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1.
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
2.
Catalytic reduction of NO by propene in the presence of oxygen was studied over SnO 2-doped Ga 2O 3–Al 2O 3 prepared by sol–gel method. Although SnO 2-doped Ga 2O 3–Al 2O 3 gave lower NO conversion than Ga 2O 3–Al 2O 3 in the absence of H 2O, the activity was enhanced considerably by the presence of H 2O and much higher than that of Ga 2O 3–Al 2O 3. The presence of SnO 2 and Ga 2O 3–Al 2O 3 species having intimate Ga–O–Al bondings was found to be essential for the promotional effect of H 2O. The promotional effect of H 2O was interpreted by the following two reasons. The first one is the removal of carbonaceous materials deposited on the catalyst surface by H 2O. The other is the selective inhibition by H 2O of the reaction steps resulting in propene oxidation to CO x without reducing NO. 相似文献
3.
Well crystallised aluminium borate Al 18B 4O 33 has been synthesised from alumina and boric acid with a BET area of 18 m 2/g after calcination at 1100 °C. Afterwards, 2 wt.% Pd/Al 18B 4O 33 was prepared by conventional impregnation of Pd(NO 3) 2 aqueous solution and calcination in air at 500 °C. The catalytic activity of Pd/Al 18B 4O 33 in the complete oxidation of methane was measured between 300 and 900 °C and compared with that of Pd/Al 2O 3. Pd/Al 18B 4O 33 exhibited a much lower activity than Pd/Al 2O 3 when treated in hydrogen at 500 °C or aged in O 2/H 2O (90:10) at 800 °C prior to catalytic testing. Surprisingly, a catalytic reaction run up to 900 °C in the reaction mixture induced a steep increase of the catalytic activity of Pd/Al 18B 4O 33 which became as active as Pd/Al 2O 3. Moreover, the decrease of the catalytic activity observed around 750 °C for Pd/Al 2O 3 and attributed to PdO decomposition into metallic Pd was significantly shifted to higher temperatures (820 °C) in the case of Pd/Al 18B 4O 33. The existence of two distinct types of PdO species formed on Al 18B 4O 33 and being, respectively, responsible for the improvement of the activity at low and high temperature was proposed on the basis of diffuse reflectance spectroscopy and temperature-programmed desorption of O 2. 相似文献
4.
A series of LaAl 11O 18- and Al 2O 3-supported LaCrO 3 and Cr 2O 3 combustion catalysts was prepared. Different active phase–support combinations were prepared and applied to cordierite monoliths. The washcoat materials were aged in flowing humid air at temperatures between 1100°C and 1400°C, after which they were characterized by BET, XRD, TPR, and EDS. The monolith catalysts were evaluated in methane combustion. The presence of an active phase retarded sintering of the Al 2O 3 support, whereas the active phase slightly decreased the thermal stability of LaAl 11O 18. X-ray measurements revealed extensive interaction between support and active phase in the washcoat materials. A substituted perovskite, LaCr 1−xAl xO 3, is proposed to be formed in nearly all samples containing both lanthanum and chromium. The accessibility of chromium decreased rapidly after aging. The activities of the Al 2O 3-supported catalysts were higher than of those supported on LaAl 11O 18, which was related to the higher surface area of the former. 相似文献
5.
以Al_2O_3为载体,RuCl_3·xH_2O和FeCl_3·6H_2O为活性组分前驱体,采用吸附-沉淀法制备了Ru-Fe/Al_2O_3和Ru/Al_2O_3催化剂,以马来酸二甲酯加氢合成丁二酸二甲酯为探针反应,结合H_2-TPR和XRD表征技术,考察Fe改性Ru基催化剂的氧化-还原性能及催化活性。经氧化-还原循环处理后,催化剂Ru-Fe/Al_2O_3上马来酸二甲酯加氢活性高于Ru/Al_2O_3。XRD结果显示,经处理的Ru-Fe/Al_2O_3上未见金属Ru的特征衍射峰,而Ru/Al_2O_3上出现了金属Ru的特征衍射峰。结合H_2-TPR结果推断,Ru与Fe之间发生了相互作用,这种协同作用可以改善Ru/Al_2O_3催化剂的热稳定性。 相似文献
6.
Three compounds, K 2(H 2O) 4H 2SiMo 12O 40 · 7H 2O (1), K 2Na 2(H 2O) 4SiW 12O 40 · 4H 2O (2), and Na 4(H 2O) 8SiMo 12O 40 · 6H 2O (3) have been synthesized and structurally characterized by single-crystal X-ray analysis, IR, and thermogravimetry. Compounds 1 and 2 both show the high symmetry trigonal space group P3 221 and a novel 3D network structure. The Keggin anions [SiM 12O 40] 4−(M = Mo, W) are linked by potassium or sodium cations to generate hexagon-shaped channels along the c-axis, in which water molecules are accommodated. Compound 3 is tetragonal, space group P4/mnc constructed from [SiMo 12O 40] 4− anions and Na ions. 相似文献
7.
Nanosized particles dispersed uniformly on Al 2O 3 particles were prepared from the decomposition of precursor Cr(CO) 6 by metal organic chemical vapor deposition (MOCVD) in a fluidized chamber. These nanosized particles consisted of Cr 2O 3, CrC 1−x, and C. A solid solution of Al 2O 3–Cr 2O 3 and an Al 2O 3–Cr 2O 3/Cr 3C 2 nanocomposite were formed when these fluidized powders were pre-sintered at 1000 and 1150 °C before hot-pressing at 1400 °C, respectively. In addition, an Al 2O 3–Cr 2O 3/Cr-carbide (Cr 3C 2 and Cr 7C 3) nanocomposite was formed when the particles were directly hot pressed at 1400 °C. The interface between Cr 3C 2 and Al 2O 3 is non-coherent, while the interface between Cr 7C 3 and Al 2O 3 is semi-coherent. 相似文献
8.
Phase changes in high temperature treated (>900 °C) 8 or 20 wt% BaO supported on γ-Al 2O 3 model lean NO x trap (LNT) catalysts, induced by NO 2 and/or H 2O adsorption, were investigated with powder X-ray diffraction (XRD), solid state 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and NO 2 temperature programmed desorption (TPD) experiments. After calcination in dry air at 1000 °C, the XRD and solid state 27Al MAS NMR results confirm that stable surface BaO and bulk BaAl 2O 4 phases are formed for 8 and 20 wt% BaO/Al 2O 3, respectively. Following NO 2 adsorption over these thermally treated samples, some evidence for nanosized Ba(NO 3) 2 particles are observed in the XRD results, although this may represent a minority phase. However, when water was added to the thermally aged samples after NO 2 exposure, the formation of bulk crystalline Ba(NO 3) 2 particles was observed in both samples. Solid state 27Al MAS NMR is shown to be a good technique for identifying the various Al species present in the materials during the processes studied here. NO 2 TPD results demonstrate a significant loss of uptake for the 20 wt% model catalysts upon thermal treatment. However, the described phase transformations upon subsequent water treatment gave rise to the partial recovery of NO x uptake, demonstrating that such a water treatment of thermally aged catalysts can provide a potential method to regenerate LNT materials. 相似文献
9.
水合硝酸镁是红土镍矿硝酸湿法冶金工艺中产生的副产品,其资源化利用是决定湿法冶金工艺绿色化工艺链条贯通的关键环节之一。水合硝酸镁热解生产氧化镁是其资源化利用最具潜力的发展方向。为此,以稳定的硝酸镁水合物——六水硝酸镁为实验物料,采用热重分析(TG-DTG)、红外光谱(FT-IR)、X射线衍射(XRD)和差示扫描量热分析(DSC)等技术手段研究了其热解基本过程,旨在为水合硝酸镁资源化工艺参数的确定提供理论支撑。研究结果表明,水合硝酸镁热解过程可以分为脱水和分解两个阶段:脱水阶段,六水硝酸镁在68~170 ℃失去4个结晶水生成二水硝酸镁,二水硝酸镁在170~389 ℃失去2个结晶水生成无水硝酸镁;分解阶段,无水硝酸镁在389~510 ℃分解生成氧化镁、二氧化氮和氧气。六水硝酸镁热解过程是一个吸热反应,其反应热约为940.50 J/g。 相似文献
10.
A systematic reactivity study of N 2O, NO, and NO 2 on highly dispersed CuO phases over modified silica supports (SiO 2–Al 2O 3, SiO 2–TiO 2, and SiO 2–ZrO 2) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N 2O) to selective reductions by hydrocarbons (N 2O, NO, and NO 2) and oxidation (NO to NO 2). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO 2–Al 2O 3 and SiO 2–ZrO 2, led to a better activity and selectivity of CuO for the reactions of N 2O, NO, and NO 2 reductions and N 2O decomposition than SiO 2–TiO 2. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values. 相似文献
11.
以Zr(NO 3) 4·5H 2O和Na 2SiO 3·9H 2O为原料,利用共沉淀法制备前驱体,浸渍添加稀土Ce和La,一定温度焙烧后制得掺杂稀土S 2O 82-/ZrO 2-SiO 2固体超强酸。通过XRD、FT-IR和SEM对催化剂进行表征,以硬脂酸的酯化合成反应为探针,考察制备条件对催化剂性能的影响以及催化剂的重复使用率。结果表明,相对于未改性的S 2O 82-/ZrO 2-SiO 2催化剂,添加了Ce或La的固体超强酸酯化催化活性及重复使用性能均有提高。 相似文献
12.
Layered double hydroxide pillared by Paratungstate A ion, Mg 12Al 6(OH) 36(W 7O 24)·4H 2O, was prepared via anion exchange reaction of the synthetic precursor, Mg 4Al 2(OH) 12TA· xH 2O (TA 2−=terephthalate), and [W 7O 24] 6− ion. Some physico-chemical properties were measured and the preparation conditions were studied. Trace aqueous organocholorine pesticide, hexachlorocyclohexane (HCH), was totally degraded and mineralized into CO 2 and HCl by irradiating a Mg 12Al 6(OH) 36(W 7O 24)·4H 2O suspension in the near UV area. Disappearance of trace HCH follows Langmuir–Hinshelwood first-order kinetics. The model and mechanism for the photocatalytic degradation of HCH on the Mg 12Al 6(OH) 36(W 7O 24)·4H 2O were proposed, indicating that the interlayer space is the reaction field, and that photogeneration of OH√ radicals are responsible for the degradation pathway. 相似文献
13.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
14.
Al 2O 3–30 wt.%TiCN composites have been fabricated successfully by a two-stage gas pressure sintering schedule. The gas pressure sintered Al 2O 3–30 wt.%TiCN composite achieved a relative density of 99.5%, a bending strength of 772 MPa, a hardness of 19.6 GPa, and a fracture toughness of 5.82 MPa m 1/2. The fabrication procedure involves solid state sintering of two phases without solubility to prepare Al 2O 3–TiCN composite. Little grain growth occurred for TiCN during sintering while Al 2O 3 grains grew about three times to an average size of 3–5 μm. The interface microstress arising during cooling from the processing temperature because of the thermal and/or mechanical properties mismatch between the Al 2O 3 and TiCN phase is about 50 MPa. Such a compressive microstress is not high enough to cause grain boundary cracking that may weaken the composite but it can introduce dislocations within grains, which is very good to enhance the composite properties. 相似文献
15.
Mixed oxides of alumina and zirconia having a relative composition of 50, 80 and 100% Zr 2O were synthesized by means of sol–gel methods. The catalysts were sulfated with H 2SO 4 1N, and were loaded with 0.3% Pt metal using the incipient wetness technique. The characterization of the physicochemical properties was carried out using XRD, N 2-adsorption at 78 K, and SEM. The catalytic properties of the Al 2O 3–ZrO 2 series were studied by means of dehydration of 2-propanol at 180°C and isomerization of n-hexane at 250°C, 1 atm. The sulfated solids presented a high surface acidity and a limited crystallinity, together with high activity for alcohol dehydration (i.e. 2-propanol). On the other hand, the Al 2O 3–ZrO 2 solid solutions (i.e. those having a 20–80% composition) turned out to be the most active ones for the isomerization of n-hexane. 相似文献
16.
The synthesis of cancrinite in the system Na 2O–SiO 2–Al 2O 3–Na 2CO 3–H 2O was studied under low-temperature hydrothermal conditions in the 353 K< T<473 K interval. The aim was to reveal the suitable range for the crystallization of pure-phase carbonate cancrinite with the ideal composition Na 8[AlSiO 4] 6CO 3(H 2O) 2 without cocrystallization of sodalite or intermediate disordered phases between cancrinite and sodalite. It was found that cancrinite formation reacts very sensitive on the temperature within the autoclaves whereas the concentration of reactants and the alkalinity of the hydrothermal solution have a much lower influence on the phase formation. Thus the temperature of crystallization of carbonate cancrinite without any by-products should not remain below 473 K. At the lower reaction temperature of 353 K the formation of a disordered intermediate phase between the cancrinite and the sodalite structure has been obtained in every case, independent of the template concentrations and the base. Some problems to detect this in a typical powder product mixture are discussed. Besides the 29Si and 27Al MAS NMR characterization of the products, the crystal structure refinement of pure carbonate cancrinite of ideal composition Na 8[AlSiO 4] 6CO 3(H 2O) 3.4, has been carried out from X-ray powder data using the Rietveld method: P6 3, a=1271.3(1) pm, c=518.6(1) pm, RWP=0.073, RF=0.016 for 347 structure factors and 45 variable positional parameters. 相似文献
17.
The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl 2O 4·10H 2O converted to Ca 3Al 2(OH) 12 and amorphous aluminum hydroxide. Ca 2Al 2O 5·8H 2O transformed via the intermediate phase Ca 4Al 2O 7·13H 2O to Ca 3Al 2(OH) 12 and gibbsite, Al(OH) 3. The phase Ca 4Al 2O 7·19H 2O reacted via the same intermediate phase to Ca 3Al 2(OH) 12 and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported. 相似文献
18.
In an attempt to better understand interactions occuring at hydrated cement/organic polymer interfaces, the reaction mechanism and products formed at the interfaces between poly(acrylic acid), p(AA) or poly(acrylamide), p(AM), and Ca(OH) 2 or gibbsite, Al 2O 3·3H 2O, were explored using x-ray photoelectron spectroscopy (XPS). It was estimated that at p(AA)/Ca(OH) 2 interfaces, a Ca-complexed carboxylate interfacial reaction product was formed by an ionic reaction between the COOH in p(AA) and Ca 2+ ions from Ca(OH) 2. A similar reaction product was formed at p(AM)/Ca(OH) 2 interfaces as a result of an inter-facial transformation of amide in p(AM) into carboxylic acid, caused by the alkali-catalyzed hydrolysis of the amide. The proton-accepting hydroxyl groups existing at the outermost surface sites of Al 2O 2·3H 2O react favorably with proton-donating COOH groups in p(AA). This acidbase interaction at the p(AA)/Al 2O 3·3H 2O joint formed hydrogen bonds. Whereas, when the p(AM) was applied on Al 2O 3·3H 2O surfaces, interfacial electrostatic bonds were formed through charge-transferring reaction mechanisms in which the charge density was transferred from the Al in Al 2O 3·3H 2O to the C=0 oxygen in p(AM). 相似文献
19.
Catalytic performance of Sn/Al 2O 3 catalysts prepared by impregnation (IM) and sol–gel (SG) method for selective catalytic reduction of NO x by propene under lean burn condition were investigated. The physical properties of catalyst were characterized by BET, XRD, XPS and TPD. The results showed that NO 2 had higher reactivity than NO to nitrogen, the maximum NO conversion was 82% on the 5% Sn/Al 2O 3 (SG) catalyst, and the maximum NO 2 conversion reached nearly 100% around 425 °C. Such a temperature of maximum NO conversion was in accordance with those of NO x desorption accompanied with O 2 around 450 °C. The activity of NO reduction was enhanced remarkably by the presence of H 2O and SO 2 at low temperature, and the temperature window was also broadened in the presence of H 2O and SO 2, however the NO x desorption and NO conversion decreased sharply on the 300 ppm SO 2 treated catalyst, the catalytic activity was inhibited by the presence of SO 2 due to formation of sulfate species (SO 42−) on the catalysts. The presence of oxygen played an essential role in NO reduction, and the activity of the 5% Sn/Al 2O 3 (SG) was not decreased in the presence of large oxygen. 相似文献
20.
In this work, we explored the potential of mesoporous zeolite-supported Co–Mo catalyst for hydrodesulfurization of petroleum resids, atmospheric and vacuum resids at 350–450°C under 6.9 MPa of H 2 pressure. A mesoporous molecular sieve of MCM-41 type was synthesized; which has SiO 2/Al 2O 3 ratio of about 41. MCM-41 supported Co–Mo catalyst was prepared by co-impregnation of Co(NO 3) 2·6H 2O and (NH 4) 6Mo 7O 24 followed by calcination and sulfidation. Commercial Al 2O 3 supported Co–Mo (criterion 344TL) and dispersed ammonium tetrathiomolybdate (ATTM) were also tested for comparison purposes. The results indicated that Co–Mo/MCM-41(H) is active for HDS, but is not as good as commercial Co–Mo/Al 2O 3 for desulfurization of petroleum resids. It appears that the pore size of the synthesized MCM-41 (28 Å) is not large enough to convert large-sized molecules such as asphaltene present in the petroleum resids. Removing asphaltene from the resid prior to HDS has been found to improve the catalytic activity of Co–Mo/MCM-41(H). The use of ATTM is not as effective as that of Co–Mo catalysts, but is better for conversions of >540°C fraction as compared to noncatalytic runs at 400–450°C. 相似文献
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