共查询到20条相似文献,搜索用时 640 毫秒
1.
Guoyi Bai Chenfang Zhang Yuecheng Zhang Haijun Yu Fei He Huisen Ning Ligong Chen 《Reaction Kinetics and Catalysis Letters》2007,90(2):373-380
The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al2O3 catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield
of over 83% at using the Mg modified Co/γ-Al2O3 catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H2. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous
for dispersing and stabilizing the active species of the Co/γ-Al2O3 catalyst, protecting from sintering, significantly improving its catalytic activity and stability. 相似文献
2.
Sataporn Komhom Piyasan Praserthdam Okorn Mekasuwandumrong Joongjai Panpranot 《Reaction Kinetics and Catalysis Letters》2008,94(2):233-241
Pd catalysts supported on the solvothermal-derived nanocrystalline α-Al2O3 (45 nm) exhibited superior performances in the selective acetylene hydrogenation than those supported on micron-sized ones
(44–149 μm). Reduction at 500°C led to an improvement of the ethylene yield for the Pd/nanocrystalline α-Al2O3, but not for the Pd/micron-sized α-Al2O3. 相似文献
3.
Junseo Choi Ji-Young Ban Suk-Jin Choung Jinsoo Kim Haznan Abimanyu Kye Sang Yoo 《Journal of Sol-Gel Science and Technology》2007,44(1):21-28
Mesoporous TiO2/γ-Al2O3 composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules
can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of
the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH3 decomposition, TiO2/γ-Al2O3 granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO2/γ-Al2O3 granules using titania made by hydrothermal method had comparable performance in NH3 decomposition. 相似文献
4.
Jifei Jia Liwu Lin Jianyi Shen Zhusheng Xu Tao Zhang Dongbai Liang Yi Chen 《中国科学B辑(英文版)》1998,41(6):606-615
CO adsorption microcalorimetry was employed in the study of γ-Al2O3-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the
Pt/γ-Al2O3 catalyst was 125 kJ/mol. As CO coverage increased, the differential heat of adsorption decreased. At higher coverages, the
differential heat of adsorption decreased significantly. 60% of the differential heat of CO adsorption on the Pt/γ-N2O3 catalyst was higher than 100 kJ/mol. No significant effect on the initial differential heat was found after adding Sn and
Fe to the Pt/γ-Al2O3 catalyst. The amount of strong CO adsorption sites decreased, while the portion of CO adsorption sites with differential
heat of 60–110 kJ/mol increased after increasing the Sn or Fe content. This indicates that the surface adsorption energy was
changed by adding Sn or Fe to Pt/γ-N2O3. The distribution of differential heat of CO adsorption on the Pt-Sn(C)/γ-Al2O3 catalyst was broad and homogeneous. Comparison of the dehydrogenation performance of C4 alkanes with the number of CO adsorption sites with differential heat of 60–110 kJ/mol showed a good correlation. These results
indicate that the surface Pt centers with differential heats of 60–110 kJ/mol for CO adsorption possess superior activity
for the dehydrogenation of alkanes.
Project supported by FORD and the National Natural Science Foundation of China (Grant No. 09412302) and the Transcentury Training
Program Foundation for the Talents by The State Education Commission of China. 相似文献
5.
Jifei Jia Yuan Kou Liwu Lin Zhusheng Xu Tao Zhang Jianzhong Niu Dongbai Liang 《Reaction Kinetics and Catalysis Letters》1998,63(2):391-396
Pt LIII-edge XANES and EXAFS were employed to investigate the nature of Pt/γ-Al2O3, Pt−Sn/γ-Al2O3 and Pt−Fe/γ-Al2O3 catalysts. The results indicated that Pt species on these catalysts were all in the oxidized states before reduction, and
in the metallic states after reduction. The dispersity of the Pt species on the catalysts was very high after reduction. The
electronic properties of the highly dispersed Pt species were different from that of the bulk Pt in large crystallites. An
interaction between Pt and the metal-oxide modified γ-Al2O3 support is proposed. The interaction improved the dispersity of the Pt species on the catalysts and is thought to be the
reason for the enhanced activity and selectivity for dehydrogenation reactions over these catalysts. 相似文献
6.
Ozao R. Ochiai M. Yoshida H. Ichimura Y. Inada T. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):923-932
Gamma-alumina membrane was prepared from anodic (amorphous) alumina (AA) obtained in a sulphuric acid electrolyte. The transformation
scheme, i.e., the crystallization to form metastable alumina polymorphs and the final transition to α-Al2O3 with heating was studied by TG-DTA and X-ray diffraction (XRD) using fixed time (FT) method. When heating at a constant rate,
the crystallization occurred at 900°C or higher and the final formation of α-Al2O3 occurred at 1250°C or higher, which temperatures were higher than the case of using anodic (amorphous) alumina prepared from
oxalic acid electrolyte. Relative content of S of the products was obtained by transmission electron microscope (TEM)-energy
dispersive spectroscopy (EDS). The proposed thermal change of anodic alumina membrane prepared from sulphuric acid is as follows:
1. At temperatures lower than ca 910°C: Formation of a quasi-crystalline phase or a polycrystalline phase (γ-, δ- and θ-Al2O3);
2. 910–960°C: Progressive crystallization by the migration of S toward the surface within the amorphous or the quasi-crystalline
phase, forming S-rich region near the surface;
3. 960°C: Change of membrane morphology and the quasi-crystalline phase due to the rapid discharge of gaseous SO2;
4. 960–1240°C: Crystallization of γ-Al2O3 accompanying δ-Al2O3; and
5. 1240°C: Transition from γ-Al2O3 (+tr. δ-Al2O3) into the stable α-Al2O3.
The amorphization which occurs by the exothermic and the subsequent endothermic reaction suggests the incorporation of SO3 groups in the quasi-crystalline structure.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Sergio Cava Renata Benincá Sergio M. Tebcherani Iedo A. Souza Carlos A. Paskocimas Elson Longo José A. Varela 《Journal of Sol-Gel Science and Technology》2007,43(1):131-136
Al2O3 and Al2−x
Cr
x
O3 (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution
of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy
(reflectance spectra and CIEL*a*b* color data). The obtained results allow to identify the γ-Al2O3 to α-Al2O3 phase transition. The single-phase α-Al2O3 powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and
ruby luminescence lines observed for the powders of Al2−x
Cr
x
O3 are related to the γ to α-Al2O3 phase transition and the temperature and time range for such transition depends on the chromium content. 相似文献
8.
The Er3+-doped Al2O3 nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC3H7)3]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO3)3·5H2O]. The five phases of γ-(Al,Er)2O3, θ-(Al,Er)2O3, α-(Al,Er)2O3, ErAlO3, and Al10Er6O24 were detected with the 0–20 mol% Er3+-doped Al2O3 nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm
for phase transformation of undoped γ-Al2O3→α-Al2O3 at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with
increase of the Er3+ doping concentration. Infrared absorption spectra of γ-Al2O3 and θ-Al2O3 nanopowders showed the two broad bands of 830–870 and 550–600 cm−1, the three broad bands of 830–870, 750–760, and 550–600 cm−1, respectively. The infrared absorption spectra for the α-Al2O3 nanopowder showed three characteristic bands, 640, 602, and 453 cm−1. The two characteristic bands of 669 and 418 cm−1 for Er2O3 clusters were observed for the Er3+-doped Al2O3 nanopowders when Er3+ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm−1 are the characteristic bands of Al10Er6O24 phase. 相似文献
9.
A. E. Goncharov A. A. Politov N. A. Pankrushina O. I. Lomovskii 《Chemistry of Natural Compounds》2006,42(3):336-339
Extracts of Aconitum septentrionale Koelle roots obtained using chloroform, isopropanol, and ethanol were purified using chloroform and basic γ-Al2O3. Ballast materials were selectively adsorbed by γ-Al2O3, increasing the mass fraction of lappaconitine in the extract. The ethanol extract was purified most. The degree of lappaconitine
extraction by chloroform was unaffected by the presence of γ-Al2O3. However, the mass fraction in the extract and lappaconitine extraction from Aconitum septentrionale were increased more than twice.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 274–276, May–June, 2006. 相似文献
10.
Lifeng Cao Lingxia Li Ping Zhang Haitao Wu 《Journal of Sol-Gel Science and Technology》2009,51(2):251-254
Perovskite-type Ag(Nb0.6Ta0.4)O3 nanopowder was prepared by the sol–gel process from the AgNO3, Ta2O5 and Nb2O5, with help of K2CO3, avoiding use of strong corrosive acid or expensive niobium ethoxide and tantalum ethoxide. The results suggested that thermal
decomposition of the xerogel took place when the xerogel was heated at 450 °C. Well-crystallized single-phased powder was
obtained at low temperature about 680 °C. With the heat-treatment temperature increasing (680–1,100 °C), the intensity of
the diffraction peaks increased. The crystallite size determined by Scherer formula and the result suggested that higher temperature
lead to larger crystallite size. Moreover, the average grain size 30–50 nm was estimated by a field emission scanning electron
microscope. The influence of holding time on microstructures indicated that the homogeneous and small grains were obtained
at 800 °C for 2–4 h while larger ones for 8–16 h. 相似文献
11.
Guo-Jia Wang Hong-chao Ma Ying Li Zi-Yu Liu 《Reaction Kinetics and Catalysis Letters》2001,74(1):103-110
The effect of the type of the support and the amount of V2O5 loading on the activity of V2O5/γ-Al2O3 catalyst for the dehydrogenation of isobutane have been investigated. Based on the experimental results of TPR, XRD and ESR
spectroscopy, it is suggested that there are strong interactions between vanadia and carrier and that the V4+ species on the surface is the active site of V2O5/γ-Al2O3 for this reaction.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
Fe-Mn, Co-Mn and Ni-Mn composite oxide catalysts based on high specific surface area MnO2 precursor were prepared and applied to catalytic combustion of CH4. Results were compared with that of unmodified MnOx and 1wt.% Pd/-Al2O3. Below 450°C, manganese oxide catalysts show higher activity than Pd/-Al2O3, while the modified manganese oxide catalysts exhibit higher activity than the unmodified one below 420°C. All catalysts were characterized by means of N2-BET, XRD, TG-DTA and H2-TPR. Due to the interaction between Fe, Co or Ni oxides and manganese oxide, the activity of the oxygen species of the modified catalysts is improved, which leads to the increase of their CH4 combustion activity. 相似文献
13.
Tatiya Sangkhum Okorn Mekasuwandumrong Piyasan Praserthdam Joongjai Panpranot 《Reaction Kinetics and Catalysis Letters》2009,97(1):115-123
The use of nanocrystalline Fe-modified α-Al2O3 prepared by sol–gel and solvothermal method as supports for Pd catalysts resulted in an improved catalyst performance in
selective acetylene hydrogenation. Moreover, the amount of coke deposits was reduced due to lower acidity of the Fe-modified
α-Al2O3 supports. 相似文献
14.
X. J. Zhang Q. Li S. Y. Zhao C. X. Gao Z. G. Zhang 《Journal of Sol-Gel Science and Technology》2008,47(1):107-114
Al2O3/ZrO2 duplex films were deposited on a γ-TiAl based alloy by sol–gel processing starting from aluminum isopropoxide (Al(OC3H7)3) and zirconium (IV) oxychloride octahydrate (ZrOCl2 · 8H2O) as raw materials. Isothermal oxidation at 900 and 1,000 °C in 0.1 MPa O2 and cyclic oxidation at 1,000 °C in air of the coated and uncoated specimens were performed to investigate the effect of
the duplex films on the oxidation behavior of the γ-TiAl alloy. The results of the isothermal oxidation tests indicated that
the parabolic rate constants of the alloy were decreased due to the applied thin film. Additionally, the present film exhibited
a beneficial effect on the cyclic oxidation resistance of the alloy in air. The duplex film could restrain the growth of TiO2, causing an increase of the Al2O3 content in the oxide mixture and thus decreased the oxidation rate. 相似文献
15.
Oxidation resistance of metal at high temperature can be improved by an environmentally friendly solution deposition approach.
Stable precursor solution with high oxide concentration, favorable viscosity and low surface tension was prepared using aluminum
sec-butoxide (ASB) and polyvinylpyrrolidone (PVP) as starting raw materials. Alumina sol-gel films were deposited onto metal
by spin-coating followed by heat treatment. When PVP was added according to an amount of 50 mg/mL into a sol with an ASB/H2O molar ratio of 1:35, the as-obtained sol exhibited favorable gelation time and viscosity. The surface tension of the alumina
sol with PVP was examined to be lower by 32% than the sol (ASB:H2O = 1:100) without PVP. TG-DTA analyses show the densification of the alumina gel film with PVP was progressed within a wide
temperature range from 200 to 650 °C. Crack-free Al2O3 film with a thickness up to 1.5 μm was successfully produced on metallic substrate by three spin-coating cycles. SEM and
XRD analyses revealed the gel film transformed into compact α-Al2O3 material after calcined at 1,000 °C for 0.5 h. The weight gained by the samples during firing at 1,000 °C indicated that
the Al2O3 coating film could reduce the rate of oxidation by ∼81%. The hardness of the Al2O3 film coated metal was higher by 260% than the uncoated metal that was calcined at 1,000 °C for 0.5 h. It was confirmed by
adhesion test that both the alumina/PVP hybrid film and the as-produced α-Al2O3 coating film had strong adhesion. 相似文献
16.
El-Sayed A. El-Sharkawy 《Monatshefte für Chemie / Chemical Monthly》2006,137(12):1487-1498
Summary. The textural characteristics, including surface area, mean pore diameters, and total pore volume of Cr2O3–CuO/Al2O3 solid catalysts were determined from the low temperature adsorption of N2 at 77 K. The structural properties were investigated using XRD. The surface acidity of calcined samples was determined using
two comparable methods, including the non-aqueous titration of acidic groups with n-butylamine and dehydration/dehydrogenation activity of cyclohexanol.
XRD patterns assigned a crystalline CuO and γ-Al2O3 for 723 K calcinations products of lower Cr2O3 content. The gradual increase of calcinations temperature promoted the crystallinity of Cr2O3 and resulted in solid–solid interaction of CuO and Cr2O3 forming CuCr2O4. The textural parameters varied with both calcinations temperature and catalyst composition. The surface acid density (DAS)
increased with the increase of chromia content up to 0.132 mole% Cr2O3, while the rise of calcinations temperature led to a decrease of surface acidity.
The dehydration/dehydrogenation of cyclohexanol as well as n-butylamine titration succeeded in characterizing of surface acidity.
Present address: Chemistry Department, College of Science, King Faisal University, Al-Hofuf 31982, Saudi Arabia 相似文献
17.
Griselda Corro Gelacio Aguilar Ramon Montiel Sylvain Bernes 《Reaction Kinetics and Catalysis Letters》2001,73(2):317-323
An easy, inexpensive method for metal dispersion measurements in Pt-Sn/γ -Al2O3 catalysts is proposed. The method is based in avoiding Sn oxidation during catalyst evacuation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
18.
Ozao R. Yoshida H. Ichimura Y. Inada T. Ochiai M. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):915-922
The thermal change of anodic alumina (AA), particularly the exothermic peak followed by the endothermic peak at ca 950°C was
studied in detail by mainly using simultaneous TG-DTA/FTIR. The gradual loss of mass up to ca 910°C is attributed to dehydration.
When heated at a constant rate by using TG-DTA, an exothermic peak with subsequent endothermic peak is observed at ca 950°C,
but the exothermic peak becomes less distinct with decreasing heating rate. It has been found that gaseous SO2 accompanying a small amount of CO2 is mainly discharged at this stage. The reaction in this stage can be considered roughly in two schemes. The first scheme
can be said collectively as crystallization, in which the migration of S or C trapped inside the crystal lattice of the polycrystalline
phase (γ-, δ-, and θ-Al2O3, which presumably accompanies a large amount of amorphous or disordered phase) occurs. In the second scheme, the initial
polycrystalline (+amorphous) phase crystallizes into a quasi-crystallineγ-Al2O3-like metastable phase after amorphization. Conclusively,after the distinct exo- and endothermic reactions, the amorphous
phase crystallizes intoγ-Al2O3, presumably accompanying small amount of δ-Al2O3. It is also found that, when maintained isothermally, the metastable phases undergo transformation into the stable α-Al2O3 at 912°C.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Petre A. L. Auroux A. Gervasini A. Caldararu M. Ionescu N. I. 《Journal of Thermal Analysis and Calorimetry》2001,64(1):253-260
The surface properties of supported gallium oxide catalysts prepared by impregnation of various supports (γ-Al2O3, SiO2, TiO2, ZrO2) were investigated by adsorption microcalorimetry, using ammonia and water as probe molecules. In the case of acidic supports
(γ-Al2O3, ZrO2, TiO2), the acidic character of supported gallium catalysts always decreased in comparison with gallium-free supports; on very
weakly acidic SiO2, new acidic centers were created when depositing Ga2O3. The addition of gallium oxide decreased the hydrophilic properties of alumina, titania and zirconia, but increased the amount
of water adsorbed on silica. The catalytic performances in the selective catalytic reduction of NO by C2H4 in excess oxygenwere in the order Ga/Al2O3>Ga/TiO2>Ga/ZrO2>>Ga/SiO2. This order is more related to the quality of the dispersion of Ga2O3 on the support than to the global acidity of the solids.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
A ZrO2-γ-Al2O3 supported Pd catalyst was prepared and characterized by XRD, XPS, H2-TPR and TEM techniques. The catalytic activity was evaluated in the liquid-phase hydrogenation of 2-ethylanthraquinone. Comparing
with Pd/γ-Al2O3, it showed high catalytic activity. 相似文献