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1.
The activity toward hydrogen production in steam reforming of ethanol (SRE) reaction has been evaluated for CuO/ZrO2 catalysts doped with Mn, Ni, Ga at 350 °C. The copper based catalysts were synthesised by co-precipitation method at constant pH = 7 and fixed (wt.%) CuO/ZrO = 2.3. The catalysts were characterised by means of N2 adsorption, temperature programmed reduction (H2-TPR), N2O dissociative chemisorption, X-ray diffraction (XRD), CO2 temperature programmed desorption (CO2-TPD), and temperature programmed oxidation (TPO). It has been found that copper based catalysts exhibit high ethanol conversion in SRE (>86%) at 350 °C. Due to basic character of catalysts, the formation of acetaldehyde is observed. The CuO/ZrO2 catalyst modification with dopants increases the hydrogen yield with maximum (52%) for CuO/ZrO2/NiO. The addition of Ni changes the distribution of carbon-containing products. In this case, the increase in selectivity to CO, CO2 and CH4 is observed whereas selectivity to acetaldehyde is significantly decreased. This shows that presence of Ni facilities the C–C bond cleavage. On the other hand, the formation of acetic acid is limited upon addition of Mn and Ga. For all modified catalysts, decrease in carbon deposition rate during SRE is pronounced according to TPO experiments. The modification of Cu/Zr with Mn, Ni and Ga causes the decrease in copper particle size, which hinders the carbon deposit formation.  相似文献   

2.
Ethanol steam reforming is a promising reaction which produces hydrogen from bio and synthetic ethanol. In this study, the nano-structured Ni-based bimetallic supported catalysts containing Cu, Co and Mg were synthesized through impregnation method and characterized by XRD, BET, SEM, TPR and TPD analysis. The prepared catalysts were tested in steam reforming of ethanol in the S/C = 6, GHSV of 20,000 mL/(gcat h) at the temperature range of 450–600 °C. Among the xNi/CeO2 (x = 10, 13, 15 wt%) catalyst, the sample containing 13 wt% Ni with surface area of 64 m2/g showed the best performance with 89% ethanol conversion and 71% H2 selectivity as well as low CO selectivity of 8% at 600 °C and The addition of Cu, Mg, and Co to catalyst structure were evaluated and it was found that the nature of second metal has a strong influence on the catalyst selectivity for H2 production. Considering to results of TPR analysis, the 13Ni–4Cu/CeO2 catalyst showed proper reduction which caused in better activity. On the other side based on TPD analysis, the more basic property of 13Ni–4Mg/CeO2 bimetallic catalyst provided a better condition to methane steam reforming, leading to lower CH4 selectivity and consequently more H2 production. The 13Ni–4Cu/CeO2 exhibited the highest activity and lowest selectivity towards ethanol conversion and CO production about 99% and 4%, while the 13Ni–4Mg/CeO2 catalyst possessed the highest H2 selectivity and lowest CH4 selectivity about 74% and 1% respectively at 600 °C. The Ni–Cu and Ni–Mg bimetallic catalysts shows good stability with time on stream.  相似文献   

3.
Biogas can be highlighted as a renewable raw material for the production of hydrogen. In this study, Ni-M-Al catalysts were evaluated to obtain hydrogen from the biogas reforming. The catalysts were synthesized by coprecipitation with Ni and Al with a molar percentage of 55 and 33%, respectively, varying the third component M = Mg, Li, Ca, La, Cu, Co, Zn, with a molar percentage of 11%. The reactions were carried out in a fixed bed tubular reactor using a synthetic biogas (70% of CH4 and 30% of CO2). The results showed that the CH4 conversion increased with the temperature up to 700 °C for La11, Cu11, and Zn11 catalysts. CO2 conversion increased for all catalysts in the range of 500–700 °C. The H2/CO molar ratios observed in the reactions were higher than 1 due to the contribution of the CH4 decomposition reaction. The catalyst containing La presented better stability in the reactions due to the stronger acid sites and high resistance to sintering. Carbon filaments were produced by all catalysts at 600 and 700 °C. Sintering was the main cause of deactivation of the catalysts, except for La11.  相似文献   

4.
Biogas, a mixture of CO2/CH4, is reasonable for conversion to syngas (H2/CO) by dry methane reforming (DMR) reaction. The modification of Ni/SBA-16 with a lanthanum promoter using the co-impregnation technique is investigated in this study. The temperature of reaction (600–750 °C), La loading (3.85–11.56 wt%), and Ni loading (10–30 wt%) are the parameters that are varied for maximizing reaction conversions. The synthesized catalysts and SBA-16 supporting material were characterized by several methods before and after reaction. According to the analysis, the existence of La2O3 particles on the catalyst's surface has decreased the particle sizes, as well as enhanced their dispersion. Therefore, the maximum CH4 conversion of 94.21%, CO2 conversion of 90.12%, H2 yield of 90.53%, and H2/CO molar ratio of 2.03 are achieved using 20Ni-5.78La/SBA16 at 700 °C. Besides, this catalyst showed lower deposited coke and higher stability compared with other synthesized catalysts.  相似文献   

5.
A two-stage system involving alkaline thermal gasification of cellulose with Ca(OH)2 sorbent and catalytic reforming with Ni/Fe dual-functional CaO based catalysts is proposed and applied to enhance H2 production and in-situ CO2 capture. The results show that the H2 concentration is maximized at a considerably lower temperature (500 °C) than commercialized biomass gasification processes, reducing energy consumption. Sol-gel method is deemed better than impregnation method for its lower cost and higher-concentration H2 production. Among the prepared catalysts, sol-NiCa catalyst exhibits the best performance in CO2 absorption, resistance to carbon deposition, and cyclic stability, creating maximum H2 concentration (79.22 vol%), H2 yield (27.36 mmol g−1 cellulose), and H2 conversion (57.61%). Introduction of Ni rather than Fe on the CaO based catalyst promotes steam methane reforming at moderate temperature range of 400–600 °C, generating low contents of CH4 (5.38 vol%), CO2 (4.82 vol%), and CO (10.58 vol%).  相似文献   

6.
In this work, a sol-gel Ni–Mo2C–Al2O3 catalyst is employed for the first time in the glycerol steam reforming for syngas production. Catalyst stability and activity are investigated in the temperature range of 550 °C–700 °C and time on stream up to 30 h. As reaction temperature increases, from 550 °C to 700 °C, H2 yield boosts from 22% to 60%. The stability test, carried out at milder conditions (600 °C and Gas-Hourly Space-Velocity (GHSV) of 50,000 mL h−1.gcat−1), shows high catalyst stability, up to 30 h, with final conversion, H2 yield, and H2/CO ratio of 95%, 53% and 1.95, respectively. Both virgin and spent catalysts have been characterized by a multitude of techniques, e.g., Atomic-Absorption spectroscopy, Raman spectroscopy, N2-adsorption-desorption, and Transmission Electron Microscopy (TEM), among others. Regarding the spent catalysts, carbon deposits’ morphology becomes more graphitic as the reaction temperature increases, and the total coke formation is mitigated by increasing reaction temperature and lowering GHSV.  相似文献   

7.
The effect of preparation method on the performance of Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol (EtOH) has been investigated. The first catalyst was prepared by a sol–gel (SG) method and for the second one the Al2O3 support was made by a solution combustion synthesis (SCS) route and then the metal was loaded by standard wet impregnation. The catalytic activity of these catalysts of different Ni loading was compared with a commercial Al2O3 supported Ni catalyst [CM (10%)] at different temperatures, pressures, feed flow rates, and feed concentrations. Based on the product distribution, the proposed reaction pathway is a mixture of dehydrogenation of EtOH to CH3CHO followed by C–C bond breaking to produce CO + CH4 and oxidation of CH3CHO to CH3COOH followed by decarbonylation to CO2 + CH4. CH4(C2H6 and C3H8) also can form via Fischer–Tropsch reactions of CO/CO2 with H2. The CH4 (C2H6 and C3H8) reacts to form hydrogen and carbon monoxide through steam reforming, while CO converts to CO2 mostly through the water–gas shift reaction (WGSR). SG catalysts showed poorer WGSR activity than the SCS catalysts. The activation energies for H2 and CO2 production were 153, 155 and 167 kJ/mol and 158, 160 and 169 kJ/mol for SCS (10%), SG (10%), and CM (10%) samples, respectively.  相似文献   

8.
Hydrocalumite derived nickel (Ni) catalysts with different loading of magnesium (Mg) (7.5/10/15 wt%, as promoters) were for the first time prepared and tested for ethanol steam reforming (ESR) in this work. The catalytic performances of different Mg promoted catalysts were mainly evaluated in the temperature range between 550 and 700 °C as determined by thermodynamic simulation. Experimental results showed that the optimal reaction temperature was 650 °C in terms of the hydrogen yields for these ESR catalysts, especially for 15Ni7.5Mg/HCa which presented a remarkable catalytic performance. Its hydrogen yields reached 90% while ethanol was almost fully converted at 650 °C. Based on the characterization results, it's believed that 15Ni7.5Mg/HCa with a certain amount of Mg loading can get the smallest Ni0 crystallite sizes, better H2 reducibility and suitable basicities on strong basic sites. The catalytic performances of ESR catalysts were mainly related to the Ni0 crystallite size, reducibility and basicity for the prepared hydrocalumites derived Ni catalysts, and 15Ni7.5Mg/HCa could be considered as one of the best catalysts for ESR.  相似文献   

9.
Dry reforming of methane (DRM) reaction can convert primary greenhouse gases (CH4 and CO2) to value-added chemicals (H2 and CO), but generally suffers from harsh reaction conditions (>700 °C) and inevitable deactivation of catalysts. In this work, we report supported Ni catalysts based on a topotactic transformation process from the layered double hydroxides (NiZnAl?LDHs) precursors. Structural characterizations (XRD, HRTEM, CO chemisorption) verify a uniform distribution of Ni nanoparticles (~7 nm) on the mixed metal oxides support with a high dispersion (denoted as Ni/MMO). With the assistance of non-thermal plasma (NTP), the optimal sample (Ni/MMO?S2) exhibits a good catalytic conversion of CH4 (~69%) and CO2 (~54%) at low temperatures (30–60 °C), which is comparable with the activity of thermocatalytic process at ~650 °C without NTP. The energy efficiency of NTP-assisted catalysis process is an order of magnitude higher than that of thermocatalytic process at ~650 °C and enhances by 80% relative to NTP-alone process at low temperatures. The Ni/MMO?S2 catalyst shows satisfactory stability after 600 min stability test, with a slight decrease in conversion (within ~1%). In addition, a combined study including catalytic evaluations, operando OES, XAFS and XPS verifies that metallic Ni species acts as active center, which can promote the dissociation of CH4 and CO2 into highly reactive intermediate species with the assistance of NTP. This synergistic effect between plasma and Ni catalyst remarkably decreases the apparent activation energy by ~50%, accounting for the high catalytic performance at low temperatures. This work demonstrates a promising synergistic catalysis strategy between plasma and catalysts at low temperatures, which can be extended to other reactions operated under harsh conditions.  相似文献   

10.
Ni-La/α-Al2O3 catalysts at different Ni/La ratio of respectively 7/3, 8/2 and 9/1 to obtain a material with total loading of 10 wt% as used in industrial methane steam reforming field are prepared with incipient wetness impregnation method. Various techniques including TGA-DTA, XRF, XRD, particles size, H2-RTP and BET are used to characterize materials and their catalytic performance is evaluated during the steam reforming reaction at different temperatures ranging from 500 to 800 °C. Only NiO and α-Al2O3 phases are evidenced by DRX indicating probably the presence of small lanthanum crystallites in high dispersion state. Addition of La may cause strong change at the surface of NiO sites. Substitute Ni by La leads to smaller and well dispersed NiO particles sizes with strong metal support interaction (SMSI). TPR analysis reveals the reduction of Ni species with high Ni-La-Al interactions particularly well observed with 3 wt%La catalyst. The small Ni particles sizes highly dispersed on the support enhance the dissociative adsorption of CHx species. The highest H2 yield is obtained with 7Ni-3La/Al catalyst reaching 94% at 800 °C.  相似文献   

11.
Al2O3 and MgAl2O4 supported 10% (w/w) Ni catalysts having a dispersion of 1.5 and 2.0% are active for DRM at 600 and 750 °C. High temperature reduction of both the calcined catalysts resulted in metallic Ni being formed, suggesting strong support metal interactions. The CH4 and CO2 conversion during DRM are relatively constant with time-on-stream, and are higher for Ni/MgAl2O4 than Ni/Al2O3. Carbon-whiskers are also detected on both catalysts. O2 co-feed of 2.6% (v/v) and increasing reaction temperature to 750 °C helped in decreasing the amount of carbon deposited, except for Ni/MgAl2O4 at 600 °C. Furthermore, higher conversions and H2/CO ratios are achieved. It appears that on spent Ni/MgAl2O4 a different type of carbon species was formed, and this carbon species was difficult to remove by oxygen at 600 °C. Thus, co-feeding O2, using an appropriate temperature, and choosing a suitable support can reduce the carbon present on the nickel catalysts during DRM.  相似文献   

12.
Zirconia incorporated SBA-15 type mesoporous material was synthesized following a one-pot hydrothermal route, characterized and used as the catalyst support in the synthesis of Ni and bi-metallic Ni–W based catalysts. Performances of these catalysts were tested in steam reforming of AcOH. Catalytic activity tests proved that the performances of SBA-15 and Zr-SBA-15 supported Ni based catalysts were highly stable and they also showed very high activity in steam reforming of acetic acid, giving complete conversion at temperatures over 700 °C. Product distributions were shown to be strongly influenced by the composition of the catalyst. In the case of 5Ni@Zr-SBA-15, syngas produced at 750 °C contained about 54% H2, 22% CO, 20% CO2 and 4% CH4. These results indicated that decarboxylation reaction of AcOH to CH4 and CO2 was minimized over this catalyst. Results were considered to be highly promising for the production of hydrogen rich syngas. It was most interesting to observe that modification of this catalyst by the addition of tungsten caused significant changes in the product distribution. For instance, syngas produced over 5Ni-50W@Zr-SBA-15 at the same reaction conditions, contained equimolar quantities of H2 and CO (about 47.5% each) with very small amounts of CO2 and CH4 (about 3% and 2%, respectively). Production of a syngas with such a composition was considered to be highly attractive from the point of view of a resource gas for dimethyl ether and Fischer-Tropsch synthesis.  相似文献   

13.
Catalysts of Ni supported on home-made mesoporous alumina (Ni/M-Al2O3) were prepared via facile incipient impregnation method and calcined under different temperature (500–800 °C). Compared with catalysts of Ni supported on commercial alumina, they showed much higher conversion and lower carbon deposition in methane dry reforming (DRM). Among the catalysts, Ni/M-Al2O3-700 exhibited the highest DRM activity, with 77.6% CH4 conversion and 85.4% CO2 conversion at 700 °C. TPR revealed that almost all the Ni was in the form of NiAl2O4 spinel after calcination at 700 °C. Due to the strong metal-support interaction of NiAl2O4 structure, the Ni crystal size of Ni/M-Al2O3-700 after reduction was around 5 nm. TGA and TEM results showed its carbon deposition after 20 h DRM test was only 3.8% and mainly in the form of amorphous carbon. This work indicates that the formation of NiAl2O4 spinel is beneficial to activity and stability towards DRM reaction and controlling calcination temperature is crucial.  相似文献   

14.
Methane steam reforming is currently the most widely used hydrogen production reaction in industry today. Ni/Nb–Al2O3 catalysts were prepared by treatment under H2, N2, and air atmosphere prior to reduction and applied for methane steam reforming reaction at low temperature (400–600 °C). The hydrogen-treated catalysts increased catalytic activity, with 55.74% methane conversion at S/C = 2, GSVH of 14400 mL g?1 h?1 and 550 °C. The H2 atmosphere treatment enhanced the Ni–Nb interaction and the formation of stable, tiny, homogeneous Ni particles (6 nm), contributing to good activity and stability. In contrast, the catalysts treated with nitrogen and air showed weaker interactions between Ni and Nb species, whereas the added Nb covered the active sites, which caused the decrease in activity. Meanwhile, carbon accumulation was also observed. This work is informative for preserving small nano-sized nickel particles to enhance catalytic performance.  相似文献   

15.
The structural “memory effect” of a hydrotalcite (HT)-derived mixed oxide is utilized to prepare a shell–core Ni/Mg–Al catalyst for ethanol steam reforming (ESR). The reconstruction proceeds rapidly in a Ni2+ nitrate solution on the outer layer of the Mg–Al mixed oxide particle, being accompanied with the growth of large flake-like sheets. A part of Ni2+ ions can incorporate into the reconstructed HT-like structure, leading to the formation of the shell-type Ni loading catalyst after calcination. At 700 °C, the shell–core catalysts with much lower Ni contents perform better activities than that of the bulk Ni/Mg–Al catalyst prepared directly via the calcination of the HT-like precursor. Further investigations reveal that temperature and space-time significantly affect the contribution of WGS, CH4 reforming reactions to the product distribution in the ESR reaction. Most interestingly, C2H4 is observed in the reactions carried out at 700 °C and very low space-time.  相似文献   

16.
Dry reforming of methane (DRM) is a sustainable chemical process that can simultaneously transform methane and carbon dioxide, which are generally considered greenhouse gases, into syngas with H2/CO ratio close to 1. The deposition of carbon on the active sites during long-period DRM tests will lead to severe deactivation of Ni-based catalysts. Thus, in this work, we proposed a series of uniformly dispersed Fe-decorated Ni/Al2O3 catalysts via atomic layer deposition (ALD) to solve this key issue. Modification with trace amounts of Fe (0.3–0.6%) had multiple effects on facilitating the CH4 dissociation on Ni0, improving the low-temperature catalytic activity, moderating the carbon species and accelerating coke oxidation. The sample denoted as 0.3%Fe/Ni/Al2O3 exhibited almost no activity loss in the 72 h test at 650 °C. The Fe-decorated Ni/Al2O3 structure achieved a balance between the enhancement of CH4 cracking and the elimination of coke. Furthermore, this advanced ALD approach of preparing uniform secondary metal nanoparticle-decorated catalysts provided guidance to other bimetallic systems, such as Pt/Ni, Mn/Ni, and Cu/Ni.  相似文献   

17.
Six types of alumina-support Ni catalysts were studied in dry reforming of methane to find out the influence that calcination rate, calcination temperature, and reduction temperature had on the activity and stability of the catalysts. BET, XRD, H2-TPR, TGA-DTA were carried out to analyzed the physicochemical properties of these catalysts. The H2-TPR results indicated that the proper parameters in preparing and reaction process could increase the amount of Ni reduced from NiAl2O4. And Ni reduced from NiAl2O4 could decrease the amount of inert carbon forming on catalysts' surfaces, so it was crucial to Ni/Al2O3 catalysts’ performance. Also, the results showed that the best condition was 5 °C/min calcination rate, 600 °C calcination temperature, and 700 °C reduction temperature. With this condition, TGA-DTA results showed that carbon deposition could be less and active.  相似文献   

18.
The goal of this study was to investigate Cr-free, Fe/Ni, metal oxide catalysts for the high temperature shift (HTS) reaction of a fuel processor using liquefied natural gas (LNG). As hexavalent chromium (Cr6+) in commercial HTS catalyst is a hazardous material, we selected Ni as a substitute for chromium in the Fe-based HTS catalyst and investigated the HTS activities of these Cr-free, metal oxide catalysts under the LNG reformate condition. Cr-free, Fe/Ni-based catalysts containing Ni instead of Cr were prepared by coprecipitation and their performance was evaluated under a gas mixture condition (56.7% H2, 10% CO, 26.7% H2O, and 6.7% CO2) that simulated the gas composition from a steam methane reformer (SMR, at H2O/CH4 ratio = 3 with 100% CH4 conversion). Under this condition, the Fe/Ni catalysts showed higher CO removal activities than Fe-only and Cr-containing catalysts, but the methanation was promoted when the Ni content in the catalyst exceeded 50 wt%. Brunner-Emmett-Teller (BET), X-ray diffraction (XRD), inductively coupled plasma (ICP) and X-ray photoelectron spectroscopy (XPS) analyses were performed to explain the HTS activity of the Fe/Ni catalysts based on the catalyst structure.  相似文献   

19.
The aim of this study is to investigate the promotional effect of Ce on Ni/ZSM-5 catalysts in the CO2 reforming of CH4 reaction. The evaluation of the catalytic performances of the composite catalysts was conducted in a fixed-bed reactor at atmospheric pressure. The influencing factors, including temperature, Ni and Ce loadings, molar feed ratio of CO2/CH4, and time-on-stream (TOS), were investigated. The characteristics of the catalysts were checked with Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The reduction and the basic properties of the composite catalysts were elucidated by temperature-programmed reduction by H2 (H2-TPR) and temperature-programmed desorption of CO2 (CO2-TPD), respectively. The reactivity of deposited carbon was studied by sequential temperature-programmed surface reaction of CH4 (CH4-TPSR) and temperature-programmed oxidation using CO2 and O2 (CO2-TPO and O2-TPO). Results indicate that higher CH4 conversion, H2 selectivity, and desired H2/CO ratio for 5 wt% Ni & 5 wt% Ce/ZSM-5 could be achieved with CO2/CH4 feed ratio close to unity over the temperature range of 500–900 °C. Moreover, the addition of Ce could not only promote CH4 decomposition for H2 production but also the gasification of deposited carbon with CO2. The dispersion of Ni particles could be improved with Ce presence as well. A partial reduction of CeO2 to CeAlO3 was observed from XPS spectra over 5 wt% Ni & 5 wt% Ce/ZSM-5 after H2 reduction and 24 h CO2–CH4 reforming reaction. Benefiting from the introduction of 5 wt% Ce, the calculated apparent activation energies of CH4 and CO2 over the temperature range of 700–900 °C could be reduced by 30% and 40%, respectively.  相似文献   

20.
The activity of Ni supported on MCM-41 catalyst with/without scandium promoter was investigated for hydrogen production. The performance of the catalysts with different Sc loadings (0.00, 0.10, 0.25, 0.50, 0.75, 1.00 and 3.00 wt%) was examined. N2 adsorption-desorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for the characterization of the catalytic materials. The prepared catalysts were tested in dry reforming of methane. The effect of Sc addition on activity, hydrogen yield, H2/CO ratio and stability are discussed. CH4 and CO2 conversions were measured under atmospheric pressure at 800 °C. Low Sc loading (<0.75 wt%) showed a positive effect on H2 yield, CH4 and CO2 conversions. Addition of Sc strengthened the interaction of Ni with support and also increased the basicity which in turn affected the amount of CO2 adsorbed on the surface of the catalyst. Notably, promoting with Sc almost suppressed the carbon formation leading to outstanding catalytic stability; thus 17% carbon deposition reduction was attained. The effect of different reaction temperatures, GHSV and CH4:CO2 ratio was also investigated.  相似文献   

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