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1.
Nickel on zirconium-modified silica was prepared and tested as a catalyst for reforming methane with CO2 and O2 in a fluidized-bed reactor. A conversion of CH4 near thermodynamic equilibrium and low H2/CO ratio (1<H2/CO<2) were obtained without catalyst deactivation during 10 h, in a most energy efficient and safe manner. A weight loading of 5 wt% zirconium was found to be the optimum. The catalysts were characterized using X-ray diffraction (XRD), H2-temperature reaction (H2-TPR), CO2-temperature desorption (CO2-TPD) and transmission election microscope (TEM) techniques. Ni sintering was a major reason for the deactivation of pure Ni/SiO2 catalysts, while Ni dispersed highly on a zirconium-promoted Ni/SiO2 catalyst. The different kinds of surface Ni species formed on ZrO2-promoted catalysts might be responsible for its high activity and good resistance to Ni sintering.  相似文献   

2.
The reverse water–gas shift chemical (RWGS) reaction is a promising technique of converting CO2 to CO at low operating temperatures, with high CO selectivity and negligible side products. In this study, we investigate the synthesis of Cu/CeO2 catalyst using Solution Combustion Synthesis (SCS) technique and its performance for the RWGS reaction using a tubular packed bed reactor. Results indicate that the catalytic activity and stability of CeO2 at low and moderate temperatures can be effectively improved by the addition of a small quantity of copper (1 wt%). The conversion of CO2 improves with an increase in temperature, with a maximum value of 70% at 600 °C, showing a steady time on stream (TOS) performance for 1200 min with negligible carbon deposition of <0.05 wt%. The high catalyst activity is due to the synergistic interaction between the active Cu0 species and Ce3+-oxygen vacancy. The Cu/CeO2 catalyst was also found to have 100% selectivity for CO, and no CH4 was detected in the outlet stream. Moreover, the morphological characteristics of the support and catalysts (fresh and post-reaction samples), as well as the impact of reaction on the catalysts surface were investigated using various methods such as x-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy with energy dispersive x-ray spectra (SEM/EDX). The results demonstrate that Cu/CeO2 offers a good potential for being a robust RWGS catalyst with exclusive selectivity for CO without the undesired methanation side-reaction.  相似文献   

3.
A series of xMnCu/Ce catalysts with constant low Cu loading of 1 wt% were prepared by the simple impregnation method. The obtained catalysts were characterized by XRD, BET, H2-TPR and XPS, and the preferential oxidation of CO was evaluated in CO2/H2-rich atmospheres. It was shown that partial Mn and Cu could be incorporated into the Ceria lattice, forming surface ternary Cu–Mn–Ce oxide solid solutions. At Mn/Cu = 0.6, the catalyst presented strong interaction among Cu, Mn and Ce, had more Ce3+ and Mn4+ at the surface and showed the best catalytic performance, making CO conversion increase of 23.57% at 90 °C as compared with the Cu/Ce catalyst. For CO-Prox, the highest CO conversion was 94.7% with an oxidation selectivity of 78.9% at 125 °C. At this temperature, the catalyst revealed stable catalytic performance for a total TOS of 205 h. In addition, with CO/Ar as feed gas, CO conversion was 100%, confirming the negative effects of CO2/H2.  相似文献   

4.
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   

5.
The efficiency of CO2 methanation was estimated through gas chromatography in the presence of Co–Fe catalysts. Scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy were applied for ex-situ analysis of the catalysts after their test in the methanation reaction. Thermal programmed desorption mass spectroscopy experiments were performed to identify gaseous species adsorbed at the catalyst surface. Based on the experimental results, surface reaction model of CO2 methanation on Co–Fe catalysts was proposed to specify active ensemble of metallic atoms at the catalyst surface, orientation of adsorbed CO2 molecule on the ensemble and detailed reaction mechanism of CO2→CH4 conversion. The reaction step when OH group in the FeOOH complex recombined with the H atom adsorbed at the active ensemble to form H2O molecule was considered as the rate-limiting step.  相似文献   

6.
The reverse water gas shift (RWGS) process is considered a feasible method for lowering greenhouse gas emissions by utilizing CO2 and converting it to CO. Herein, we evaluated the catalytic conversion of CO2 through the RWGS reaction over transition metal nanoparticles supported on lanthanum. Catalysts of selected active metals (Cu, Ni, and CuNi) on lanthanum oxide support were investigated in a packed bed tubular reactor within a temperature range of 100–600 °C to assess their catalytic activity and selectivity towards CO. The results of the catalyst's activity and stability experiments showed maximum CO2 conversions of 57%, 68% and 74% for Cu–La2O3, Ni–La2O3, and CuNi–La2O3, respectively, at 600 °C and excellent stability over a 1440-min time on stream (TOS) with a carbon deposition rate of less than 3 wt%. However, among all investigated catalysts, only the 1 wt% Cu–La2O3 catalyst displayed a CO selectivity of 100% at all the studied temperatures, whereas the nickel-containing catalysts showed selectivity for methane along with carbon monoxide. Furthermore, the morphological properties of the support and catalysts, as well as the effect of the reaction conditions on the catalysts surface, were studied using a variety of techniques, including XRD, TEM, SEM-EDX and TPR. The results showed promising potential for the application of transition metal catalysts on lanthanum oxide support for RWGS that could be extended to other hydrogenation reactions.  相似文献   

7.
The high thermal stability of CO2 makes its conversion low in conventional thermal catalysis. Comparatively, non-equilibrium plasma technique provides an efficient way for CO2 hydrogenation under mild reaction conditions. Introducing effective catalysts to the dielectric barrier discharge (DBD) plasma reactor may further improve CO2 hydrogenation performance. In this way, the interaction between plasma and catalysts is important to contribute CO2 hydrogenation performance. Considering Ni-based catalyst is active for CO2 hydrogenation, we used three different kinds of carrier materials including CeO2, γ-Al2O3 and ZSM-5 as supports to prepare nickel-based catalysts by incipient impregnation in this paper. The supported Ni catalysts were tested for the plasma-induced CO2 hydrogenation to CH4 and C2+ hydrocarbons in the DBD-plasma reactor. It was found that the 15Ni/CeO2 catalyst achieved the best CO2 conversion of 85.7% and nearly 100% CH4 selectivity at 300 °C due to its high reducibility and CO2 chemisorption capacity. In addition, a significant synergistic effect was found between DBD plasma and catalyst. The performance of plasma-catalysis was considerably better than that of thermal catalysis plus pure plasma reaction, and the synergistic effects were enhanced with increase of reaction temperature. Moreover, the mechanism of the synergistic effect was proposed by analyzing the optical emission spectroscopy (OES) of DBD plasma, which provides a theoretical basis for further optimizing and application of plasma-catalysis for CO2 hydrogenation reaction.  相似文献   

8.
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   

9.
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   

10.
The design and development of a high performance hydrogenation catalyst is an important challenge in the utilization of CO2 as resources. The catalytic performances of the supported catalyst can be effectively improved through the interaction between the active components and the support materials. The obtained results demonstrated that the oxygen vacancies and active Cu0 species as active sites can be formed in the Cu/CeO2-δ catalysts by the H2 reduction at 400 °C. The synergistic effect of the surface oxygen vacancies and active Cu0 species, and Cu0–CeO2-δ interface structure enhanced catalytic activity of the supported xCu/CeO2-δ catalysts. The electronic effect between Cu and Ce species boosted the adsorption and activation performances of the reactant CO2 and H2 molecules on the corresponding Cu/CeO2-δ catalyst. The Cu/CeO2-δ catalyst with the Cu loading of 8.0 wt% exhibited the highest CO2 conversion rate in the RWGS reaction, reaching 1.38 mmol·gcat−1 min−1 at 400 °C. Its excellent catalytic performance in the RWGS reaction was related to the complete synergistic interaction between the active species via Ce3+-□-Cu0 (□: oxygen vacancy). The Cu/CeO2-δ composite material is a superior catalyst for the RWGS reaction because of its high CO2 conversion and 100% CO selectivity.  相似文献   

11.
The development of catalysts with resistance to sintering and coke deposition is the key to tar cracking during biomass gasification technology. In this work, the core-shell catalysts with mesoporous and microporous silica-coated nickel nanoparticles were prepared for the CO2 reforming of toluene as a model compound for biomass tar. The influence of thickness of SiO2 shell layer on catalyst activity, coke and sintering resistance of the catalysts in the CO2 reforming of toluene was explored. Appropriate increasing in the thickness of the silica shell can significantly increase the specific surface area, pore volume and the interaction between core and shell of the catalysts, which can further improve the reactivity and coke resistance ability. However, excessive increase in shell thickness can lead to a drastic decrease in the specific surface area and pore volume of the catalyst, resulting in significant coke deposition. The Ni@SiO2-4 catalyst showed the highest catalytic activity of toluene conversion of around 50% within 300 min, stability H2/CO ratio of 0.25~0.3 and durability of 26 h lifetime in the CO2 reforming of toluene. Overall, the optimization of the silica shell thickness can improve the reactivity and coke resistance ability of Ni@SiO2.  相似文献   

12.
In this work, the solution plasma-assisted method was used to prepare NiMnAl-LDO (layered double oxides) catalysts with different treatment times, which were used for the CO2 methanation reaction. Solution plasma treatment can enhance the dispersibility of the catalyst, create oxygen defects and improve the chemical adsorption capacity of the catalyst. The results show that the low-temperature activity of the catalyst has been improved after the solution plasma treatment. We demonstrate that the NiMnAl-LDO-P(20) catalyst with high dispersion has the highest catalytic activity in CO2 methanation (81.3% CO2 conversion and 96.7% CH4 selectivity at 200 °C). Even though working for 70 h, the catalyst is still highly stable. This work provides a great promise for improving the low-temperature activity of Ni-based catalysts.  相似文献   

13.
In this paper, a series of mesoporous supported nickel based catalysts on nanocrystalline alumina carrier promoted with various metals (Fe, CO, Zr, La and Cu) were prepared and employed in carbon dioxide methanation reaction. The samples were characterized by XRD, BET, TPR and SEM techniques. The BET results showed that the incorporation of promoters into nickel based catalysts decreased the surface area. The results showed that among the prepared catalysts, 30 wt.%Ni-5 wt.%La/Al2O3 and 30 wt.%Ni-5 wt.%Fe/Al2O3 possessed the highest surface area and the largest pore volume, respectively. Likewise, there was a slight decrease in the pore volume and the average pore diameters of the promoted samples. The TPR results depicted that the incorporation of the promoters enhanced the reducibility of the catalysts and shifted the reduction of NiO species to a lower reduction temperature. The CO2 conversions of all promoted catalysts except Cu-promoted sample were higher peculiarly at low temperatures compared to those attained for the unpromoted catalyst. 30 wt.%Ni-5 wt.%Fe/Al2O3 catalyst exhibited the best catalytic performance (70.63% CO2 conversion and 98.87% CH4 selectivity at 350 °C), high stability and desirable resistance against sintering.  相似文献   

14.
The development of catalysts for the water-gas shift (WGS) reaction is attracting attention because of the increased interest in on-site small-scale hydrogen production, which requires highly active and stable catalytic performance under severe conditions. In this study, metal–organic frameworks (MOF), which have been adopted in various fields because of their high surface area, diversity of assemblies, and uniform porosity, were applied to prepare Cu/CeO2 catalysts for the WGS reaction. MOF-derived CeO2 (MDC) was obtained from a Ce-BTC-based MOF calcined at different temperatures. Various techniques were used to investigate the physicochemical properties of the Cu/MDC catalysts. Important properties that determine the catalytic performance, such as crystallinity, surface area, Cu dispersion, reducibility, and oxygen storage capacity (OSC), were affected by the treatment temperature of MDC. Among the Cu/MDC catalysts, Cu/MDC prepared with MDC that was treated at 400 °C (Cu/MDC(400)) exhibited the highest CO conversion at reaction temperatures of 200–400 °C. In addition, Cu/MDC(400) maintained 80% of its initial CO conversion after 48 h on stream, even at a very high gas hourly specific velocity of 50,233 mL·gcat−1·h−1. This result was attributed to the high surface area, Cu dispersion, OSC, and easier reducibility of the Cu/MDC(400) catalyst compared to Cu supported on MDC calcined at other temperatures.  相似文献   

15.
Powder and structured catalysts based on CuO–CeO2 nanoparticles dispersed on different silica are studied in CO preferential oxidation. Silica of natural origin (Celite) and fumed silica (aerosil), both commercial materials, and synthesized mesoporous SBA-15 with 20, 200 and 650 m2g-1 respectively, are selected as supports. CuCe/Celite coated on cordierite monolith displays the highest activity, reaching CO conversion above 90% between 140 and 210 °C and more than 99% around 160 °C. The addition of 10% CO2 and 10% H2O partially deactivates the monolithic catalyst.The lower surface area of CuCe/Celite favors the contact between CuO and CeO2 nanoparticles promoting a better interaction of Cu+2/Cu+ and Ce+3/Ce+4 redox couples. Raman spectroscopy reveals oxygen vacancies and XPS results show high metal lattice surface oxygen concentration and surface enrichment of Cu and Ce which promote the catalytic activity.  相似文献   

16.
The purposes of this study were to prepare a copper catalyst by the microwave-heated polyol (MP) process and subsequently to evaluate the feasibility of the preferential oxidation of CO (CO-PROX) in excess H2. A CeO2-TD support was firstly prepared by the thermal decomposition from Ce(NO3)3·6H2O precursor. For comparison, commercial ceria (CeO2-C) and activated carbon (AC) selected as support materials. Experimental results of CO-PROX indicated that the highest catalytic activity is achieved when the Cu/CeO2-TD used as catalysts. Correlating to the characteristic results, it is found that the CeO2-TD support prepared by the thermal decomposition has a large surface area and high mesoporosity; these properties contribute to the easy adsorption of pollutants and the effective dispersion of metal particles. Further investigation of feed composition found that Cu/CeO2-TD catalysts possess 100% CO conversion even existence of CO2 and H2O in H2-rich streams at 150 °C. Besides, a decrease in CO conversion was clearly observed above 175 °C for Cu/CeO2-TD catalysts due to the reverse water gas shift reaction tending to reform CO from CO2 and H2.  相似文献   

17.
The self-regeneration of Ni-based catalysts has been considered as a promising approach to maintain not only a continuous but also economical process. However, the effect of catalyst nature, operating temperature, amount and types of carbon deposits on the effectiveness of the in-situ regeneration is still not well-investigated. Therefore, in this work, the self-regeneration ability of the undoped and Dy-doped Ni/SiO2 catalysts, which were prepared by the same impregnation method, were examined in the dry reforming of methanol. The physicochemical properties of the fresh and spent catalysts were analyzed by various techniques such as X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), transmission electron microscopy (TEM), N2-BET isothermal adsorption. The nature and chemical reactivity of coke deposits formed during dry reforming at various temperatures (550, 600, and 650 °C) and the regeneration possibility of used catalysts through CO2 gasification at these temperatures were investigated by the in-situ temperature-programmed gasification by CO2 (TPCO2). The Dy additive significantly improves the dispersion of the nickel active sites of Ni/SiO2 catalyst, as demonstrated by the decreased Ni crystal size as well as the increased specific surface area and reduction degree of the catalyst. Furthermore, Dy promotion increases the quantity of oxygen vacancies and the nature of oxygen species, thereby improving the catalyst activity and stability. Specifically, methanol conversion dropped from 93% to 96%–61% and 31% for undoped Ni/SiO2 at 600 °C and 650 °C, respectively and from about 99% to 87% (at 600 °C) and 52% (at 650 °C) for Dy-doped catalyst.  相似文献   

18.
This work introduces LaCo1-xNixO3 (x = 0, 0.1, 0.25, and 0.4) perovskite catalysts for enhancing the low temperature performance of reverse water-gas shift (RWGS) reaction. Incorporating Ni lowers the interaction between La-site and B-site, weakening the electron donation from La-site to B-site. The B-site elements with the weak interaction can be easily diffused from the bulk to form exsolved bimetallic Co–Ni alloy on the surface. This different interaction trends further control H2 dissociation activity and CO desorption that affect CO2 conversion and CO selectivity, respectively. While the Ni-incorporated catalyst shows a higher metal dispersion to enhance H2 dissociation activity and increases CO2 conversion, the La-sites with the weak electron donation further drive the strong adsorption of CO molecules to be additionally hydrogenated, eventually lower CO selectivity. However, incorporating 10 at% Ni into the B site of LaCoO3 (LaCo0.9Ni0.1O3) achieved a balanced effect between facile H2 dissociation and CO desorption to maximize RWGS activity. The LaCo0.9Ni0.1O3 catalyst displayed outstanding activity with an average CO2 conversion of 30.8%, which is close to the equilibrium conversion, and a CO selectivity of 98.8% at 475 °C over 50 h.  相似文献   

19.
Running dry reforming of methane (DRM) reaction at low-temperature is highly regarded to increase thermal efficiency. However, the process requires a robust catalyst that has a strong ability to activate both CH4 and CO2 as well as strong resistance against deactivation at the reaction conditions. Thus, this paper examines the prospect of DRM reaction at low temperature (400–600 °C) over CeO2–MgO supported Nickel (Ni/CeO2–MgO) catalysts. The catalysts were synthesized and characterized by XRD, N2 adsorption/desorption, FE-SEM, H2-TPR, and TPD-CO2 methods. The results revealed that Ni/CeO2–MgO catalysts possess suitable BET specific surface, pore volume, reducibility and basic sites, typical of heterogeneous catalysts required for DRM reaction. Remarkably, the activity of the catalysts at lower temperature reaction indicates the workability of the catalysts to activate both CH4 and CO2 at 400 °C. Increasing Ni loading and reaction temperature has gradually increased CH4 conversion. 20 wt% Ni/CeO2–MgO catalyst, CH4 conversion reached 17% at 400 °C while at 900 °C it was 97.6% with considerable stability during the time on stream. Whereas, CO2 conversions were 18.4% and 98.9% at 400 °C and 900 °C, respectively. Additionally, a higher CO2 conversion was obtained over the catalysts with 15 wt% Ni content when the temperature was higher than 600 °C. This is because of the balance between a high number of Ni active sites and high basicity. The characterization of the used catalyst by TGA, FE-SEM and Raman Spectroscopy confirmed the presence of amorphous carbon at lower temperature reaction and carbon nanotubes at higher temperature.  相似文献   

20.
15 wt.%Ni-12.5 wt.%Co–Al2O3 catalysts promoted with Fe, Mn, Cu, Zr, La, Ce, and Ba were prepared by a novel solid-state synthesis method and employed in CO2 methanation reaction. BET, XRD, EDS, SEM, TPR, TGA, and FTIR analyses were conducted to identify the chemicophysical characteristics of the prepared samples. The addition of Fe, Mn, La, Ce, and Ba was effective to improve the catalytic performance of the 15 wt%Ni-12.5 wt%Co–Al2O3 due to the higher CO2 adsorption capacity of the promoted catalysts. Among the studied promoters, the Fe-promoted catalyst possessed the highest catalytic activity (XCO2 = 61.2% and SCH4 = 98.87% at 300 °C). Also, the effect of calcination temperature, feed composition, and GHSV on the performance of the 15 wt%Ni-12.5 wt%Co-5wt%Fe–Al2O3 catalyst in CO2 methanation reaction was assessed. The outcomes confirmed that the 15 wt%Ni-12.5 wt%Co-5wt%Fe–Al2O3 catalyst with the BET area of 122.4 m2/g and the highest pore volume and largest pore diameter had the highest catalytic activity. Also, the catalytic performance in the methanation of carbon monoxide was studied, and 100% conversion of carbon monoxide was observed at 250 °C.  相似文献   

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