Influence of tungsten loading on CO2/O2 reforming of methane over Co‐W–promoted NiO‐Al2O3 nanocatalyst designed by sol‐gel‐plasma

Co‐W–promoted NiAl₂O₄ nanocatalyst with various amount of tungsten (0, 1, 3, and 7 wt.%) was fabricated via hybrid sol‐gel‐plasma method. The nanocatalysts were evaluated by XRD, FESEM, EDX, BET, and FTIR analyses. The samples were utilized in CO₂/O₂ reforming of methane to syngas. EDX results proved the existence of all the applied elements in synthesis. FESEM and BET results illustrated that tungsten addition led to lower surface area, larger particle size, and roughly worse particles scattering. Therefore, Co‐NiAl₂O₄ (NCW0A) presented higher yield; however, yields were reduced for the other samples due to the covering impact of tungsten. As a result of time on streams performance (2880 minutes and at 750°C), the 7 wt.% tungsten promoted sample exhibited stable but lower yield (Y_H2 = 64%). Moreover, NCW1A exhibited more stable and higher yield than NCW0A. Optimum operating parameters were obtained as GHSV = 24 l/g_cat.h, CH₄/CO₂ = 1, and CH₄/CO₂/O₂ = 1/1/0.08. TG‐DTG, EDX, and FESEM analyses were applied for the used samples. TG‐DTG graphs demonstrated that by rising of tungsten loading, lighter and lower amount of coke was formed. Some agglomerations were observed in the EDX images of NCW0A and NCW1A while lower agglomeration was found for the tungsten‐rich sample. Carbon fiber formation was detected in the FESEM images of the used NCW0A while for the others, amount of the deposited coke and carbon fibers decreased.     

Hydrogen generation via supercritical water gasification of lignin using Ni‐Co/Mg‐Al catalysts

In this study, a group of Ni‐Co/Mg‐Al catalysts was prepared for hydrogen production via supercritical water gasification of lignin. The effects of different supports and preparation methods were examined. All catalysts were evaluated under the operation conditions of 650 °C, 26 MPa, and water to biomass mass ratio of 5 in a batch reactor. The Cop.2.6Ni‐5.2Co/2.6Mg‐Al catalyst showed the best performance with highest gas yield (12.9 wt%) and hydrogen yield (2.36 mmol·g^?1). The results from catalyst characterization suggest that the properties of this type of catalyst are dependent on multiple factors including support Mg‐Al molar ratio and preparation method, and better coke resistance of the catalyst could be obtained by the preparation method of coprecipitation. Therefore, coprecipitation method should be applied for the preparation of Ni‐Co/Mg‐Al catalysts for hydrogen production via supercritical water gasification of lignin. Copyright © 2017 John Wiley & Sons, Ltd.     

Syngas and hydrogen production via stepwise methane reforming over Cu‐ferrite/YSZ

This report investigates the effect of an yttria‐stabilized zirconia (YSZ) supported Cu‐ferrite for the production of syngas and hydrogen via stepwise methane reforming and water splitting reactions. The Cu‐ferrite/YSZ samples were prepared by co‐precipitation and impregnation methods. The samples were characterized by X‐ray diffraction spectroscopy and non‐isothermal hydrogen reduction. To investigate syngas and hydrogen production reactivities, isothermal methane reforming and water splitting reactions were performed at 900 °C and 700 °C, respectively. For Cu‐ferrite/YSZ prepared by impregnation, methane conversion was maintained at high levels of ca. 85% and an H₂/CO ratio close to 2 was observed. A lower methane conversion (>30%) was observed for Cu‐ferrite/YSZ prepared by co‐precipitation. No significant deposited carbon and aggregation of Cu‐ferrite/YSZ (prepared by impregnation) were observed over 10 repeated methane reforming and water splitting reactions. Copyright © 2014 John Wiley & Sons, Ltd.     

Syngas production via dry reforming of methane over CeO2 modified Ni/Al2O3 catalysts

Syngas production via dry reforming of methane (DRM) was experimentally investigated using Ni-based catalyst. Ni/Al₂O₃ modification with CeO₂ addition and O₂ addition in the reactant were employed in this study to suppress carbon deposition and to enhance catalyst activity. It was found that DRM performance can be enhanced using CeO₂ modified Ni/Al₂O₃ catalyst due to CeAlO₃ formation. However, an optimum amount of CeO₂ loading exists to obtain the best DRM performance due to the decrease in specific surface area as the CeO₂ loading increases. Without O₂ addition, the reverse water-gas shift reaction plays an important role in DRM. It was found that CH₄ conversion and CO yield were enhanced while CO₂ conversion and H₂ yield are decreased as the CO₂ amount in feedstock increased in DRM. With O₂ addition in the fed reactant, it was found that the methane oxidation reaction plays an important role in DRM. CH₄ conversion can be enhanced by O₂ addition. However, decreases in CO₂ conversion and H₂ and CO yields occurred due to greater H₂O and CO₂ productions from the methane oxidation reaction. The thermogravimetric analysis (TGA) results showed that CeO₂ modified Ni/Al₂O₃ catalyst would have the lowest amount of carbon deposition when O₂ is introduced into the reaction.     

Cu/La2O3/Al2O3催化剂上甲醇水蒸气重整制氢反应

研究以并流共沉淀法制备Cu/La2 O3 /Al2 O3 系列催化剂催化甲醇水蒸气重整制氢反应过程 ,考察了La2 O3含量、反应温度、水醇比、液体空速 (WHSV)等因素对催化剂活性的影响。结果表明 :催化剂表现出较好的低温活性、高氢气选择性和稳定性。La2 O3 质量分数为 15 % ,在 2 5 0℃反应时 ,催化剂活性表现最佳 ,甲醇摩尔转化率为94 .5 % ,氢气选择性为 10 0 % ,CO摩尔分数为 1.0 5× 10 -7。     

The steam reforming of guaiacol for hydrogen via Ni/Al2O3: The influence of dispersion

In this paper, three Ni/Al₂O₃ catalysts with different structure were prepared by different methods. The differences between the catalysts had been compared by H₂ temperature program reduction (H₂-TPR), X-ray diffraction, thermogravimetric analysis, scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. The results showed that synthesis method had significant effect on the combination of Ni particle with carrier. The method of coprecipitation could help to improve the combination of Ni and Al₂O₃, and the effect was further enhanced after adding polyethylene glycol (PEG). Due to the enhanced interaction between the active metal and the carrier, the NiO could be easily deoxidized and hard to sinter, which could obtain smaller and more dispersed Ni particles. Moreover, the addition of PEG improved the Ni particle size and its dispersion, and promoted the formation of the unique acicular Al₂O₃. The performance of guaiacol steam catalytic reforming via different catalysts was further analyzed, and the results showed the catalyst obtained by coprecipitation method with PEG exhibited best activity with 73.8% guaiacol conversion and 23.1 wt% H₂ yield.     

Syngas production from glycerol-dry(CO2) reforming over La-promoted Ni/Al2O3 catalyst

A 3 wt% La-promoted Ni/Al₂O₃ catalyst was prepared via wet co-impregnation technique and physicochemically-characterized. Lanthanum was responsible for better metal dispersion; hence higher BET specific surface area (96.0 m² g⁻¹) as compared to the unpromoted Ni/Al₂O₃ catalyst (85.0 m² g⁻¹). In addition, the La-promoted catalyst possessed finer crystallite size (9.1 nm) whilst the unpromoted catalyst measured 12.8 nm. Subsequently, glycerol dry reforming was performed at atmospheric pressure and temperatures ranging from 923 to 1123 K employing CO₂-to-glycerol ratio from zero to five. Significantly, the reaction results have yielded syngas as main gaseous products with H₂:CO ratios always below than 2.0 with concomitant maximum 96% glycerol conversion obtained at the CO₂-to-glycerol ratio of 1.67. In addition, the glycerol consumption rate can be adequately captured using power law modelling with the order of reactions equal 0.72 and 0.14 with respect to glycerol and CO₂ whilst the activation energy was 35.0 kJ mol⁻¹. A 72 h longevity run moreover revealed that the catalyst gave a stable catalytic performance.     

Hydrogen production from glycerol steam reforming over Ni/La/Co/Al2O3 catalyst

Hydrogen production by steam reforming reaction of glycerol over Co/La/Ni-Al₂O₃ was studied in tubular fixed-bed reactor. The influences of operating parameters such as temperature, steam/carbon ratio, and weight hourly space velocity (WHSV) on hydrogen yield and carbon conversion were examined under atmospheric pressure. The results showed that carbon conversion increased with the increase of temperature and steam-to-carbon mole ratio (S/C). At 700°C, S/C=3:1, and WHSV=2.5h^?1, hydrogen yield and potential hydrogen yield were up to 77.64% and 89.64%, respectively; meanwhile, the carbon conversion reached 96.36%.     

Non-thermal plasma assisted synthesis and physicochemical characterizations of Co and Cu doped Ni/Al2O3 nanocatalysts used for dry reforming of methane

Ni/Al₂O₃ nanocatalysts doped with Co and Cu were prepared by co-impregnation and modified by non-thermal plasma. The nanocatalysts were characterized by XRD, FESEM, TEM, EDX dot-mapping, BET, FTIR, TGA-DTG, and XPS analysis. According to XRD and XPS results, good interaction between active phase and support can be observed in both Ni–Co/Al₂O₃ and Ni–Cu/Al₂O₃ nanocatalysts. A uniform morphology, high surface area, and well dispersed particles of active sites in Ni–Co/Al₂O₃ nanocatalyst were observed that shows the effect of cobalt in controlling Ni ensemble size. In contrast Ni–Cu/Al₂O₃ nanocatalyst had no homogenous dispersion of active phase due to sintering of copper particles. The activity measurements illustrated better Ni–Co/Al₂O₃ nanocatalyst activity in comparison to Ni/Al₂O₃ and Ni–Cu/Al₂O₃ in terms of CH₄ and CO₂ conversion. H₂ and CO yield were higher for Ni–Co/Al₂O₃ and higher H₂/Co ratio was obtained as well. Whereas Ni/Al₂O₃ and Ni–Co/Al₂O₃ did not experience deactivation, Ni–Cu/Al₂O₃ suffered from activity loss by ca. 22% and 16% for CH₄ and CO₂ conversion, respectively. Sintering most likely happened in Ni–Cu/Al₂O₃ nanocatalyst due to high temperature of calcination while cobalt by controlling the size of Ni particles, alternated the size of active sites to a size range in which carbon formation was suppressed. Ni/Al ratio from XPS analysis which signifies Ni dispersion on alumina support was 5.15, 9.16, and 6.35 for Ni/Al₂O₃, Ni–Co/Al₂O₃, and Ni–Cu/Al₂O₃ nanocatalysts respectively. The highest ratio of Ni/Al was for Ni–Co/Al₂O₃ nanocatalyst that shows the best coverage of support by Ni active phase in this nanocatalyst.     

Direct conversion of syngas to DME over CuO–ZnO–Al2O3/HZSM‐5 nanocatalyst synthesized via ultrasound‐assisted co‐precipitation method: New insights into the role of gas injection

In this study, direct synthesis of dimethyl ether (DME) is conducted over a bifunctional CuO–ZnO–Al₂O₃/H Zeolite Socony Mobil‐5 (HZSM‐5) nanocatalyst. A hybrid method of ultrasound‐assisted co‐precipitation is used for the synthesis of catalysts, and the effect of gas injection during sonication is investigated. The physicochemical characteristics of the catalysts are analysed by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), particle size distribution (PSD), energy dispersive X‐ray (EDX), Brunauer–Emmett–Teller (BET) and Fourier‐transformed infrared (FTIR) methods. In the absence of gas injection, the acetate‐based catalysts have a better morphology and higher surface area than the nitrate‐based catalyst. Gas injection significantly changes the morphology and structural properties of the acetate‐based catalyst. High surface area, narrow PSD and better dispersion of small CuO crystals are obtained in a gas‐injected synthesized sample. DME synthesis experiments showed that the CO conversion and DME selectivity are correlated with surface area, nanocatalyst particle size and its dispersion. The gas‐injected CuO–ZnO–Al₂O₃/HZSM‐5 nanocatalyst that has the highest surface area and the smallest dispersed particles showed more than 70% DME selectivity. The gas‐injected CuO–ZnO–Al₂O₃/HZSM‐5 nanocatalyst exhibited high stability in terms of CO conversion and DME yield over 1440‐min time on a stream test at 275°C, 40 bar and 18 000 cm³ g.h^?1. Copyright © 2014 John Wiley & Sons, Ltd.     

Promotion effect of different lanthanide doping on Co/Al2O3 catalyst for dry reforming of methane

In this paper, a series of cobalt catalysts modified by different lanthanide metals were synthesized via co-impregnation method using inexpensive industrial-grade alumina as a support for dry reforming of methane. The effect of lanthanide metals as accelerators of cobalt-based catalysts on catalytic performance and anti-coking properties was mainly investigated. The textural relationships between the catalytic performance and physicochemical properties of cobalt-based catalysts doped with different lanthanide metals were further investigated. Different characterization techniques demonstrate the positive effect of lanthanide metals on the physicochemical properties of catalysts. The results show that the electron transfer between cobalt species and lanthanide metal oxides is significantly enhanced due to the introduction of lanthanide elements. The process generates more active sites, which is favorable for the adsorption and activation of methane. In addition, the abundant medium basic sites and oxygen vacancies on the surface of cobalt-based catalysts with the effect of lanthanides promoted the adsorption and activation of carbon dioxide and the gasification of carbon accumulation, which greatly improved the anti-carbon accumulation performance of the catalysts. Therefore, the prepared cobalt-lanthanum-based catalysts showed the best catalytic effect and have great potential for application.     

Cooperation of Fe2O3@C and Co3O4/C subunits enhances the cyclic stability of Fe2O3@C/Co3O4 electrodes for lithium‐ion batteries

A Fe₂O₃@C/Co₃O₄ hybrid composite anode is synthesized via a two‐step hydrothermal method in which the acetylene carbon black component serves as a conductive matrix and as an effective elastic buffer to relieve the stress from Fe₂O₃@C and Co₃O₄/C during the electrochemical testing. The crystallinity, structure, morphology, and electrochemical performance of the composites are systematically characterized. Galvanostatic charge/discharge measurements of Fe₂O₃@C/Co₃O₄ present the excellent rate performance and cyclic stability. Its reversible capacity reaches 1478 mAh·g^?1 after 45 cycles, and it is equal to 1035 mAh·g^?1 after 350 cycles at a current density of 200 mA·g^?1. Furthermore, the changes after 30, 45, 60, 90, and 120 cycles are investigated. It is found that the electrochemical performance varies with the morphological change of the electrode surface. Correspondingly, the microstructure, cyclic voltammetry curves, and Nyquist plots significantly change as a consequence of cycling. The results of this study provide an understanding of the increased capacity and excellent cyclic performance of a new anodic material for Li‐ion batteries.     

A highly active catalyst, Ni/Ce–ZrO2/θ-Al2O3, for on-site H2 generation by steam methane reforming: pretreatment effect

The steam treatment effect has been investigated over the doubly impregnated catalyst, Ni/Ce–ZrO₂/θ-Al₂O₃, in steam methane reforming (SMR). The catalyst was remarkably deactivated by steam treatment but reversibly regenerated by H₂-reduction. XRD results showed that the steam treatment resulted in the formation of NiAl₂O₄ which is inactive for SMR but it was reversibly converted to Ni by the reduction. The reversible oxidation-reduction of Ni state was also evidenced by XPS and it was observed that the formation of NiAl₂O₄ is more favorable at higher temperature. It is most likely that the alumina support is only partially covered with Ce–ZrO₂ and most Ni directly interacts with θ-Al₂O₃ which would probably make easy formation of NiAl₂O₄ in the presence of steam alone. The results imply that, during the start-up procedure in SMR, too high concentration of steam could deactivate seriously Al₂O₃ supported Ni catalysts.     

Dry reforming of methane over nano-Mo2C/Al2O3 catalyst: Effect of carburization conditions on excess carbon deposition

In this study, temperature-programmed carburization (TPC) has been used to prepare Mo₂C/Al₂O₃ catalyst for carbon dioxide reforming of methane. Also, the effect of carburization conditions has been examined on excess carbon formation over the prepared catalysts. Minimum excess carbon of 0.51 wt% was obtained in a flow of 12.5 vol% CH₄/H₂ gas mixture, final carburization temperature of 750°C, and Mo loading of 12.5 wt%. This catalyst exhibited better initial activity due to lower excess carbon and higher carbide dispersion compared with other examined catalysts. However, the results of time on stream performance in the dry reforming of methane (DRM) revealed an increase in durability with an increase in Mo loading.     

Syngas production via the biogas dry reforming reaction over Ni supported on zirconia modified with CeO2 or La2O3 catalysts

The catalytic efficiency and bench scale time on steam stability of Ni dispersed on three commercially available catalytic supports (ZrO₂, La₂O₃–ZrO₂ and CeO₂–ZrO₂) has been studied for the dry reforming of methane (DRM) in the temperature range of 500–800 °C and a CH₄/CO₂ ratio equal to 1.5, simulating typical biogas quality. Ni supported on LaZr and CeZr carriers that obeyed enhanced basicity and oxygen ion lability values than Zr, exhibited superior catalytic efficiency and stability. A variety of techniques, namely N₂ physisorption-desorption (BET method), powder X-ray diffraction (XRD), hydrogen temperature programmed reduction (H₂-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, potentiometric titration and inductively coupled plasma emission spectroscopy (ICP), were applied for the characterization of particles morphology, textural, structural and other physical properties of the materials, as well as the type of carbon deposited on the catalytic surface after exposure to DRM reaction conditions. Post-reaction analysis of the deposited carbon on the catalysts surfaces showed that the prominent trend of the carbon deposits on the Ni/Zr and Ni/LaZr samples was to have a filamentous tube like morphology (graphite-2H). In contrast, on the Ni/CeZr used catalyst, the formation of small amount of carbon tube-like architectures was detected. The enhanced basicity and Ni dispersion of the Ni/LaZr and Ni/CeZr samples as well as the high oxygen ion lability of the lattice oxygen in the latter, were considered to be the major factors involved in the superior efficiency and durability of these samples in comparison to Ni/Zr sample.     

基于Ni/Al2O3整体式催化剂的生物质气化合成气甲烷化研究

以生物质气化模拟合成气H2/CO/N2为原料气,以堇青石蜂窝陶瓷为基体制备Ni/Al2O3整体式催化剂,通过扫描电镜(SEM)、比表面积(BET)、X射线衍射(XRD)、程序升温反应法(TPR)、热重分析(TG)等表征分析手段,考察催化剂制备方法(浸渍法和溶胶-凝胶法)、温度(250~550℃)及空速GHSV(6000~14000 mL/(g·h))对催化剂甲烷化性能的影响。结果表明:浸渍法制备的Ni/Al2O3催化剂(DIP-Ni/Al2O3)与溶胶-凝胶法制备的Ni/Al2O3催化剂(SGNi/Al2O3)相比,前者甲烷化性能较好。在H2、CO、N2物质的量之比为3∶1∶1且空速为10000 mL/(g·h)条件下,浸渍法制备的Ni/Al2O3催化剂在400℃时甲烷化性能最佳,且该条件下CO转化率为98.6%,CH4选择性为90.9%。当H2、CO、N2物质的量之比为3∶1∶1且温度为400℃时,在实验空速范围内,浸渍法制备的Ni/Al2O3催化剂CO转化率和CH4选择性均基本稳定在90%,甲烷化性能较好。     

Numerical investigation of hydrogen production via autothermal reforming of steam and methane over Ni/Al2O3 and Pt/Al2O3 patterned catalytic layers

In this study a numerical analysis of hydrogen production via an autothermal reforming reactor is presented. The endothermic reaction of steam methane reforming and the exothermic combustion of methane were activated with patterned Ni/Al₂O₃ catalytic layer and patterned Pt/Al₂O₃ catalytic layer, respectively. Aiming to achieve a more compacted process, a novel design of a reactor was proposed in which the reforming and the combustion catalysts were modeled as patterned thin layers. This configuration is analyzed and compared with two configurations. In the first configuration, the catalysts are modeled as continuous thin layers in parallel, while, in the second configuration the catalysts are modeled as continuous thin layers in series (conventional catalytic autothermal reactor). The results show that the pattern of the catalyst layers improves slightly the hydrogen yield, i.e. 3.6%. Furthermore, for the same concentration of hydrogen produced, the activated zone length can be decreased by 38% and 15% compared to the conventional catalytic autothermal reforming and the configuration where the catalysts are fitted in parallel, respectively. Besides, the oxygen consumption is lowered by 5%. The decrement of the catalyst amount and the oxygen feedstock in the novel studied design lead to lower costs and compact process.     

Cu/ZnO/Al2O3催化剂涂层工艺参数的优化

针对甲醇水蒸汽重整制氢反应，研制了一种新型的适用于微槽道反应器的Cu/ZnO/Al2O3催化剂涂层。通过对其关键制备参数的优化，筛选出COAT-14-6（CuO 14wt．％，ZnO6wt．％）为性能最佳的催化剂涂层。研究发现Cu，ZnO／Al2O3涂层催化剂的活性与活性铜的表面积和催化剂的还原性密切相关。100h的连续性实验结果表明，涂覆了COAT-14-6的微槽道反应器可以与10W的燃料电池配套。     

Hydrogen production from ethanol steam reforming over Ni/SiO2 catalysts: A comparative study of traditional preparation and microwave modification methods

Four silica‐supported nickel catalysts with Ni content of 10 wt% were prepared by impregnation and coprecipitation methods with or without microwave‐assisted calcination. The prepared catalysts were characterized by some techniques (BET, XRD, TEM, XPS, H₂‐TPR, etc.) and evaluated with respect to steam reforming of ethanol (SRE) for hydrogen production. The results show that the prepared Ni/SiO₂ catalysts are all very active and selective for SRE. The high activity of the four catalysts may benefit from their high specific areas and the good dispersion of active components on the carrier. The rate of carbon deposition decreases with reaction temperature especially below 450 °C. The maximum hydrogen yield of 4.54 mol H₂/mol EtOH‐reacted can be obtained over the Ni/SiO₂ catalyst by the microwave‐assisted coprecipitation method at a reaction temperature of 600 °C, EtOH/H₂O molar ratio of 1:12, liquid hourly space velocity of 11.54 h^?1 and time on stream within 600 min. The Ni/SiO₂ catalysts with microwave modification exhibits better performances of hydrogen production, stability and resistance to carbon deposition than that without microwave modification preparation, which is mainly attributed to that the microwave‐assisted treatment can decrease the catalyst acidity and enhance the interaction between metal support. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface modification of LiNi0.5Co0.2Mn0.3O2 cathode materials with Li2O‐B2O3‐LiBr for lithium‐ion batteries

LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode material suffers from phase transformation and electrochemical performance degradation as its main drawbacks, which are strongly dependent on the surface state of NCM523. Herein, an effective surface modification approach was demonstrated; namely, the fast lithium‐ion conductor (Li₂O‐B₂O₃‐LiBr) was coated on NCM523. The Li₂O‐B₂O₃‐LiBr coating layer as a protecting shell can prevent NCM523 particles from corrosion by the acidic electrolyte, leading to a superior discharge capacity, rate capability, and cycling stability. At room temperature, the Li₂O‐B₂O₃‐LiBr–coated NCM523 exhibited an excellent capacity retention of 87.7% after 100 cycles at the rate of 1 C, which is remarkably better than that (29.8%) without the uncoated layer. Furthermore, the coating layer also increased the discharge capacity of NCM523 cathode material from 68.7 to 117.0 mAh g^?1 at 5 C. Those can be attributed to the reduction in the electrode polarization and improvement in the electrode conductivity, which was supported by electrochemical impedance spectroscopy and cyclic voltammetry measurements.