1,527 exp( - 14,820/RT) P^{1.014} _{CH_4 } P^{ - 0.9577} _{H_2 0} $$ Thus reaction order was close to one for methane and close to minus one for steam, respectively.     

H2 production through steam reforming of ethanol over Pt/ZrO2, Pt/CeO2 and Pt/CeZrO2 catalysts

The effect of the support nature and metal dispersion on the performance of Pt catalysts during steam reforming of ethanol was studied. H₂ and CO production was facilitated over Pt/CeO₂ and Pt/CeZrO₂, whereas the acetaldehyde and ethene formation was favored on Pt/ZrO₂. According to the reaction mechanism, determined by temperature-programmed desorption (TPD) and Diffuse Reflectance Infrared Spectroscopy (DRIFTS) analysis, some reaction pathways are favored depending on the support nature, which can explain the differences observed on the resulting product distribution.     

Catalyst deactivation and regeneration in low temperature ethanol steam reforming with Rh/CeO2–ZrO2 catalysts

Rh/CeO₂–ZrO₂ catalysts with various CeO₂/ZrO₂ ratios have been applied to H₂ production from ethanol steam reforming at low temperatures. The catalysts all deactivated with time on stream (TOS) at 350 °C. The addition of 0.5% K has a beneficial effect on catalyst stability, while 5% K has a negative effect on catalytic activity. The catalyst could be regenerated considerably even at ambient temperature and could recover its initial activity after regeneration above 200 °C with 1% O₂. The results are most consistent with catalyst deactivation due to carbonaceous deposition on the catalyst.     

Steam reforming of ethanol over Pt/ceria with co-fed hydrogen

Metal/ceria catalysts are receiving great interest for reactions involving steam conversion, including CO for low-temperature water–gas shift, and the conversion of chemical carriers of hydrogen, among them methanol, and ethanol. The mechanism by which ROH model reagents are activated on the surface of the Pt/partially reduced ceria catalyst was explored using a combination of reaction testing and infrared spectroscopy. In this particular investigation, the activation and turnover of ethanol were explored and compared with previous investigations of methanol steam reforming and low-temperature water–gas shift under H₂-rich conditions, where the surface of ceria is in a partially reduced state. Under these conditions, activation of ethanol was found to proceed by dissociative adsorption at reduced defect sites on ceria (i.e., Ce surface atoms in the Ce³⁺ oxidation state), yielding an adsorbed type II ethoxy species and an adsorbed H species, the latter identified to be a type II bridging OH group. In the presence of steam, the ethoxy species rapidly undergoes molecular transformation to an adsorbed acetate intermediate by oxidative dehydrogenation. This is analogous to the conversion of type II methoxy species to formate observed in previous investigations of methanol steam reforming. In addition, although formate then decomposes in steam to CO₂ and H₂ during methanol steam reforming, in an analogous pathway for ethanol steam reforming, the acetate intermediate decomposes in steam to CO₂ and CH₄. Therefore, further H₂ production requires energy-intensive activation of CH₄, which is not required for methanol conversion over Pt/ceria.     

Ethanol steam reforming over Co-based catalysts: Role of oxygen mobility

The effect of oxygen mobility on the bio-ethanol steam reforming of ZrO₂- and CeO₂-supported cobalt catalysts was investigated. The supported catalysts were prepared by incipient wetness impregnation (IWI) and characterized through N₂ physisorption, X-ray photoelectron spectroscopy, temperature programmed oxidation, laser Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, O₂ pulse chemisorption, isotopic labeling, and transmission electron microscopy techniques at various life stages of the catalyst. The results indicated that the catalyst deactivation was due mostly to deposition of various types of carbon on the surface although cobalt sintering could also be contributing to the deactivation. The addition of ceria was found to improve the catalytic stability as well as activity, primarily due to the higher oxygen mobility of ceria.     

乙醇在Pt/ZSM-5上催化氧化动力学

在内径为4 mm的石英管燃烧器中进行了富氧条件下乙醇在Pt/ZSM-5上的催化深度氧化动力学实验,反应温度控制在428 K以下,建立了Power-rate law模型和Langmuir-Hinshelwood模型来表征乙醇的低温深度氧化反应,Power-rate law模型和Langmuir-Hinshelwood模型的活化能分别为95.96和103.72 kJ·mol^-1,乙醇和氧气的反应级数分别为0.38和1.38。Langmuir-Hinshelwood模型中,乙醇的吸附常数比氧气的吸附常数大,说明乙醇在催化剂表面的吸附能力比氧气强,提高氧气的浓度比提高乙醇的浓度更有利于提高反应速率,这一点同样反映在氧气的反应级数比乙醇的反应级数大。     

Carbon deposition and catalytic deactivation during CO2 reforming of CH4 over Co/MgO catalyst

The deactivation mechanism of Co/MgO catalyst for the reforming of methane with carbon dioxide was investigated. The conversion of CH₄ displayed a significant decrease in the initial stage caused by carbon deposition. There were two types of cokes, carbon nanotubes (CNTs) and carbon nano-onions (CNOs). The number of the CNO layers that coated on the surface of Co nanoparticles (NPs) increased rapidly in the initial reforming time, which was responsible for the deactivation of the Co/MgO catalyst. The deposition of CNOs was attributed to the oxidation of Co NPs. Therefore, the deactivation of the Co/MgO catalyst was originated from the first oxidization of the Co NPs into Co₃O₄ by O species (OH intermediate, CO₂, H₂O) during the reforming reaction, which accelerates the formation of coke that blocked the active metal, thus led to catalyst deactivation.     

Effect of ZnO facet on ethanol steam reforming over Co/ZnO

The effects of ZnO facets on ethanol steam reforming (ESR) were investigated over Co/ZnO catalysts synthesized using ZnO with different fractions of (10–10) non-polar facet. Co supported on ZnO with a higher fraction of (10–10) non-polar facet shows higher C–C cleavage activity and higher selectivity to CO₂ (lower selectivity to CO) compared with Co supported on ZnO with less (10–10) non-polar facet exposed. The improved ethanol steam reforming performances are attributed to the high fraction of metallic Co stabilized by the ZnO (10–10) non-polar facet, which enhanced C–C cleavage and water-gas-shift (WGS) activities.     

A study of the deactivation of low loading Ni/Al2O3 steam reforming catalyst by tetrahydrothiophene

The steam reforming (SR) of ethanol/phenol mixture (168 g_TOT/N m³, ethanol:phenol 2:1 mol, GHSV = 54,000 h^− 1), assumed as a model for tar mixtures, has been studied over a 5% Ni/Al₂O₃ catalyst (155 m²/g), in the presence and in the absence of 210 ppm tetrahydrothiophene (THT) as a sulphur containing contaminant. The sulphidation of the catalyst by THT has been studied by IR spectroscopy. Infrared spectra of CO adsorbed at low temperature over the oxidized, the reduced and the sulphurized catalyst have also been recorded. The catalyst acts as a bifunctional one, with the behaviour attributed to the uncovered support (alumina modified by nickel ions) at 773 K (dehydration of ethanol to ethylene, dehydrogenation to acetaldehyde and alkylation of phenol with ethanol) that fully disappears at 973 K when steam reforming occurs very selectively. By lowering back the reaction temperature, the support behaviour reappears. THT poisons selectively the Ni component, thus causing the appearance of the support behaviour also at 973 K. IR experiments show that THT deposes sulphur at the catalyst surface with the production of gas-phase 1,3-butadiene, thus converting the catalyst into a “sulphided” SR-inactive state. The steam reforming activity of the poisoned catalyst progressively reappears upon feeding back S-free feed at 973 K. IR study suggests that steam “cleans” the catalyst surface by sulphur, generating a “disordered” surface with dispersed Ni^2 + and Ni⁰ species, that could slowly re-approach the initial active state.     

Ethanol steam reforming study over ZSM-5 supported cobalt versus nickel catalyst for renewable hydrogen generation

The renewable hydrogen generation through ethanol steam reforming is one of the anticipated areas for sustainable hydrogen generation. To elucidate the role of Ni and Co with ZSM-5 support, catalysts were prepared by wet impregnation method and ethanol steam reforming(ESR) was performed. The catalysts were characterized by HR-XRD, ATR–FTIR, HR-SEM, TEM with SAED, EDAX, surface area analyzer and TPR. It had shown complete ethanol conversion at 773 K, but the selectivity in hydrogen generation was found higher for 10% Ni/ZSM-5 catalyst as compared to 10% Co/ZSM-5. The 10% Ni/ZSM-5 catalyst has about 72% hydrogen selectivity at temperature 873 K. It indicates that Ni is a more sustainable catalyst as compared to Co with ZSM-5 support for ESR. The C_2H_4 was found major undesirable products up to 823 K temperature. Nevertheless, the 10% Ni/ZSM-5 catalyst had shown its stability for high temperature(873 K) ESR performance.     

Pt/TiO_2催化二甲醚部分氧化重整制氢

二甲醚是一种理想的氢载体,可用于解决氢的储存和运输。以Pt/TiO_2为部分氧化催化剂,结合Ni/Al_2O_3重整催化剂,考察钛前驱体和焙烧温度对二甲醚部分氧化重整制氢反应的影响。结果表明,以Ti(C4H9O)4为原料制备的TiO_2为金红石相,Ti(SO4)2或Ti O(OH)2为原料制备的TiO_2为锐钛矿相;以Ti(C4H9O)4为原料制备的Pt/TiO_2-E催化剂催化性能略好,转化率接近100%,H2收率约90%,表明金红石相TiO_2负载的Pt催化剂略佳;以Ti(SO4)2为原料制备的Pt/TiO_2-S催化剂500℃焙烧可获得金红石相TiO_2。与Pt/Al_2O_3催化剂相比,Pt/TiO_2催化剂具有更好的催化性能,H2收率超过90%,而Pt/Al_2O_3催化剂H2收率约80%。