Carbon dioxide reforming of methane in kilohertz spark‐discharge plasma at atmospheric pressure

The spark‐discharge plasma, generated between tubular and rotary‐disc electrodes using a sine‐wave high voltage with 5 kHz frequency, was explored for CO₂ reforming of CH₄. Based upon the investigation on the effects of specific energy input and CO₂/CH₄ ratio, the energy costs (EC) and fuel‐production efficiencies (η) at various CO₂/CH₄ ratios (r) in the same conversion range were compared and accordingly their sequences were given: EC (r = 0.5) and EC (r = 3) are the lowest; η(r = 0.5) is the highest. Compared with other nonthermal discharge techniques, the kilohertz spark discharge exhibits low EC and high fuel‐production efficiency, especially at high total‐carbon conversions. Preliminary investigation on partial oxidation and CO₂ mixed reforming at (O₂ + CO₂)/CH₄ = 0.5 exhibited high H₂/CO ratio (nearly 2) and low total‐carbon EC (0.59–0.96 MJ/mol, 58–77% of total‐carbon conversion, and O₂/(CO₂ + O₂) = 0.8). © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Dry reforming of methane to synthesis gas over supported molybdenum carbide catalysts

The dry reforming of methane at elevated pressure over supported molybdenum carbide catalysts, prepared from oxide precursors using ethane TPR, has been studied. The relative stability of the catalysts is Mo₂C/Al₂O₃>Mo₂C/ZrO₂>Mo₂C/SiO₂>Mo₂C/TiO₂, and calcination of the oxide precursor for short periods was found to be beneficial to the catalyst stability. Although the support appears to play no beneficial role in the methane dry reforming reaction, the alumina-supported material was stable for long periods of time; this may be important for the production of pelletised industrial catalysts. The evidence suggests that the differences in the stabilities may be due to interaction at the precursor stage between MoO₃ and the support, while catalyst deactivation is due to oxidation of the carbide to MoO₂, which is inactive for methane dry reforming.     

Mechanistic aspects of carbon dioxide reforming of methane to synthesis gas over Ni catalysts

A study of the kinetic isotope effect (CH₄/CO₂ CD₄/CO₂) for carbon dioxide reforming of methane to synthesis gas shows that an isotope effect exists with k_{CH 4}/k_{CD 4} ratio of 1.05–1.97, depending on reaction temperature and catalyst applied. The attainment of stable performance over Ni/La₂O₃ catalyst is found to be related to the strong chemisorption of CO₂, weak chemisorption of CH₄ and slow rate of CH_x formation, and fast rate for CH_x removal by oxidation.     

Intrinsic kinetics of nickel/calcium aluminate catalyst for methane steam reforming

A new catalyst for steam reforming of methane based on nickel/calcium aluminate is prepared. The new catalyst has shown stability and high activity at low steam to methane ratios. In this paper the intrinsic rate equations are derived and parameters estimation made. The rate equations show non-monotonic dependence on steam partial pressure. The rate equations also show that the primary product is CO₂ while CO is formed via the reverse water-gas shift reaction. The mechanism proposed and the rate equations obtained indicate that it may be essential to propose specific rate models for any given catalyst rather than generalized mechanism and rate models.     

助剂MgO对甲烷二氧化碳重整Co/BaTiO3催化剂催化性能的影响

采用溶胶-凝胶法在Co/BaTiO3催化剂中引入助剂MgO,考察了其对甲烷二氧化碳重整Co/BaTiO3催化剂的催化反应性能的影响,利用X射线衍射仪(XRD)、H2程序升温还原(H2-TPR)对催化剂进行了表征,结果表明,助剂MgO使钴催化剂中的活性Co2O3组分增多,还原性和分散性能较好;在n(CO2)∶n(CH4)为1∶1、气相空速(GHSV)为12 000 h-1、反应温度为700℃的条件下,催化剂Co-MgO/BaTiO3表现出良好的催化性能,且反应初期甲烷转化率可达到94.87%,CO选择性可达85.21%,H2收率可达74.08%。     

Investigating dry reforming of methane with spatial reactor profiles and particle‐resolved CFD simulations

Dry reforming of methane (DRM) over nickel in a fixed‐bed reactor of spheres was studied experimentally and with CFD simulations. Temperature and mole fraction profiles were measured in a dedicated profile reactor as function of axial coordinate. Particle‐resolved CFD simulations took into account conjugate heat transfer, surface‐to‐surface radiation, and surface reactions described by microkinetics. Energy transport of CFD simulations were verified by studying heat transfer without chemical reactions. DRM experiments could not be reproduced with the original microkinetics formulation, even with the axial temperature profile applied. A detailed analysis of the microkinetics showed that thermodynamic inconsistencies are present, which are amplified by high surface coverage of CO*. After modifying the mechanism the experiments could be reproduced. This study shows how complex interactions between local transport phenomena and local kinetics can be quantified without relying on transport correlations. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4436–4452, 2016     

Effect of particle shape on fluid flow and heat transfer for methane steam reforming reactions in a packed bed

Numerical simulations of a cylindrical packed bed with tube to particle diameter ratio of 1.4, containing 10 particles, were performed to understand the effect of particle shape on pressure drop, heat transfer and reaction performance. Six particle shapes namely, cylinder as the reference, trilobe and daisy having external shaping, hollow cylinder, cylcut, and 7‐hole cylinder including internal voids were chosen. Methane steam reforming reactions were considered for the heat transfer and reaction performance evaluation. The present study showed that the external shaping of particles offered lower pressure drop, but lower values of effectiveness factor indicating strong diffusion limitations. The internally shaped particles offered increased surface area, led to higher effectiveness factor and allowed to overcome the diffusion limitations. The effective heat transfer and effectiveness factor of the trilobe‐shaped particle per unit pressure drop was found to be the best among the particle shapes considered in the present work. © 2016 American Institute of Chemical Engineers AIChE J, 63: 366–377, 2017     

CH4与CO2催化重整制合成气研究进展

本文综述了CH4与CO2重整制合成气的研究进展,对重整催化剂、重整反应机理及重整动力学进行了评述。     

甲烷与二氧化碳催化重整制取合成气的研究进展

综述了甲烷与二氧化碳催化重整制取合成气的最新研究进展,比较了不同类型的催化剂在重整反应过程中的性能差异,分析了催化剂的积炭过程和重整反应机理,对非常规供能方式进行了阐述,指出了甲烷与二氧化碳催化重整制取合成气的研究方向。     

Modulating morphology and textural properties of ZrO2 for supported Ni catalysts toward dry reforming of methane

This work presents a facile and efficient approach to modulate morphology and textural properties of ZrO₂ through ammonium fluoride‐urea assisted hydrothermal (FUAH) method with diverse parameters including molar ratio of NH₄F to zirconium (n_f/z), molar ratio of urea to zirconium (n_u/z), hydrothermal temperature (T_hydroth), and hydrothermal time (t_hydroth), which serve as support for supported Ni catalysts toward dry reforming of methane (DRM) to produce synthesis gas. The plausible mechanism for forming ZrO₂ supports with different morphologies under diverse hydrothermal conditions was proposed. Various characterization techniques were employed to investigate the effect of preparation parameters on the morphology and textural properties of the as‐synthesized ZrO₂ supports, as well as to reveal the structure‐performance relationship of the Ni/ZrO₂ catalysts prepared by L‐arginine assisted incipient wetness impregnation method toward DRM reaction. The developed supported Ni catalyst on hierarchically structured ZrO₂ with pinecone shape prepared by FUAH method (Ni/ZrO₂‐FUAH) demonstrates higher activity and stability for DRM than that on ZrO₂ prepared by traditional hydrothermal method (Ni/ZrO₂‐H). The higher activity of Ni/ZrO₂‐FUAH than Ni/ZrO₂‐H can be ascribed to the higher Ni dispersion, smaller Ni crystalline size, and enhanced reducibility of NiO, significantly affected by morphology of support, as well as the higher coke‐resistance catalytic stability can be ascribed to smaller Ni particle size and stronger Ni‐support interaction, strongly dependent on morphology and textural properties of ZrO₂ supports that affected by FUAH process parameters. The outstanding catalytic performance of the developed Ni/ZrO₂‐FUAH catalyst allows it to be a promising candidate for synthesis gas production through DRM reaction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2900–2915, 2017     

Model‐based optimization of hydrogen generation by methane steam reforming in autothermal packed‐bed membrane reformer

An autothermal membrane reformer comprising two separated compartments, a methane oxidation catalytic bed and a methane steam reforming bed, which hosts hydrogen separation membranes, is optimized for hydrogen production by steam reforming of methane to power a polymer electrolyte membrane fuel cell (PEMFC) stack. Capitalizing on recent experimental demonstrations of hydrogen production in such a reactor, we develop here an appropriate model, validate it with experimental data and then use it for the hydrogen generation optimization in terms of the reformer efficiency and power output. The optimized reformer, with adequate hydrogen separation area, optimized exothermic‐to‐endothermic feed ratio and reduced heat losses, is shown to be capable to fuel kW‐range PEMFC stacks, with a methane‐to‐hydrogen conversion efficiency of up to 0.8. This is expected to provide an overall methane‐to‐electric power efficiency of a combined reformer‐fuel cell unit of ～0.5. Recycling of steam reforming effluent to the oxidation bed for combustion of unreacted and unseparated compounds is expected to provide an additional efficiency gain. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Comparative study of atmospheric and high pressure CO2 reforming of methane over Ni/MgO-AN catalyst

Catalytic activity of Ni/MgO-AN prepared from alcogel derived MgO was studied for the dry reforming of methane under atmospheric as well as high pressure (1.5 MPa). Different catalytic performances are observed in the atmospheric and high-pressure reactions; while the catalyst was highly active and extremely stable under atmospheric pressure it shows a self-stabilization process under high pressure. The self-stabilization process was characterized initially by a decrease in deactivation rate with increasing the reaction time-on-stream (TOS) up to ca. 12 h and then by a thereafter stabilization during the reaction. Characterizations of the coked catalyst with TPO, TEM, SEM, TPH and XRD techniques detected very little carbon deposits (ca. 0.2 wt% of the catalyst charge) on the used catalyst under atmospheric pressure. In contrast, large amount of whisker carbon deposit (ca. 100 wt% of the catalyst charge) were formed on the used catalyst under high pressure. In the high-pressure reaction, the activity decline during the initial stage was closely related to the amount of carbon deposits on the catalyst, which also became stabilized after the catalyst had served the reaction for ca. 12 h. The carbon deposits on the used catalyst in the high-pressure reaction contained two different components (-carbon and -carbon) while the carbon deposits in the atmospheric pressure reaction were in the form of -carbon. No notable sintering of metallic nickel was detected by XRD on the used catalyst in the reaction under atmospheric pressure whereas unavoidable sintering of metallic Ni particles happened within the very first hours of the high-pressure reaction.     

Catalytic properties of Rh, Ni, Pd and Ce supported on Al-pillared montmorillonites in dry reforming of methane

A natural Maghnia clay was pillared by Al₁₃ and impregnated by 3–10 wt.% Me (Me = Rh, Ni, Pd, Ce) to be used as catalysts in the reforming of methane with carbon dioxide to synthesis gas. The structural and textural properties of materials calcined at 450 °C were determined by several techniques (XRD, FT-IR, ²⁷Al magic angle spinning (MAS) NMR, X-ray photoelectron spectroscopy (XPS), BET, thermogravimetric analysis (TGA)–DSC, H₂-temperature programmed reduction (TPR) and NH₃-TPR). Although impurities are present in the Al-pillared layered clay (PILC) support, most properties are close to those of pure Al-pillared Na-montmorillonite. Impregnation and calcination leads to the plugging of most micropores by clusters or microparticles of oxides. The NMR resonances of Al_VI and Al_IV specie are not modified after impregnation, and Al_VI/Al_IV ratio only varies on loading when compared to Al-PILC. Catalytic experiments show that the most active catalyst is 3% Rh/Al-PILC on which 88 mol.% of methane is converted at 650 °C with a minimum amount of carbon deposit. The conversions decrease along the 3% Rh ≈ 10% Ni > 3% Pd > 3% Ni > 3% Ce series. The H₂/CO ratio amounts to 1.1 with Rh and to 0.85 with Pd which are metallic at the temperature of reaction, but it has a lower value with Ni and Ce due to the RWGS reaction known to proceed in the presence of oxides.     

Ni-Fe/BaTiO3-γ-Al2O3催化剂在低温条件下CO2和CH4重整中的应用

采用等体积浸渍法制备了一系列不同Ni和Fe添加量的Ni-Fe/BaTiO3/γ-Al2O3双金属催化剂,并在固定床反应装置上考察了在873～1 073 K温度范围内催化剂对CO2和CH4重整反应的催化活性。实验结果表明:Ni、Fe负载质量分数均为5.0%的Ni-Fe/BaTiO3/γ-Al2O3催化剂活性最好。通过TPR、TPD和TPO表征并与单金属催化剂Ni/BaTiO3/γ-Al2O3相比,Ni-Fe/BaTiO3/γ-Al2O3催化剂具有更高的催化活性、脱附和抗积炭性能。     

甲烷自热重整制氢技术的研究进展

综述了甲烷自热重整反应制氢的研究进展情况,介绍了催化剂的活性组分、助催化剂、载体、钙钛矿型催化剂的研究现状以及新的研究动向,并对积碳的形成及消除进行了简单介绍;另外,对金属膜分离法、水煤气变换法及一氧化碳选择性氧化法等氢气纯化方法进行了讨论,指出钯膜反应器的甲烷转化率高,且能直接得到纯净的氢气。     

Beneficial effects of the use of a nickel membrane reactor for the dry reforming of methane: Comparison with thermodynamic predictions

The development of a nickel composite membrane with acceptable hydrogen permselectivity at high temperature in a membrane reactor for the highly endothermic dry reforming of methane reaction was the purpose of this work. A thin, catalytically inactive nickel layer, deposited by electroless plating on asymmetric porous alumina, behaved simply as a selective hydrogen extractor, shifting the equilibrium in the direction of a higher hydrogen production and methane conversion. The main advantage of such a nickel/ceramic membrane reactor is the elimination or limitation of the side reverse water gas shift reaction. For a Ni/Al₂O₃ catalyst, containing free Ni particles, normally sensitive to coking, the use of the membrane reactor allowed an important reduction of carbon deposition (nanotubes) due to restriction of the Boudouard reaction. For a Ni–Co/Al₂O₃ catalyst, where the metallic nickel phase was stabilized by the alumina, the selective removal of the hydrogen significantly enhanced both methane conversion (+67% at 450 °C, +22% at 500 °C and +18% at 550 °C) and hydrogen production (+42% at 450 °C, +32% at 500 °C and +22% at 550 °C) compared to the results obtained for a packed-bed reactor. The hydrogen selectivity during the catalytic tests at 550 °C, maintained with constant separation factors (7 for H₂/CH₄, 8 for H₂/CO and 10 for H₂/CO₂), higher than Knudsen values, attested to the high thermal stability of the nickel composite membrane.     

Catalytic test of supported Ni catalysts with core/shell structure for dry reforming of methane

Supported nickel catalysts with core/shell structures of Ni/Al₂O₃ and Ni/MgO-Al₂O₃ were synthesized under multi-bubble sonoluminescence (MBSL) conditions and tested for dry reforming of methane (DRM) to produce hydrogen and carbon monoxide. A supported Ni catalyst made of 10% Ni loading on Al₂O₃ and MgO-Al₂O₃, which performed best in the steam reforming of methane (97% methane conversion at 750 °C) and in the partial oxidation of methane (96% methane conversion at 800 °C), showed also good performance in DRM and excellent thermal stability for the first 150 h. The supported Ni catalysts Ni/Al₂O₃ and Ni/MgO-Al₂O₃ yielded methane conversions of 92% and 92.5%, respectively and CO₂ conversions of 95.0% and 91.8%, respectively, at a reaction temperature of 800 °C with a molar ratio of CH₄/CO₂ = 1. Those were near thermodynamic equilibrium values.     

Nano‐engineered nickel catalysts supported on 4‐channel α‐Al2O3 hollow fibers for dry reforming of methane

A nickel (Ni) nanoparticle catalyst, supported on 4‐channel α‐Al₂O₃ hollow fibers, was synthesized by atomic layer deposition (ALD). Highly dispersed Ni nanoparticles were successfully deposited on the outside surfaces and the inside porous structures of hollow fibers. The catalyst was employed to catalyze the dry reforming of methane (DRM) reaction and showed a methane reforming rate of 2040 Lh^?1gNi^?1 at 800°C. NiAl₂O₄ spinel was formed when Ni nanoparticles were deposited on alpha‐alumina substrates by ALD, which enhanced the Ni‐support interaction. Different cycles (two, five, and ten) of Al₂O₃ ALD films were applied on the Ni/hollow fiber catalysts to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Both the catalyst activity and stability were improved with the deposition of Al₂O₃ ALD films. Among the Al₂O₃ ALD coated catalysts, the catalyst with five cycles of Al₂O₃ ALD showed the best performance. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2625–2631, 2018     

Novel circulating fast fluidized-bed membrane reformer for efficient production of hydrogen from steam reforming of methane

The coupling of steam reforming and oxidative reforming of methane for the efficient production of hydrogen is investigated over Ni/Al₂O₃ catalyst in a novel circulating fast fluidized-bed membrane reformer (CFFBMR) using a rigorous mathematical model. The removal of product hydrogen using palladium hydrogen membranes “breaks” the thermodynamic equilibrium barrier exists among the reversible reactions. Oxygen can be introduced into the adiabatic CFFBMR for oxidative reforming by direct oxygen (or air) feed and through dense perovskite oxygen membranes. The simulations show that high productivity of hydrogen can be obtained in the CFFBMR. The combination of these two different processes does not only enhance the hydrogen productivity but also save the energy due to the exothermicity of the oxidative reforming. Based on the preliminary investigations, four parameters (number of hydrogen membranes, number of oxygen membranes, direct oxygen feed rate and steam-to-carbon feed ratio) are carefully chosen as main variables for the process optimization. The optimized result shows that the hydrogen productivity (moles of hydrogen produced per hour per m³ of reactor) in the novel CFFBMR is about 8.2 times higher than that in typical industrial fixed-bed steam reformers.     

On the reported attempts to radically improve the performance of the steam methane reforming reactor

Steam reforming of light hydrocarbons is a key step for producing hydrogen and syngas for important processes in the petroleum and petrochemical industries. Since the establishment of the SMR process in 1930, research and development have led to improved catalyst performance and improved reactor tube materials. Since about 1970, new reactor configurations have been considered. The authors critically review recent attempts to radically improve the SMR reactor performance, analyze the areas of improvement and the suitability of proposed configurations for different reforming applications.