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1.
Mesostructured MnO x–Cs 2O–Al 2O 3 nanocomposites have been synthesized by reverse microemulsion method combined with hydrothermal treatment and then applied to the catalytic combustion of methane. Compared to impregnation-derived conventional MnO x/Cs 2O/Com-Al 2O 3 catalyst, the microemulsion-derived catalyst showed higher activity and stability for methane combustion. The T10% of the fresh and of the 72 h aged Mn xO–Cs 2O–Al 2O 3 were 475 and 490 °C, respectively, recommending it as a potential candidate catalyst for application in hybrid gas turbines. The homogeneous composition of the microemulsion-derived nanocomposite catalyst can hinder the loss of Cs + and accelerate the formation of Cs–β-alumina phase, ensuring thus higher activity and stability for methane combustion. 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.
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
4.
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
5.
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
6.
Crystallization of diamond was studied in the CO 2–C, CO 2–H 2O–C, H 2O–C, and CH 4–H 2–C systems at 5.7 GPa and 1200–1420°C. Thermodynamic calculations show generation of CO 2, CO 2–H 2O, H 2O and CH 4–H 2 fluids in experiments with graphite and silver oxalate (Ag 2C 2O 4), oxalic acid dihydrate (H 2C 2O 4·2H 2O), water (H 2O), and anthracene (C 14H 10), respectively. Diamond nucleation and growth has been found in the CO 2–C, CO 2–H 2O–C, and H 2O–C systems at 1300–1420°C. At a temperature as low as 1200°C for 136 h there was spontaneous crystallization of diamond in the CO 2–H 2O–C system. For the CH 4–H 2–C system, at 1300–1420°C no diamond synthesis has been established, only insignificant growth on seeds was observed. Diamond octahedra form from the C–O–H fluids at all temperature ranges under investigation. Diamond formation from the fluids at 5.7 GPa and 1200–1420°C was accompanied with the active recrystallization of metastable graphite. 相似文献
7.
Fe/ZSM-5 catalysts with high Fe loading (Fe/Al1) have been prepared by sublimation of FeCl 3 onto H-ZSM-5 samples of different Si/Al ratios. They catalyze NO x reduction with hydrocarbons in an excess of O 2 and H 2O. TPR shows that the Fe in the zeolite cavities is different from Fe 2O 3 particles. Naked Fe 3+ ions are absent; oxo-ions, which are equally well reducible by CO and H 2, prevail. A minority of the Fe complexes lose oxygen upon mere heating to 500°C; some of the reduced sites are reoxidized only by N 2O. The population of oxo-complexes that lose oxygen by heating depends on the Si/Al ratio, this dependence is in qualitative agreement with the model of (2+) charged binuclear ions [HO–Fe–O–Fe–OH] 2+. Upon reacting with NO, the bridging O atom is transferred and NO 2 is formed. This step is not rate limiting for active catalysts with high Al/Si ratio and high Fe loading, but it becomes critical with zeolites of low Al/Si ratio. 相似文献
8.
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
9.
采用等温溶解平衡法研究了298.2 K下四元体系Rb +, Cs +, Mg 2+ // SO 42- - H 2O的相平衡关系,测定了该体系的溶解度、密度以及折射率,并绘制了相应的稳定相图、水图、密度-组成图和折射率-组成图。研究表明:298.2 K下,该四元体系为复杂四元体系,有复盐Cs 2SO 4·MgSO 4·6H 2O和Rb 2SO 4·MgSO 4·6H 2O以及固溶体[(Rb, Cs) 2SO 4]生成。其稳定相图由4个四元共饱点、9条单变量曲线以及6个结晶区组成。四元共饱点中 E1、 E2、 E3为相称共饱点, E4为不相称共饱点。6个结晶相区分别对应3种单盐Rb 2SO 4、MgSO 4·7H 2O、Cs 2SO 4,2种复盐Cs 2SO 4·MgSO 4·6H 2O、Rb 2SO 4·MgSO 4·6H 2O和1种固溶体[(Rb,Cs) 2SO 4]。其中,复盐Rb 2SO 4·MgSO 4·6H 2O结晶区最大,表明其在该体系中最易结晶析出;Cs 2SO 4结晶区最小。平衡液相的密度和折射率随着溶液中Cs 2SO 4含量变化呈规律性变化。该体系稳定相图将为硫酸镁亚型盐湖卤水中的铷、铯等资源开发利用提供理论依据。 相似文献
10.
The role of La 2O 3 loading in Pd/Al 2O 3-La 2O 3 prepared by sol–gel on the catalytic properties in the NO reduction with H 2 was studied. The catalysts were characterized by N 2 physisorption, temperature-programmed reduction, differential thermal analysis, temperature-programmed oxidation and temperature-programmed desorption of NO. The physicochemical properties of Pd catalysts as well as the catalytic activity and selectivity are modified by La2O3 inclusion. The selectivity depends on the NO/H2 molar ratio (GHSV = 72,000 h−1) and the extent of interaction between Pd and La2O3. At NO/H2 = 0.5, the catalysts show high N2 selectivity (60–75%) at temperatures lower than 250 °C. For NO/H2 = 1, the N2 selectivity is almost 100% mainly for high temperatures, and even in the presence of 10% H2O vapor. The high N2 selectivity indicates a high capability of the catalysts to dissociate NO upon adsorption. This property is attributed to the creation of new adsorption sites through the formation of a surface PdOx phase interacting with La2O3. The formation of this phase is favored by the spreading of PdO promoted by La2O3. DTA shows that the phase transformation takes place at temperatures of 280–350 °C, while TPO indicates that this phase transformation is related to the oxidation process of PdO: in the case of Pd/Al2O3 the O2 uptake is consistent with the oxidation of PdO to PdO2, and when La2O3 is present the O2 uptake exceeds that amount (1.5 times). La2O3 in Pd catalysts promotes also the oxidation of Pd and dissociative adsorption of NO mainly at low temperatures (<250 °C) favoring the formation of N2. 相似文献
11.
Complete Ni 2+ exchange of a single crystal of zeolite X of composition Na 92Si 100Al 92O 384 per unit cell was attempted at 73°C with flowing aqueous 0.05 M NiCl 2 (pH=4.3 at 23°C). After partial dehydration at 23°C and ≈10 −3 Torr for two days, its structure, now of composition Ni 2(NiOH) 35(Ni 4AlO 4) 2(H 3O) 46Si 101Al 91O 384 per unit cell, was determined by X-ray diffraction techniques at 23°C (space group Fd
, a0=24.788(5) Å). It was refined using all intensities; R1=0.080 for the 236 reflections for which Fo>4σ( Fo), and wR2=0.187 using all 1138 unique reflections measured. At four crystallographic sites, 45 Ni 2+ ions were found per unit cell. Thirty of these are at two different site III′ positions. Twenty of those are close to the sides of 12-rings near O–Si–O sequences, where each coordinates octahedrally to two framework oxygens, to three water molecules which hydrogen bond to the zeolite framework, and to an OH − ion. The remaining 10 are near O–Al–O sequences; only three members of a likely octahedral coordination sphere could be found. In addition, two Ni 2+ ions are at site I, eight are at site I′, and five are at site II. Forty six H 3O + ions per unit cell, 24 at site II′ and 22 at site II, each hydrogen bond triply to six rings of the zeolite framework. Each of the 22 H 3O + ions also hydrogen bonds to a H 2O molecule that coordinates to a site III′ Ni 2+ ion. Six of the eight sodalite cages each contain four H 3O + ions at site II′; the remaining two each contains a tetrahedral orthoaluminate anion at its center. Each tetrahedral face of each orthoaluminate ion is centered by a site I′ Ni 2+ ion to give two Ni 4AlO 4 clusters. The five site II Ni 2+ ions each coordinate to a OH − ion. With 46 H 3O + ions per unit cell, the great tendency of hydrated Ni 2+ to hydrolyze within zeolite X is demonstrated. With a relatively weak single-crystal diffraction pattern, with dealumination of the zeolite framework, and with an apparent decrease in long-range Si/Al ordering likely due to the formation of antidomains, this crystal like others treated with hydrolyzing cations appears to have been damaged by Ni 2+ exchange and partial dehydration. 相似文献
12.
考察了SiO2-Al2O3-TPABr-NH3·H20—H2O体系晶化时间、晶化温度和原料用量等对合成HZSM-5性能的影响。当n(SiO2):n(Al2O3)=100、n(TPABr):n(SiO2)=0.1、n(NH3):n(SiO2)=1.5、n(H2O):n(SiO2)=22和晶种添加质量分数为4%时,180℃静态晶化72h,合成收率与相对结晶度分别为10.1%和99.8%,对应理论收率为11.4%,合成收率与理论收率比为0.89。当投料n(SiO2):n(A1203)从50增加到400,合成收率与结晶度分别超过8.9%和82.8%,合成收率与理论收率比为0.76—0.89;样品酸量随着n(SiO:):n(Al2O3)的增加逐渐减小,比表面积为405m2·g-1,合成样品HZSM-5对甲醇制烯烃反应具有良好的酸催化活性。设定反应条件,采用投料n(SiO2):n(AlO3)=250的样品,甲醇转化率、丙烯选择性和C=2~C=4选择性分别为100%、39.27%和62.01%。 相似文献
13.
The inhibition effect of H 2O on V 2O 5/AC catalyst for NO reduction with NH 3 is studied at temperatures up to 250 °C through TPD, elemental analyses, temperature-programmed surface reaction (TPSR) and FT-IR analyses. The results show that H 2O does not reduce NO and NH 3 adsorption on V 2O 5/AC catalyst surface, but promotes NH 3 adsorption due to increases in Brønsted acid sites. Many kinds of NH 3 forms present on the catalyst surface, but only NH 4+ on Brønsted acid sites and a small portion of NH 3 on Lewis acid sites are reactive with NO at 250 °C or below, and most of the NH 3 on Lewis acid sites does not react with NO, regardless the presence of H 2O in the feed gas. H 2O inhibits the SCR reaction between the NH 3 on the Lewis acid sites and NO, and the inhibition effect increases with increasing H 2O content. The inhibition effect is reversible and H 2O does not poison the V 2O 5/AC catalyst. 相似文献
14.
采用水热合成法,选择合理的原料和配料比合成ZSM-5分子筛,对影响分子筛合成的主要因素如n(SiO_2)∶n(Al_2O_3)、n(H_2O)∶n(SiO_2)、晶化时间和晶化温度进行考察优化。XRD和SEM表征结果表明,合成的分子筛为典型的ZSM-5结构分子筛,晶粒均匀且呈单分散。通过不同因素的调控,可以合成一系列粒度(350~650)nm的ZSM-5分子筛。 相似文献
15.
以硝酸铁和十二烷基三甲基溴化铵为原料,采用固相法制备了 γ-氧化铁纳米粒子。通过X射线衍射、氮气吸附-脱附、磁性测试等手段对 γ-氧化铁样品进行了表征。研究了 γ-氧化铁对有机染料直接耐酸大红4BS的吸附性能。结果表明,制备的 γ-氧化铁样品为 γ-氧化铁纳米粒子,平均晶粒尺寸为18.5 nm; γ-氧化铁的比表面积为83.2 m 2/g,孔容为0.25 cm 3/g,最可几孔径为3.8 nm,属于介孔范围; γ-氧化铁的最大饱和磁化强度为63.7 A·m 2/kg;介孔 γ-氧化铁对直接耐酸大红4BS的吸附过程符合准二级吸附动力学模型; γ-氧化铁对直接耐酸大红4BS的吸附符合Langmuir吸附等温式,极限吸附量为113.3 mg/g;将 γ-氧化铁脱附处理后可重复使用。 相似文献
16.
Esterification of acrylic acid with 1-butanol has been studied in a heterogeneous solid–liquid reaction system using a variety of solid acids including an acidic salt of H 3PW 12O 40, Cs 2.5H 0.5PW 12O 40. The catalytic activity (per proton) of liquid acids such as heteropolyacids, H 2SO 4, and para-toluenesulfonic acid increased as the acid strength of the solution increased, but the difference in the activity among them was not significant. In the solid–liquid reaction system, Cs 2.5H 0.5PW 12O 40 exhibited the highest catalytic activity in the unit of catalyst weight among the solid oxide catalysts, while the activity of Cs 2.5H 0.5PW 12O 40 was less than those of organic resins such as Nafion and Amberlyst 15. Contrary to the liquid acids, the specific activity values (per proton) of solid acids were significantly different. It was demonstrated that the activity of Cs 2.5H 0.5PW 12O 40 was almost retained after the addition of water, while the activities of the organic resins greatly decreased. The water-tolerant property of Cs 2.5H 0.5PW 12O 40 is presumed to be due to the hydrophobic nature of the surface. 相似文献
17.
本文利用溶液法制备了K 2Ba[B 4O 5(OH) 4] 2·8H 2O,并将其进行热处理制备得到了KBaB 5O 9,利用XRD、FT-IR、TG-DTA-DTG对样品进行了表征。分析研究了由K 2Ba[B 4O 5(OH) 4] 2·8H 2O热处理制备KBaB 5O 9过程中的物相变化过程,其物相变化经历脱结晶水、脱羟基、重结晶、再分解、熔融再结晶5个阶段,其中结晶水的脱失分两步进行。运用Kissinger法、Flynn-Wall-Ozawa法、atava-esták法对K 2Ba[B 4O 5(OH) 4] 2·8H 2O结晶水第二步脱失过程的动力学参数进行了计算,可知K 2Ba[B 4O 5(OH) 4] 2·8H 2O结晶水第二步脱失过程的活化能 Es为151.94 kJ/mol,指前因子的对数值lg As为21.25 min -1,机理函数 G(α)=(1-2 α/3)-(1- α) 2/3(其中 α为转化率)。 相似文献
18.
以餐厨垃圾为原料运用溶剂热法制备了负载铁的球状生物质炭,系统研究了pH、醋酸锌(C 4H 6O 4Zn·2H 2O)与六水合三氯化铁(FeCl 3·6H 2O)投料质量比、碳化温度、碳化时间等条件对生物质炭制备的影响。在此基础上利用响应曲面法对生物质炭的制备条件进行了优化,分析了不同因素之间的交互作用。结果表明,在pH为2.26、C 4H 6O 4Zn·2H 2O与FeCl 3·6H 2O的质量比为0.51、碳化温度为203.96 ℃、碳化时间为2.92 h时,生物质炭的实际得炭率达到最大为56.82%,回归模型在研究区域内的水平显著,且预测的准确性较高。生物质炭的物相和形貌表征证明了四氧化三铁(Fe 3O 4)负载在球状生物质炭的表面,生物质炭的比表面积可以达到52 m 2/g,负载Fe 3O 4相较于未负载Fe 3O 4的生物质炭对铜离子具有更好的吸附性,且吸附过程可以使用准二级动力学方程进行描述。 相似文献
19.
采用等温溶解平衡法研究四元体系硼酸锂-硼酸钾-硼酸镁-水在308.15 K时固液相平衡,测定了体系溶解度和平衡液相的密度、折光率和pH。研究发现:该体系308.15 K时的稳定相图中包含一个共饱点(L+Li 2B 4O 7·3H 2O+K 2B 4O 7·4H 2O+Mg 2B 6O 11·15H 2O),其液相组成: w(Li 2B 4O 7)=3.112%、 w(K 2B 4O 7)=16.64%、 w(Mg 2B 6O 11)=0.101 8%;3个固相结晶区:Li 2B 4O 7·3H 2O、K 2B 4O 7·4H 2O、Mg 2B 6O 11·15H 2O,体系无复盐或固溶体生成。溶液中硼酸锂、硼酸钾对多水硼镁石有很强的盐析效应,液相的密度、折光率和pH随溶液中硼酸盐浓度的增加呈规律性变化。 相似文献
20.
New and ordered 2D-hexagonal ( p6 mm) mesoporous aluminosilicates (CMI-11) have been synthesized in strongly alkaline media using aluminosilicate ester ((Bu sO) 2-Al-O-Si-(OEt) 3) as single-source molecular precursor and CTMABr as surfactant and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 adsorption–desorption and 27Al and 29Si MAS NMR spectroscopy. These mesoproous aluminosilicates exhibit a very low Si/Al ratio of 1.9 and highly thermal stable tetrahedral aluminum sites in the mesoporous walls. 27Al and 29Si MAS NMR spectroscopy indicates that the pore walls of CMI-11 are fully condensed with molecular homogeneity of Si–O–Al linkage. These materials are highly important in catalysis, in particular for the petroleum processing and the bulky molecules treatment. 相似文献
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