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1.
Hyoung Lim Koh Sang Ho Lee Kyung Lim Kim 《Reaction Kinetics and Catalysis Letters》2000,71(2):239-244
The effect of MoO3 addition to alumina supported vanadia catalysts on the catalytic activity for the selective catlaytic reduction of NO is investigated. Upon the addition of MoO3, catalytic activity is enhanced and the particle size of V2O5 which is shown by the results of XRD and Raman spectroscopy is decreased. The MoO3-V2O5/Al2O3 catalyst also exhibits more resistance to SO2 deactivation than V2O5/Al2O3 does. 相似文献
2.
Anna Blonska-Tabero 《Central European Journal of Chemistry》2009,7(2):252-258
Phase diagrams in the subsolidus area of the systems FeVO4 - CdO and FeVO4 - Cd2V2O7 have been deduced using the results of XRD and DTA analyses. On the basis of these diagrams and some additional verifying
research, a projection of the subsolidus area of the CdO - V2O5 - Fe2O3 system onto the plane that comprises the components’ concentration triangle has been presented. The H-type phase is the only
phase formed in this system. It co-exists at equilibrium with other phases in six subsidiary subsystems.
相似文献
3.
Gary A. Pozarnsky Lisa Wright Alon V. Mccormick 《Journal of Sol-Gel Science and Technology》1994,3(1):57-62
Vanadium pentoxide (V2O5) sols have been used in conductive coatings and related applications [1, 2, 3]; however, the changes which may occur in the properties of these coatings with sols of different ages have not been carefully shown. Properties which may be dependent on the age of the sol (sol viscosity, film morphology and conductance) were measured in this work. The coating sols were prepared by ion-exchange of sodium metavanadate solutions.It was found that the coating thickness, sol viscosity, and surface morphology of the coatings were directly related to the age of the sol used. The dried coating thickness increased from 3 microns to 20 microns over a 30 day period. The sol viscosity increased from 1 centipoise to near 2 centipoise. The surface morphology of the coatings changed from that of a featureless surface at day 1 to a continual coverage of micron-sized fibers as the coating sols aged. The conductivity of the coatings, though, was unaffected by the age of the sol. The coating properties were correlated to the amount of polymerization of dissolved precursors in solution. 相似文献
4.
M. Turco G. Bagnasco L. Lisi P. Ciambelli 《Journal of Thermal Analysis and Calorimetry》1992,38(12):2631-2638
Thermal analysis (TG and DTA) was employed for the characterization of V2O5/TiO2 catalysts supported on high surface area TiO2. The results obtained are consistent with a uniform spreading of vanadium oxide on TiO2 surface for V2O5 content less than 15% by weight.The presence of V2O5 on the surface of TiO2 affects the anatase-rutile phase transition lowering the temperature at which it occurs.DTA measurements, performed on catalysts after many months from the preparation, show the appearance of an exothermic peak in the range 280°–340°C. This signal has been related to the oxidation of V(IV) to V(V) on the catalyst surface.Catalysts characterization, performed by chemical analysis and FT-IR spectroscopy, has confirmed this interpretation.It has been suggested that a slow modification of the catalyst occurs, leading to an increase of the V(IV) content during the time.
Zusammenfassung Zur Charakterisierung von V2O5/TiO2-Katalysatoren auf hochoberflächigem TiO2 Trägermaterial wurde die Thermoanalyse (TG und DTA) angewendet. Für einen V2O5-Gehalt von weniger als 15 Gew.% entsprechen die erhaltenen Ergebnisse einer gleichmäßigen Verteilung des Vanadiumoxides an der TiO2-Oberfläche.Die Gegenwart von V2O5 an der Oberfläche von TiO2 beeinflußt die Anatas-Rutil-Phasenumwandlung, indem sie die zugehörige Temperatur verringert.DTA-Messungen an Katalysatoren mehrere Monate nach ihrer Herstellung zeigten das Auftreten eines exothermen Peaks im Bereich 280°–340°C. Dieses Signal wurde der Oxidation von V(IV) zu V(V) an der Katalysatoroberfläche zugeschrieben.Diese Interpretation konnte durch eine Charakterisierung des Katalysatoren durch chemische Analyse und FT-IR-Spektroskopie bestätigt werden.Es wurde angedeutet, daß der Katalysator mit der Zeit einer langsamen Modifikation unterliegt, die zu einem Ansteigen des V(IV)-Gehaltes führt.相似文献
5.
Yoshio Toda Takashi Ohno Fumikazu Hatayama Hisashi Miyata 《Reaction Kinetics and Catalysis Letters》2000,71(1):159-164
Acidity and structure of Ca-doped V2O5/ZrO2 catalysts have been studied by FTIR. Both Lewis and Brønsted acidity decreased with Ca loading. New surface vanadate species seemed to be formed by Ca addition. 相似文献
6.
Effect of K promotion on the CO hydrogenation activity and selectivity of coprecipitated Co/Al2O3 has been studied. K addition is found to lower total activity while enhancing C2-C4 olefins selectivity; kinetic data indicate that the reaction mechanism is not affected. 相似文献
7.
Jadwiga Walczak Izabella Rychłowska-Himmel Elżbieta Mikos-Nawłatyna 《Journal of Thermal Analysis and Calorimetry》1995,43(1):201-204
Phase equilibria being established in the solid state in the system V2O5?Fe8V10W16O85 were examined by X-ray phase powder diffraction and DTA. It has been found that the system of interest is a real two-component system with an eutectic temperature 620±5°C. 相似文献
8.
The variation of dispersion of Pt on Al2O3 support with sintering time is measured and the value of equilibrium dispersion of Pt is obtained directly. It is found that a General Power Law Expression can fit the experimental data well. 相似文献
9.
Lee Jinn-Shing Hsu C.-K. Huang Chin-Wang 《Journal of Thermal Analysis and Calorimetry》1999,56(1):137-142
The effects of Al2O3 and SiO2 additives on the crystallization of calcium phosphate glasses were studied. When the Al2O3 content was higher than 7 mol%, surface devitrification occurred in the glasses. However, for glasses with Al2O3 contents higher than 10 mol%, bulk devitrification predominanted. For the glasses with SiO2, a surface devitrification mechanism predominanted. Non-isothermal DTA techniques were applied in order to establish the
devitrification mechanism, and the kinetic parameters of crystal growth were obtained. The parameter m depends on the mechanism
and morphology of devitrification of calcium phosphate, glass containing SiO2 as additive, the values of m being lower than 1.2. These results indicate that the devitrification is controlled by the reaction
at the glass-crystal interface, or occurs from surface nuclei.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Effect of Preparation Conditions on the Stability of Pt/Al2O3 Catalysts in Methane Combustion 总被引:2,自引:0,他引:2
Alumina supported platinum catalysts were prepared by sol-gel method using aluminum-sec-butoxide, platinum acetylacetonate and sec-butanol. Various gelation process were performed either by the help of a gelation agent (water or acetic acid) or by a slow condensation without hydrolysis source. The textural and the structural study of the catalysts using the nitrogen physical adsorption and the hydrogen chemisorption showed that the BET surface area and the metal dispersion varied when the hydrolysis and the gelation processes were modified. The catalytic activities for methane combustion performed on the fresh and aged catalysts were correlated to the metal dispersion values. In addition the catalytic activity loss under reaction mixture seemed to be caused by the metal dispersion decrease. When the catalysts were aged under the reaction mixture at 600°C for 72 h, a BET surface area decrease and a metallic surface area loss were observed. The resistance to sintering observed to be dependant on the hydrolysis and the gelation processes was in favor of the catalyst prepared by acetic acid. 相似文献
11.
Yun Guo Shuben Li Bin Zhang Jianzhong Niu Qiang Gao Ling Gao 《Reaction Kinetics and Catalysis Letters》2000,69(1):153-159
The influence of ZrO2 on the properties of Al2O3 and performances of Pd/Al2O3 catalyst in CO oxidation have been investigated. TPD results show that the activity enhanced is due to the increase of the adsorptive capacity of CO and the activation of C=O bond after the introduction of ZrO2. 相似文献
12.
A.K.H. Nohman 《Reaction Kinetics and Catalysis Letters》2000,69(1):73-76
-Mn2O3 and KMn8O16 were detected on catalysts prepared by pore volume impregnation of -alumina using manganous nitrate and ammonium permanganate, respectively. While the surface texture was not remarkably affected: decomposition activities towards H2O2 and 2-propanol were higher for the later. 相似文献
13.
A.K. Chakraborty 《Journal of Sol-Gel Science and Technology》2003,28(1):87-95
Diphasic Al2O3-SiO2 gels have been synthesized by hydrolyzing ethyl orthosilicate at three different pH ranges in presence of colloidal boehmite. Result shows that dominant mullitization process are sensitive to pH of the gelation process. At highly acidic pH range, solid state reaction between corundum and cristobalite occurs, and develops liquid phase for mullite nucleation. At moderately acidic pH, nucleation and crystallization are most operative for nucleation in aluminosilicate matrix. In highly basic pH region, Al-Si spinel phase develops by incorporation of Si in aluminous phase as intermediary phase. Polymorphic transformation of it may be the cause of sudden mullitization. The changes in crystallization sequence in three distinct processes may be due to variation in the nature and size of silicic acid particle formed by hydrolysis and condensation of TEOS at different pH. 相似文献
14.
15.
The preparation of synthesis gas from carbon dioxide reforming of methane (CDR) has attracted increasing attention. The present
review mainly focuses on CDR to produce synthesis gas over Ni/MOx/Al2O3 (X = La, Mg, Ca) catalysts. From the examination of various supported nickel catalysts, the promotional effects of La2O3, MgO, and CaO have been found. The addition of promoters to Al2O3-supported nickel catalysts enhances the catalytic activity as well as stability. The catalytic performance is strongly dependent
on the loading amount of promoters. For example, the highest CH4 and CO2 conversion were obtained when the ratios of metal M to Al were in the range of 0.04–0.06. In the case of Ni/La2O3/Al2O3 catalyst, the highest CH4 conversion (96%) and CO2 conversion (97%) was achieved with the catalyst (La/Al = 0.05 (atom/atom)). For Ni/CaO/Al2O3 catalyst, the catalyst with Ca/Al = 0.04 (atom/atom) exhibited the highest CH4 conversion (91%) and CO2 conversion (92%) among the catalysts with various CaO content. Also, Ni/MgO/Al2O3 catalyst with Mg/Al = 0.06 (atom/atom) showed the highest CH4 conversion (89%) and CO2 conversion (90%) among the catalysts with various Mg/Al ratios. Thus it is most likely that the optimal ratios of M to Al
for the highest activities of the catalysts are related to the highly dispersed metal species. In addition, the improved catalytic
performance of Al2O3-supported nickel catalysts promoted with metal oxides is due to the strong interaction between Ni and metal oxide, the stabilization
of metal oxide on Al2O3 and the basic property of metal oxide to prevent carbon formation. 相似文献
16.
Gel of platinum and aluminum was prepared by an anhydrous gelation process using a mixture of aluminum sec butoxid, platinum acetylacetonate and Butanol-2. The investigation of this gelation by FTIR, UV-vis and 27Al NMR spectroscopies suggest that a slow polymerization of aluminum precursors occurs according to an etheration mecanism likely catalysed by metallic platinum which could be formed by the reduction of platinum in Pt(acac)2 by sBuOH in the mixture during aging. 相似文献
17.
Vesselin Dimitrov Yanko Dimitriev Vili Mihailova 《Monatshefte für Chemie / Chemical Monthly》1983,114(6-7):669-674
The structure of glasses in the Fe2O3-V2O5 system in the 0–50 mol% Fe2O3 range is studied by IR-spectroscopy. It is found that the introduction of Fe2O3 favours the transformation of the VO5-groups into VO4 ones. This effect may be shown with the aid of IR-spectra, owing to the fact that these glasses are characterized by two high-frequency bands at 1020 and 930 cm–1. The first is determined by the vibrations of the short V=O nonbridging bonds in the VO5-groups, while the second is assigned to the vibrations of the V—O-bonds in deformed VO4-tetrahedra.
IR-spektroskopische Strukturuntersuchung von Gläsern des Systems Fe2O3-V2O5
Zusammenfassung Die Struktur von Gläsern des Systems Fe2O3-V2O5 in dem Bereich von 0–50 Molprozent Fe2O3 wurde mit Hilfe der IR-Spektroskopie untersucht. Zusatz von Fe2O3 begünstigt die Umwandlung der VO5- in VO4-Gruppen. Das kann in den IR-Spektren durch zwei Banden bei 1020 und 930 cm–1 festgestellt werden. Die erste wird durch Schwingungen der kurzen V=O-Nichtbrücken-bindungen in den VO5-Gruppen verursacht, die zweite wird auf Schwingungen der V—O-Bindungen in dem deformierten VO4-Tetraeder zurückgeführt.相似文献
18.
Phase equilibria being established in the subsolidus area of the V2O5?Cr2(MoO4)3 system at the whole component concentration range have been studied basing on DTA and X-ray phase powder diffraction. It has been established that the system is not a real two-component system in the subsolidus area. The fact has been proved by the presence of fields in that area, where three solid phases remain in mutual equilibrium. 相似文献
19.
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
20.
S. Kittaka N. Uchida M. Katayama A. Doi M. Fukuhara 《Colloid and polymer science》1991,269(8):835-842
The colloidal stability of V2O5
nH2O was studied on the basis of the measurements of critical flocculation concentration (CFC) by metal ions, amount of ions exchanged (or intercalated), and -potential. In total, the CFC values obeyed the Schulze Hardy law and strong Hofmeister's series was found in the systems including alkaline ions. The sequence of colloidal stability of V2O5
nH2O in the electrolyte solutions was related to the intercalation of metal ions in the interlayer spaces of the solid. The largest CFC value for Li+ (87 mmol dm–3) was explained by smaller affinity of Li+ to be intercalated in V2O5
nH2O as well as smaller Hamaker constant of the intercalated solid compared to the other systems.Effect of intercalation of metal ions on the crystalline properties of the materials was measured by use of XRD and electron microscope. Under highly dehydrated condition the ions whose radii are smaller than 0.1 nm are captured in the structure of V2O5
nH2O without changing interlayer distances, while those larger than 0.1 nm increase the interlayer distance. In a saturated H2O vapor interlayer distances increased with increasing charge of intercalated ions. However, when intercalated with ions carrying the same valency the interlayer distances of the sample decreased with decrease in the hydration property of ions. Hydrolyzable Cr3+ gave exceptionally larger interlayer distances, both in a vacuum and in H2O vapor. 相似文献