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1.
采用等体积浸渍的方法制备V 2O 5-CeO 2/TiO 2催化剂,考查了V 2O 5/CeO 2比、负载顺序、焙烧温度、反应空速对催化剂协同脱硝脱二噁英性能的影响。结果表明,所制备的催化剂活性组分在载体表面分散均匀。采用共同浸渍法制备,V 2O 5/CeO 2质量比为1∶3,焙烧温度为550℃的催化剂协同脱硝脱二氯苯性能最佳,在200℃反应温度下脱硝率为93%,二氯苯的脱除率达到90%。 相似文献
2.
通过浸渍沉淀法分别制备Ni/Al 2O 3、Ni/CeO 2和Ni/CeO 2-Al 2O 3催化剂,并对其分别进行不同CO/CO 2比例下COx共甲烷化性能评价。发现Ni/Al 2O 3催化剂催化CO转化为CH4的能力明显高于Ni/CeO 2,而催化CO 2甲烷化的性能则相反。采用Ni/CeO 2-Al 2O 3催化剂,可以在提高CO转化率的同时而不降低CO 2转化率。结合BET、XRD、TPR、TPD和原位红外等各种表征手段,发现CeO 2掺杂虽然降低了催化剂的比表面积和金属Ni的分散度,但却可明显提高其吸附活化CO 2的能力,这主要是由于具有较高含量氧空位的CeO 2的掺杂可以提高载体表面碱性位,促使共甲烷过程中CO ... 相似文献
3.
以MMT为载体,采用原位聚合-配位沉积法制备3种不同Co负载量的Co 3O 4-MMT催化剂。采用N 2物理吸附、XRD和TEM对载体和催化剂进行表征,并在连续流动微反装置上考察其N 2O催化分解性能。结果表明,与Co 3O 4催化剂相比,Co 3O 4-MMT催化剂的比表面积显著增大,且活性组分Co 3O 4具有较高的分散状态。Co 3O 4-MMT催化剂的催化活性随着Co含量的增加先升后降,其中0.015Co-MMT表现出最佳的催化活性,其活性远高于Co 3O 4催化剂,同时,该催化剂还表现出良好的催化稳定性和较好的杂质气体耐受性。 相似文献
4.
以碱法水热合成径向尺寸6~10nm的CeO_2纳米棒,采用湿法浸渍在纳米棒上负载不同含量的Co氧化物。通过实验探究Co含量改变对脱硝性能的影响原理,实验结果显示浸渍方案为3g CeO_2∶30ml 10%(质量分数)硝酸钴溶液时,脱硝效率最高,在NO与CO摩尔比为1∶5,体积空速为30000h~(-1),无氧状态下,250℃即能达到70%以上的效率。采用氮气吸附、XPS、TEM以及XRD测试不同钴含量催化剂的物化性质,与催化性能结果比对分析后得出Co的添加是通过改变催化剂表面的活性官能团来提高效率,其中Co_2O_3对于催化CO与NO_x进行反应具有较高的效率,提高催化剂中Co_2O_3的比重可以将高效率温度段降低,CoO在一定程度上对CO与NO_x反应具有负面作用,而Co_3O_4对低温阶段N_2O选择性影响较大。 相似文献
5.
采用等体积浸渍法制备CeO 2改性Ni/γ-Al 2O 3催化剂,通过BET、XRD、H 2-TPR和SEM等对催化剂结构及物化性能进行表征,考察Ni-CeO 2/γ-Al 2O 3催化剂对顺酐催化加氢制备丁二酸酐催化性能的影响。结果表明,引入适量CeO 2可提高催化剂活性组分Ni的分散度,增加催化剂比表面积,提高催化剂热稳定性。采用负载CeO 2质量分数5%的Ni-CeO 2/γ-Al 2O 3催化剂,在反应温度120 ℃、反应压力2.0 MPa和空速0.6 h -1条件下,顺酐转化率为99.5%,丁二酸酐选择性为99.4%。 相似文献
6.
考察了不同CeO 2含量对柴油机商用稀土选择性催化还原(SCR)催化剂NH 3-SCR性能的影响。通过X射线衍射、N 2吸附-脱附、X射线光电子能谱、H 2-程序升温还原和NH 3-程序升温脱附等表征手段对催化剂的结构及性能进行了研究。研究发现,CeO 2含量对催化剂的晶体结构没有影响,添加后促进了稀土催化剂表面SiO 2的分散,从而对催化剂的脱硝性能及水热老化性能产生影响;CeO 2含量影响催化剂的织构性质,较大的孔体积和适当的比表面有利于催化剂水热老化后催化剂的脱硝性能的提高;随着CeO 2含量从14%增加到20%,其表面Ce含量呈先降低后升高的趋势,其中Ce 4+含量与催化剂的水热老化后催化剂的脱硝性能成正相关;CeO 2含量的增加会阻碍稀土催化剂中其他组分的还原或增加其热稳定性,从而影响催化剂的还原能力和酸性位数量;通过脱硝性能测试,稀土催化剂中CeO 2的最佳含量为16%。 相似文献
7.
利用静电自组装法制备了V 2O 5@CeO 2核壳微球结构,并负载在TiO 2上。考察了分散剂六偏磷酸钠(SHP(对表面zeta电位的影响,采用扫描电镜(SEM(、投射电镜(TEM(观察了核壳结构的形貌,并在固定床上进行了脱硝性能测试,并通过比表面积(BET(、氨气吸附漫反射(in situ DRIFTS(等进行表征。结果表明:SHP使纳米颗粒表面带负电,且一定范围内SHP浓度越高,zeta电位越大;含质量分数1%V 2O 5、5% CeO 2的催化剂,在260~400℃间具有80%以上的脱硝效率,对比了该核壳结构与传统浸渍法制备催化剂的抗硫抗水性,烟气中含15%(体积分数(H 2O,SO 2含量较低时,脱硝性能优于传统浸渍法制备的催化剂。 相似文献
8.
催化剂是选择性催化还原(SCR)脱硝技术的核心,研究Fe对钒钛系SCR催化剂脱硝活性及SO 2/SO 3转化率的影响具有重要意义。采用等体积浸渍法制备了不同Fe/V质量比的Fe 2O 3-V 2O 5-WO 3/TiO 2催化剂,并进行表征,研究Fe对钒钛系SCR催化剂脱硝活性及SO 2/SO 3转化率的影响,并讨论Fe对于钒钛系SCR催化剂表面性质的影响。结果表明,随着催化剂表面Fe 2O 3含量增加,催化剂的脱硝效率及二氧化硫氧化率均是先上升后下降,当Fe/V质量比为3.0时,催化剂的脱硝效率和二氧化硫氧化率均达到最大值91.78%、1.01%。XPS及H 2-TPR结果表明,随着Fe 2O 3含量增加,催化剂表面钒活性组分的相对含量及V 4+/V 5+比减小,催化剂表面吸附氧(O α)浓度增加,催化剂的氧化能力增强。NO-TPD结果表明,随着Fe 2O 3含量增加,催化剂表面吸附NO的能力增强。 相似文献
9.
以CeO 2为载体、Cu物种为主要活性位点,采用浸渍法制备了一系列WO 3改性Cu/CeO 2催化剂。研究了WO 3质量分数对乙二胺(EDA)选择性催化氧化(SCO)性能的影响,并通过XRD、XPS、H 2-TPR、NH 3-TPD等方法对催化剂的物理化学性质进行了分析表征。结果表明,WO 3改性的Cu/CeO 2催化剂的N 2选择性大幅提高,其中Cu/5W/CeO 2在337℃时对EDA实现了100%的转化率,该温度条件下NO x的浓度大幅降低,同时具有较好的活性和选择性。表征结果表明,WO 3的引入显著提高了催化剂的酸性位点数量,促进了对反应副产物NO x的催化还原,提高了反应的N 2选择性。 相似文献
10.
以Co(NO 3) 2·6H 2O和尿素为原料制备了9种Co 3O 4催化材料,考察了其对水中酮基布洛芬(KTP)的催化臭氧氧化降解效能。结果表明,与单独臭氧氧化相比,所制备的Co 3O 4对水中KTP的催化臭氧氧化降解率提高了12.0%~63.8%,且在n[Co(NO 3) 2·6H 2O]:n(尿素)=4:1、煅烧温度400℃下制备得到的Co 3O 4催化剂催化活性最高。SEM、XRD、FTIR、XPS、BET等表征分析显示,该Co 3O 4催化剂表面呈覆盖细小微粒的球状颗粒,晶相为立方相,且表面含有丰富的羟基,表面羟基密度为1.075×10 -5 mol/m 2。机理研究证实,Co 3O 4对水中KTP的非均相催化臭氧氧化降解... 相似文献
11.
The influence of catalyst pre-treatment temperature (650 and 750 °C) and oxygen concentration ( λ = 8 and 1) on the light-off temperature of methane combustion has been investigated over two composite oxides, Co 3O 4/CeO 2 and Co 3O 4/CeO 2–ZrO 2 containing 30 wt.% of Co 3O 4. The catalytic materials prepared by the co-precipitation method were calcined at 650 °C for 5 h (fresh samples); a portion of them was further treated at 750 °C for 7 h, in a furnace in static air (aged samples). Tests of methane combustion were carried out on fresh and aged catalysts at two different WHSV values (12 000 and 60 000 mL g−1 h−1). The catalytic performance of Co3O4/CeO2 and Co3O4/CeO2–ZrO2 were compared with those of two pure Co3O4 oxides, a sample obtained by the precipitation method and a commercial reference. Characterization studies by X-ray diffraction (XRD), BET and temperature-programmed reduction (TPR) show that the catalytic activity is related to the dispersion of crystalline phases, Co3O4/CeO2 and Co3O4/CeO2–ZrO2 as well as to their reducibility. Particular attention was paid to the thermal stability of the Co3O4 phase in the temperature range of 750–800 °C, in both static (in a furnace) and dynamic conditions (continuous flow). The results indicate that the thermal stability of the phase Co3O4 heated up to 800 °C depends on the size of the cobalt oxide crystallites (fresh or aged samples) and on the oxygen content (excess λ = 8, stoichiometric λ = 1) in the reaction mixture. A stabilizing effect due to the presence of ceria or ceria–zirconia against Co3O4 decomposition into CoO was observed. Moreover, the role of ceria and ceria–zirconia is to maintain a good combustion activity of the cobalt composite oxides by dispersing the active phase Co3O4 and by promoting the reduction at low temperature. 相似文献
12.
Co 3O 4/CeO 2 composite oxides with different cobalt loading (5, 15, 30, 50, 70 wt.% as Co 3O 4) were prepared by co-precipitation method and investigated for the oxidation of methane under stoichiometric conditions. Pure oxides, Co 3O 4 and CeO 2 were used as reference. Characterization studies by X-ray diffraction (XRD), BET, temperature programmed reduction/oxidation (TPR/TPO) and X-ray photoelectron spectroscopy (XPS) were carried out. An improvement of the catalytic activity and thermal stability of the composite oxides was observed with respect to pure Co3O4 in correspondence of Co3O4–CeO2 containing 30% by weight of Co3O4. The combined effect of cobalt oxide and ceria, at this composition, strongly influences the morphological and redox properties of the composite oxides, by dispersing the Co3O4 phase and promoting the efficiency of the Co3+–Co2+ redox couple. The presence in the sample Co3O4(30 wt.%)–CeO2 of a high relative amount of Ce3+/(Ce4+ + Ce3+) as detected by XPS confirms the enhanced oxygen mobility. The catalysts stability under reaction conditions was investigated by XRD and XPS analysis of the used samples, paying particular attention to the Co3O4 phase decomposition. Methane oxidation tests were performed over fresh (as prepared) and thermal aged samples (after ageing at 750 °C for 7 h, in furnace). The resistance to water vapour poisoning was evaluated for pure Co3O4 and Co3O4(30 wt.%)–CeO2, performing the tests in the presence of 5 vol.% H2O. A methane oxidation test upon hydrothermal ageing (flowing at 600 °C for 16 h a mixture 5 vol.% H2O + 5 vol.%O2 in He) of the Co3O4(30 wt.%)–CeO2 sample was also performed. All the results confirm the superiority of this composite oxide. 相似文献
13.
In this paper, Co 3O 4/CeO 2 catalysts for steam reforming of ethanol (SRE) were prepared by co-precipitation and impregnation methods. The catalysts prepared by co-precipitation were very active and selective for SRE. Over 10%Co 3O 4/CeO 2 catalyst, ethanol conversion was close to 100% and hydrogen selectivity was about 70% at 450 °C. The catalysts were characterized by X-ray diffraction, temperature-programmed reduction (TPR) and BET surface area measurements. The preparation method influenced the interaction between cobalt and CeO 2 evidently. The incorporation of Co ions into CeO 2 crystal lattice resulted in weaker interaction between cobalt and ceria on catalyst surface. In comparison with catalysts prepared by impregnation, more cobalt ions entered into CeO 2 lattice, and resulted in weaker interaction between active phase and ceria on surface of Co 3O 4/CeO 2 prepared by co-precipitation. Thus, cobalt oxides was easier to be reduced to metal cobalt which was the key active component for SRE. Meanwhile, the incorporation of Co ions into CeO 2 crystal lattice was beneficial for resistance to carbon deposition. 相似文献
14.
The direct decomposition of nitric oxide (NO) over barium catalysts supported on various metal oxides was examined in the absence and presence of O 2. Among the Ba catalysts supported on single-component metal oxides, Ba/Co 3O 4 and Ba/CeO 2 showed high NO decomposition activities, while Ba/Al 2O 3, Ba/SiO 2, and Ba/TiO 2 exhibited quite low activities. The effect of an addition of second components to Co and Ce oxides was further examined, and it was found that the activities were significantly enhanced using Ce–Mn mixed oxides as support materials. XRD results indicated the formation of CeO 2–MnO x solid solutions with the cubic fluorite structure. O 2-TPD of the CeO 2–MnO x solid solutions showed a large desorption peak in a range of relatively low temperature. The BET surface areas of the CeO 2–MnO x solid solutions were larger than those of pure CeO 2 and Mn 2O 3. These effects caused by the addition of Mn are responsible for the enhanced activities of the Ba catalysts supported on Ce–Mn mixed oxides. 相似文献
15.
The one-step highly selective oxidation of cyclohexane into cyclohexanone and cyclohexanol as the essential intermediates of nylon-6 and nylon-66 is considerably challenging. Therefore, an efficient and low-cost catalyst must be urgently developed to improve the efficiency of this process. In this study, a Co 3O 4–CeO 2 composite oxide catalyst was successfully prepared through ultrasound-assisted co-precipitation. This catalyst exhibited a higher selectivity to KA-oil, which was benefited from the synergistic effects between Co 3+/Co 2+ and Ce 4+/Ce 3+ redox pairs, than bulk CeO 2 and/or Co 3O 4. Under the optimum reaction conditions, 89.6% selectivity to KA-oil with a cyclohexane conversion of 5.8% was achieved over Co 3O 4–CeO 2. Its catalytic performance remained unchanged after five runs. Using the synergistic effects between the redox pairs of different transition metals, this study provides a feasible strategy to design high-performance catalysts for the selective oxidation of alkanes. 相似文献
16.
A series of cobalt–cerium mixed oxide catalysts (Co 3O 4–CeO 2) with a Ce/Co molar ratio of 0.05 were prepared by co-precipitation (with K 2CO 3 and KOH as the respective precipitant), impregnation, citrate, and direct evaporation methods and then tested for the catalytic decomposition of N 2O. XRD, BET, XPS, O 2-TPD and H 2-TPR methods were used to characterize the catalysts. Catalysts with a trace amount of residual K exhibited higher catalytic activities than those without. The presence of appropriate amount of K in Co 3O 4–CeO 2 may improve the redox property of Co 3O 4, which is important for the decomposition of N 2O. When the amount of K was constant, the surface area became the most important factor for the reaction. The co-precipitation-prepared catalyst with K 2CO 3 as precipitant exhibited the best catalytic performance because of the presence of ca. 2 mol% residual K and the high surface area. We also discussed the rate-determining step of the N 2O decomposition reaction over these Co 3O 4–CeO 2 catalysts. 相似文献
17.
A series of CeO 2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N 2O). Addition of CeO 2 to Co 3O 4 led to an improvement in the catalytic activity for N 2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N 2O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O 2, H 2O or NO. Methods of XRD, FE-SEM, BET, XPS, H 2-TPR and O 2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO 2 could increase the surface area of Co 3O 4, and then improve the reduction of Co 3+ to Co 2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N 2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO 2, are responsible for the enhancement of catalytic activity of Co 3O 4. 相似文献
18.
The reduction of NO by propene in the presence of excess oxygen over mechanical mixtures of Au/Al 2O 3 with a bulk oxide has been investigated. The oxides studied were: Co 3O 4, Mn 2O 3, Cr 2O 3, CuO, Fe 2O 3, NiO, CeO 2, SnO 2, ZnO and V 2O 5. Under lean C 3H 6-SCR conditions, these oxides (with the exception of SnO 2) convert selectively NO to NO 2. When mechanically mixed with Au/Al 2O 3, the Mn 2O 3 and Co 3O 4 oxides and, to a much greater extent, CeO 2 act synergistically with this catalyst greatly enhancing its SCR performance. It was found that their synergistic action is not straightforwardly related to their activity for NO oxidation to NO 2. The exhibited catalytic synergy may be due to the operation of either remote control or a bifunctional mechanism. In the later case, the key intermediate must be a short-lived compound and not the NO 2 molecule in gas-phase. 相似文献
19.
The effect of cobalt precursor, catalyst pretreatment and promotion with ruthenium and rhenium on the formation of cobalt metal nanoparticles and catalytic performance of supported Fischer–Tropsch (FT) catalysts was studied using a combination of techniques (DSC–TGA, UV–vis spectroscopy, XPS, XRD, EXAFS–XANES, in situ magnetization measurements, propene chemisorption and catalytic measurements). The cobalt promoted and unpromoted catalysts were prepared by aqueous co-impregnation using cobalt nitrate or acetate, ruthenium nitrosyl nitrate or perrhenic acid. In both unpromoted and Ru and Re-promoted cobalt catalysts after impregnation and drying, cobalt is present mainly in octahedrally coordinated complexes. The repartition of cobalt species between Co 3O 4 and cobalt silicate depends essentially on the exothermicity of precursor decomposition. Cobalt nitrate precursor, with an endothermic decomposition, favors Co 3O 4 crystallites. Lower temperature of cobalt nitrate decomposition and catalyst calcination generally leads to higher dispersion of supported cobalt oxide. Cobalt acetate precursor, with an exothermic decomposition, favors cobalt silicate. By optimizing the conditions of cobalt acetate decomposition, the fraction of cobalt silicate can be decreased favoring a more reducible Co 3O 4 phase. For the catalysts prepared from cobalt nitrate, promotion with ruthenium increases the cobalt dispersion, while maintaining high reducibility. For the catalyst prepared via low temperature decomposition of cobalt acetate, addition of ruthenium increases the fraction of Co 3O 4 crystalline phase and decreases the concentration of barely reducible cobalt silicate. The Fischer–Tropsch reaction rates over unpromoted and promoted cobalt catalysts were found to be primarily a function of the number of cobalt metal sites, which are generated by the reduction of Co 3O 4 crystallites. 相似文献
20.
Catalytic performance of Ni/CeO 2/Al 2O 3 catalysts prepared by a co-impregnation and a sequential impregnation method in steam gasification of real biomass (cedar wood) was investigated. Especially, Ni/CeO 2/Al 2O 3 catalysts prepared by the co-impregnation method exhibited higher performance than Ni/Al 2O 3 and Ni/CeO 2/Al 2O 3 prepared by the sequential impregnation method, and the catalysts gave lower yields of coke and tar, and higher yields of gaseous products. The Ni/CeO 2/Al 2O 3 catalysts were characterized by thermogravimetric analysis, temperature-programmed reduction with H 2, transmission electron microscopy and extended X-ray absorption fine structure, and the results suggested that the interaction between Ni and CeO 2 became stronger by the co-impregnation method than that by sequential method. Judging from both results of catalytic performance and catalyst characterization, it is found that the intimate interaction between Ni and CeO 2 can play very important role on the steam gasification of biomass. 相似文献
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