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.     

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.     

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.     

Autothermal syngas production from model gasoline over Ni,Rh and Ni–Rh/Al2O3 monolithic catalysts

On-board reforming of liquid fuels is attractive for fuel cell-powered auxiliary power units in vehicles. In this work, monometallic Ni/Al₂O₃/cordierite, Rh/Al₂O₃/cordierite and bimetallic Ni–Rh/Al₂O₃/cordierite monolithic catalysts were prepared, characterized and tested in ATR of isooctane for syngas production. Compared to monometallic formulations, the bimetallic Ni–Rh/Al₂O₃ catalyst was active for ATR at lower temperature and H₂ production already reached the equilibrium composition in 400–550 °C temperature range. The Ni–Rh/Al₂O₃ catalyst exhibited stable performances for 140 h in ATR of isooctane at 700 °C, and was unaffected by oxidizing conditions at 700 °C. Thermoneutral reactions conditions at H₂O/C = 2 were obtained with O/C = 0.66. Carbon deposition was marginal during ATR of isooctane and no carbons whiskers were detected. Post-reaction characterizations showed that the Ni particles were small enough to prevent filamentous carbon formation, while Rh also prevented carbon film deposition by improving the gasification of adsorbed C with steam.     

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.     

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.     

High-performance Ni–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) membranes for hydrogen separation

Cermet membranes composited of Ni and doped barium cerate have been widely studied for hydrogen separation; however, their practical application is limited primarily by the relatively low permeation rate and instability of doped barium cerate in H₂O and CO₂ containing gases. Here we report our findings on the development of a thin-film cermet membrane consisting of Ni and BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb), supported on a porous Ni–BZCYYb substrate. High fluxes of 1.12 and 0.49 ml min⁻¹ cm⁻² have been demonstrated at 900 °C and 700 °C, respectively, when hydrogen was used as the feed gas on one side and N₂ as the sweep gas on the other side. Most importantly, the high-performance membrane can be easily fabricated by a cost-effective particle-suspension coating/co-firing process, offering great promise for large scale hydrogen separation applications.     

Oxidative steam reforming of ethanol over Ni/Al2O3 catalysts promoted by CeO2, ZrO2 and CeO2–ZrO2

Oxidative steam reforming of ethanol at low oxygen to ethanol ratios was investigated over nickel catalysts on Al₂O₃ supports that were either unpromoted or promoted with CeO₂, ZrO₂ and CeO₂–ZrO₂. The promoted catalysts showed greater activity and a higher hydrogen yield than the unpromoted catalyst. The characterization of the Ni-based catalysts promoted with CeO₂ and/or ZrO₂ showed that the variations induced in the Al₂O₃ by the addition of CeO₂ and/or ZrO₂ alter the catalyst's properties by enhancing Ni dispersion and reducing Ni particle size. The promoters, especially CeO₂–ZrO₂, improved catalytic activity by increasing the H₂ yield and the CO₂/CO and the H₂/CO values while decreasing coke formation. This results from the addition of ZrO₂ into CeO₂. This promoter highlights the advantages of oxygen storage capacity and of mobile oxygen vacancies that increase the number of surface oxygen species. The addition of oxygen facilitates the reaction by regenerating the surface oxygenation of the promoters and by oxidizing surface carbon species and carbon-containing products.     

Effects of Y2O3-modification to Ni/γ-Al2O3 catalysts on autothermal reforming of methane with CO2 to syngas

The effects of Y₂O₃-modification to Ni/γ-Al₂O₃ catalysts on autothermal reforming of methane to syngas were investigated. It was found that the introduction of Y₂O₃ (5%, 8%, 10%) lead to significant improvement in catalytic activity and stability, and the H₂/CO ratio could be adjusted via controlling the O₂/CO₂ ratio of the feed gas. According to the characterization results of catalysts before and after reaction, it was found that the Y₂O₃·γ-Al₂O₃ supported Ni catalysts had higher NiO reducibility, smaller Ni particle size, higher Ni dispersion and stronger basicity than those of the Ni/γ-Al₂O₃ catalysts. The analysis of catalysts after reaction showed that the addition of Y₂O₃ inhibited the Ni sintering, changed the type of coke and decreased the amount of coke on the catalysts. All the experimental results indicated that the introduction of Y₂O₃ to Ni/γ-Al₂O₃ resulted in excellent catalytic performances in autothermal reforming of methane, and Y₂O₃ played important roles in preventing metal sintering and coke deposition via controlling NiO reducibility, Ni particle size and dispersion, and basicity of catalysts.     

Ni–SiO2 and Ni–Fe–SiO2 catalysts for methane decomposition to prepare hydrogen and carbon filaments

Active and stable Ni–Fe–SiO₂ catalysts prepared by sol–gel method were employed for direct decomposition of undiluted methane to produce hydrogen and carbon filaments at 823 K and 923 K. The results indicated that the lifetime of Ni–Fe–SiO₂ catalysts was much longer than Ni–SiO₂ catalyst at a higher reaction temperature such as 923 K, however, a reverse trend was shown when methane decomposition took place at a lower reaction temperature such as 823 K. XRD studies suggested that iron atoms had entered into the Ni lattice and Ni–Fe alloy was formed in Ni–Fe–SiO₂ catalysts. The structure of the carbon filaments generated over Ni–SiO₂ and Ni–Fe–SiO₂ was quite different. TEM studies showed that “multi-walled” carbon filaments were formed over 75%Ni–25%SiO₂ catalyst, while “bamboo-shaped” carbon filaments generated over 35%Ni–40%Fe–25%SiO₂ catalysts at 923 K. Raman spectra of the generated carbons demonstrated that the graphitic order of the “multi-walled” carbon filaments was lower than that of the “bamboo-shaped” carbon filaments.