Catalytic partial oxidation of CH4–H2 mixtures over Ni foams modified with Rh and Pt

The catalytic partial oxidation (CPO) of methane–hydrogen mixtures in air, intended for the first stage of hybrid radiant catalytic burners, was investigated under self-sustained short contact time conditions on commercial Ni foam catalysts eventually modified with Rh and Pt. The modified catalysts were prepared by a simple novel method based on the spontaneous deposition of noble metals via metal exchange reactions onto those Ni foam substrates. SEM-EDS, electrochemical methods and H₂-TPR analysis were integrated to characterize morphology, surface area of metal deposits and reducibility of foam catalysts before and after exposure to severe conditions in the CPO reactor. In particular Rh forms finely dispersed deposits that retain their high specific surface area at temperatures up ca. 1100 °C. Modification with noble metals enhances stability and reducibility of the Ni foam whereas the overall CPO performance is not significantly improved. Safe operation of the CPO reactor with up to 70% vol. H₂ in the fuel mixture has been achieved by properly increasing the feed equivalence ratio to avoid catalyst overheating, while guaranteeing high methane conversions and a persistent net hydrogen production.     

Ru,Rh,Pd,Ni/PPh3均相催化精制生物油的试验研究

研究4种均相催化剂RuCl2(PPh3)3、RhCl(PPh3)3、PdCl2(PPh3)2及NiCl2(PPh3)2各自对生物油催化加氢的活性,并对精制前后生物油中各类物质变化进行分析。结果表明,4种催化剂对醛、酮、酚及酸等转化均有一定的催化活性,其中RuCl2(PPh3)3可将90%以上的醛加氢转化,并对50%以上的酚类支链中的C C加氢;RhCl(PPh3)3则可将约85%的酚类支链上的C C加氢;后两种催化剂除了对醛酚有一定的催化加氢作用外,对酸转化为酯也具有催化活性。实验中未发现结焦物生成,说明均相催化技术非常适合精制生物油这种高热敏性体系。     

Plasma-reduced Ni/γ–Al2O3 and CeO2–Ni/γ–Al2O3 catalysts for improving dry reforming of propane

Pristine Ni/γ–Al₂O₃ and CeO₂–Ni/γ–Al₂O₃ catalysts were prepared by co-impregnation technique for dry reforming of propane. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to examine the structure and morphology of the catalysts before and after the reforming reactions. The excellent interaction between catalyst active phases was observed in both CeO₂–Ni/γ–Al₂O₃ and Ni/γ–Al₂O₃ stabilized with polyethelene glycol (Ni/γ–Al₂O₃–PEG). Towards C₃H₈ and CO₂ conversion, the CeO₂–Ni/γ–Al₂O₃ and Ni/γ–Al₂O₃–PEG showed improved catalytic activity when compared to the pristine Ni/γ–Al₂O₃ catalyst. Interestingly, high H₂ concentration was achieved with the CeO₂–Ni/γ–Al₂O₃ and high CO concentration with the Ni/γ–Al₂O₃–PEG, which is due to the nanoconfinement of nickel particles within the support and favorable metal-support interaction as a result of plasma reduction. The CeO₂–Ni/γ–Al₂O₃ catalyst exhibited better stability for anti-sintering and coke resistance, thus exhibiting high reactivity and durability in the dry reforming.     

Rh promoted and ZrO2/Al2O3 supported Ni/Co based catalysts: High activity for CO2 reforming,steam–CO2 reforming and oxy–CO2 reforming of CH4

Ni (2.5 wt%) and Co (2.5 wt%) supported over ZrO₂/Al₂O₃ were prepared by following a hydrolytic co-precipitation method. The synthesized catalysts were further promoted by Rh incorporation (0.01–1.00 wt%) and tested for their catalytic performance for dry CO₂ reforming, combined steam–CO₂ reforming and oxy–CO₂ reforming of methane for production of syngas. The catalysts were characterized by using N₂ physical adsorption, XRD, H₂–TPR, SEM, CO₂–TPD, NH₃–TPD, TEM and TGA. The results revealed that ZrO₂ phase was in crystalline form in the catalysts along with amorphous Al oxides. Ni and Co were confirmed to be in their respective spinel phases that were reducible to metallic form at 800 °C under H₂. Ni and Co were well dispersed with their nano-crystalline nature. The catalyst with 0.2% loading of Rh showed superior performance in the studied reactions for reforming of methane. This catalyst also showed good coke resistance ability for dry CO₂ reforming reaction with 3.8 wt% of carbon formation during the reaction as compared to 11.6 wt% carbon formation over the catalyst without Rh. The catalyst performance was stable throughout the reaction time for CH₄ conversions, irrespective of carbon formation with slight decline (～1%) in CO₂ conversion. For dry CO₂ reforming reaction, this catalyst showed good conversion for both CH₄ and CO₂ (67.6% and 71.8% respectively) with a H₂/CO ratio of 0.84, while for the Oxy-CO₂ reforming reaction, the activity was superior with CH₄ and CO₂ conversions (73.7% and 83.8% respectively) and H₂/CO ratio of 1.05.     

Hydrogen production by biomass gasification in supercritical water over Ni/γAl2O3 and Ni/CeO2-γAl2O3 catalysts

Hydrogen production by supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. Ni catalyst can realize the high gasification efficiency of biomass near the critical temperature of water. In this paper, Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts were prepared by an impregnation method. The catalyst performance for glucose gasification in supercritical water was tested in autoclave reactor. All experiments were carried out in the autoclave at 673 K, 24.5 MPa, and the concentration of glucose was 9.09 wt.%. The catalysts before and after reaction were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurements, X-ray fluorescence spectrum (XRF) and Thermo-gravimetric analyses (TGA) in order to investigate on the chemical property and catalytic mechanism. The experimental results showed that hydrogen yield and hydrogen selectivity increased sharply with addition of Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts. The catalytic activity and H₂ selectivity of Ni/CeO₂-γAl₂O₃ was higher than that of Ni/γ-Al₂O₃ catalyst. The results revealed that carbon deposition and coking led to the deactivation of the catalysts. Ce in the Ni/CeO₂-γAl₂O₃ catalyst had a certain role in the inhibition of carbon deposition and coking.     

Methane dry reforming on Ni/Ce0.75Zr0.25O2–MgAl2O4 and Ni/Ce0.75Zr0.25O2–γ-alumina: Effects of support composition and water addition

Nickel catalysts (10wt.%) supported on MgAl₂O₄ and γ-Al₂O₃ were prepared by the wet impregnation method and promoted with various contents of Ce_0.75Zr_0.25O₂. X-ray diffraction (XRD), BET surface area, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), H₂-temperature programmed reduction (TPR) and CO₂-temperature programmed desorption (TPD) were employed to observe the characteristics of the prepared catalysts. Ni/γ-Al₂O₃ and Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ showed better activity in CO₂ methane reforming with 75.7(0.93) and 75.4(0.82) CH₄ conversions (and H₂/CO ratio). H₂O was added to feed in the range of H₂O/(CH₄ + CO₂): 0.1–0.5 to suppress reverse water gas shift (RWGS) effect and adjusting H₂/CO ratio. The CH₄ conversions (and H₂/CO) increased to 81(1.1) with 0.5 water/carbon mole ratio in Ni/γ-Al₂O₃ and 85(1.2) with 0.2 water/carbon mole ratio in Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄. The stability of Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ in the presence and absence of water was investigated. Coke formation and amount in used catalysts were examined by SEM and TGA, respectively. The results showed that the amount of carbon was suppressed and negligible coke formation (less than 3%) was observed in the presence of 0.2 water/carbon mole ratio over Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ catalyst.     

Glycerol steam reforming over Ni/mg/γ-Al2O3 catalysts effect of Ni(II) content

The aim of the present work is to analyse the effect of the Ni(II) content for the Ni(II)-Mg(II)/γ-Al₂O₃ catalysts on the textural and structural characteristics of the solid, as well on the catalytic activity and selectivity to H₂ for the steam reforming of glycerol at atmospheric pressure.     

Catalysts of Ni/α-Al2O3 and Ni/La2O3-αAl2O3 for hydrogen production by steam reforming of bio-oil aqueous fraction with pyrolytic lignin retention

This paper reports on the steam reforming, in continuous regime, of the aqueous fraction of bio-oil obtained by flash pyrolysis of lignocellulosic biomass (sawdust). The reaction system is provided with two steps in series: i) thermal step at 200 °C, for the pyrolytic lignin retention, and ii) reforming in-line of the treated bio-oil in a fluidized bed reactor, in the range 600–800 °C, with space-time between 0.10 and 0.45 g_catalyst h (g_bio-oil)⁻¹. The benefits of incorporating La₂O₃ to the Ni/α-Al₂O₃ catalyst on the kinetic behavior (bio-oil conversion, yield and selectivity of hydrogen) and deactivation were determined. The significant role of temperature in gasifying coke precursors was also analyzed. Complete conversion of bio-oil is achieved with the Ni/La₂O₃-αAl₂O₃ catalyst, at 700 °C and space-time of 0.22 g_catalyst h (g_bio-oil)⁻¹. The catalyst deactivation is low and the hydrogen yield and selectivity achieved are 96% and 70%, respectively.     

Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared Ni–Cu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al₂O₃, commercial Cu/ZnO/Al₂O₃ and prepared Ni–Cu/Al₂O₃ catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in Ni–Cu/Al₂O₃ catalyst with respect to the commercial Ni/Al₂O₃ (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al₂O₃ (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H₂ selectivity, CO₂ and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H₂, with H₂ selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275–325 °C). However, methane steam reforming can be carried out at a relatively low temperature on Ni–Cu catalyst (600–650 °C) and at higher temperature in commercial methane reforming catalyst (700–800 °C). Commercial Ni/Al₂O₃ catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared Ni–Cu/Al₂O₃ (8.9%) and commercial Cu/ZnO/Al₂O₃ catalysts (3.5%).     

Combination of CO2 reforming and partial oxidation of methane to produce syngas over Ni/SiO2 and Ni–Al2O3/SiO2 catalysts with different precursors

Ni/SiO₂ and Ni–Al₂O₃/SiO₂ catalysts were prepared by incipient wetness impregnation using citrate and nitrate precursors and tested with a reaction of combination of CO₂ reforming and partial oxidation of methane to produce syngas (H₂/CO). The catalytic activity of Ni/SiO₂ and Ni–Al₂O₃/SiO₂ greatly depended on interaction between NiO and support. NiO strongly interacted with support formed small nickel particles (about 4 nm for NiSC which is abbreviation of Ni/SiO₂ prepared with Nickel citrate precursor) after reduction. The small nickel particles over NiSC catalysts exhibited a good catalytic performance.     

Thermocatalytic decomposition of methane over mesoporous Ni/xMgO·Al2O3 nanocatalysts

This paper describes a facile method to produce mesoporous nanostructure Ni/Al₂O₃, Ni/MgO, and Ni/xMgO.Al₂O₃ (x: MgO/Al₂O₃ molar ratio) catalysts prepared by “one-pot” evaporation-induced self-assembly (EISA) method with some modifications for investigating in the thermocatalytic decomposition of methane. Detailed characterizations of the material were performed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and N₂ adsorption/desorption, hydrogen temperature-programmed reduction (H₂-TPR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed oxidation (TPO). The characterizations demonstrated that the synthesized catalysts with various MgO/Al₂O₃ molar ratios possessed mesoporous structure with the high BET area in the range of 216.79 to 31.74 m² g^?1. The effect of different surfactants and calcination temperatures on the characterizations and catalytic activity of the catalysts were also examined in details. The experimental results showed that the catalysts exhibited high catalytic potential in this process and the 55 wt.% Ni/2 MgO·Al₂O₃ catalyst calcined at 600^οC possessed an acceptable methane conversion (～60%) under the harsh reaction conditions (GHSV = 48000 (mL h^?1 g_cat^?1)).     

Metallic Ni monolith–Ni/MgAl2O4 dual bed catalysts for the autothermal partial oxidation of methane to synthesis gas

A dual bed catalyst system consisting of a metallic Ni monolith catalyst in the front followed by a supported nickel catalyst Ni/MgAl₂O₄ has been studied for the autothermal partial oxidation of methane to synthesis gas. The effects of bed configuration, reforming bed length, feed temperature and gas hourly space velocity on the reaction as well as the stability are investigated. The results show that the metallic Ni monolith in the front functions as the oxidation catalyst, which prevents the exposure of the reforming catalyst in the back to the very high temperature, while the supported Ni/MgAl₂O₄ in the back functions as the reforming catalyst which further increases the methane conversion by 5%. A typical 5 mmNi monolith–5mmNi/MgAl₂O₄ dual bed catalyst exhibits methane conversion and hydrogen and carbon monoxide selectivities of 85.3%, 91.5% and 93.0%, respectively, under autothermal conditions at a methane to oxygen molar ratio of 2.0 and gas hourly space velocity of 1.0 × 10⁵ h⁻¹. The dual bed catalyst system is also very stable.     

Hydrogen production from CH4 dry reforming over bimetallic Ni–Co/Al2O3 catalyst

Bimetallic 5%Ni–10%Co/Al₂O₃ catalyst was synthesized using impregnation method and evaluated for methane dry reforming reaction at different reaction temperatures. NiO, Co₃O₄ and spinal metal aluminates, namely, CoAl₂O₄ and NiAl₂O₄ phases were formed on γ-Al₂O₃ support surface during calcination process. 5%Ni–10%Co/Al₂O₃ catalyst exhibited reasonable surface area of 86.93 m² g^?1 with small crystallite dimension of less than 10 nm suggesting that both Co₃O₄ and NiO phases were finely dispersed on the surface of support in agreement with results from scanning electron microscopy (SEM) measurement. Temperature-programmed calcination measurement indicates the complete thermal decomposition and oxidation of metal precursors, viz. Ni(NO₃)₂ and Co(NO₃)₂ to metal oxides and metal aluminates at below 700 K. Both CH₄ and CO₂ conversions were stable over a period of 4 h on-stream and attained an optimum at about 67% and 71%, respectively at 973 K whilst H₂ selectivity and yield were higher than 49%. The ratio of H₂/CO was always less than unity for all runs indicating the presence of reverse water–gas shift reaction. The activation energy for CH₄ and CO₂ consumption was computed as 55.60 and 40.25 kJ mol^?1, correspondingly. SEM micrograph of spent catalyst detected the formation of whisker-like carbon on catalyst surface whilst D and G bands characteristic for the appearance of amorphous and graphitic carbons in this order were observed on surface of used catalyst by Raman spectroscopy analysis. Additionally, the percentage of filamentous carbon was greater than that of graphitic carbon.     

Hydrogen production from oxidative steam-reforming of n-propanol over Ni/Y2O3–ZrO2 catalysts

Oxidative steam reforming (OSR) of n-propanol was studied over new Ni catalysts (ca. 7% Ni wt/wt) supported on Y₂O₃–ZrO₂ oxides with different yttrium content (2–41 % Y₂O₃ wt/wt). Materials were characterized by X-ray diffraction, temperature-programmed reduction, X-ray photoelectron and Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray analysis and high resolution transmission electron microscopy. Samples were used in calcined form and tested in the temperature range 673–773 K using a reactant feed of n-propanol/water/O₂ at a molar ratio 1/9/0.5. Hydrogen production is related with the support composition and Ni dispersion.     

Rapid charging characterization of MmNi3.03Si0.85Co0.60Mn0.31Al0.08 alloy used as anodes in Ni–MH batteries

The use of Nickel–Metal Hydride (Ni–MH) batteries for traction application in electric and hybrid vehicles is on the rise. High-rate charge/discharge characteristics are important parameters for electric vehicle applications. The ability to reduce charging time is essential in these traction applications. In this paper, the performance of assembled Ni–MH batteries (1.2 V, 0.5 Ah specimen cells) when subjected to different charging rates is described. Changes in battery voltage during charging were monitored with a particular emphasis on the quest for fast recharge characteristics. The charging curves reveal the formation of different types of phases. Hydrogen evolution resulted in flat charge profile after certain amount of overcharging. The changes in discharge level after different rates of charging are insignificant. This paper describes the fast rechargeability of assembled Ni–MH cells under various fast-charge regimes.     

Organic-inorganic composite of g-C3N4–SrTiO3:Rh photocatalyst for improved H2 evolution under visible light irradiation

The organic-inorganic composite g-C₃N₄–SrTiO₃:Rh was prepared for the first time as a photocatalyst for hydrogen production and the resulting hydrogen evolution rate under visible light irradiation from aqueous methanol solution was measured. A high hydrogen evolution rate of 223.3 μmol h⁻¹ was achieved by using 0.1 g of as-prepared photocatalyst powder comprised of 20 wt.% g-C₃N₄ 80 wt.% SrTiO₃:Rh (0.3 mol%). The hydrogen evolution rate was greater than that obtained by SrTiO₃:Rh (0.3 mol%) by a factor of 3.24. The quantum efficiency of as-prepared composite photocatalyst was 5.5% at 410 nm for hydrogen evolution. The high activity of the composite photocatalyst for hydrogen evolution stemmed from its electron–hole separation and transportation capabilities due to the hetero-junctions of the organic-inorganic composite materials. The proposed mechanism for the electron–hole separation and hydrogen evolution of the g-C₃N₄–SrTiO₃:Rh composite under visible light irradiation featured the reduced recombination of the photo-generated charge carriers. The doping of Rh ions into the SrTiO₃ has contributed to the high photocatalytic activity by forming a donor level from the valance band to the conduction band.     

Novel Ni–ZrO2 catalyst doped with Yb2O3 for ethanol steam reforming

A type of Yb₂O₃ doped Ni–ZrO₂ catalyst for ethanol steam reforming was developed, and displayed excellent catalyzing performance for the selective formation of H₂ and CO₂. Over a Ni_1.25Zr₁Yb_0.8 catalyst, STY(H₂) can maintain stable at the level of 0.396 mol h⁻¹ g⁻¹ (data taken 120 h after the reaction started) under the reaction conditions of 0.5 MPa and 723 K, which was 1.6 times that (0.247 mol h⁻¹ g⁻¹) of the Yb-free counterpart Ni_1.25Zr₁. Characterization of the catalyst revealed that dissolution of an appropriate amount of Yb³⁺ ions in the zirconia host resulted in the formation of the Zr–Yb composite oxide with cubic-ZrO₂ structure, c-(Zr–Yb)O_z, which inhibited effectively the transformation of c-ZrO₂ to thermodynamically more stable m-ZrO₂, thus avoiding sintering of the (Zr–Yb)O_z composite. It was demonstrated that the doping of Yb₂O₃ to Ni–ZrO₂ changed also the valence states or the micro-environments of the Ni-species at the quasi-active surface of the tested catalyst, which was conducive to inhibiting agglomeration of the Ni_x⁰–Niⁿ⁺ species active catalytically, with resulting in maintaining the high metallic nickel dispersion and inhibiting coking. The aforementioned two factors both contributed to improving the activity and operating stability as well as heat-resistant quality of the catalyst.     

Syngas production by CO2 reforming of coke oven gas over Ni/La2O3–ZrO2 catalysts

Syngas production by CO₂ reforming of coke oven gas (COG) was studied in a fixed-bed reactor over Ni/La₂O₃–ZrO₂ catalysts. The catalysts were prepared by sol–gel technique and tested by XRF, BET, XRD, H₂-TPR, TEM and TG–DSC. The influence of nickel loadings and calcination temperature of the catalysts on reforming reaction was measured. The characterization results revealed that all of the catalysts present excellent resistance to coking. The catalyst with appropriate nickel content and calcination temperature has better dispersion of active metal and higher conversion. It is found that the Ni/La₂O₃–ZrO₂ catalyst with 10 wt% nickel loading provides the best catalytic activity with the conversions of CH₄ and CO₂ both more than 95% at 800 °C under the atmospheric pressure. The Ni/La₂O₃–ZrO₂ catalysts show excellent catalytic performance and anti-carbon property, which will be of great prospects for catalytic CO₂ reforming of COG in the future.     

CO2 reforming of CH4 by combination of cold plasma jet and Ni/γ-Al2O3 catalyst

CO₂ reforming of CH₄ to synthesis gas was investigated by cold plasma jet (CPJ) only and combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst at atmospheric pressure. The higher selectivity of H₂ and CO, and higher energy efficiency was obtained by this novel process. The optimum experimental conditions are: CH₄ = 3.33 Nl/min, CO₂ = 5.00 Nl/min, N₂ = 8.33 Nl/min, and the input power at 770 W. The results showed that, for the plasma only, the conversions of CH₄ and CO₂ were 46% and 34%, the selectivities of CO and H₂ were 85% and 78%, the energy efficiency was 2.9 mmol/kJ, respectively; for the combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst, the conversions of CH₄ and CO₂ were increased by 14% and 6%, the yield of H₂ and CO increased by 18% and 11%, the energy efficiency reached at 3.7 mmol/kJ, respectively. And the catalyst hasn't accessorial heating. The CPJ method has the advantage of simple processing and is easy to be industrialized.