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1.
Mesoporous Ni-CaO-ZrO2 nanocomposites with high thermal stability were designed and employed in the CO2/CH4 reforming. The nanocomposites with appropriate Ni/Ca/Zr molar ratios exhibited excellent activity and prominent coking resistivity. The Ni crystallites were effectively controlled under the critical size for coke formation in such nanocomposites. It was found that low Ni content resulted in high metal dispersion and good catalytic performance. Moreover, the basicity of the matrices improved the chemisorption of CO2 and promoted the gasification of deposited coke on the catalyst. 相似文献
2.
M. Rezaei S.M. Alavi S. Sahebdelfar Peng Bai Xinmei Liu Zi-Feng Yan 《Applied catalysis. B, Environmental》2008,77(3-4):346-354
Mesoporous nanocrystalline zirconia with high-surface area and pure tetragonal crystalline phase has been prepared by the surfactant-assisted route, using Pluronic P123 block copolymer surfactant. The synthesized zirconia showed a surface area of 174 m2 g−1 after calcination at 700 °C for 4 h. The prepared zirconia was employed as a support for nickel catalysts in dry reforming reaction. It was found that these catalysts possessed a mesoporous structure and even high-surface area. The activity results indicated that the nickel catalyst showed stable activity for syngas production with a decrease of about 4% in methane conversion after 50 h of reaction. Addition of promoters (CeO2, La2O3 and K2O) to the catalyst improved both the activity and stability of the nickel catalyst, without any decrease in methane conversion after 50 h of reaction. 相似文献
3.
Highly-ordered TiO2 nanotube arrays (TiNTA) were prepared by an electrochemical anodization method and used as the carrier material to load 1 wt.% Ru. The Ru/TiNTA catalyst was then applied to the combination reactions of the partial oxidation of methane reaction (POM) with the carbon dioxide reforming with methane reaction (CRM) for syngas production. In comparison with the commercial TiO2 powder (P25) supported 1 wt.% Ru catalyst, Ru/TiNTA shows higher activity and much better stability. The superior performance of Ru/TiNTA is attributed to the specific monolithic-like structure and confinement effect of TiNTA. 相似文献
4.
Zeolite Y supported rhodium catalysts were prepared by ion-exchange starting from an aqueous solution of [Rh[(NH3)5Cl]Cl2·6H20]. Previous work in this laboratory had shown that this procedure results in a Rh dispersion of near 100%. The catalysts were tested for their activity in the CO2 reforming of CH4. They were found to combine extraordinary stability with high activity and selectivity. At 923 K, 90 mol-% of the CH4 was converted giving a H2/CO ratio near unity. A weight loading of 0.5 to 0.93% Rh gives the highest turnover frequencies. Thermodynamic equilibrium is reached near 873 K. With a given Rh loading, the zeolite supports are superior to amorphous supports and NaY is superior to the HY. No deactivation was observed in tests of 30 h time on stream at atmospheric pressure or after repeated thermal cycles. No coke deposition was detected by temperature programmed oxidation of used catalysts. Temperature programmed reduction indicates the presence of three discernible Rh species. 相似文献
5.
This paper presents an investigation into the complex interactions between catalytic combustion and CH4 steam reforming in a co-flow heat exchanger where the surface combustion drives the endothermic steam reforming on opposite sides of separating plates in alternating channel flows. To this end, a simplified transient model was established to assess the stability of a system combining H2 or CH4 combustion over a supported Pd catalyst and CH4 steam reforming over a supported Rh catalyst. The model uses previously reported detailed surface chemistry mechanisms, and results compared favorably with experiments using a flat-plate reactor with simultaneous H2 combustion over a γ-Al2O3-supported Pd catalyst and CH4 steam reforming over a γ-Al2O3-supported Rh catalyst. Results indicate that stable reactor operation is achievable at relatively low inlet temperatures (400 °C) with H2 combustion. Model results for a reactor with CH4 combustion indicated that stable reactor operation with reforming fuel conversion to H2 requires higher inlet temperatures. The results indicate that slow transient decay of conversion, on the order of minutes, can arise due to loss of combustion activity from high-temperature reduction of the Pd catalyst near the reactor entrance. However, model results also show that under preferred conditions, the endothermic reforming can be sustained with adequate conversion to maintain combustion catalyst temperatures within the range where activity is high. A parametric study of combustion inlet stoichiometry, temperature, and velocity reveals that higher combustion fuel/air ratios are preferred with lower inlet temperatures (≤500 °C) while lower fuel/air ratios are necessary at higher inlet temperatures (600 °C). 相似文献
6.
Yuta Suga Rie YoshinagaNaoki Matsunaga Yoshihiro HirataSoichiro Sameshima 《Ceramics International》2012
This paper reports on the composition and flow rate of outlet gas and current density during the reforming of CH4 with CO2 using three different electrochemical cells: cell A, with Ni−GDC (Gd-doped ceria: Ce0.8Gd0.2O1.9) cathode/porous GDC electrolyte/Cu−GDC anode, cell B, with Cu−GDC cathode/ porous GDC electrolyte/Cu−GDC anode and cell C, with Ru−GDC cathode/ porous GDC electrolyte/ Cu−GDC anode. In the cathode, CO2 reacts with supplied electrons to form CO fuel and O2− ions (CO2+2e−→CO+O2−). Too low affinity of Cu cathode to CO2 in cell B reduced the reactivity of the CO2 with electrons. The CO fuel, O2− ions and CH4 gas were transported to the anode through the porous GDC mixed conductor of O2− ions and electrons. In the anode, CH4 reacts with O2− ions to produce CO and H2 fuels (CH4+O2−→2 H2+CO+2e−). The reforming efficiency at 700−800 °C was lowest in cell B and highest in cell A. The Cu anode in cells A and C worked well to oxidize CH4 with O2− ions (2Cu+O2−→Cu2O+2e−, Cu2O+CH4→2Cu+CO+2H2). However, a blockage of the outlet gas occurred in all the cells at 700−800 °C. The gas flow is inhibited due to a reduction in pore size in the cermet cathode, as well as sintering and grain growth of Cu metal in the anode during the reforming. 相似文献
7.
The reforming of CH4 with CO2 over activated carbon- or silica-supported cobalt catalysts with and without added MgO as promoter has been studied over a range of temperatures (500–700°C). A significant effect of the MgO on catalyst efficiency was observed. The presence of MgO markedly reduces the carbon deposition on the surface of the catalyst and therefore, contributes to the stability of the catalyst. Based on temperature-programmed surface reaction experiments of chemisorbed CO2, the role of MgO may be ascribed to the formation of strongly adsorbed CO2 species over its surface. These CO2 species can easily react with the surface carbon deposits under CO2-reforming reaction conditions, preventing in this way catalyst deactivation. 相似文献
8.
Yongfa Zhang Meng Zhang Guojie Zhang Huirong Zhang 《Frontiers of Chemical Engineering in China》2010,4(4):481-485
An investigation was made using a continuous fixed bed reactor to understand the influence of carbon deposition obtained under
different conditions on CH4-CO2 reforming. Thermogravimetry (TG) and X-ray diffraction (XRD) were employed to study the characteristics of carbon deposition.
It was found that the carbonaceous catalyst is an efficient catalyst in methane decomposition and CH4-CO2 reforming. The trend of methane decomposition at lower temperatures is similar to that at higher temperatures. The methane
conversion is high during the initial of stage of the reaction, and then decays to a relatively fixed value after about 30
min. With temperature increase, the methane decomposition rate increases quickly. The reaction temperature has significant
influence on methane decomposition, whereas the carbon deposition does not affect methane decomposition significantly. Different
types of carbon deposition were formed at different methane decomposition reaction temperatures. The carbon deposition Type
I generated at 900°C has a minor effect on CH4-CO2 reforming and it easily reacts with carbon dioxide, but the carbon deposition Type II generated at 1000°C and 1100°C clearly
inhibits CH4-CO2 reforming and it is difficult to react with carbon dioxide. The results of XRD showed that some graphite structures were
found in carbon deposition Type II. 相似文献
9.
CO_2吸附强化CH_4/H_2O重整制氢是提供低成本高纯氢气和实现CO_2减排的方法之一。其中,催化剂和吸附剂是该工艺的重要组成部分,其活性与选择性制约了反应速率和产率,寿命长短关系到生产成本。综述了CO_2吸附强化CH_4/H_2O重整制氢催化剂和吸附剂的研究现状及存在的问题,机械混合的催化剂与吸附剂在反应过程中存在吸附产物包覆催化活性位点的问题,导致催化剂活性迅速下降。针对该问题,进一步探讨了不同结构双功能复合催化剂的结构特性、研究现状及其在循环-再生过程中存在的问题,核壳型双功能催化剂具有吸附组分与催化剂组分相对独立、催化组分分散分布和比表面积大等优点,在吸附强化制氢中有进一步研究的潜力。利用双功能催化剂的结构特点,实现反复循环再生过程中催化与脱碳反应的匹配,是推动CO_2吸附强化CH_4/H_2O重整制氢技术工业化发展的关键。 相似文献
10.
In this work, the microwave-assisted CO2 reforming of CH4 over mixtures of carbonaceous materials and an in-lab prepared Ni/Al2O3 was studied. Ni/Al2O3 is not heated by microwave radiation, and for this reason, microwave receptors, such as carbonaceous materials, must be mixed with this catalyst. In order to evaluate the role of the carbonaceous component of the blend, two different carbonaceous materials were used: an activated carbon, FY5, and a metallurgical coke, CQ. The carbonaceous component acted not only as microwave receptor but also as catalyst and, consequently, it influenced the catalytic activity of the mixture. FY5 + Ni/Al2O3 was found to be a better catalyst than CQ + Ni/Al2O3, since FY5 on its own showed a better catalytic activity than CQ. Ni/FY5, which consists of Ni impregnated directly onto the microwave receptor, was also evaluated as a catalyst. It was found that the catalytic activity of the mixture FY5 + Ni/Al2O3 was better than that of Ni/FY5. Finally, the influence of the heating device on the catalytic activity of FY5 + Ni/Al2O3 was studied. Conversions over FY5 + Ni/Al2O3 and microwave heating were found to be similar to conversions over Ni/Al2O3 and conventional heating. 相似文献
11.
Pt/MgO catalysts were prepared by wet impregnation. At 800 °C and atmospheric pressure, Pt/MgO catalysts exhibited a high stability at high gas hourly space velocity of 36,000 ml/g h with a CH4/CO2 ratio of 1.0. During 72 h time on stream, the conversion of CH4 and CO2 remained almost constant, at about 88% and 90%, respectively. There was no loss of Pt. After reaction, the XRD peaks of MgO became broader, indicating amorphization of MgO, which was supported by TEM results. XPS indicated that the reforming reaction had little influence on Pt. CO2-TPSR results showed that some carbon deposition occurred under stoichiometric feed of CH4 and CO2, but it did not result in the deactivation of the catalyst. The deposited carbon came mainly from the decomposition of methane. 相似文献
12.
In this study, gas separation properties of Matrimid/MIL-53 mixed matrix membranes with different MOF weight percentages (0–20 wt.%) were investigated. TEM, XRD and DLS analysis were implemented to investigate MIL-53, structure and particles size distribution. SEM, FTIR, DSC and TGA analyses were conducted to characterize the fabricated membranes. The SEM images of these membranes showed good adhesion between polymer and particles, although for 20% MIL-53 loading, particles agglomeration was observed in some areas. Moreover, surface images of the membranes showed adequate dispersion of the particles in the polymer matrix, especially at lower MOF loadings. The permeability of pure CO2 and CH4 gases for all membranes were measured and the ideal CO2/CH4 selectivity was calculated. CH4 permeability of membranes increased slightly as the percentage of loading increased. At 20 wt.% MOF loading, void formation led to a significant increase in CH4 permeability (300% over pure Matrimid). CO2 permeability showed the same trend; there was a 94% increase in permeability compared to pure Matrimid for 15 wt.% MMMs. CO2/CH4 selectivity also increased as MOF loading increased. The highest selectivity was shown for 15 wt.% MOF loading. This membrane had 84% growth in selectivity over pure Matrimid. Although at 20 wt.% MIL-53 loading, membrane separation performance was destroyed. 相似文献
13.
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
14.
Several important chemicals can potentially be manufactured from natural gas (mostly methane) by first converting it to syngas (CO+H2). The high cost of converting methane to syngas currently limits the large scale commercial use of syngas to produce methanol. This study focuses on the CO2/steam reforming of methane to produce inexpensive syngas using nickel and magnesium containing hydrotalcite clay-derived catalysts. Several of these catalysts were prepared and evaluated. The results are compared with commercial Ni/Al2O3 or Ni/MgAl2O4 catalysts. At 815°C and 300 psi pressure, the fresh clay-derived catalysts showed identical performance as the commercial catalysts. However, under more severe operating conditions, the clay-derived catalysts exhibited superior activity and stability. Aging studies clearly showed that the clay-derived catalysts are more stable and coke resistant than commercial catalysts. 相似文献
15.
Zheng Xu Yumin Li Jiyan Zhang Liu Chang Rongqi Zhou Zhanting Duan 《Applied Catalysis A: General》2001,210(1-2):45-53
The effects of nickel loading, calcination temperature, support, and basic additives on Ni-based catalyst structure and reactivity for CH4 reforming with CO2 were investigated. The results show that the structure of the nickel active phase strongly depends on the interactions of the metal and the support, which are related to the support properties, the additives and the preparation conditions. “Free” Ni species can be formed when the interaction is weak and their mobility makes them easily deactivated by coking and sintering. The effect of strong metal-support interaction (SMSI effect) is different for various supports. The formation of solid solution of Ni–Mg–O2 and the blocking of TiOx by the partially reduced TiO2 can both decrease the availability of Ni active sites in Ni/MgO and Ni/TiO2. The spinel NiAl2O4 formed in Ni/γ-Al2O3 might be responsible for its high activity and resistance to coking and sintering because it can produce a highly dispersed active phase and a large active surface area as bound-state Ni species when the catalyst is prepared at high calcined temperatures or with low nickel loading. The addition of La2O3 or MgO as alumina modifiers can also be beneficial for the performance of the Ni/γ-Al2O3 catalyst. 相似文献
16.
Using a manometric experimental setup, high-pressure sorption measurements with CH4 and CO2 were performed on three Chinese coal samples of different rank (VRr = 0.53%, 1.20%, and 3.86%). The experiments were conducted at 35, 45, and 55 °C with pressures up to 25 MPa on the 0.354-1 mm particle fraction in the dry state. The objective of this study was to explore the accuracy and reproducibility of the manometric method in the pressure and temperature range relevant for potential coalbed methane (CBM) and CO2-enhanced CBM (CO2-ECBM) activities (P > 8 MPa, T > 35 °C). Maximum experimental errors were estimated using the Gauss error propagation theorem, and reproducibility tests of the high-pressure sorption measurements for CH4 and CO2 were performed. Further, the experimental data presented here was used to explicitly study the CO2 sorption behaviour of Chinese coal samples in the elevated pressure range (up to 25 MPa) and the effects of temperature on supercritical CO2 sorption isotherms.The experiments provided characteristic excess sorption isotherms which, in the case of CO2 exhibit a maximum around the critical pressure and then decline and level out towards a constant value. The results of these manometric tests are consistent with those of previous gravimetric sorption studies and corroborate a crossover of the 35, 45, and 55 °C CO2 excess sorption isotherms in the high-pressure range. The measurement range could be extended, however, to significantly higher pressures. The excess sorption isotherms tend to converge, indicating that the temperature dependence of CO2 excess sorption on coals at high-pressures (>20 MPa) becomes marginal. Further, all CO2 high-pressure isotherms measured in this study were approximated by a three-parameter excess sorption function with special consideration of the density ratio of the “free” phase and the sorbed phase. This function provided a good representation of the experimental data.The maximum excess sorption capacity of the three coal samples for methane ranged from 0.8 to 1.6 mmol/g (dry, ash-free) and increased from medium volatile bituminous to subbituminous to anthracite. The medium volatile bituminous coal also exhibited the lowest overall excess sorption capacity for CO2. However, the subbituminous coal was found to have the highest CO2 sorption capacity of the three samples. The mass fraction of adsorbed substance as a function of time recorded during the first pressure step was used to analyze the kinetics of CH4 and CO2 sorption on the coal samples. CO2 sorption proceeds more rapidly than CH4 sorption on the anthracite and the medium volatile bituminous coal. For the subbituminous coal, methane sorption is initially faster, but during the final stage of the measurement CO2 sorption approaches the equilibrium value more rapidly than methane. 相似文献
17.
Surface-phase ZrO2 on SiO2 (SZrOs) and surface-phase La2O3 on Al2O3 (SLaOs) were prepared with various loadings of ZrO2 and La2O3, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH4/CO2 reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al2O3 and Pt/SiO2 catalysts. CO2 or CH4 pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.
The zirconia can be homogeneously dispersed on SiO2 to form a stable surface-phase oxide. The lanthana cannot be spread well on Al2O3, but it forms a stable amorphous oxide with Al2O3. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO2 and Pt/Al2O3 by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO2 and Pt/Al2O3 catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO2 adsorbed on the basic sites of SZrOs and SLaOs. 相似文献
18.
Youssef Belmabkhout 《Chemical engineering science》2009,64(17):3729-107
Adsorption equilibrium capacity of CO2, CH4, N2, H2 and O2 on periodic mesoporous MCM-41 silica was measured gravimetrically at room temperature and pressure up to 25 bar. The ideal adsorption solution theory (IAST) was validated and used for the prediction of CO2/N2, CO2/CH4, CO2/H2 binary mixture adsorption equilibria on MCM-41 using single components adsorption data. In all cases, MCM-41 showed preferential CO2 adsorption in comparison to the other gases, in agreement with CO2/N2, CO2/CH4, CO2/H2 selectivity determined using IAST. In comparison to well known benchmark CO2 adsorbents like activated carbons, zeolites and metal-organic frameworks (MOFs), MCM-41 showed good CO2 separation performances from CO2/N2, CO2/CH4 and CO2/H2 binary mixtures at high pressure, via pressure swing adsorption by utilizing a medium pressure desorption process (PSA-H/M). The working CO2 capacity of MCM-41 in the aforementioned binary mixtures using PSA-H/M is generally higher than 13X zeolite and comparable to different activated carbons. 相似文献
19.
Seung-Ho Lee Wonihl Cho Woo-Sung Ju Byoung-Hak Cho Young-Chul Lee Young-Soon Baek 《Catalysis Today》2003,87(1-4):133-137
In general, there are three processes for production of synthesis gas; steam reforming, CO2 reforming and partial oxidation of methane or natural gas. In the present work, we refer to tri-reforming of methane to synthesize syngas with desirable H2/CO ratios by simultaneous oxy-CO2-steam reforming of methane. In this study, we report the results obtained on tri-reforming of methane over the Ni/ZrO2 based catalyst in order to restrain the carbon deposition and to evaluate the catalytic performance. Results of tri-reforming of CH4 by three catalysts (Ni/Ce–ZrO2, Ni/ZrO2 and Haldor Topsoe R67-7H) are showed that the coke on the reactor wall and the surface of catalyst were reduced dramatically. It was found that the weak acidic site, basic site and redox ability of Ce–ZrO2 play an important role in tri-reforming of methane conversion. Carbon deposition depends not only on the nature of support, but also on the oxidant as like steam or oxygen. Therefore, the process optimization by reactant ratios is important to manufacture the synthesis gas from natural gas and carbon dioxide. 相似文献
20.
Lu Gang Zhang Chengfang Cang Yanqing Zhu Zhibin Ni Yianhui Cheng Linjun Yu Fong 《Applied Catalysis A: General》1997,150(2):1-252
The performances of active carbon supported molybdenum sulfide catalysts prepared by different procedures or promoted by different elements in the synthesis of mixed alcohols from CO2 containing syngas were examined. The results showed that high alcohol activity and selectivity could be obtained by employing a rapid drying procedure and employing a H2S---H2 stream for (NH4)2MoS4 decomposition. Addition of Co, Cr and Cl to K---Mo/C catalyst led to an increase in the alcohol activity or selectivity. The presence of CO2 in the feed caused a greater amount of water to be produced but reduced the formation of CO2. The product distribution was also strongly influenced by the presence of either CO2 or H2S in the feed. Addition of CO2 reduces the formation of higher alcohols while H2S increases higher alcohol formation. 相似文献