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1.
Production of hydrogen (H2) from catalytic steam reforming of bio-oil was investigated in a fixed bed tubular flow reactor over nickel/alumina (Ni/Al2O3) supported catalysts at different conditions. The features of the steam reforming of bio-oil, including the effects of metal content, reaction temperature, WbHSV (defined as the mass flow rate of bio-oil per mass of catalyst) and S/C ratio (the molar ratio of steam to carbon fed) on the hydrogen yield were investigated. Carbon conversion (moles of carbon in the outlet gases to moles of the carbon feed) was also studied, and the outlet gas distributions were obtained. It was revealed that the Al2O3 with 14.1% Ni content gave the highest yield of hydrogen (73%) among the catalysts tested, and the best carbon conversion was 79% under the steam reforming conditions of S/C = 5, WbHSV = 13 1/h and temperature = 950 °C. The H2 yield increased with increasing temperature and decreasing WbHSV; whereas the effect of the S/C ratio was less pronounced. In the S/C ratio range of 1 to 2, the hydrogen yield was slightly increased, but when the S/C ratio was increased further, it did not have an effect on the H2 production yield. 相似文献
2.
This work investigates the improvement of Ni/Al2O3 catalyst stability by ZrO2 addition for H2 gas production from CH4/CO2 reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO2 loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH4:CO2 ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al2O3 was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO2, as it enhances dissociation of CO2 forming oxygen intermediates near the contact between ZrO2 and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO2–Al2O3 composite and the plugging of Al2O3 pore by ZrO2. The 15% Ni/10% ZrO2/Al2O3 co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made. 相似文献
3.
Ni/Al2O3 aerogel catalysts were synthesized by a sol-gel method combined with a supercritical drying route. The catalytic performances of the catalysts in methane reforming with CO2 were investigated in a quartz micro-reactor. The results indicated that the aerogel catalyst showed higher specific surface area and higher dispersivity of nickel species than those of impregnation catalyst. The excellent catalytic performances and stabilities were achieved over the aerogel catalysts in the fluidized bed reactor. Comprehensive characterization with TG, XRD and FESEM revealed that the aerogel catalyst in the fluidized bed had much lower carbon deposition than that in the fixed bed. The fluidization of the aerogel catalyst greatly improved the contact efficiency of gas-solid phase, which accelerated the gasification of the deposited carbon. In contrast, the deactivation of the aerogel catalyst was caused by the carbon deposition due to the catalyst without moving in the fixed bed. Moreover, decreasing activity of the impregnation catalyst in the fluidized bed resulted from the poor fluidization state of catalyst particles and low effective active sites on surface of catalyst. 相似文献
4.
Ethanol steam reforming was studied over Ni/Al2O3 catalysts. The effect of support (- and γ-Al2O3), metal loading and a comparison between conventional H2 reduction with an activation method employing a CH4/O2 mixture was investigated. The properties of catalysts were studied by N2 physisorption, X-ray diffraction (XRD) and temperature programmed reduction (TPR). After activity tests, the catalysts were analyzed by scanning electron microscopy (SEM) and thermogravimetric analysis (TG/DTA). Ni supported on γ-Al2O3 was more active for H2 production than the catalyst supported on -Al2O3. Metal loading did not affect the catalytic performance. The alternative activation method with CH4/O2 mixture affected differently the activity and stability of the Ni/γ-Al2O3 and the Ni/-Al2O3 catalyst. This activation method increased significantly the stability of Ni/-Al2O3 compared to H2 reduction. SEM and TG/DTA analysis indicate the formation of filamentous carbon during the CH4/O2 activation step, which is associated with the increasing catalyst activity and stability. The effect of temperature on the type of carbon formed was investigated; indicating that filamentous coke increased activity while encapsulating coke promoted deactivation. A discussion about carbon formation and the influence on the activity is presented. 相似文献
5.
Jeong Gil Seo Min Hye Youn Sunyoung Park Joohyung Lee Sang Hee Lee Howon Lee In Kyu Song 《Korean Journal of Chemical Engineering》2008,25(1):95-98
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
6.
Previous results on different catalysts revealed that methylcyclohexane underwent selective dehydrogenation to form toluene and hydrogen. This reaction system is a useful prototype model for similar systems in the chemical process and petroleum refining industries, such as hydrotreating for aromatics reduction, desulfurization, denitrogenation, reforming for aromatics reduction, dehydrocyclization, and fuel processing of liquid hydrocarbons in the generation of hydrogen feed for fuel cells. Dehydrogenation of methylcyclohexane to toluene is a method for hydrogen storage in the form of liquid organic hydrides. The efficiency of the dehydrogenation reactions and the quantity of products depend on the catalyst used. In the case of the dehydrogenation of methylcyclohexane to toluene, a metallic function, usually platinum is required as the catalyst. Although, there were some different catalysts used by former researchers, there was almost no investigation about the use of the nickel catalysts for this reaction. From the economical point of view, more efficient catalysts and reaction engineering methods should be developed for these reactions.In this work dehydrogenation of methylcyclohexane was performed in a fixed-bed catalytic reactor in the temperature range of 653–713 K on prepared Ni/Al2O3 catalysts having 5, 10, 15 and 20 wt.% Ni content. The inlet flowrates of methylcyclohexane and hydrogen to the reactor were changed by keeping one of them constant in order to investigate their effects on this reaction. 相似文献
7.
Jorge D.A. Bellido Eurico Y. Tanabe Elisabete M. Assaf 《Applied catalysis. B, Environmental》2009,90(3-4):485-488
Supported nickel catalysts of composition Ni/Y2O3–ZrO2 were synthesized in one step by the polymerization method and compared with a nickel catalyst prepared by wet impregnation. Stronger interactions were observed in the formed catalysts between NiO species and the oxygen vacancies of the Y2O3–ZrO2 in the catalysts made by polymerization, and these were attributed to less agglomeration of the NiO during the synthesis of the catalysts in one step. The dry reforming of ethanol was catalyzed with a maximum CO2 conversion of 61% on the 5NiYZ catalyst at 800 °C, representing a better response than for the catalyst of the same composition prepared by wet impregnation. 相似文献
8.
Gang WangHui Wang Weilong Li Zhaoyu RenJintao Bai Jinbo Bai 《Fuel Processing Technology》2011,92(3):531-540
Fe/Al2O3 catalysts with different Fe loadings (10-90 mol%) were prepared by hydrothermal method. Ethanol decomposition was studied over these Fe/Al2O3 catalysts at temperatures between 500 and 800 °C to produce hydrogen and multi-walled carbon nanotubes (MWCNTs) at the same time. The results showed that the catalytic activity and stability of Fe/Al2O3 depended strongly on the Fe loading and reaction temperature. The Fe(30 mol%)/Al2O3 and Fe(40 mol%)/Al2O3 were both the effective catalyst for ethanol decomposition into hydrogen and MWCNTs at 600 °C. Several reaction pathways were proposed to explain ethanol decomposition to produce hydrogen and carbon (including nanotube) at the same time. 相似文献
9.
Y. Wang Y.H. Chin R.T. Rozmiarek B.R. Johnson Y. Gao J. Watson A.Y.L. Tonkovich D.P. Vander Wiel 《Catalysis Today》2004,98(4):575-581
Highly active and coke-resistant Rh catalysts were developed for methane steam reforming in microchannel chemical reactors. Rh loading was optimized on a stable MgOAl2O3 support to improve the volumetric productivity for methane conversion. Catalyst activities were stable over a wide range of steam/carbon ratios. In particular, experimental results demonstrated that Rh/MgOAl2O3 catalysts are extremely active for methane steam reforming and are resistant to coke formation at stoichiometric steam/carbon ratio of 1 for over 14 h time-on-stream with no sign of deactivation. Methane steam reforming activities on this catalyst is compared in both a microchannel reactor and a conventional micro-tubular reactor. Significant performance enhancement was observed in microchannel reactors owing to improved heat and mass transfer. 相似文献
10.
Sang Hyun Ahn Oh Joong Kwon Insoo Choi Jae Jeong Kim 《Catalysis communications》2009,10(15):2018-2022
Commercial Cu–ZnO–Al2O3 catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al2O3 catalyst with Pt–Al2O3 catalyst. The Pt–Al2O3 and Cu–ZnO–Al2O3 catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al2O3 and Cu–ZnO–Al2O3 catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al2O3 and Cu–ZnO–Al2O3 catalyst mixture was used. 相似文献
11.
The CH4-CO2 reforming was investigated in a fluidized bed reactor using nano-sized aerogel Ni/Al2O3 catalysts, which were prepared via a sol–gel method combined with a supercritical drying process. The catalysts were characterized with BET, XRD, H2-TPR and H2-TPD techniques. Compared with the impregnation catalyst, aerogel catalysts exhibited higher specific surface areas, lower bulk density, smaller Ni particle sizes, stronger metal-support interaction and higher Ni dispersion degrees. All tested aerogel catalysts showed better catalytic activities and stability than the impregnation catalyst. Their catalytic stability tested during 48 h reforming was dependent on their Ni loadings. Characterizations of spent catalysts indicated that only limited graphitic carbon formed on the aerogel catalyst, while massive graphitic carbon with filamentous morphology was observed for the impregnation catalyst, leading to significant catalytic activity degradation. An aerogel catalyst containing 10% Ni showed the best catalytic stability and the lowest rate of carbon deposition among the aerogel catalysts due to its small Ni particle size and strong metal-support interaction. 相似文献
12.
Jae-Sung Choi Kwang-Ik Moon Young Gul Kim Jae Sung Lee Cheol-Hyun Kim David L. Trimm 《Catalysis Letters》1998,52(1-2):43-47
CO2 reforming of methane was studied over modified Ni/Al2O3 catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al2O3, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO2 reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction
in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher
activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even
in the absence of diluent gas and the activity changed only slightly during 100 h operation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Chunshan Li Daisuke Hirabayashi Kenzi Suzuki 《Applied catalysis. B, Environmental》2009,88(3-4):351-360
Newly synthesized nickel calcium aluminum catalysts (Ni/Ca12Al14O33) were tested in a fixed bed reactor for biomass tar steam reforming, toluene as tar destruction model compound. Four catalysts (Ni/Ca12Al14O33) were prepared with Ni loading amount from 1, 3, 5 to 7 wt%, even 1% loading catalyst also showed excellent performance. Catalysts aged experiments in the absence (60 h on stream) and presence of H2S were characterized by BET, X-ray diffraction (XRD), and Raman spectra. It was observed that Ni/Ca12Al14O33 showed excellent sustainability against coke formation due to the “free oxygen” in the catalysts. It also exhibited higher H2S-poisoning resistance property compared to the commercial catalysts Ni/Al2O3 (5%) and Ni/CaO0.5/MgO0.5. Raman spectra revealed that “free oxygen O2− and O22−” in the structure of the catalysts could be substituted by sulfur then protected Ni poisoning on some degree, but reactivation experiments by O2 flowing showed that the sulfide Ni/Ca12Al14O33 was difficult to completely restore, incorporation of sulfur in the structure only partly regain by O2. The kinetic model proposes, as generally accepted, a first-order reaction for toluene with activation energy of 82.06 kJ mol−1 was coincident with the literature data. The Ni/Ca12Al14O33 catalyst was effective and relative cheap, which may be lead to reduction in the cost of hot gas cleaning process. 相似文献
14.
XPS measurements have shown that tin oxides are more readily reduced to metallic tin by hydrogen in Ni/Al2O3 systems than on pure Al2O3. During the reductive activation of Sn doped Ni/Al2O3 catalysts, surface segregation of the dopant was observed. This finding may explain that tin enhances the selectivity of the steam reforming catalysts only when added in very low concentrations and that it acts as a poison at higher loadings. 相似文献
15.
Lifeng Zhang 《Fuel》2009,88(3):511-24
Nickel-based catalysts supported on Al2O3 · SiO2 were prepared with modification of the second metal involving La, Co, Cu, Zr or Y, of which the catalytic behaviors were assessed in the ethanol steam reforming reaction. Activity test indicated that addition of La resulted in higher selectivity of hydrogen and lower selectivity of carbon monoxide, compared with Co-doped nickel catalyst. Influences of lanthanum amounts on catalytic performance were studied over 30NixLa/Al2O3 · SiO2 (x = 5, 10, 15), and characterizations by XRD, TPR and XPS indicated that low amount of lanthanum additives (5%) was superior to inhibit the crystal growth of nickel as well as beneficial to the reduction of nickel oxide. Finally 100 h test for the optimal catalyst 30Ni5La/Al2O3 · SiO2 indicated its good long-term stability to provide high hydrogen selectivity and low carbon monoxide formation, as well as good resistance to coke deposition at low temperature. 相似文献
16.
J.D.A. Bellido 《Fuel》2009,88(9):1673-1034
ZrO2, γ-Al2O3 and ZrO2/γ-Al2O3-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H2, Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO2/γ-Al2O3 matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO2. Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO2. 相似文献
17.
18.
Composite coatings Ni/Al2O3 were electrochemically deposited from a Watts bath. Al2O3 powder with particle diameter below 1 μm was codeposited with the metal. The obtained Ni/Al2O3 coatings contained 5-6% by weight of corundum. The structure of the coatings was examined by scanning electron microscopy (SEM). It has been found that the codeposition of Al2O3 particles with nickel disturbs the nickel coating's regular surface structure, increasing its microcrystallinity and surface roughness. DC and AC electrochemical tests were carried out on such coatings in a 0.5 M solution of Na2SO4 in order to evaluate their corrosion resistance. The potentiodynamic tests showed that the corrosion resistance of composite coating Ni/Al2O3 is better than that of the standard nickel coating. After 14 days of exposure the nickel coating corrodes three times faster than the Ni/Al2O3 coating. The electrochemical behaviour of the coatings in the corrosive solution was investigated by electrochemical impedance spectroscopy (EIS). An equivalent circuit diagram consisting of two RC electric circuits: one for electrode, nickel corrosion processes and the other for processes causing coating surface blockage, were adopted for the analysis of the impedance spectra. The changes in the charge transfer resistance determined from the impedance measurements are comparable with the changes in corrosion resistance determined from potentiodynamic measurements. 相似文献
19.
The SSITKA measurements were performed in the steady state of complete methane oxidation on the Pd/Al2O3 and Pt/Al2O3 catalysts. It was found that the number of intermediates and their average life-time on the catalyst surface changes with
the increase of reaction temperature. On the Pd/Al2O3 catalyst there is larger number of active centres than on Pt/Al2O3 catalyst which permits the course of methane oxidation at lower temperatures. 相似文献
20.
B. Grbic N. Radic Z. Arsenijevic R. Garic-Grulovic Z. Grbavcic 《Applied catalysis. B, Environmental》2009,90(3-4):478-484
The deep oxidation of dimethylamine (DMA) was studied over Pt/Al2O3 catalysts with small (1 nm) and large (7.8–15.5 nm) Pt crystallite sizes. The turnover frequency (TOF) was higher for the large than for the small Pt crystallites, indicating that the reaction is structure sensitive. Two kinetic models were used to interpret the obtained results, i.e., the Mars van Krevelen and a mechanism based on the adsorption of oxygen and adsorption of dimethylamine on different active sites were employed. Both models showed that the activation energy for the oxygen chemisorption rate constant (ko) decreased with increasing of Pt crystallite size and that the activation energy for the surface reaction rate constant (ki) was independent of the Pt crystallite size. The structure sensitivity may be explained by differences in the reactivity of the oxygen adsorbed on these Pt crystallites.The Mars van Krevelen model fits the TOF values very well at concentrations of DMA higher than 1500 ppm, while in the lower concentrations region, the model under predicts the experimental data. The model based on the adsorption of oxygen and DMA on different active sites fits the experimental data quite well over the whole temperature and concentration range. The fitted values of the Henry adsorption constant are independent of the Pt crystallite size. 相似文献