An Al2O3-ZrO2 xerogel (AZ-SG) was prepared by a sol-gel method for use as a support for a nickel catalyst. The Ni/AZ-SG catalyst was then
prepared by an impregnation method, and was applied to hydrogen production by steam reforming of LNG. A nickel catalyst supported
on commercial alumina (A-C) was also prepared (Ni/A-C) for comparison. The hydroxyl-rich surface of the AZ-SG support increased
the dispersion of nickel species on the support during the calcination step. The formation of a surface nickel aluminate-like
phase in the Ni/AZ-SG catalyst greatly enhanced the reducibility of the Ni/AZ-SG catalyst. The ZrO2 in the AZ-SG support increased the adsorption of steam onto the support and the subsequent spillover of steam from the support
to the active nickel sites in the Ni/AZ-SG catalyst. Both the high surface area and the well-developed mesoporosity of the
Ni/AZ-SG catalyst improved the gasification of adsorbed surface hydrocarbons in the reaction. In the steam reforming of LNG,
the Ni/AZ-SG catalyst showed a better catalytic performance than the Ni/A-C catalyst. Moreover, the Ni/AZ-SG catalyst showed
strong resistance toward catalyst deactivation. 相似文献
A co-precipitation method was employed to prepare Ni/Al2O3-ZrO2, Co/Al2 O3-ZrO2 and Ni-Co/Al2O3-ZrO2 catalysts. Their properties were characterized by N2 adsorption (BET), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR), temperature-programmed desorption (CO2-TPD), and temperature-programmed surface reaction (CH4-TPSR and CO2-TPSR). Ni-Co/Al2O3-ZrO2 bimetallic catalyst has good performance in the reduction of active components Ni, Co and CO2 adsorption. Compared with mono-metallic catalyst, bimetallic catalyst could provide more active sites and CO2 adsorption sites (C + CO2 = 2CO) for the methane-reforming reaction, and a more appropriate force formed between active components and composite support (SMSI) for the catalytic reaction. According to the CH4-CO2-TPSR, there were 80.9% and 81.5% higher CH4 and CO2 conversion over Ni-Co/Al2O3-ZrO2 catalyst, and its better resistance to carbon deposition, less than 0.5% of coke after 4 h reaction, was found by TGA. The high activity and excellent anti-coking of the Ni-Co/Al2O3-ZrO2 catalyst were closely related to the synergy between Ni and Co active metal, the strong metal-support interaction and the use of composite support. 相似文献
The effect of La2O3 content in Ni-La-Zr catalyst was investigated for the autothermal reforming (ATR) of CH4. The catalysts were prepared by the coprecipitation method and had a mesoporous structure. Temperature programmed reduction
(TPR) and X-ray photoelectron spectroscopy (XPS) indicated that a strong interaction developed between Ni species and the
support with the addition of La2O3. Thermogravimetric analysis (TGA) and H2-pulse chemisorption showed that the addition of La2O3 led to well dispersed NiO molecules on the support. Ni-La-Zr catalysts gave much higher CH4 conversion than Ni-Zr catalyst. The Ni-La-Zr containing 3.2 wt% La2O3 showed the highest activity. The optimum conditions for maximal CH4 conversion and H2 yield were H2O/CH4=1.00, O2/CH4=0.75. Under these conditions, CH4 conversion of 83% was achieved at 700 °C. In excess O2 (O2/CH4>0.88), the catalytic activity was decreased due to sintering of the catalyst. 相似文献
CO2 reforming of CH4 was performed using Ni catalyst supported on La-hexaaluminate which has been an well-known material for high-temperature
combustion. La-hexaaluminate was synthesized by sol-gel method at various conditions where different amount of Ni (5–20 wt%)
was loaded. Ni/La-hexaaluminate experienced 72 h reaction and its catalytic activity was compared with that of Ni/Al2O3, Ni/La-hexaaluminate shows higher reforming activity and resistance to coke deposition compared to the Ni/Al2O3 model catalyst. Coke deposition increases proportionally to Ni content. Consequently, Ni(5)/La-hexaaluminate(700) is the
most efficient catalyst among various Ni/La-hexaaluminate catalysts regarding the cost of Ni in Ni(X)/La-hexaaluminate catalysts.
BET surface area, XRD, EA, TGA and TPO were performed for surface characterization.
This work was presented at the 6th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
A K-promoted 10Ni-(x)K/MgAl2O4 catalyst was investigated for the combined H2O and CO2 reforming (CSCR) of coke oven gas (COG) for syngas production. The 10Ni-(x)K/MgAl2O4 catalyst was prepared by co-impregnation, and the K content was varied from 0 to 5 wt%. The BET, XRD, H2-chemisorption, H2-TPR, and CO2-TPD were performed for determining the physicochemical properties of prepared catalysts. Except under the condition of a K/Ni=0.1 (wt%/wt%), the Ni crystal size and dispersion decreased with increasing K/Ni. The coke resistance of the catalyst was investigated under conditions of CH4: CO2: H2: CO:N2=1 : 1 : 2 : 0.3 : 0.3, 800 °C, 5 atm. The coke formation on the used catalyst was examined by SEM and TG analysis. As compared to the 10Ni/MgAl2O4 catalyst, the Kpromoted catalyst exhibited superior activity and coke resistance, attributed to its strong interaction with Ni and support, and the improved CO2 adsorption characteristic. The 10Ni-1K/MgAl2O4 catalyst exhibited optimum activity and coke resistance with only 1wt% of K. 相似文献
The catalytic performance during combined steam and carbon dioxide reforming of methane (SCR) was investigated on Ni/MgAl2O4 catalyst promoted with CeO2. The SCR catalyst was prepared by co-impregnation method using nickel and cerium metal precursors on hydrotalcite-like MgAl2O4 support. In terms of catalytic activity and stability, CeO2-promoted Ni/MgAl2O4 catalyst is superior to Ni–CeO2/Al2O3 or Ni/MgAl2O4 catalysts because of high resistance to coke formation and suppressed aggregation of nickel particles. The role of CeO2 on Ni/MgAl2O4 catalyst was elucidated by carrying out the various characterization methods in the viewpoint of the aggregation of nickel
particles and metal-support interactions. The observed superior catalytic performance on CeO2-promoted Ni/MgAl2O4 catalyst at the weight ratio of MgO/Al2O3 of 3/7 seems to be closely related to high dispersion and low aggregation of active metals due to their strong interaction
with the MgAl2O4 support and the adjacent contact of Ni and CeO2 species. The CeO2 promoter also plays an important role to suppress particle aggregation by forming an appropriate interaction of NiO–CeO2 as well as Ni–MgAl2O4 with the concomitant enhancement of mobile oxygen content. 相似文献
Ni/SiO2-ZrO2 catalysts with Ni loadings of 1 to 13 wt-% were prepared, characterized by elemental analysis, X-ray diffraction, N2 sorption, temperature programmed oxidation, temperature programmed reduction, and tested for their activity and stability in the dry reforming of methane with carbon dioxide at 850 °C, gas hourly space velocity of 6000 and 1800 h–1 and atmospheric pressure. The SiO2-ZrO2 support as obtained through a simple and efficient sol-gel synthesis is highly porous (ABET = 90 m2?g–1, dP = 4.4 nm) with a homogeneously distributed Si-content of 3 wt-%. No loss of Si or formation of monoclinic ZrO2, even after steaming at 850 °C for 160 h, was detectable. The catalyst with 5 wt-% Ni loading in its fully reduced state is stable over 15 h on-stream in the dry reforming reaction. If the catalyst was not fully reduced, a reduction during the early stages of dry reforming is accompanied by the deposition of up to 44 mg?g–1carbon as shown by experiments in a magnetic suspension balance. Rapid coking occurs for increased residence times and times-on-stream starting at 50 h. The Ni loading of 5 wt-% on SiO2-ZrO2 was shown to provide an optimal balance between activity and coking tendency.
The catalytic properties of Ni/Al2O3 composites supported on ceramic cordierite honeycomb monoliths in oxidative methane reforming are reported. The prereduced
catalyst has been tested in a flow reactor using reaction mixtures of the following compositions: in methane oxidation, 2–6%
CH4, 2–9% O2, Ar; in carbon dioxide and oxidative carbon dioxide reforming of methane, 2–6% CH4, 6–12% CO2, and 0–4% O2, and Ar. Physicochemical studies include the monitoring of the formation and oxidation of carbon, the strength of the Ni-O
bond, and the phase composition of the catalyst. The structured Ni-Al2O3 catalysts are much more productive in the carbon dioxide reforming of methane than conventional granular catalysts. The catalysts
performance is made more stable by regulating the acid-base properties of their surface via the introduction of alkali metal
(Na, K) oxides to retard the coking of the surface. Rare-earth metal oxides with a low redox potential (La2O3, CeO2) enhance the activity and stability of Ni-Al2O3/cordierite catalysts in the deep and partial oxidation and carbon dioxide reforming of methane. The carbon dioxide reforming
of methane on the (NiO + La2O3 + Al2O3)/cordierite catalyst can be intensified by adding oxygen to the gas feed. This reduces the temperature necessary to reach
a high methane conversion and does not exert any significant effect on the selectivity with respect to H2. 相似文献
Hydrogen production from glycerol reforming in liquid (aqueous phase reforming, APR) and vapor (steam reforming SR) phase over alumina-supported nickel catalysts modified with Ce, Mg, Zr and La was studied. Characterization of catalysts by temperature programmed reduction and XPS analyses revealed important structural effects: (i) the intercalation of Mg between nickel and alumina that inhibited the alumina incorporation to nickel phases, (ii) the close contact between Ni and Zr phases and, (iii) the close surface interaction of La and Ce ions with NiO phases. The catalytic activity of the samples studied in this work clearly indicated the different catalyst functionalities necessary to carry out aqueous-phase and vapor-phase steam reforming of glycerol. For aqueous phase reforming of glycerol, the addition of Ce, La and Zr to Ni/Al2O3 improves the initial glycerol conversions obtained over the Ni/Al2O3 supported catalyst. It is suggested that the differences in catalytic activities are related with geometric effects caused by the decoration of Ni phases by Ce and La or by the close interaction between Ni and Zr. In spite that nickel catalysts showed high APR activities at initial times on stream, all samples showed, independently of support, important deactivation rates that deactivate the catalysts after few hours under operation. Catalysts characterization after APR showed the oxidation of the active metallic Ni during reaction as the main cause of the observed deactivation. In the case of the glycerol steam reforming in vapor phase, the use of Ce, La, Mg and Zr as promoters of Ni based catalysts increases the hydrogen selectivity. Differences in activity were explained in terms of enhancement in: surface nickel concentration (Mg), capacity to activate steam (Zr) and stability of nickel phases under reaction conditions (Ce and La). 相似文献
A series of Zr-doped ordered mesoporous Al2O3 with various Zr contents were synthesized by evaporation-induced self-assembly strategy and the Ni-based catalysts supported on these Al2O3 materials were prepared by impregnation method. These catalysts with large specific surface area, big pore volume, uniform pore size possess excellent catalytic performance for the low-temperature carbon dioxide reforming of methane. The activities of these catalysts were tested in carbon dioxide reforming of methane reaction with temperature increasing from 500 to 650?°C and the stabilities of these catalysts were evaluated for long time reaction at 650?°C. It was found that when Zr/(Zr?+?Al) molar ratio?=?0.5%, the Ni/0.5ZrO2–Al2O3 catalyst showed the highest activity, and exhibited superior stabilization compared to the Ni-based catalyst supported on traditional ordered mesoporous Al2O3. The “confinement effect” from mesoporous channels of alumina matrix is helpful to stabilize the Ni nanoparticles. As a promoter, Zr could stabilize the ordered mesoporous framework by reacting with Al2O3 to form ZrO2–Al2O3 solid solution. Since ZrO2 enhances the dissociation of carbon dioxide, more oxygen intermediates are given to remove the carbon formed during the reaction. 相似文献
Catalytic steam reforming of glycerol for renewable hydrogen generation has been investigated over Ni/CeO2 catalyst prepared by precipitation-deposition method. The fresh and used catalysts were characterized by surface area and
pore size analysis, X-ray diffraction patterns and scanning electron micrographs. Reforming experiments were carried out in
a fixed bed tubular reactor at different temperatures (400–700 °C), glycerol concentrations (5–15 wt%) and contact times.
(W/FAo=2−80 g-cat·h/mol of glycerol). The investigation revealed that the Ni/CeO2 catalyst prepared by the above method is effective to produce high yield of hydrogen up to 5.6 (moles of H2/moles of glycerol fed). The formation of methane and carbon monoxide was greatly reduced over this catalyst. Significantly
low amount of coke deposition was observed on the CeO2 supported catalyst. From the kinetic analysis, the activation energy for the steam reforming of glycerol was found to be
36.5 kJ/mol. 相似文献
To develop an efficient catalyst for steam reforming of propane, Ni/LaAlO3 catalysts were prepared by deposition precipitation, impregnation, and solvo-thermal methods, and characterized by XRD, BET,
H2-TPR, elemental analyses, and TEM. Ni/Al2O3 and Ni/CeO2 catalysts were also synthesized by the solvo-thermal method for comparison. The Ni/LaAlO3 catalysts exhibited better catalytic performance than both Ni/Al2O3 and Ni/CeO2 catalysts, and activities with Ni/LaAlO3 were found to be dependent upon the preparation methods. In particular, the Ni/LaAlO3 catalyst synthesized by the solvo-thermal method exhibited the highest activity presumably because tetrahydrofuran helps
distribute generated Ni nanoparticles onto the catalyst surface in a uniform fashion. In addition, the solvo-thermally prepared
Ni/LaAlO3 catalyst was found to be highly stable, with its activity being maintained at least during 100 h. The observed high stability
is attributed to the excellent oxygen storage capacity of LaAlO3, which was first determined by thermogravimetric methods as well as by soot oxidations in the presence of Al2O3, CeO2, and LaAlO3. Compared to the Ni/Al2O3 and Ni/CeO2 catalysts, Ni/LaAlO3 exhibited suppressed carbon formation even at lower S/C ratios due to the superior oxygen transport ability of the LaAlO3 support. 相似文献
A series of Mn-promoted 15 wt-% Ni/Al2O3 catalysts were prepared by an incipient wetness impregnation method. The effect of the Mn content on the activity of the Ni/Al2O3 catalysts for CO2 methanation and the comethanation of CO and CO2 in a fixed-bed reactor was investigated. The catalysts were characterized by N2 physisorption, hydrogen temperature-programmed reduction and desorption, carbon dioxide temperature-programmed desorption, X-ray diffraction and highresolution transmission electron microscopy. The presence of Mn increased the number of CO2 adsorption sites and inhibited Ni particle agglomeration due to improved Ni dispersion and weakened interactions between the nickel species and the support. The Mn-promoted 15 wt-% Ni/Al2O3 catalysts had improved CO2 methanation activity especially at low temperatures (250 to 400 °C). The Mn content was varied from 0.86% to 2.54% and the best CO2 conversion was achieved with the 1.71Mn-Ni/Al2O3 catalyst. The co-methanation tests on the 1.71Mn-Ni/Al2O3 catalyst indicated that adding Mn markedly enhanced the CO2 methanation activity especially at low temperatures but it had little influence on the CO methanation performance. CO2 methanation was more sensitive to the reaction temperature and the space velocity than the CO methanation in the co-methanation process.
An Al2O3-ZrO2 support was prepared by grafting a zirconium precursor onto the surface of commercial γ-Al2O3. A physical mixture of Al2O3-ZrO2 was also prepared for the purpose of comparison. Ni/Al2O3-ZrO2 catalysts were then prepared by an impregnation method, and were applied to the hydrogen production by steam reforming of
liquefied natural gas (LNG). The effect ZrO2 and preparation method of Al2O3-ZrO2 on the performance of supported nickel catalysts in the steam reforming of LNG was investigated. The Al2O3-ZrO2 prepared by a grafting method was more efficient as a support for nickel catalyst than the physical mixture of Al2O3-ZrO2 in the hydrogen production by steam reforming of LNG. The well-developed tetragonal phase of ZrO2 and the high dispersion of ZrO2 on the surface of γ-Al2O3 were responsible for the enhanced catalytic performance of Ni/Al2O3-ZrO2 prepared by way of a grafting method. 相似文献
Two types of CeO2-modified Ni/Al2O3 catalysts were prepared by a consecutive impregnation method with different sequences in the impregnation of Ni and CeO2, and their performance in autothermal reforming (ATR) of isooctane was investigated. Catalysts prepared by adding CeO2 prior to the addition of Ni, Ni/CeO2-Al2O3, produced larger amounts of hydrogen than those obtained using catalysts prepared by adding the two components in an opposite
sequence, Ni-CeO2/Al2O3. The results of H2 chemisorption and temperature-programmed reduction revealed that added CeO2 increased the dispersion of the Ni species on Al2O3 and suppressed the formation of NiAl2O4 in the catalyst such that large amounts of Ni species were present as NiO, the active species for the ATR. The elemental
and thermogravimetric analyses of deactivated catalysts indicated that Ni/CeO2-Al2O3, which showed a longer lifetime than Ni-CeO2/Al2O3, contained lesser amounts and different types of coke on the surface. 相似文献
Oxidative dehydrogenation of n-butene to 1,3-butadiene over Co9Fe3Bi1Mo12O51 catalyst was conducted in a continuous flow fixed-bed reactor. The effect of reaction conditions (steam/n-butene ratio, reaction
temperature, and space velocity) on the catalytic performance of Co9Fe3Bi1Mo12O51 was investigated. Steam played an important role in decreasing contact time, suppressing total oxidation of n-butene, and
removing coke during the reaction. Yield for 1,3-butadiene showed a volcano-shaped curve with respect to steam/n-butene ratio.
The compensation between thermodynamic effect and kinetic effect led to a volcano-shaped curve of 1,3-butadiene yield with
respect to reaction temperature. The Co9Fe3Bi1Mo12O51 catalyst showed the best catalytic performance at a certain value of space velocity. The optimum steam/n-butene ratio, reaction
temperature, and gas hourly space velocity were found to be 15, 420 °C, and 675 h−1, respectively. 相似文献
Catalytic steam reforming of bio‐oil is an economically‐feasible route which produces renewable hydrogen. The Ni/MgO‐La2O3‐Al2O3 catalyst was prepared with Ni as active agent, Al2O3 as support, and MgO and La2O3 as promoters. The experiments were conducted in fixed bed and fluidized bed reactors, respectively. Temperature, steam‐to‐carbon mole ratio (S/C), and liquid hourly space velocity (LHSV) were investigated with hydrogen yield as index. For the fluidized bed reactor, maximum hydrogen yield was obtained under temperatures 700–800 °C, S/C 15–20, LHSV 0.5–1.0 h–1, and the maximum H2 yield was 75.88 %. The carbon deposition content obtained from the fluidized bed was lower than that from the fixed bed. The maximum H2 yield obtained in the fluidized bed was 7 % higher than that of the fixed bed. The carbon deposition contents obtained from the fluidized bed was lower than that of the fixed bed at the same reaction temperature. 相似文献
The catalytic behavior of Ni/Ce-ZrO2/θ-Al2O3 has been investigated in the partial oxidation of methane (POM) toward synthesis gas. The catalyst showed high activity and
selectivity due to the heat treatment of the support and the promotional effect of Ce-ZrO2. It is suggested that the support was stabilized through the heat treatment of γ-Al2O3 and the precoating of Ce-ZrO2, on which a protective layer was formed. Moreover, sintering of the catalyst was greatly suppressed for 24 h test. Pulse
experiments of CH4, O2 and/or CH4/O2 with a molar ratio of 2 were systematically performed over fresh, partially reduced and well reduced catalyst. Results indicate
that CH4 can be partially oxidized to CO and H2 by the reactive oxygen in complex NiOx species existing over the fresh catalyst. It is demonstrated that POM over Ni/Ce-ZrO2/θ-Al2O3 follows the pyrolysis mechanism, and both the carbonaceous materials from CH4 decomposition over metallic nickel and the reactive oxygen species present on NiOx and Ce-ZrO2 are intermediates for POM. 相似文献
The performance of La0.75Sr0.25Cr0.9M0.1O3 (M = Mn, Fe, Co, and Ni) perovskitic materials as anodes was studied for a CO-fueled solid oxide fuel cell. The electrocatalytic performance and the tolerance to carbon deposition were investigated, while electrochemical characterization was carried out via AC impedance spectroscopy and cyclic voltammetry. The La0.75Sr0.25Cr0.9Fe0.1O3 perovskite showed the best anode performance at temperatures above 900 °C; while at temperatures below 900 °C, the best performance was achieved with the La0.75Sr0.25Cr0.9Co0.1O3 material. AC impedance spectroscopy was used for a semi-quantitative analysis of the LSC-M0.1 anodes performance in view of total cell and charge transfer resistance. All anode materials exhibit high electronic conductivity and presumably do not substantially contribute to the overall cell resistance and concomitant ohmic losses. 相似文献
Ni(x)/Al2O3 (x=wt%) catalysts with Ni loadings of 5–25 wt% were prepared via a wet impregnation method on an γ-Al2O3 support and subsequently applied in the reductive amination of ethanol to ethylamines. Among the various catalysts prepared, Ni(10)/Al2O3 exhibited the highest metal dispersion and the smallest Ni particle size, resulting in the highest catalytic performance. To reveal the effects of reaction parameters, a reductive amination process was performed by varying the reaction temperature (T), weight hourly space velocity (WHSV), and NH3 and H2 partial pressures in the reactions. In addition, on/off experiments for NH3 and H2 were also carried out. In the absence of NH3 in the reactant stream, the ethanol conversion and selectivities towards the different ethylamine products were significantly reduced, while the selectivity to ethylene was dominant due to the dehydration of ethanol. In contrast, in the absence of H2, the selectivity to acetonitrile significantly increased due to dehydrogenation of the imine intermediate. Although a small amount of catalyst deactivation was observed in the conversion of ethanol up to 10 h on stream due to the formation of nickel nitride, the Ni(10)/Al2O3 catalyst exhibited stable catalytic performance over 90 h under the optimized reaction conditions (i.e., T=190 °C, WHSV=0.9 h?1, and EtOH/NH3/H2 molar ratio=1/1/6). 相似文献