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1.
In this work the effects of different promoters (Cr, Al, Mn, Ce, Ni, Co and Cu) on the structural and catalytic properties of Nanocrystalline iron based catalysts for high temperature water gas shift reaction were investigated. The catalysts were prepared in active phase (Fe3O4) via a facile direct synthesis routs without any additive and characterized using X-ray diffraction (XRD), N2 adsorption (BET), temperature-programmed reduction (TPR), transmission and scanning electron microscopies (TEM,SEM) techniques. The obtained results indicated that synergic effect of Mn and Ni promoters can lead to obtain a Cr-free catalyst with high activity. In addition, the effect of Ni content on the structural and catalytic properties of the Fe–Mn–Ni catalysts was investigated. It was found that Fe–Mn–Ni catalyst with Fe/Mn = 10 and Fe/Ni = 5 weight ratios showed the highest catalytic activity among the prepared catalysts and possessed a stable catalytic performance without any decrease during 10 h time on stream. Moreover, the effect of GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.  相似文献   

2.
Water gas shift reaction is an essential process of hydrogen production and carbon monoxide removal from syngas. Fe–Cr–Cu catalysts are typical industrial catalysts for high temperature water gas shift reaction but have environmental and safety concerns related to chromium content. In this work nanocrystalline metal (M)-modified ferrite catalysts (M = Cr, Al, Mn, Ce, Ni, Co and Cu) for replacement of chromium were prepared by coprecipitation method and the effects of promoters on the structural and catalytic properties of the iron based catalysts were studied. Prepared catalysts were characterized using X-ray diffraction (XRD), N2 adsorption (BET), temperature-programmed reduction (TPR) and transmission electron microscopies (TEM) techniques. Temperature-programmed reduction measurements inferred that copper favors the active phase formation and significantly decreased the reduction temperature of hematite to magnetite. In addition, water gas shift activity results revealed that Fe–Al–Cu catalyst with Fe/Al = 10 and Fe/Cu = 5 weight ratios showed the highest catalytic activity among the prepared catalysts. Moreover, the effect of calcination temperature, GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.  相似文献   

3.
La0.8Sr0.2Ni0.8M0.2O3 (LSNMO) (where M = Bi, Co, Cr, Cu and Fe) perovskite catalyst precursors have been successfully developed for CO2 dry-reforming of methane (DRM). Among all the catalysts, Cu-substituted Ni catalyst precursor showed the highest initial catalytic activity due to the highest amount of accessible Ni and the presence of mobile lattice oxygen species which can activate C–H bond, resulting in a significant improvement of catalytic activity even at the initial stage of reaction. However, these Ni particles can agglomerate to form bigger Ni particle size, thereby causing lower catalytic stability. As compared to Cu-substituted Ni catalyst, Fe-substituted Ni catalyst has low initial activity due to the lower reducibility of Ni–Fe and the less mobility of lattice oxygen species. However, Fe-substituted Ni catalyst showed the highest catalytic stability due to: (1) strong metal–support interaction which hinders thermal agglomeration of the Ni particles; and (2) the presence of the abundant lattice oxygen species which are not very active for C–H bond activation but active to react with CO2 to form La2O2CO3, hence minimizing carbon formation by reacting with surface carbon to form CO.  相似文献   

4.
A series of Y2O3-promoted NiO/SBA-15 (9 wt% Ni) catalysts (Ni:Y weight ratio = 9:0, 3:1, 3:2, 1:1) were prepared using a sol–gel method. The fresh as well as the catalysts used in CO2 reforming of methane were characterized using N2-physisorption, XRD, FT-IR, XPS, UV, HRTEM, H2-TPR, O2-TPD and TG techniques. The results indicate that upon Y2O3 promotion, the Ni nanoparticles are highly dispersed on the mesoporous walls of SBA-15 via strong interaction between metal ions and the HO–Si-groups of SBA-15. The catalytic performance of the catalysts were evaluated at 700 °C during CH4/CO2 reforming at a gas hourly space velocity of 24 L gcat−1 h−1(at 25 °C and 1 atm) and CH4/CO2molar ratio of 1. The presence of Y2O3 in NiO/SBA-15 results in enhancement of initial catalytic activity. It was observed that the 9 wt% Y–NiO/SBA-15 catalyst performs the best, exhibiting excellent catalytic activity, superior stability and low carbon deposition in a time on stream of 50 h.  相似文献   

5.
A series of composite catalysts Ni/CeO2–ZrO2 were prepared via impregnation method with Ni as the active metal. A laboratory-scale fixed-bed reactor was employed to investigate the catalyst performance during hydrogen production by steam reforming bio-oil aqueous fraction. Effects of water-to-bio-oil ratio (W/B), reaction temperature, and the loaded weight of Ni and Ce on the hydrogen production performance of Ni/CeO2–ZrO2 catalysts were examined. The obtained results were compared with commercial nickel-based catalysts (Z417). The best performance of Ni/CeO2–ZrO2 catalyst was observed when the Ni and Ce loaded weight were 12% and 7.5% respectively. At W/B = 4.9, T = 800 °C, H2 yield reaches the highest of 69.7% and H2 content of 61.8% were obtained. Under the same condition, H2 yield and H2 content were higher than commercial nickel-based catalysts (Z417).  相似文献   

6.
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   

7.
A mesoporous Ni–Al2O3–ZrO2 aerogel (Ni–AZ) catalyst was prepared by a single-step epoxide-driven sol–gel method and a subsequent supercritical CO2 drying method. For comparison, a mesoporous Al2O3–ZrO2 aerogel (AZ) support was prepared by a single-step epoxide-driven sol–gel method, and subsequently, a mesoporous Ni/Al2O3–ZrO2 aerogel (Ni/AZ) catalyst was prepared by an incipient wetness impregnation method. The effect of preparation method on the physicochemical properties and catalytic activities of Ni–AZ and Ni/AZ catalysts was investigated. Although both catalysts retained a mesoporous structure, Ni/AZ catalyst showed lower surface area than Ni–AZ catalyst. From TPR, XRD, and H2–TPD results, it was revealed that Ni–AZ catalyst retained higher reducibility and higher nickel dispersion than Ni/AZ catalyst. In the hydrogen production by steam reforming of ethanol, both catalysts showed a stable catalytic performance with complete conversion of ethanol. However, Ni–AZ catalyst showed higher hydrogen yield than Ni/AZ catalyst. Superior textural properties, high reducibility, and high nickel surface area of Ni–AZ catalyst were responsible for its enhanced catalytic performance in the steam reforming of ethanol.  相似文献   

8.
Steam reforming of methanol was investigated over Cu–ZnO–ZrO2–Al2O3 catalysts at 473 and 573 K. The Cu:Zn:(Al + Zr) molar ratio was 3:3:4; however, the Zr:Al molar ratio was varied and the catalysts were pretreated at different calcination and reduction temperatures. The synthesized catalysts were characterized by N2 physisorption, temperature-programmed reduction with H2 (H2-TPR), X-ray diffraction, oxidized surface TPR, and infrared spectroscopy after carbon monoxide chemisorption. The crystalline size of Cu decreased on increasing the calcination temperatures from 573 to 623 K and increased on increasing the reduction temperatures from 523 to 573 K. Among the tested catalysts, the Cu–ZnO–ZrO2 catalyst exhibited the highest and lowest hydrogen-formation rates at 473 and 573 K, respectively. After the reaction at 573 K, all the tested catalysts exhibited an increase in the Cu crystalline size, causing the catalyst deactivation. Among the tested catalysts, the Cu–ZnO–ZrO2–Al2O3 catalyst, where the Cu:Zn:Al:Zr molar ratio was 3:3:2:2, showed the highest and most stable catalytic activity at 573 K. Cu dispersion and catalyst composition affected the catalytic performance for steam reforming of methanol.  相似文献   

9.
Steam reforming of toluene as a biomass tar model compound was performed over Ni supported CaO–Al2O3 (Ca–Al) and CeO2 promoted CaO–Al2O3 (Ca–Al–Ce) catalysts to explore promotional effect of CeO2 on Ca–Al support. Among all the catalysts tested, Ni/Ca–Al–Ce(0.2) catalyst gave superior catalytic performance over other catalysts. The basic strength of catalytic supports measured by CO2 TPD and Hammett indicator methods indicates Ca–Al–Ce(0.2) support has higher surface basicity and base strength compared to Ca–Al and other Ca–Al–Ce(x) supports. Furthermore, CO pulse chemisorption results showed that Ni/Ca–Al–Ce(0.2) catalyst has a higher amount of surface metallic nickel compared to other Ni/Ca–Al–Ce catalysts. TPR analysis reveals that the redox property of CeO2 can enhance the reducibility of supported nickel species, which is further confirmed using XPS analysis, where addition of CeO2 enhanced the interaction of Ni species with Ce by reducing the interaction of Ni species with the Al support, resulting in the formation of Ni° rich surface. However, formation of bulk NiO species was also observed for the catalyst having higher amount of CeO2. TGA analysis on spent catalysts reveals that all CeO2-containing catalysts generally result in lower carbon formation rates as compared to Ni/Ca–Al catalyst.  相似文献   

10.
Ni/xY2O3–Al2O3 (x = 5, 10, 15, 20 wt%) catalysts were prepared by sequential impregnation synthesis. The catalytic performance for the autothermal reforming of methane was evaluated and compared with Ni/γ-Al2O3 catalyst. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H2-temperature programmed reduction techniques (TPR). The decrease of nickel particle size and the change of reducibility were found with Y modification. The CH4 conversion increased with elevating levels of Y2O3 from 5% to 10%, then decreased with Y content from 10% to 20%. Ni/xY2O3–Al2O3 catalysts maintained high activity after 24 h on stream, while Ni/Al2O3 had a significant deactivation. The characterization of spent catalysts indicated that the addition of Y retarded Ni sintering and decreased the amount of coke.  相似文献   

11.
A series of mesoporous Ni–Al2O3–ZrO2 xerogel catalysts (denoted as Ni-AZ-X) with different Zr/Al molar ratio (X) were prepared by a single-step epoxide-driven sol–gel method, and they were applied to the hydrogen production by steam reforming of ethanol. The effect of Zr/Al molar ratio of Ni-AZ-X catalysts on their physicochemical properties and catalytic activities was investigated. Textural and chemical properties of Ni-AZ-X catalysts were strongly influenced by Zr/Al molar ratio. Surface area of Ni-AZ-X catalysts decreased with increasing Zr/Al molar ratio due to the lattice contraction of ZrO2 caused by the incorporation of Al3+ into ZrO2. Interaction between nickel oxide species and support (Al2O3–ZrO2) decreased with increasing Zr/Al molar ratio through the formation of NiO–Al2O3–ZrO2 composite structure. Acidity of reduced Ni-AZ-X catalysts decreased with increasing Zr/Al molar ratio due to the loss of acid sites of Al2O3 by the addition of ZrO2. Acidity of Ni-AZ-X catalysts served as a crucial factor determining the catalytic performance in the steam reforming of ethanol; an optimal acidity was required for maximum production of hydrogen. Among the catalysts tested, Ni-AZ-0.2 (Zr/Al = 0.2) catalyst with an intermediate acidity exhibited the best catalytic performance in the steam reforming of ethanol.  相似文献   

12.
Syngas production by CO2 reforming of coke oven gas (COG) was studied in a fixed-bed reactor over Ni/La2O3–ZrO2 catalysts. The catalysts were prepared by sol–gel technique and tested by XRF, BET, XRD, H2-TPR, TEM and TG–DSC. The influence of nickel loadings and calcination temperature of the catalysts on reforming reaction was measured. The characterization results revealed that all of the catalysts present excellent resistance to coking. The catalyst with appropriate nickel content and calcination temperature has better dispersion of active metal and higher conversion. It is found that the Ni/La2O3–ZrO2 catalyst with 10 wt% nickel loading provides the best catalytic activity with the conversions of CH4 and CO2 both more than 95% at 800 °C under the atmospheric pressure. The Ni/La2O3–ZrO2 catalysts show excellent catalytic performance and anti-carbon property, which will be of great prospects for catalytic CO2 reforming of COG in the future.  相似文献   

13.
A highly dispersed 50 wt% Ni/MgO–Al2O3 catalyst was prepared by deposition–precipitation (DP) method for the diesel pre-reforming reaction. The pH of the precursor solution was controlled from pH 9.5 to 12.0 to examine the effects on NiO crystallite size and metal dispersion. The increase of pH of the precursor solution causes an increase of specific surface area and metal dispersion, and reduces NiO crystallite size. The pre-reforming reaction was carried out using n-tetradecane as surrogate compound of diesel. The coke formation of used catalysts was examined by TGA, TEM, SEM, and Raman analysis. The 50 wt% Ni/MgO–Al2O3 catalyst prepared at pH 11.5 showed a high catalytic activity and excellent coke resistance due to high metal dispersion (8.71%), small NiO crystallite size (3.5 nm), and strong interaction between Ni and support. Furthermore, this catalyst showed a good stability in the pre-reforming reaction at S/C ratio of 3.5 and 450 °C for 88 h.  相似文献   

14.
Activated carbon (AC) supported Fe–Al2O3 catalysts were prepared by impregnation method and used for catalytic methane decomposition to hydrogen. The XRD and H2-TPR results showed that ferric nitrate on AC support was directly reduced to Fe metal by the reducibility of carbon at 870 °C. The loading amount and Fe/Al2O3 weight ratio affect the textural properties and catalytic methane decomposition. The surface area and pore volume of the catalyst decrease with the loading of Fe and Al2O3. Mesopores with size of about 4.5 nm can be formed at the loading of 20–60% and promote the catalytic activity and stability. The mesopores formation is thought that Fe accelerates burning off of carbon wall and enlarging pore sizes during the pretreatment. When the Fe/Al2O3 ratio is 16/24 to 24/16 at the loading of 40%, the resultant catalysts show narrow mesopore distributions and relative high methane conversion. Al2O3 as the promoter can improve catalytic activity and shorten transitional period of AC supported Fe catalyst.  相似文献   

15.
Nanostructured Ni-incorporated mesoporous alumina (MAl) materials with different Ni loading (7, 10 and 15 wt %) were prepared by a template assisted hydrothermal synthesis method and tested as catalysts for CO2 reforming of methane under different conditions (nickel loading, gas hourly space velocity (GHSV), reaction temperature and time-on-stream (TOS)). The most active catalyst tested (Ni(10 wt%)-MAl) showed a very high stability over 200 h compared to a Ni(10 wt%)/γ-Al2O3 prepared using a co-precipitation method which had a significant loss in activity after only ∼4 h of testing. The high stability of the Ni-MAl materials prepared by the template assisted method was due to the Ni nanoparticles in these catalysts being highly stable towards migration/sintering under the reaction conditions used (800 °C, 52,000 mL h−1 g−1). The low susceptibility of the Ni nanoparticles in these catalysts to migration/sintering was most likely due to a strong Ni-support interaction and/or active metal particles being confined to the mesoporous channels of the support. The Ni-MAl catalysts also had significantly lower amounts of carbon deposited compared to the catalyst prepared using the co-precipitation method.  相似文献   

16.
A series of gold catalysts supported on ZnO–TiO2 with various ZnO contents were prepared. ZnO–TiO2 was prepared by incipient-wetness impregnation using aqueous solution of Zn(NO3)2 onto TiO2. Gold catalysts with nominal gold loading of 1 wt. % were prepared by deposition-precipitation (DP) method. Various preparation parameters, such as pH value and Zn/Ti ratio on the characteristics of the catalysts were investigated. The catalysts were characterized by inductively-coupled plasma–mass spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The preferential oxidation of CO in H2 stream (PROX) on these catalysts was carried out in a fixed bed micro-reactor with a feed of CO: O2: H2: He = 1: 1: 49: 49 (volume ratios) and a space velocity of 30,000 ml/g h. Limited amount of oxygen was used in the feed. A high gold dispersion and narrow gold particle size distribution was obtained. Au/ZnO–TiO2 with Zn/Ti atomic ratio of 5/95 showed the highest CO conversion at room temperature. The conversion increased with increasing temperature even in the presence of limited amount of oxygen, showing suppression in H2 oxidation. Au/ZnO–TiO2 prepared at pH 6 had a higher CO conversion and higher selectivity of CO oxidation than those prepared at other pH values. The addition of ZnO on TiO2 resulted in higher dispersion of gold particles and narrow particle size distribution. The stronger the Au–Zn(OH)2 interaction, the finer the supported Au nanoparticles, and the better the catalytic performance of the catalyst for PROX reaction. Part of Au was in Au+ state due to the interaction with Zn(OH)2 and nano Au size. The oxidation state of gold species played an important role in determining its CO conversion and selectivity of CO oxidation in hydrogen stream. The catalysts were stable at 80 °C for more than 80 h.  相似文献   

17.
A highly active and stable bimetallic nano-hybrid catalyst Graphene–Cobalt–Platinum (G–Co–Pt) is proposed for the enhanced and cost effective generation of hydrogen from Sodium Borohydride. Three different nano-hybrid catalysts namely Graphene–Cobalt (G–Co), Graphene–Platinum (G–Pt) and Graphene–Cobalt–Platinum (G–Co–Pt) are synthesized, characterized using XRD, FTIR, SEM, HRTEM, EDAX and Cyclic voltammetry (CV) analysis and tested for hydrogen generation. The activity and stability of the catalysts are analyzed by estimating the turnover frequency (TOF), the electrochemically active surface area (ECSA), the percentage decay of current density over ten cycles of CV and the decay in the rate of hydrogen generation with the age of catalyst. Among the three catalysts G–Co–Pt exhibits the highest catalytic activity (TOF = 107 min−1, ECSA = 75.32 m2/gm) and stability. The evaluated value of activation energy of the catalytic hydrolysis using G–Co–Pt is 16 ± 2 kJ mol−1.  相似文献   

18.
Dry reforming of methane has been studied over Pt/ZrO2 catalysts promoted with Ce for different temperatures and feed compositions. The influence of the impregnation strategy and the cerium amount on the activity and stability of the catalysts were investigated. The results have shown that introduction of 1 wt.% Ce to the Pt/ZrO2 catalyst via coimpregnation method led to the highest catalytic activity and stability. 1 wt.%Ce–1 wt.%Pt/ZrO2 catalyst prepared by sequential impregnation displayed inferior CH4 and CO2 conversion performances with lowest H2/CO production ratios. 1 wt.%Ce–1 wt.%Pt/ZrO2 catalyst prepared by coimpregnation showed the highest activity even for the feed with high CH4/CO2 ratio. The reason for high activity was explained by the intensive interaction between Pt and Ce phases for coimpregnated sample, which had been verified by X-ray photoelectron spectroscopy and Energy Dispersive X-Ray analyses. Strong and extensive Pt–Ce surface interaction results in an increase in the number of Ce3+ sites and enhances the dispersion of Pt.  相似文献   

19.
Cu and Ni were supported on ZrO2 by co-impregnation and sequential impregnation methods, and tested in the oxidative steam reforming of methanol (OSRM) reaction for H2 production as a function of temperature. Surface area of the catalysts showed differences as a function of the order in which the metals were added to zirconia. Among them, the Cu/ZrO2 catalyst had the lowest surface area. XRD patterns of the bimetallic catalysts did not show diffraction peaks of the Cu, Ni or bimetallic Cu–Ni alloys. In addition, TPR profiles of the bimetallic catalysts had the lowest reduction temperature compared with the monometallic samples. The reactivity of the catalysts in the range of 250–350 °C showed that the bimetallic samples prepared by successive impregnation had highest catalytic activity among all the catalysts studied. These results were also confirmed by theoretical calculations. The reactivity of the monometallic and bimetallic structures obtained by molecular simulation followed the next order: NishellCucore/ZrO2 ≅ CushellNicore/ZrO2 > Ni/Cu/ZrO2 > Cu/Ni/ZrO2 > Cu–Ni/ZrO2 > Cu/ZrO2 > Ni/ZrO2. These findings agree with the experimental results, indicating that the bimetallic catalysts prepared by successive impregnation show a higher reactivity than the Cu–Ni system obtained by co-impregnation. In addition, the selectivity for H2 production was higher on these catalysts. This result could be associated also to the presence of the bimetallic Cu–Ni and core–shell Ni/Cu nanoparticles on the catalysts, as was evidenced by TEM–EDX analysis, suggesting that the OSRM reaction may be a structure–sensitive reaction.  相似文献   

20.
Metal oxide-stabilized mesoporous zirconia supports (M–ZrO2) with different metal oxide stabilizer (M = Zr, Y, La, Ca, and Mg) were prepared by a templating sol–gel method. 20 wt% Ni catalysts supported on M–ZrO2 (M = Zr, Y, La, Ca, and Mg) were then prepared by an incipient wetness impregnation method for use in hydrogen production by auto-thermal reforming of ethanol. The effect of metal oxide stabilizer (M = Zr, Y, La, Ca, and Mg) on the catalytic performance of supported nickel catalysts was investigated. Ni/M–ZrO2 (M = Y, La, Ca, and Mg) catalysts exhibited a higher catalytic performance than Ni/Zr–ZrO2, because surface oxygen vacancy of M–ZrO2 (M = Y, La, Ca, and Mg) and reducibility of Ni/M–ZrO2 (M = Y, La, Ca, and Mg) were enhanced by the addition of lower valent metal cation. Hydrogen yield over Ni/M–ZrO2 (M = Zr, Y, La, Ca, and Mg) catalyst was monotonically increased with increasing both surface oxygen vacancy of M–ZrO2 support and reducibility of Ni/M–ZrO2 catalyst. Among the catalysts tested, Ni catalyst supported on yttria-stabilized mesoporous zirconia (Ni/Y–ZrO2) showed the best catalytic performance.  相似文献   

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