1,721,015 research outputs found
Preparation and characterization of nano cobalt oxide
No full textCobalt oxide Co(3)O(4) is prepared according to several methods i.e. oxalate decomposition (CoAO), surfactant-assisted precipitation (CoCTAB), sol-gel technique (CoSG) and polymer combustion (CoPVA). The solids are characterized by XRD, FTIR, TPR and TEM analysis. The method via oxalate decomposition (CoAO) appears as that giving the smallest particles nanostructured with an almost monomodal distribution, whereas the CoPVA needs to be calcined at the highest temperature in order to have pure Co(3)O(4). As a consequence on CoPVA the largest particle size is found. The reducibility by H(2) of cobalt oxide particles having the smallest (CoAO) and the largest particle size (CoPVA) is found to depend on the particle dimensions and, where the distribution is monomodal, the reduction steps Co(3)O(4) -> CoO -> Co appear clearly distinct and the temperatures relative to the two reduction steps are well beyond those monitored on microprepared oxide, where only a gross and unique reduction peak is envisaged
Green synthesis and characterization of titanium dioxide nanoparticles and their photocatalytic activity
No full textDry reforming of methane on bimetallic Co-Ni/CeO2 catalyst
No full textIn the present work, monometallic Co/CeO2 (Co 7.5 wt.%) and Ni/CeO2 (Ni 7.5 wt.%) catalysts, were compared with the bimetallic Co-Ni/CeO2 (Co 3.75 wt.%, Ni 3.75 wt.%) catalyst. CeO2 has been selected for its redox properties that may mitigate the carbon deposition. The synthesis by surfactant assisted co-precipitation method allowed us to obtain powders with high surface area and homogeneous dispersion of cobalt and nickel nanometric particles. Samples were characterized by XRD, BET, TPR, TG-DTA and tested for DRM with CH4:CO2:Ar 20:20:60 vol.% (GHSW = 30000 mL g-1 h-1). After activation in H2 at 800°C, Co-Ni/CeO2 clearly showed the presence of a cobalt and nickel alloy phase. The bimetallic Co-Ni/CeO2 catalyst was more active and more selective for the DRM reaction than monometallic Co/CeO2 and Ni/CeO2 samples. In particular the CH4 conversion on Co-Ni/CeO2 was 50% at 600°C, and 97% at 800°C, with a H2/CO ratio in the range 0.9-1.0. After 16 hours streaming, Ni/CeO2 showed 25 wt.% of carbonaceous deposit and a catalytic activity decrease of 8%, while both cobalt containing catalysts showed 6 wt.% of carbon on the surface and a decrease of activity less than 2%. Theses features suggest that cobalt-nickel alloy combines the high activity of nickel with the carbon suppression property of cobalt
CO2-recycling for CH4 production on rare-earth modified Ni-Alumina catalysts
No full textThe chemical recycling of greenhouse gas CO2 produced in hydrocarbon combustion is an attractive alternative to CO2 storage in the underground [1]. Recently have attracted particular interest the conversion of CO2 into syn-gas by the dry reforming of methane [2] and the direct conversion of CO2 into synthetic natural gas (CH4) by the methanation reaction CO2 + 4H2 CH4 + 2H2O [3]. In addition to abating the CO2 emission, the methanation has the advantage to convert hydrogen into a more easily exploitable source of energy, as is CH4. This reaction also have the advantage being thermodinamically favoured at low temperatures (H° = −165 kJ mol−1). However the methanation is helpful for greenhouse gas mitigation only if it utilizes H2 produced by non-fossil sources. Nickel containing catalysts have been reported to be very active for this reaction []. Nickel loading, support nature and the effect of promoters have been widely investigated for the removal of CO2 and CO from H2-rich streams, but only scarcely studied for CH4 production using concentrated CO2 flow. In the present work, catalysts based on nickel supported on -Al2O3, modified by rare earth oxides CeO2 and La2O3, and by MgO were prepared by wet impregnation and tested for the production of synthetic natural gas. The catalyst metal compositions were tailored in order to improve the catalytic performances at low temperature (300-400°C) and high space velocity (75000 mL h-1 g-1). Catalysts were characterized by XRD, SEM, H2-TPR, CO2-TPD, BET in order to investigate the role of promoters on nickel dispersion and surface basicity, and tested with pure reagent CO2:H2 stechiometric flow. Some tests were performed on structured catalyst, prepared washcoating active powder on cordierite monolith, with the aim of increase the gas-solid interface and the temperature stability and reduce the pressure drop along the catalyst bed
Dry Reforming of Methane on Ni/Nanorod-CeO2 Catalysts Prepared by One-Pot Hydrothermal Synthesis: The Effect of Ni Content on Structure, Activity, and Stability
Full text linkThe nanorod morphology of the CeO2 support has been recognized as more beneficial
than other morphologies for catalytic activity in the dry reforming of methane. Ni/nanorod-CeO2
catalysts with different Ni contents were prepared by one-pot hydrothermal synthesis. Samples were
characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), H2-
temperature-programmed desorption (H2-TPD), field emission scanning electron microscopy/energy
dispersive spectroscopy (FE-SEM/EDS), Brunauer–Emmet–Teller (BET) and Barrett–Joyner–Halenda
(BHJ) analysis. The effect of Ni content on the size and the intrinsic strain of ceria was analyzed by the
Size–Strain plot and Williamson–Hall plot of XRD data. The average Ni particle size and Ni dispersion
were determined by H2-TPD. XRD and H2-TPR analysis revealed a strong Ni–support interaction that
limited nickel sintering. The activity for the dry reforming of methane was tested with the stoichiometric mixture CO2:CH4:N2:He = 20:20:20:140, gas hourly space velocity (GHSV) = 300 L g−1 h−1,
and temperatures in the range of 545–800 ◦C. The turnover frequency (TOF) value increased linearly
with the average Ni particle size in the range of 5.5–33 nm, suggesting the structure sensitivity of the
reaction. Samples with Ni loading of 4–12 wt.% showed high H2/CO selectivity and stability over
time on stream, whereas the sample with a Ni loading of 2 wt.% was less selective and underwent
rapid deactivation. Only a small amount of nanotubular carbon was observed by FE-SEM after
the time-on-stream experiment. Deactivation of the low-Ni-content sample is ascribed to the easier
oxidation of the small Ni particles
Zirconia-supported Nickel catalysts for CO2 reforming of Methane
No full textThe production of syngas by catalytic dry reforming of CO2 (DR) with methane is one of the attractive routes for an efficient use of greenhouse gases such as methane and CO2. Nickel-based catalysts, developed using different types of supports and preparation methods, show high performances in this reaction although presenting sintering problems and a rapid deactivation due to coke deposition.
In the search for systems with enhanced properties, catalysts consisting of nickel supported on ZrO2 having different textural and morphological properties have been prepared and tested in the dry reforming of CH4 for syngas production. The influence of composition, thermal treatments and support properties on the chemical state, dispersion and stability of the Ni species were studied
Ni/CeO2-Al2O3 catalysts for the dry reforming of methane: the effect of CeAlO3 content and nickel crystallite size on catalytic activity and coke resistance
Full text linkThe catalytic performances of Ni/CeO2–Al2O3 catalysts for the dry reforming of CH4 (DRM) were investigated. Catalysts with different Ni dispersion and different amounts of CeAlO3 species were prepared by
different methods and characterized by BET, XRD, XPS, Raman, TPR, and TPO techniques. Catalytic activity
was studied during the time on stream in the range 873–1073K with a mixture of CH4:CO2:Ar = 40:40:20 vol.%
and GHSV 90,000 cm3 g−1 h−1. The intrinsic catalytic activity increased with the increase of Ni crystallite
size. Carbon was deposited as nano-fibers and graphite when catalysts worked at lower temperatures, and
the largest amount was found on the catalyst with the largest Ni crystallite size. The formation of graphitic
deposits is limited by the presence of CeAlO3 species formed during catalyst activation. CA preparation
method results particularly attractive because it allows obtaining catalysts with small Ni crystallite size
and high content of CeAlO3 species, which both have a role in suppressing the carbon deposition and
therefore in obtaining stable catalytic performances
Packed and Monolithic Reactors for the Dry Reforming of Methane: Ni Supported on γ-Al2O3 Promoted by Ru
No full textThe CO2 reforming of CH4 or dry reforming (DRM) is as an efficient way for the CH4 and CO2 valorisation.
The DRM plays also an important role on the electrochemical performances and the long-term stability of solid oxide fuel cells (SOFCs) fed by CH4 or biogas.
Nickel is so far the most active catalyst for the DRM, but also highly prone to carbon formation, because, together with the ability to activate the C-H bond, Ni has high affinity to carbon. The Ni particle size has a strong effect on the carbon tolerance of the catalyst, therefore, the stabilization of small Ni nanoparticles at high temperatures is a promising way for the lifetime increase [1, 2]. Another strategy is the addition of a second metal (i.e Ru, Pt, Cu, Co) resulting in the formation of less C-sensitive alloys or in the increase of Ni dispersion.
The development of structured and unstructured catalysts for DRM based on Ni nanoparticles (10 wt%) supported on γ-Al2O3 promoted by a small amount of Ru (0.05 wt%), has been investigated. Unstructured catalysts (packed powder) were prepared by wet impregnation method and a combination of wash coating-wet impregnation methods was used for structured catalysts (cordierite monoliths). Samples were characterized by XRD, BET, H2-TPR, TEM and FE-SEM techniques and the catalytic activity for DRM was studied at 800 °C during time on stream with a mixture of CH4:CO2:Ar=45:45:10 vol.% and a gas space hourly velocity GHSV=11400 h-1 (150 cm3 min-1)
Morphological analysis confirmed that a large amount of carbon filament was deposited on Ni catalyst mainly by a tip growth mechanism, whereas on Ni-Ru, few carbon filaments were deposited with a base growth mechanism mainly in the inlet region. Moreover, the comparison between structured and unstructured catalyst underlined the advantages of structured catalysts over conventional packed bed reactors such as: increased mass and heat transfer, lower pressure drop, larger surface to-volume ratio and compact reactor design
Nickel Supported on Y2O3-ZrO2 as Highly Selective and Stable CO2 Methanation Catalyst for in-Situ Propellant Production on Mars
No full textProduction of propellant for the return to Earth from in-situ resources allows not transporting the return fuel in space explorations. CO2 from Martian atmosphere may react with H2 to produce methane and water by Sabatier reaction. The activity of Ni (10 wt%) supported on Y2O3-ZrO2, by different preparation methods, was compared. Structural characterization by XRD, TPR and TEM, evidenced that catalytic performances for CO2 methanation mainly depended on the Ni0 particle size and morphology. In particular, the catalyst prepared by wet impregnation with Ni(EDTA)-2 complex, having high nickel dispersion and strong Ni-support interaction, showed remarkable activity, selectivity and stability over time on stream using stoichiometric flow (CO2:H2 = 1:4), appearing like a reliable catalyst for Sabatier process
The catalytic activity of cobalt-exchanged mordenites for the abatement of NO with CH4 in the presence of excess O2
No full textThe abatement of NO with methane in the presence of oxygen was studied on various commercial MOR in the Na-form (Na-MOR) and H-form (H-MOR), or exchanged to various extents with cobalt (Co-MOR). The sodium and cobalt contents were determined by atomic absorption. Samples were characterized by FTIR and volumetric measurements of CO adsorption. Chemical analysis indicated that one cobalt species replaced two Brønsted acid sites in H-MOR and two Na + ions in Na-MOR. The IR analysis of the OH stretching region, evidencing an unexpected presence of Brønsted acid sites (band at 3610 cm-1) in Co-MOR, indicated that the exchange process had a more complex stoichiometry. The adsorption of CO at RT on Co-MOR, in addition to the bands of the corresponding H-MOR and Na-MOR matrices, yielded two types of CoII-carbonyls, the first type occupied the mordenite main channels, and the second one the mordenite smaller channels. Brønsted acid sites in mordenites were active for the selective catalytic reduction of NO with CH4. Co-MOR samples were far more active than Na-MOR and H-MOR samples, showing that acid protons play a negligible role when Co is present. Co-MOR catalysts showing the highest activity had the largest amount of Co II-carbonyls in the main channels. This result strongly suggests that CoII in the main channels of MOR are the active sites for the CH4 + NO + O2 reaction. © 2003 Elsevier B.V. All rights reserved
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