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1.
The solvothermal reaction of mixtures of aluminum isopropoxide (AIP) and gallium acetylacetonate (Ga(acac) 3) directly yielded the mixed oxides of γ-Ga 2O 3-Al 2O 3. In the solvothermal synthesis, the crystal structure of mixed oxides was controlled by the initial formation of γ-Ga 2O 3 nuclei. The mixed oxides prepared in diethylenetriamine have extremely high activities for selective catalytic reduction (SCR) of NO with methane as a reducing agent. With increasing crystallite size of the spinel structure, the catalytic activity increased. The ratio of the amount of methane consumed by combustion to total methane conversion was proportional to the density of acid sites on the surface of the mixed oxides. The mixed oxide catalysts prepared in diethylenetriamine had lower densities of acid sites and showed a higher methane-efficiency for CH 4-SCR than those prepared in other solvents. These catalysts maintained their high activity even when the reaction was carried out under the severe conditions (i.e., high space velocity and low NO concentration). 相似文献
2.
Catalytic activity of ZrO 2 supported PdO catalysts for methane combustion has been investigated in comparison with Al 2O 3 supported PdO catalysts. It was found that the drop of catalytic activity owing to decomposition of PdO at a high temperature region (600–900°C) was suppressed by using ZrO 2 support. Temperature-programmed reduction (TPR) measurements of the catalyst with hydrogen revealed that the PdO of PdO/Al 2O 3 catalyst was reduced at the temperature less than 100°C, whereas in PdO/ZrO 2 catalyst the consumption of hydrogen was also observed at 200–300°C. This result indicates that the stable PdO species were present in the PdO/ZrO 2 catalyst. In order to confirm the formation of the solid solution of PdO and ZrO 2, X-ray diffraction (XRD) analyses of the mixtures of ZrO 2 and PdO calcined at 700–900°C in air were carried out. The lattice volume of ZrO 2 in the mixture was larger than that of ZrO 2. Furthermore, the Pd thin film on ZrO 2 substrate was prepared as a model catalyst and the depth profile of the elements in the Pd thin film was measured by Auger electron spectroscopy (AES). It was confirmed that Zr and O as well as Pd were present in the Pd thin film heated at 900°C in air. It was considered that the PdO on ZrO 2 support might be stabilized by the formation of the solid solution of PdO and ZrO 2. 相似文献
3.
Effect of additives, In 2O 3, SnO 2, CoO, CuO and Ag, on the catalytic performance of Ga 2O 3–Al 2O 3 prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H 2O, CoO, CuO and Ag showed good additive effect. When H 2O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga 2O 3–Al 2O 3 was depressed considerably, while an intensifying effect of H 2O was observed for In 2O 3- and SnO 2-doped Ga 2O 3–Al 2O 3. Of several metal oxide additives, In 2O 3-doped Ga 2O 3–Al 2O 3 showed the highest activity for NO reduction by propene in the presence of H 2O. Kinetic studies on NO reduction over In 2O 3–Ga 2O 3–Al 2O 3 revealed that the rate-determining step in the absence of H 2O is the reaction of NO 2 formed on Ga 2O 3–Al 2O 3 with C 3H 6-derived species, whereas that in the presence of H 2O is the formation of C 3H 6-derived species. We presumed the reason for the promotional effect of H 2O as follows: the rate for the formation of C 3H 6-derived species in the presence of H 2O is sufficiently fast compared with that for the reaction of NO 2 with C 3H 6-derived species in the absence of H 2O. Although the retarding effect of SO 2 on the activity was observed for all of the catalysts, SnO 2–Ga 2O 3–Al 2O 3 showed still relatively high activity in the lower temperature region. 相似文献
4.
Polycylic aromatic hydrocarbons (PAHs) are listed as carcinogenic and mutagenic priority pollutants, belonging to the environmental endocrine disrupters. Most PAHs in the environment stem from the atmospheric deposition and diesel emission. Consequently, the elimination of PAHs in the off-gases is one of the priority and emerging challenges. Catalytic oxidation has been widely used in the destruction of organic compounds due to its high efficiency (or conversion of reactants), its economic benefits and good applicability. This study investigates the application of the catalytic oxidation using Pt/γ-Al2O3 catalysts to decompose PAHs and taking naphthalene (the simplest and least toxic PAH) as a target compound. It studies the relationships between conversion, operating parameters and relevant factors such as treatment temperatures, catalyst sizes and space velocities. Also, a related reaction kinetic expression is proposed to provide a simplified expression of the relevant kinetic parameters. The results indicate that the Pt/γ-Al2O3 catalyst used accelerates the reaction rate of the decomposition of naphthalene and decreases the reaction temperature. A high conversion (over 95%) can be achieved at a moderate reaction temperature of 480 K and space velocity below 35,000 h−1. Non-catalytic (thermal) oxidation achieves the same conversion at a temperature beyond 1000 K. The results also indicate that Rideal–Eley mechanism and Arrhenius equation can be reasonably applied to describe the data by using the pseudo-first-order reaction kinetic equation with activation energy of 149.97 kJ/mol and frequency factor equal to 3.26 × 1017 s−1. 相似文献
5.
A kinetic study on CH 4 combustion over a very active PdO/ZrO 2 catalyst with high Pd loading (10% w/w of Pd) is presented as an example of a demanding problem which requires both the development of appropriate experimental tools and a theoretical insight on surface chemistry. The use of an annular catalytic reactor as a tool to collect kinetic data under unusually severe conditions (high temperature and CH4 concentration) is described in comparison with the use of a conventional packed bed reactor. In particular, problems related to the biasing effects of mass, heat and momentum transfer are addressed. Kinetic data addressing the effects of CH4, O2, H2O and CO2 concentration in a temperature range from 400 to 550 °C are analysed by means of a purely empirical power law model and of a formal kinetic model based on literature indication assuming methane dissociative adsorption as the rate controlling step. 相似文献
6.
采用浸渍法制备Fe/Al_2O_3催化剂,采用BET、XRD和穆斯堡尔谱等进行结构和性能表征。以自制Fe/Al_2O_3为催化剂,应用催化湿式过氧化氢氧化技术处理COD为6 742 mg·L-1的兰炭废水,通过建立正交实验确定最佳实验条件,结果表明,在p H=4、过氧化氢添加量9.6 m L、反应时间150 min和反应温度80℃条件下,兰炭废水COD去除率达66.30%。对催化氧化后的废水进行GC-MS分析,确定最终氧化产物主要为乙酸。表明自制Fe/Al_2O_3催化剂具有优良的催化效果,并使大分子难降解有机污染物分解为易生化的小分子污染物,甚至被完全分解矿化。 相似文献
7.
In this contribution, a commercial spherical SiO 2 was modified with different amounts of La 2O 3, and used as the support of Ni catalysts for autothermal reforming of methane in a fluidized-bed reactor. Nitrogen adsorption, XRD and H 2-TPR analysis indicated that La 2O 3-modified SiO 2 had higher surface area, strengthened interaction between Ni and support, and improved dispersion of Ni. CO 2-TPD found that La 2O 3 increased the alkalescence of SiO 2 and improved the activation of CO 2. Coking reaction (via both temperature-programmed surface reaction of CH 4 (CH 4-TPSR) and pulse decomposition of CH 4) disclosed that La 2O 3 reduced the dehydrogenation ability of Ni. CO 2-TPO, O 2-TPO (followed after CH 4-TPSR) confirmed that only part amount of carbon species derived from methane decomposition could be removed by CO 2, and O 2 in feed played a crucial role for the gasification of the inactive surface carbons. Ni/ xLa 2O 3-SiO 2 ( x = 10, 15, 30) possessed high activity and excellent stability for autothermal reforming of methane in a fluidized-bed reactor. 相似文献
8.
In the last decades, many reports dealing with technology for the catalytic combustion of methane (CH 4) have been published. Recently, attention has increasingly focused on the synthesis and catalytic activity of nickel oxides. In this paper, a NiO/CeO 2 catalyst with high catalytic performance in methane combustion was synthesized via a facile impregnation method, and its catalytic activity, stability, and water-resistance during CH 4 combustion were investigated. X-ray diffraction, low-temperature N 2 adsorption, thermogravimetric analysis, Fourier transform infrared spectroscopy, hydrogen temperature programmed reduction, methane temperature programmed surface reaction, Raman spectroscopy, electron paramagnetic resonance, and transmission electron microscope characterization of the catalyst were conducted to determine the origin of its high catalytic activity and stability in detail. The incorporation of NiO was found to enhance the concentration of oxygen vacancies, as well as the activity and amount of surface oxygen. As a result, the mobility of bulk oxygen in CeO 2 was increased. The presence of CeO 2 prevented the aggregation of NiO, enhanced reduction by NiO, and provided more oxygen species for the combustion of CH 4. The results of a kinetics study indicated that the reaction order was about 1.07 for CH 4 and about 0.10 for O 2 over the NiO/CeO 2 catalyst. 相似文献
9.
A new catalyst composed of nickel oxide and cerium oxide was studied with respect to its activity for NO reduction by CO under stoichiometric conditions in the absence as well as the presence of oxygen. Activity measurements of the NO/CO reaction were also conducted over NiO/γ-Al 2O 3, NiO/TiO 2, and NiO/CeO 2 catalysts for comparison purposes. The results showed that the conversion of NO and CO are dependent on the nature of supports, and the catalysts decreased in activity in the order of NiO/CeO 2 > NiO/γ-Al 2O 3 > NiO/TiO 2. Three kinds of CeO 2 were prepared and used as support for NiO. They are the CeO 2 prepared by (i) homogeneous precipitation (HP), (ii) precipitation (PC), and (iii) direct decomposition (DP) method. We found that the NiO/CeO 2(HP) catalyst was the most active, and complete conversion of NO and CO occurred at 210 °C at a space velocity of 120,000 h −1. Based on the results of surface analysis, a reaction model for NO/CO interaction over NiO/CeO 2 has been proposed: (i) CO reduces surface oxygen to create vacant sites; (ii) on the vacant sites, NO dissociates to produce N 2; and (iii) the oxygen originated from NO dissociation is removed by CO. 相似文献
10.
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
11.
The adsorption of HCN on, its catalytic oxidation with 6% O 2 over 0.5% Pt/Al 2O 3, and the subsequent oxidation of strongly bound chemisorbed species upon heating were investigated. The observed N-containing products were N 2O, NO and NO 2, and some residual adsorbed N-containing species were oxidized to NO and NO 2 during subsequent temperature programmed oxidation. Because N-atom balance could not be obtained after accounting for the quantities of each of these product species, we propose that N 2 and was formed. Both the HCN conversion and the selectivity towards different N-containing products depend strongly on the reaction temperature and the composition of the reactant gas mixture. In particular, total HCN conversion reaches 95% above 250 °C. Furthermore, the temperature of maximum HCN conversion to N 2O is located between 200 and 250 °C, while raising the reaction temperature increases the proportion of NO x in the products. The co-feeding of H 2O and C 3H 6 had little, if any effect on the total HCN conversion, but C 3H 6 addition did increase the conversion to NO and decrease the conversion to NO 2, perhaps due to the competing presence of adsorbed fragments of reductive C 3H 6. Evidence is also presented that introduction of NO and NO 2 into the reactant gas mixture resulted in additional reaction pathways between these NO x species and HCN that provide for lean-NO x reduction coincident with HCN oxidation. 相似文献
12.
TiO 2-SiO 2 with various compositions prepared by the coprecipitation method and vanadia loaded on TiO 2-SiO 2 were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH 3 and in the undesired oxidation of SO 2 to SO 3, using BET, XRD, XPS, NH 3-TPD, acidity measurement by the titration method and activity test. TiO 2-SiO 2, compared with pure TiO 2, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V 2O 5. The SCR activity and N 2 selectivity are found to be more excellent over vanadia loaded on TiO 2-SiO 2 with 10–20 mol% of SiO 2 than over that on pure TiO 2, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH 3 adsorbed on the catalysts. With increasing SiO 2 content, the remarkable activity decrease in the oxidation of SO 2 to SO 3, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V 4+ on TiO 2-SiO 2, while V 5+ exists on TiO 2, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO 2-SiO 2 with low SiO 2 content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NO x activity but also the low SO 2 oxidation performance. 相似文献
13.
Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。 相似文献
14.
The operation conditions for preparing a Cu/ZnO-based multicomponent catalyst by a coprecipitation method were optimized. The temperature during coprecipitation should be less than 313 K, and the removal of Na from the catalyst by washing the precipitates is most important. Furthermore, a small amount of silica added to the catalyst greatly improved its long-term stability in methanol synthesis from CO 2 and H 2. 相似文献
15.
To get the low temperature sulfur resistant V 2O 5/TiO 2 catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V 2O 5/TiO 2 catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V 2O 5/TiO 2 catalysts showed high catalytic activity for NH 3 selective catalytic reduction (NH 3-SCR) of NO x carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V 2O 5/TiO 2 > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V 2O 5/TiO 2 for maximum NO x conversion, which also showed high resistance to SO 2 in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V 2O 5/TiO 2 and compared with commercial W(10%)V 2O 5/TiO 2 catalyst. High electrical conductivity difference (Δ G) for Sb(2%)/V 2O 5/TiO 2 catalyst with temperature was observed. SO 2 deactivation experiments were carried out for Sb(2%)/V 2O 5/TiO 2 and W(10%)/V 2O 5/TiO 2 at a temperature of 230 °C for 90 h, resulted Sb(2%)/V 2O 5/TiO 2 was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V 2O 5/TiO 2 than Sb(2%)/V 2O 5/TiO 2 catalyst. 相似文献
16.
This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO 2 with C 2H 4 as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C 2H 4/SO 2, and pretreatment are all important factors affecting catalyst activity. Fe 2O 3/γ-Al 2O 3 was found to be the most active catalyst among six γ-Al 2O 3-supported metal oxide catalysts tested. With Fe 2O 3 as the active species, of the supports tested, CeO 2 is the most suitable one. Using this Fe 2O 3/CeO 2 catalyst, we found that the optimal Fe content is 10 wt.%, the optimal feed ratio of C 2H 4/SO 2 is 1:1, and the catalyst presulfidized by H 2+H 2S exhibits a higher performance than those pretreated with H 2 or He. Although the feed concentrations of C 2H 4:SO 2 being 3000:3000 ppm provide a higher conversion of SO 2, the sulfur yield decreases drastically at temperatures above 300 °C. With higher feed concentrations, maximum yield appears at higher temperatures. The C 2H 4 temperature-programmed desorption (C 2H 4-TPD) and SO 2-TPD desorption patterns illustrate that Fe 2O 3/CeO 2 can adsorb and desorb C 2H 4 and SO 2 more easily than can Fe 2O 3/γ-Al 2O 3. Moreover, the SO 2-TPD patterns further show that Fe 2O 3/γ-Al 2O 3 is more seriously inhibited by SO 2. These findings may properly explain why Fe 2O 3/CeO 2 has a higher activity for the reduction of SO 2. 相似文献
17.
ZrO 2-doped CuZnO catalyst prepared by successive-precipitation method was investigated by ICP-AES, BET, TEM, XRD, EXAFS, H 2-TPR and CO/CO 2 hydrogenation. The active phase of copper in CuZnO catalyst prepared by co-precipitation method was well-crystallized. The presence of ZrO 2 led to a high copper dispersion, which was distinctive from CuZnO. Though the activity for carbon monoxide hydrogenation was little lower than that of CuZnO catalyst, ZrO 2-doped CuZnO catalyst showed much higher activity and selectivity towards methanol synthesis from carbon dioxide hydrogenation. Moreover, ZrO 2-doped CuZnO catalyst showed high performance for methanol synthesis from CO 2-rich syngas. 相似文献
19.
An In 2O 3/Al 2O 3 catalyst shows high activity for the selective catalytic reduction of NO with propene in the presence of oxygen. The presence of SO 2 in feed gas suppressed the catalytic activity dramatically at high temperatures; however it was enhanced in the low temperature range of 473–573 K. In TPD and FT-IR studies, the formation of sulfate species on the surface of the catalyst caused an inhibition of NO X adsorption sites, and the absorbance ability of NO was suppressed by the presence of SO 2, and the amount of ad-NO 3− species decreased obviously. This leads to a decrease of catalytic activity at higher temperatures. However, addition of SO 2 enhanced the formation of carboxylate and formate species, which can explain the promotional effect of SO 2 at low temperature, because active C 3H 6 (partially oxidized C 3H 6) is crucial at low temperature. 相似文献
20.
Catalytic wall (structured) reactors and structured supports are suitable to study the catalytic properties of nanosized materials. The coating of metallic (aluminum and stainless steel) plates by thin layers of active phase is presented in two cases, VO x/TiO 2 and Co/SiO 2, catalysts used in the oxidative dehydrogenation (ODH) of propane and in Fischer–Tropsch synthesis (FTS) of clean fuels, respectively. The preparation of coated plates and their characterisation by various methods of physicochemical analysis are described. Both chemical and physical methods were used for coating. VO x/TiO 2 layers were obtained by grafting of Ti (on Al or stainless-steel plates) and V (on TiO 2) alkoxides and use of sol–gel media or suspension. A silica primer was deposited (on stainless-steel plate) by plasma-assisted chemical vapour deposition (PACVD) onto which Co oxide and silica were coprecipitated from sol–gel. The catalytic experiments in the respective reactions were carried out in special plate reactors and compared with those of catalytic powders. The study shows that the coating of a metallic substrate by a catalyst is not straightforward and requires specific studies dealing with both chemistry (chemical affinity between substrate and catalytic layers) and catalytic engineering (catalytic performance in taylor-made reactors). 相似文献
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