首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 725 毫秒
1.
A novel nickel catalyst supported on Al2O3@ZrO2 core/shell nanocomposites was prepared by the impregnation method. The core/shell nanocomposites were synthesized by depositing zirconium species on boehmite nanofibres. This contribution aims to study the effects of the pore structure of supports and the zirconia dispersed on the surface of the alumina nanofibres on the CO methanation. The catalysts and supports were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), nitrogen adsorption–desorption, and thermogravimetry and differential thermal analysis (TG-DTA). The catalytic performance of the catalysts for CO methanation was investigated at a temperature range from 300 °C to 500 °C. The results of the characterization indicate that the metastable tetragonal zirconia could be stably and evenly dispersed on the surface of alumina nanofibres. The interlaced nanorods of the Al2O3@ZrO2 core/shell nanocomposites resulted in a macropore structure and the spaces between the zirconia nanoparticles dispersed on the alumina nanofibres formed most of the mesopores. Zirconia on the surface of the support promoted the dispersion and influenced the reduction states of the nickel species on the support, so it prevented the nickel species from sintering as well as from forming a spinel phase with alumina at high temperatures, and thus reduced the carbon deposition during the reaction. With the increase of the zirconia content in the catalyst, the catalytic performance for the CO methanation was enhanced. The Ni/Al2O3@ZrO2-15 exhibited the highest CO conversion and methane selectivity at 400 °C, but they decreased dramatically above or below 400 °C due to the temperature sensitivity of the catalyst. Ni/Al2O3@ZrO2-30 exhibited a high and constant rate of methane formation between 350 °C and 450 °C. The excellent catalytic performance of this catalyst is attributed to its reasonable pore structure and good dispersion of zirconia on the support. This catalyst has great potential to be further studied for the future industrial use.  相似文献   

2.
Nickel catalysts supported on different acid-treated clays were prepared by the impregnation method in order to investigate the effect of the pore structures of supports on the dispersion and the chemical states of nickel species, and thus on the carbon depositions resulted from the dissociation of the CO molecules adsorbed on different active nickel sites. The catalysts and supports were characterized by the X-ray diffraction (XRD), the transmittance electron microscopy (TEM), the H2 temperature-programmed reduction (H2-TPR), the nitrogen adsorption–desorption, and the thermogravimetry and differential thermal analysis (TG-DTA). The CO methanation performance of the catalyst was investigated at a temperature range from 300 °C to 500 °C. The results indicated that the dispersion and the states of the nickel species on the support were influenced strongly by the pore structures of the acid-treated clays, and only the mesopores composed by partly damaged clay layers were conducive to forming the active nickel species, and thus reducing the deposition of the inactive carbon and improving the stability of the catalyst. The carbon species deposited on different active sites was slightly different in the oxidative properties when it was oxidized in air. A fraction of aluminum in the clays was leached out by acid, which decreased the possibility of forming the spinel phase of nickel aluminate in the catalyst. The highly dispersed nickel species showed little relevance to the high activity of the catalyst, but it exhibited a strong relation to the nickel sites from the bulk nickel species.  相似文献   

3.
For the first time the influence of CO, CO2 and H2O content on the performance of chlorinated NiCeO2 catalyst in selective or preferential CO methanation was studied systematically. It was shown that the rate of CO methanation over Ni(Cl)/CeO2 increases with the increasing H2 concentration, is independent of CO2 concentration and decreases with increasing CO and H2O concentrations; the rate of CO2 methanation is weakly sensitive to H2 and CO2 concentrations and decreases with increasing CO and H2O concentrations. High catalyst selectivity was attributed to Ni surface blockage by strongly adsorbed CO molecules and ceria surface blockage by Cl, which both inhibit CO2 hydrogenation.For the first time, selective CO methanation over Ni(Cl)/CeO2 was studied for deep CO removal from formic acid derived hydrogen-rich gases characterized by high CO2 (40–50 vol%), low CO (30–1000 ppm) content and trace amounts of water. Composite Ni(Cl)/CeO2-η-Al2O3/FeCrAl wire mesh catalyst was demonstrated to be effective for this process at temperatures of 180–220°С, selectivity 30–70%, WHSV up to 200 L (STP)/(g∙h). The catalyst provides high process productivity, low pressure drop, uniform temperature distribution, and appears highly promising for the development of a compact CO cleanup reactor. Selective CO methanation was concluded to be a convenient way to CO-free hydrogen produced by formic acid decomposition.  相似文献   

4.
Supported Ni/Al2O3 catalysts are widely used in chemical industries. Regeneration of the deactivated Ni catalysts caused by sintering of Ni nanoparticles and carbon deposition after long-term operation is significant but still very challenging. In this work, a feasible strategy via solid-phase reaction between NiO and Al2O3 followed by a controlled reduction is developed which can burn out the deposited carbon and re-disperse the Ni nanoparticles well, thus regenerating the deactivated Ni catalysts. To demonstrate the feasibility of this method, Ni catalyst supported on α-Al2O3 (Ni/Al2O3) for CO methanation reaction was selected as a model system. The structure and composition of the fresh, deactivated and regenerated Ni/Al2O3 catalysts were comprehensively characterized by various techniques. The reduction and redistribution of Ni species as well as the interfacial interaction between Ni nanoparticles and Al2O3 support were investigated in detail. It is found that calcining the deactivated Ni/Al2O3 in air at high temperature can burn out the coke, while the sintered Ni species can combine with superficial Al2O3 to form a surface NiAl2O4 spinel phase through the solid-phase reaction. After the controlled reduction of the NiAl2O4 spinel, highly dispersed Ni nanoparticles on Al2O3 support are re-generated, thus achieving the regeneration of the deactivated Ni/Al2O3. Interestingly, compared with the fresh Ni/Al2O3 catalyst, the sizes of Ni nanoparticles became even smaller in the regenerated ones. The regenerated Ni/Al2O3 showed much enhanced catalytic activity in CO methanation and became more resistant to carbon deposition, due to the better dispersed Ni nanoparticles and strengthened interaction between Ni and Al2O3 support. Our work not only addresses the long existing catalyst regeneration issue, but also provides effective and renewable Ni-based catalysts for CO methanation.  相似文献   

5.
Combination of the reactions by means of membrane separation techniques are of interest. The CO2 methanation was combined with NH3 decomposition by in situ H2 separation through a Pd membrane. The CO2 methanation reaction in the permeate side was found to significantly enhance the H2 removal rate of Pd membrane compared to the use of sweep gas. The reaction rate of CO2 methanation was not influenced by H2 supply through the Pd membrane in contrast to NH3 decomposition in the retentate side. However, the CH4 selectivity could be improved by using a membrane separation technique. This would be caused by the active dissociated H species which might immediately react with adsorbed CO species on the catalysts to CH4 before those CO species desorbed. From the reactor configuration tests, the countercurrent mode showed higher H2 removal rate in the combined reaction at 673 K compared to the cocurrent mode but the reaction rate in CO2 methanation should be improved to maximize the perfomance of membrane reactor.  相似文献   

6.
CO2 methanation was performed over 10 wt%Ni/CeO2, 10 wt%Ni/α-Al2O3, 10 wt%Ni/TiO2, and 10 wt%Ni/MgO, and the effect of support materials on CO2 conversion and CH4 selectivity was examined. Catalysts were prepared by a wet impregnation method, and characterized by BET, XRD, H2-TPR and CO2-TPD. Ni/CeO2 showed high CO2 conversion especially at low temperatures compared to Ni/α-Al2O3, and the selectivity to CH4 was very close to 1. The surface coverage by CO2-derived species on CeO2 surface and the partial reduction of CeO2 surface could result in the high CO2 conversion over Ni/CeO2. In addition, superior CO methanation activity over Ni/CeO2 led to the high CH4 selectivity.  相似文献   

7.
The high purity hydrogen, free from any traces of carbon monoxide is crucial for the efficient operation of hydrogen proton exchange membrane fuel cells (PEMFCs). In this study we report the low temperature (25–120 °C) carbon monoxide methanation in hydrogen-rich streams over 1 wt. % Pt nanoparticles supported on yttria-stabilized zirconia (YSZ) support. Pt nanoparticles with four average particle sizes 1.9, 3.0, 4.4 and 6.7 nm are investigated. The turnover frequency at 30 °C of CO methanation reaction rate doubles with decreasing Pt mean particle size from 6.7 to 1.9 nm. The high activity of Pt/YSZ catalyst is due to the backspillover of ionic species Oδ? from YSZ support to Pt active sites. Under the reaction conditions, Oδ? forms an “effective” double layer at the catalyst surface that weakens CO (electron acceptor) adsorption and strengthens H2 (electron donor) adsorption bonds and this effect becomes more pronounced as nanoparticle size decreases.  相似文献   

8.
In order to simultaneously inhibit the Ni sintering and coke formation as well as investigate the effects of WO3 promoter on catalytic performance, the ordered mesoporous Ni–WO3/Al2O3 catalysts were synthesized by a facile one-pot evaporation-induced self-assembly method for CO methanation reaction to produce synthetic natural gas. Addition of WO3 species could significantly promote the catalytic activity due to the enhancement of the Ni reducibility and the increase of active centers, and the optimal N10W5/OMA catalyst with NiO of 10 wt% and WO3 of 5 wt% achieved the maximum CH4 yield 80% at 425 °C, 0.1 MPa and a weight hourly space velocity of 60000 mL g−1 h−1. Besides, the reference catalyst N10W5/OMA-Im prepared by the conventional co-impregnation method was also evaluated. Compared with N10W5/OMA, N10W5/OMA-Im showed lower catalytic activity due to the partial block of channels by Ni and WO3 nanoparticles, which reduced active centers and restrict the mass transfer during the reaction. In addition, the N10W5/OMA catalyst showed superior anti-sintering and anti-coking properties in a 425oC-100 h-lifetime test, mainly because of confinement effect of ordered mesoporous structure to anchor the Ni particle in the alumina matrix.  相似文献   

9.
To address the metal sintering problem over the transitional one-dimensional-channel materials supported metal catalyst at high loadings, the 3-dimensional mesostructured cellular foam silica (MCF) supported bimetallic LaNi1–xCoxO3 perovskite catalyst was prepared via a citric acid assisted impregnation method for CO2 methanation. Highly dispersed La2O3 and bimetallic Ni–Co alloy nanoparticles with size of around 5.1 nm were immobilized inside the pores of the MCF silica with intimate contact, resulting in high catalytic activity at low temperature and superior stability at high temperature for CO2 methanation. Among all catalysts, the LaNi0.95Co0.05O3/MCF catalyst exhibited the highest catalytic activity due to its smallest Ni–Co alloy nanoparticles as well as the synergistic effect between Ni and Co species. In addition, LaNi0.95Co0.05O3/MCF catalyst also showed high long-term stability without Ni sintering in a 100 h-lifetime test, which was attributed to the confinement effect of the MCF support as well as the physical barrier of La2O3 species nearby metallic Ni nanoparticles.  相似文献   

10.
H2 was produced from aluminum/water reaction and reacted with CO2 over Ni and Rh based catalysts to optimize the process conditions for CO2 methanation at moderate temperature. Monometallic catalysts were prepared by incorporating Ni and Rh using nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and rhodium(III) chloride trihydrate (RhCl3·3H2O)as a precursor chemical. The preliminary study of the catalysts revealed higher activity and CH4 selectivity for Rh based catalyst compared to that of Ni based catalyst. Further, Rh based catalyst was investigated using response surface methodology (RSM) involving central composite design. The quadratic model was employed to correlate the effects of variable parameters including methanation temperature, %humidity, and catalyst weight with the %CO2 conversion, %CH4 selectivity, and CH4 production capacity. Analysis of variance revealed that methanation temperature and humidity play an important role in CO2 methanation. Higher response values of CO2 conversion (54.4%), CH4 selectivity (73.5%) and CH4 production capacity (8.4 μmol g?1 min?1) were noted at optimum conditions of 206.7°C of methanation temperature, 12.5% humidity and 100 mg of the catalyst. The results demonstrated the ability of Rh catalyst supported on palm shell activated carbon (PSAC) for CO2 methanation at low temperature and atmospheric pressure.  相似文献   

11.
The effect of CeO2 loading amount of Ru/CeO2/Al2O3 on CO2 methanation activity and CH4 selectivity was studied. The CO2 reaction rate was increased by adding CeO2 to Ru/Al2O3, and the order of CO2 reaction rate at 250 °C is Ru/30%CeO2/Al2O3 > Ru/60%CeO2/Al2O3 > Ru/CeO2 > Ru/Al2O3. With a decrease in CeO2 loading of Ru/CeO2/Al2O3 from 98% to 30%, partial reduction of CeO2 surface was promoted and the specific surface area was enlarged. Furthermore, it was observed using FTIR technique that intermediates of CO2 methanation, such as formate and carbonate species, reacted with H2 faster over Ru/30%CeO2/Al2O3 and Ru/CeO2 than over Ru/Al2O3. These could result in the high CO2 reaction rate over CeO2-containing catalysts. As for the selectivity to CH4, Ru/30%CeO2/Al2O3 exhibited high CH4 selectivity compared with Ru/CeO2, due to prompt CO conversion into CH4 over Ru/30%CeO2/Al2O3.  相似文献   

12.
Highly efficient and non-noble metal-based Ni/ZrO2 catalyst templated with Ni/UiO-66 precursor was successfully prepared and applied to CO selective methanation in H2-rich gases. This catalyst showed excellent activity and selectivity in an extremely wide temperature window of 215–350 °C, and it also had high stability with no deactivation during a long-term stability test (120 h). The increased specific surface area, smaller crystallite size (3.5 nm) and higher dispersion (15.3%) of Ni nanoparticles, and the enhanced chemisorption capability for CO might contribute to its excellent performance.  相似文献   

13.
CO methanation experiments showed that it was difficult to reach both goals of CO removal depth of below 10 ppm and CO2 conversion rate of below 5% by using a single catalyst in this paper. A two-stage methanation method by applying two kinds of catalysts is proposed, that is, one catalyst with relatively low activity and high selectivity for the first stage at higher temperatures, and another one with relatively high activity for the second stage at lower temperatures. CO can be removed from 1% to below 0.1% at the first stage and to below 10 ppm at the second stage with CO2 conversion rate below 1% and below 4% at each stage respectively. In addition, results also showed that the reverse water-gas shift (RWGS) reaction at the second stage was the dominant factor of CO removal depth. Temperature programmed reduction (TPR) and H2 chemisorption were applied to characterize the catalysts.  相似文献   

14.
CO methanation has attracted much attention because it transforms CO in syngas and coke oven gas into CH4. Here, porous Al2O3 microspheres were successfully used as catalyst supports meanwhile the Mn was used as a promoter of Ni/Al2O3 catalysts. The as-obtained Ni/Al2O3 and Mn–Ni/Al2O3 samples display a micro-spherical morphology with a center diameter near 10 μm. Versus the Ni/Al2O3 catalyst, the 10Mn–Ni/Al2O3 catalyst exhibits a high specific surface area of 92.5 m2/g with an average pore size of 7.0 nm. The 10Mn–Ni/Al2O3 catalyst has the best performance along with can achieve a CO conversion of 100% and a CH4 selectivity of 90.7% at 300 °C. Even at 130 °C, the 10Mn–Ni/Al2O3 catalyst shows a CO conversion of 44.0% and a CH4 selectivity of 84.1%. The higher low-temperature catalytic activity may be since the catalyst surface contains more CO adsorption sites and thus has a stronger adsorption performance for CO. Density functional theory (DFT) calculations confirm that the Mn additive enhances the adsorption of CO, especially for the 10Mn–Ni/Al2O3 catalyst with the strongest adsorption energy.  相似文献   

15.
In this study, a simple solid-state synthesis method was employed for the preparation of the Ni–Co–Al2O3 catalysts with various Co loadings, and the prepared catalysts were used in CO2 methanation reaction. The results demonstrated that the incorporation of cobalt in nickel-based catalysts enhanced the activity of the catalyst. The results showed that the 15 wt%Ni-12.5 wt%Co–Al2O3 sample with a specific surface area of 129.96 m2/g possessed the highest catalytic performance in CO2 methanation (76.2% CO2 conversion and 96.39% CH4 selectivity at 400 °C) and this catalyst presented high stability over 10 h time-on-stream. Also, CO methanation was investigated and the results showed a complete CO conversion at 300 °C.  相似文献   

16.
The Ni/ZrO2 catalyst is one of the most active systems for the methanation of CO to be employed in the hydrogen purification for PEMFC. This contribution aims to study the effect of ZrO2 on the methanation of CO and CO2. The catalytic behavior of Ni/ZrO2, Ni/SiO2, a physical mixture comprising Ni and ZrO2, and a double-bed reactor were evaluated. The TPD of CO and CO2, TPSR and the cyclohexane dehydrogenation reaction were carried out to describe the catalysts and the reactions. The high activity of Ni/ZrO2 catalyst toward the methanation of CO is related to the presence of active sites on the ZrO2 surface. The methanation of CO occurs on ZrO2 due to its ability to adsorb CO and also because of the hydrogen spillover phenomenon. Apparently, the effect of ZrO2 is less relevant for the methanation of CO2. Ni/ZrO2 is a very promising system for the purification of hydrogen.  相似文献   

17.
This study focused on the potential coordination between nickel or cobalt and alumina in Ni/Al2O3 and Co/Al2O3 catalysts and the impacts on their catalytic performances in methanation of CO2. The results exhibited that Co/Al2O3 catalyst was far more active than Ni/Al2O3 catalyst, due to the varied reaction intermediates formed in methanation. The DRIFTS results of methanation of CO2 exhibited that, over bare alumina, bicarbonate, formate and carbonate were the main intermediate species, which could be formed at even 80 °C. Over unsupported Ni catalyst, the formaldehyde species (H2CO*) and CO* species were dominated. Over the Ni/Al2O3 catalyst, however, the reaction intermediates formed were determined by alumina and accumulated on surface of the catalysts. The coordination effects between nickel and alumina in Ni/Al2O3 were thus not remarkable in terms of enhancing catalytic activity when compared to that in Co/Al2O3 catalyst. Over unsupported Co catalyst and the bare alumina, the reaction intermediates formed were roughly similar. Nevertheless, the combination of Co and alumina in Co/Al2O3 catalyst could effectively facilitate the conversion of bicarbonate, formate and carbonate species. CO2 could be activated over metallic cobalt sites, which could migrate and integrate with the hydroxyl group in alumina to form bicarbonate and further to formate and CO* species, and be further hydrogenated over cobalt sites to CH4. Such a coordination between alumina and cobalt species promoted the catalytic performances.  相似文献   

18.
In this study, tungsten oxide with a high specific surface area was fabricated using a nanocasting technique and used to prepare support for nickel catalysts for CO methanation. Additionally, Mg was further introduced as a promoter for tuning the catalytic performance. The 25Ni/WO3 catalyst demonstrated a relatively high CO conversion, but a poor CH4 selectivity; however, with the addition of 7 wt% Mg to the catalyst, the CH4 selectivity reached 92% at a temperature of 440 °C. The improved CH4 selectivity can be attributed to the enhanced CO dissociation, which was related to the reduced Ni particle size, as well as the enhanced Ni electron cloud density. The role of a physical barrier and electron transfer of MgO induces an enhancement of the metal–support interactions, which are conducive to decreasing the Ni particle size. Meanwhile, the electron transfer performance of MgO constitutes a crucial factor in enhancing the Ni electron cloud density. Furthermore, with benefit from the inhibition of agglomeration of the Ni particles by the MgO promoter, a significantly better catalytic stability was also observed on 7Mg25Ni/WO3 than with the 25Ni/WO3 catalyst.  相似文献   

19.
LaNi5 alloy can be utilized to directly store and release hydrogen in mild condition, thus it is considered as a long-term safe and stable solid-state hydrogen storage material. In this work, LaNi5H5 was used as the solid-state hydrogen source in the CO2 methanation reaction. Impressively, the carbon dioxide conversion can be achieved to nearly 100% under 3 MPa mixed gas at 200 °C. The microstructure and composition analysis results reveal that the high catalytic activity may originate from the promoted elementary steps over in situ formed metallic Ni nanoparticles during the CO2 methanation process. More importantly, as the lowered reaction temperature prevented the agglomeration of Ni nanoparticles, this catalyst exhibited durable stability with 99% conversion rate of CO2 retained after 400 h cycling test.  相似文献   

20.
Catalytic CO2 methanation is a potential solution for conversion of CO2 into valuable products, and the catalyst plays a crucial role on the CO2 conversion and CH4 selectivity. However, some details involved in the CO2 methanation over the carbon supported Ni catalysts are not yet fully understood. In this work, commercial coal char (CC) supported Ni catalysts were designed and prepared by two different methods (impregnation-thermal treatment method and thermal treatment-impregnation method) for CO2 methanation. Effects of the preparation conditions (including the thermal treatment temperature and time, the mass ratio of CC:Ni and the preparation method), as well as the reaction temperature of CO2 methanation, were investigated on the catalyst morphology, reducibility, structure and catalytic performance. Fibrous Ni-CC catalyst is achieved and shows high CO2 conversion (72.9%–100%) and CH4 selectivity (>99.0%) during the 600-min methanation process. Adverse changes of the catalyst surface and textural properties, reducibility, particle size and morphology are the potential factors leading to the catalyst deactivation, and possible solutions resistant to the deactivation were analyzed and discussed. The CO2 methanation mechanism with the CO route was proposed based on the oxidation-reduction cycle of Ni in this work.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号