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1.
The effect of calcination temperature on the state of the active component of iron-containing catalysts prepared by the impregnation of silica gel with a solution of FeSO4 and on their catalytic properties in selective H2S oxidation to sulfur was studied. With the use of thermal analysis, XPS, and Mössbauer spectroscopy, it was found that an X-ray amorphous iron-containing compound of complex composition was formed on the catalyst surface after thermal treatment in the temperature range of 400–500°C. This compound contained Fe3+ cations in three nonequivalent positions characteristic of various oxy and hydroxy sulfates and oxide and sulfate groups as anions. Calcination at 600°C led to the almost complete removal of sulfate groups; as a result, the formation of an oxide structure came into play, and it was completed by the production of finely dispersed iron oxide in the ?-Fe2O3 modification (the average particle size of 3.2 nm) after treatment at 900°C. As the calcination temperature was increased from 500 to 700°C, an increase in the catalyst activity in hydrogen sulfide selective oxidation was observed because of a change in the state of the active component. A comparative study of the samples by temperature-programmed sulfidation made it possible to establish that an increase in the calcination temperature leads to an increase in the stability of the iron-containing catalysts to the action of a reaction atmosphere.  相似文献   

2.
Iron oxide modified with single- or double-metal additives (Cr, Ni, Zr, Ag, Mo, Mo-Cr, Mo-Ni, Mo-Zr and Mo-Ag), which can store and supply pure hydrogen by reduction of iron oxide with hydrogen and subsequent oxidation of reduced iron oxide with steam (Fe3O4 (initial Fe2O3)+4H2↔3Fe+4H2O), were prepared by impregnation. Effects of various metal additives in the samples on hydrogen production were investigated by the above-repeated redox. All the samples with Mo additive exhibited a better redox performance than those without Mo, and the Mo-Zr additive in iron oxide was the best effective one enhancing hydrogen production from water decomposition. For Fe2O3-Mo-Zr, the average H2 production temperature could be significantly decreased to 276 °C, the average H2 formation rate could be increased to 360.9-461.1 μmol min−1 Fe-g−1 at operating temperature of 300 °C and the average storage capacity was up to 4.73 wt% in four cycles, an amount close to the IEA target.  相似文献   

3.
Studies were undertaken of phase transitions of iron oxide obtained from iron oxide-hydroxides of type α-, β-, γ- and δ-FeOOH, and used as a support of ruthenium catalysts Ru/Fe2O3, employed in the water-gas shift reaction. In asprepared pure supports and ruthenium catalysts the main phase was α-Fe2O3. After use in the water-gas shift reaction, the support showed the presence of different phases of iron oxide. The most active Ru/Fe2O3 catalysts prepared on the basis of α- and δ-FeOOH, after use in the water-gas shift reaction, revealed the presence of Fe3O4 or a mixture of phases Fe3O4 and γ-Fe2O3. The least active catalysts, prepared on the basis of β- and γ-FeOOH, contained a solid solution of Fe3O4-γ-Fe2O3 with traces of α-Fe2O3.  相似文献   

4.
The properties of the catalysts for partial oxidation of o-xylene depend on the structure of the supported vanadium sites. The structure itself is strongly dependent on the calcination temperature of the catalyst at which thermal deposition of the metal oxide on the oxide support takes place. We have investigated the effect of calcination temperature on the activity and selectivity of industrial V2O5-TiO2 (anatase) supported catalysts designed for partial oxidation of o-xylene in their application to methanol oxidation.This revised version was published online in December 2005 with corrections to the Cover Date.  相似文献   

5.
The catalytic performances of Co3O4/SiO2 catalysts prepared by incipient wetness impregnation for CO oxidation were investigated using three kinds of silica as carriers with different pore sizes of 7.7, 14.0 and 27.0 nm. The effects of calcination temperature on the catalyst surface and micro structure properties as well as catalytic performance for the oxidation of carbon monoxide were also studied. All catalysts were characterized by N2 adsorption-desorption, XRD, XPS, FTIR, H2-TPR and O2-TPD. It was found that the properties and crystal size of cobalt-containing species strongly depended on the pore size of silica carrier. While the silica pore size increased from 7.7 to 27.0 nm, the Co3O4 crystal size increased from 8.5 to 13.5 nm. Moreover, it was demonstrated that if the spinel crystal structure of Co3O4 was obtained at a calcination temperature as low as 150 ℃, the catalyst sample would have a high Co3O4 surface dispersion and a increase of surface active species, and thus exhibit a high activity for the oxidation of carbon monoxide.  相似文献   

6.
采用共沉淀法,在不同煅烧温度下制备一系列Mn改性γ-Fe2O3催化剂(Fe0.7Mn0.3Oz),研究了煅烧温度对Fe0.7Mn0.3Oz催化剂低温SCR脱硝活性的影响,并借助XRD、N2吸附-脱附、EDS及SEM等手段对催化剂进行表征。结果表明,350 ℃煅烧所得Fe0.7Mn0.3Oz催化剂的低温SCR活性最佳,在70 ℃时取得92%的NOx转化率,100~200 ℃可维持100%的NOx转化率,而450 ℃煅烧所得催化剂的低温SCR活性最低;煅烧温度为350 ℃时,催化剂具有最大的比表面积和比孔容、发达的孔隙结构及适当结晶度的γ-Fe2O3,而煅烧温度为400或450 ℃时,催化剂发生烧结且有α-Fe2O3生成,不利于低温SCR反应的进行,因此,Fe0.7Mn0.3Oz催化剂的最佳煅烧温度为350 ℃。  相似文献   

7.
Jinwei Li 《Acta Physico》2008,24(6):932-938
A series of Au/Fe2O3 catalysts for the water gas shift (WGS) reaction were prepared by modified deposition-precipitation method. The sample calcined at 300 °C showed higher catalytic activity and better stability than other samples. Using N2 physisorption, in situ XRD, H2-TPR, and XPS techniques, the influence of calcination temperature on properties of Au/Fe2O3 catalyst was explored, and the cause of deactivation was analyzed as well. The results showed that the catalytic behaviors were related to the interaction between Au and Fe2O3, and the reductive property of support, both of which were significantly affected by calcination temperature. Furthermore, according to the results of XPS, although stable carbonate and carbonyl surface species were found on the spent catalysts, the semiquantitative analysis of these species indicated that they were not the main cause of the deactivation. In fact, the deactivation of Au/Fe2O3 was sensitive to the structure change of support. During the water gas shift reaction, Fe3O4 particle would aggregate and crystallize leading to increase in the crystallinity of support and a significant reduction in the surface area of the catalysts, which resulted in the deactivation of Au/Fe2O3.  相似文献   

8.
The objective of this work was to study the kinetics of methane combustion for a series of Fe2O3/TiO2 catalysts. An increase in activity is observed as iron loading increases, and can be attributed to an increase of surface coverage by Fe2O3 species. Kinetic studies revealed that the reaction orders with respect to methane, oxygen, carbon dioxide and water are 1, 0, 0 and -1 respectively. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

9.
Various Au/Fe2O3 catalysts were prepared by the coprecipitation method, and CO oxidation was studied at ambient temperature and in the presence of water vapor in the feed. It was found that the precipitation method and the calcination temperatures have a significant effect on the catalytic performance of CO oxidation. The stability is related to the particle size of metallic gold and -Fe2O3 and the oxidation state of gold and the iron crystalline phase. The sintering of the gold particles, the reduction of oxide gold to metallic gold, the accumulation of carbonate, and a decrease in the specific surface area were observed during the reaction, which may contribute to the deactivation of Au/Fe2O3 catalysts.  相似文献   

10.
Pd/Al2O3 catalysts were prepared by the impregnation method and were used for the direct formation of hydrogen peroxide from H2 and O2. The H2O2 concentration and selectivity were strongly dependent on the solubility of hydrogen in the reaction medium. The modification of the support by halogenate has a beneficial effect on the selectivity. The state of the active Pd on Pd/Al2O3 catalysts was studied using X-ray photoelectron spectroscopy, and Pd(0) was found to be active.  相似文献   

11.
Summary Copper oxide catalysts supported on Ce0.8Zr0.2O2 were prepared via an impregnation method and characterized by XRD and H2-TPR techniques. The catalytic activity of the samples for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The influence of calcination temperature, calcination time and different CuO content on the catalytic activity was studied. TPR analysis indicated that well-dispersed CuO was responsible for the low-temperature CO oxidation. The results of the investigation showed that the calcination temperature and CuO loadings had larger influence than the calcination time.  相似文献   

12.
In order to elucidate the influence of preparative history of α-Fe2O3 on its reactivity, the catalytic thermal decomposition of KClO4 by α-Fe2O3 was studied by means of DTA and X-ray techniques. The catalysts were prepared by the calcination of three iron salts, Fe(OH)(CH3COO)2, FeSO4 ? 7H2O and Fe2(SO4)3 ? αH2O, at temperatures of 500–1200°C in air. The lower the preparation temperature of αFe2O3, the larger the specific surface area and reversely the smaller the crystalline size. KClO4 without α-Fe2O3 was found to begin fusion and decomposition simultaneously at about 530°C. The addition of αFe2O3 resulted in promotion of the decomposition reaction of KClO4; a lowering of 30–110°C in the initial decomposition temperature and a solid-phase decomposition before fusion of KClO4. The influence of preparative history of α-Fe2O3 on the decomposition mainly depended on the preparation temperature rather than the starting material. The initial decomposition temperature of KClO4 increased with an increase of the preparation temperature of α-Fe2O3. The effect of α-Fe2O3 was discussed on the basis of the charge transfer and the oxygen abstraction models.  相似文献   

13.
采用冷冻干燥法制备了经Cu修饰(10%)的Fe2O3/Al2O3氧载体。利用热重分析仪分别在850、900和950 ℃等温环境下,使氧载体交替接触还原气体和氧化气体,来模拟氧载体在化学链燃烧中的循环过程。结果表明,经Cu修饰的Fe2O3/Al2O3氧载体在850和900 ℃下的等温循环过程中反应性能都很稳定,在950 ℃时的循环反应前期有微量烧结,但在循环后期反应性能也很稳定。随着反应温度的升高,氧载体氧化速率增大,还原速率和载氧率先减小后增大。与未经修饰的Fe2O3/Al2O3氧载体相比较,在900 ℃下作等温循环实验,经Cu修饰的Fe2O3/Al2O3氧载体具有较高的载氧能力和还原速率,但氧化速率较低;两者都具有较好的循环稳定性。  相似文献   

14.
Co3O4/SiO2 catalysts for CO oxidation were prepared by conventional incipient wetness impregnation followed by calcination at various temperatures. Their structures were char-acterized with X-ray diffraction (XRD), laser Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and X-ray absorption fine structure (XAFS) spectroscopy. Both XRD and Raman spectroscopy only detect the ex-istence of Co3O4 crystallites in all catalysts. However, XPS results indicate that excess Co2+ ions are present on the surface of Co3O4 in Co3O4(200)/SiO2 as compared with bulk Co3O4. Meanwhile, TPR results suggest the presence of surface oxygen vacancies on Co3O4 in Co3O4(200)/SiO2, and XAFS results demonstrate that Co3O4 in Co3O4(200)/SiO2 con-tains excess Co2+. Increasing calcination temperature results in oxidation of excess Co2+ and the decrease of the concentration of surface oxygen vacancies, consequently the for-mation of stoichiometric Co3O4 on supported catalysts. Among all Co3O4/SiO2 catalysts,Co3O4(200)/SiO2 exhibits the best catalytic performance towards CO oxidation, demon-strating that excess Co2+ and surface oxygen vacancies can enhance the catalytic activity of Co3O4 towards CO oxidation. These results nicely demonstrate the effect of calcination temperature on the structure and catalytic performance towards CO oxidation of silica-supported Co3O4 catalysts and highlight the important role of surface oxygen vacancies on Co3O4.  相似文献   

15.
The structural changes of iron—molybdenum mixed oxide systems during calcination and reduction were studied. The oven-dried precipitated mass contains excess molybdenum as polymolybdic ions, which is transformed into Fe2(MoO4)3 and MoO3 on heat-treatment of the sample above 400°C. The reduction of Fe2(MoO4)3 proceeds through the formation of FeMoO4 and FeMoO3. On complete reduction, it gives a mixed crystal of iron and molybdenum. MoO3 is also simultaneously reduced to elemental molybdenum through the formation of MoO2 as an intermediate oxide.The interaction of the reduced mass with synthesis gas indicates that the iron—molybdenum mixed crystal is active for the hydrogenation of CO molecules. This mixed lattice is also stable towards the carburization process under synthesis gas.  相似文献   

16.
Summary Carbon deposits on the surface ofRu/Fe2O3 catalysts used in the water-gas shift reaction have been investigated by Auger Electron Spectrometry. A correlation has been found between the thickness of the carbon deposit and the catalytic activity in WGSR. The carbon deposit covers the metallic active centers and blocks their contact with reagents. The dotting of the iron oxide support with sodium has been found to reduce the amount of carbon deposit. .   相似文献   

17.
Fe2O3/SiO2 nanocomposites based on fumed silica A-300 (SBET = 337 m2/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)3) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)3 then oxidized in air at 400–900 °C. Samples with Fe(acac)3 adsorbed onto nanosilica and samples with Fe2O3/SiO2 including 6–17 wt% of Fe2O3 were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe2O3 deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)3 solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)3 solution in carbon tetrachloride only α-Fe2O3 phase is formed in addition to amorphous Fe2O3. The Fe2O3/SiO2 materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm3 and SBET = 265–310 m2/g.  相似文献   

18.
利用沉积沉淀法制备了Pt/TiO2催化剂, 将其在不同温度下焙烧, 以得到不同颗粒尺寸的Pt. 并将这些样品用于CO催化氧化反应以及反应动力学研究. 结果表明: 焙烧温度对催化剂有明显影响, Pt 颗粒尺寸随着焙烧温度的升高而增加; 与此同时, CO催化活性随焙烧温度的升高呈先增加后降低的趋势, 其中, 400℃焙烧的样品表现出最高的催化活性. 反应动力学结果表明, 催化剂上CO氧化反应表观速率方程为r=5.4×10-7pCO0.17pO20.36,说明在该催化剂上CO氧化遵循Langmuir-Hinshelwood机理. 同时, 对催化剂进行了CO化学吸附红外光谱和O2化学吸附表征. 结果表明, 随着焙烧温度的升高, 催化剂上CO和O2吸附量均呈现先升高后降低的趋势, 这与反应结果和反应动力学方程一致, 说明反应受到催化剂表面上CO和O2吸附浓度的影响. 而在400℃焙烧的催化剂上, CO和O2吸附量均最高, 因此其反应活性也最好. 这可能是焙烧过程影响了Pt 和TiO2之间的相互作用引起的.  相似文献   

19.
利用具有高比表面积和介孔结构的改性铝土矿为载体,采用并流共沉淀法制备不同Fe2O3含量的Cu-Fe/铝土矿催化剂。以水煤气变换反应为探针反应,考察了催化剂性能。利用X射线荧光元素分析(XRF)、X射线粉末衍射(XRD)、H2程序升温还原(H2-TPR)、CO程序升温脱附(CO-TPD)和X射线光电子能谱(XPS)等对催化剂进行了表征。结果表明:负载的Fe2O3能显著提高CuO/改性铝土矿催化剂的水煤气变换活性特别是热稳定性能,且随负载的Fe2O3含量增加而提高,当负载量为20%时达到最佳。其原因是负载的Fe2O3和CuO之间发生了相互作用,形成了类似于CuFe2O4复合氧化物,且随负载的Fe2O3含量的增加而增强,这种相互作用同时促进了CuO和Fe2O3的还原,抑制了CuO的烧结,进而提高了催化剂的性能。  相似文献   

20.
利用具有高比表面积和介孔结构的改性铝土矿为载体,采用并流共沉淀法制备不同Fe2O3含量的Cu-Fe/铝土矿催化剂。以水煤气变换反应为探针反应,考察了催化剂性能。利用X射线荧光元素分析(XRF)、X射线粉末衍射(XRD)、H2程序升温还原(H2-TPR)、CO程序升温脱附(CO-TPD)和X射线光电子能谱(XPS)等对催化剂进行了表征。结果表明:负载的Fe2O3能显著提高CuO/改性铝土矿催化剂的水煤气变换活性特别是热稳定性能,且随负载的Fe2O3含量增加而提高,当负载量为20%时达到最佳。其原因是负载的Fe2O3和CuO之间发生了相互作用,形成了类似于CuFe2O4复合氧化物,且随负载的Fe2O3含量的增加而增强,这种相互作用同时促进了CuO和Fe2O3的还原,抑制了CuO的烧结,进而提高了催化剂的性能。  相似文献   

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