共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Cimino L. Lisi S. De Rossi M. Faticanti P. Porta 《Applied catalysis. B, Environmental》2003,43(4):397-406
Structural, redox and catalytic deep oxidation properties of LaAl1−xMnxO3 (x=0.0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions prepared by the citrate method and calcined at 1073 K were investigated. XRD analysis showed that all the LaAl1−xMnxO3 samples are single phase perovskite-type solid solutions. Particle sizes and surface areas (SA) are in the 280–1180 Å and 4–33 m2 g−1 ranges, respectively. Redox properties and the content of Mn4+ were derived from temperature programmed reduction (TPR) with H2. Two reduction steps are observed by TPR for pure LaMnO3, the first attributed to the reduction of Mn4+ to Mn3+ and the second due to complete reduction of Mn3+ to Mn2+. The presence of Al in the LaAl1−xMnxO3 solid solutions produces a strong promoting effect on the Mn4+→Mn3+ reducibility and inhibits the further reduction to Mn2+. Both for methane combustion and CO oxidation all Mn-containing perovskites are much more active than LaAlO3, so pointing to the essential role of the transition metal ion in developing highly active catalysts. Partial dilution with Al appears to enhance the specific activity of Mn sites for methane combustion. 相似文献
2.
The preparation of Ti1−xSnxO2 nanocrystalline photocatalysts in reverse microemulsions is reported in this work. The obtained materials have been characterised by total reflection X-ray fluorescence (TXRF), X-ray diffraction (XRD) and Raman and UV–vis spectroscopies. Very good accordance between calculated and obtained compositions is observed. Undoped TiO2 prepared in this way crystallises in the anatase phase. Tin-doped anatase is formed with x < 0.05, while both anatase and rutile phases crystallise when x ≥ 0.05. When both phases coexist, a preferential doping of rutile seems to occur. When x = 0.10, a multiphase mixture containing TiO2(anatase), TiO2(rutile) and SnO2 was formed. No significant modification of the band gap is found in any case. The photocatalytic activity of the obtained catalysts is compared employing the trichloroethylene photocatalytic degradation as a test reaction. The beneficial effect of Sn4+ in the activity of TiO2 appears to be related to the formation of anatase–rutile mixtures, leading to the highest specific photocatalytic activity in the sample of composition Ti0.93Sn0.07O2, with anatase:rutile ratio close to 3. 相似文献
3.
Fengxiang Yin Shengfu Ji Nengzhan Chen Meili Zhang Liping Zhao Chengyue Li Hui Liu 《Catalysis Today》2005,105(3-4):372-377
A series of the Ce1−xCuxO2−x/Al2O3/FeCrAl catalysts (x = 0–1) were prepared. The structure of the catalysts was characterized using XRD, SEM and H2-TPR. The catalytic activity of the catalysts for the combustion of methane was evaluated. The results indicated that in the Ce1−xCuxO2−x/Al2O3/FeCrAl catalysts the surface phase structure were the Ce1−xCuxO2−x solid solution, -Al2O3 and γ-Al2O3. The surface particle shape and size were different with the variety of the molar ratio of Ce to Cu in the Ce1−xCuxO2−x solid solution. The Cu component of the Ce1−xCuxO2−x/Al2O3/FeCrAl catalysts played an important role to the catalytic activity for the methane combustion. There were the stronger interaction among the Ce1−xCuxO2−x solid solution and the Al2O3 washcoats and the FeCrAl support. 相似文献
4.
Fengxiang Yin Shengfu Ji Biaohua Chen Liping Zhao Hui Liu Chengyue Li 《Applied catalysis. B, Environmental》2006,66(3-4):265-273
MnOx–CeO2 mixed oxides prepared by sol–gel method, coprecipitation method and modified coprecipitation method were investigated for the complete oxidation of formaldehyde. Structure analysis by H2-TPR and XPS revealed that there were more Mn4+ species and richer lattice oxygen on the surface of the catalyst prepared by the modified coprecipitation method than those of the catalysts prepared by sol–gel and coprecipitation methods, resulting in much higher catalytic activity toward complete oxidation of formaldehyde. The effect of calcination temperature on the structural features and catalytic behavior of the MnOx–CeO2 mixed oxides prepared by the modified coprecipitation was further examined, and the catalyst calcined at 773 K showed 100% formaldehyde conversion at a temperature as low as 373 K. For the samples calcined below 773 K, no any diffraction peak corresponding to manganese oxides could be detected by XRD measurement due to the formation of MnOx–CeO2 solid solution. While the diffraction peaks corresponding to MnO2 phase in the samples calcined above 773 K were clearly observed, indicating the occurrence of phase segregation between MnO2 and CeO2. Accordingly, it was supposed that the strong interaction between MnOx and CeO2, which depends on the preparation route and the calcination temperature, played a crucial role in determining the catalytic activity toward the complete oxidation of formaldehyde. 相似文献
5.
Plinio Innocenzi Alessandro Martucci Lidia Armelao 《Journal of the European Ceramic Society》2005,25(16):3587-3591
Aluminium titanate films thicker than 0.5 μm have been synthesized by sol–gel methods. The films have been deposited via repetitive dip-coating on silicon wafers and their thermal stability has been tested as a function of the annealing time and temperature. The sol–gel approach has allowed the formation of the aluminium titanate phase at temperatures (700 °C) much lower than those necessary for solid-state reactions (1450 °C). Magnesium oxide has been used to improve the thermal stability of the films at high temperatures. The behavior of samples prepared with two different Mg content, i.e. Mg0.2Al1.6Ti0.8O5 and Mg0.6Al0.8Ti1.6O5, has been studied. The films have proven to be stable at 1150 °C, for up to 90 h. X-ray photoelectron spectroscopy has shown that after firing at 500 °C the surface chemical composition of the films is in accordance with the nominal one, whilst at higher annealing temperatures some differences, attributed to diffusion effects, have been observed. 相似文献
6.
Structural (XRD) and spectroscopic (EPR, IR and Raman) investigations were performed to elucidate the influence of CeO2 content on the phase composition and surface chemistry of CexZr1−xO2 solid solutions (x = 0.10–0.85), interacting with NO and NO2 in the absence and presence of oxygen. Strong influence of ceria loading on the adsorption modes of both nitrogen oxides and the nature of the resultant surface species was revealed. Adsorption of NO led to formation of mononitrosyl complexes, dimers and N2O, whereas interaction of NO2 with the ceria–zirconia catalyst resulted in the adsorbate disproportionation or coupling, depending on the sample composition. 相似文献
7.
Zhenfeng Bian Jie Ren Jian Zhu Shaohua Wang Yunfeng Lu Hexing Li 《Applied catalysis. B, Environmental》2009,89(3-4):577-582
Mesoporous BixTi1−xO2 spheres with core–shell chamber were prepared by alcoholysis under solvothermal conditions. The cross-condensation between Ti–OH and Bi–OH ensured complete incorporation of Bi-dopants into TiO2 lattice, though Bi atom is much bigger than Ti. Meanwhile, the aggregation of titania building clusters into spheres and their subsequent reactions including dissolution and re-deposition processes lead to the hollow spheres with tunable interior structure. The Bi-doping induced strong spectral response in visible region owing to the formation of narrow intermediate energy band gaps. Meanwhile, multiple reflections within the sphere interior voids promoted the light absorbance. As a result, the as-prepared BixTi1−xO2 spheres exhibited much higher activity than the undoped TiO2, the Bi2O3/TiO2 obtained by impregnating the TiO2 with Bi(NO3)3 solution, and the BixTi1−xO2 after being ground during photodegradation of p-chlorophenol under visible light irradiation. Meanwhile, the BixTi1−xO2 could be used repetitively for 10 times owing to the high hydrothermal stability and the absence of Bi-leaching. 相似文献
8.
Preparation, microstructure and microwave dielectric properties of ZrxTi1−xO4 (x=0.40–0.60) ceramics
S. X. Zhang J. B. Li J. Cao H. Z. Zhai B. Zhang 《Journal of the European Ceramic Society》2001,21(16):2931-2936
ZrxTi1−xO4 (x=0.40–0.60) ceramics sintered without additives were prepared from powders made by the coprecipitation of metal salts from aqueous solutions in order to investigate the existence range of a homogeneous phase and the relationships between composition, microstructure and the dielectric properties. XRD, TEM, SEM, EDS, and the dielectric measurements were used to characterize the products. A homogeneous solid solution was obtained. Its crystal structure was isomorphous with ZrTiO4. The variation of the lattice parameters with TiO2 content was discussed. The optimum sintering temperature of samples was dependent of composition. TiO2 suppressed the densification and acted as a grain growth enhancer during the sintering process. With the increase in TiO2 content the relative densities of the sintered bodies decrease, while the grain sizes increase. The dielectric properties at microwave frequency (1.8 GHz) in this system, especially Q value, were poor, due to low densification, impurities and lattice defects. The dielectric constant r and Q value exhibited a significant dependence on the relative density and composition. Both r and Q increased with the increase in relative density, but they were primarily influenced by the composition and the effect of the relative density could be ignored when the relative density was greater than 90% theoretical. r increased slightly with increasing TiO2 content, while Q value decreased. 相似文献
9.
It is known that Curie temperature of barium titanate system can be altered by the substitution of dopants into either A- or B-site. Dopants could pinch transition temperature, lower Curie temperature, and raise the rhombohedral–orthorhombic and orthorhombic–tetragonal phase transition close to room temperature. This isovalent substitution could improve the ferroelectric properties of the BaTiO3-based system. In this study, barium zirconate titanate Ba(ZrxTi1−x)O3 (BZT; x = 0, 0.02, 0.05 and 0.08) ceramics were prepared by conventionally mixed-oxide method. The ferroelectric properties of BZT ceramics were investigated. Increasing Zr content in the BaTiO3-based compositions caused a decrease in Curie temperature (Tc). At Tc, the highest relative permittivity of BZT with an addition of 0.08 mol% of Zr was 12,780. The BZT specimens with the additions of 0.05 mol% and 0.08 mol% of Zr presented the remanent polarization at 25 μC/cm2 and 30 μC/cm2, respectively. 相似文献
10.
Layered -titanate materials, NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na0.4Ni0.2Ti0.8O2 were ca. 7×103 S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm−1 K−1 at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na0.4Ni0.2Ti0.8O2 and Na0.4Co0.2Ti0.8O2 was about 1.9×10−4 and 1.2×10−4 K−1 around 700 °C, respectively. 相似文献
11.
Solid solutions belonging to the Mn-rich region of the YCuxMn1–xO3 system have been studied. The powders were prepared by solid-state reaction between the corresponding oxides. Sintered ceramics were obtained by firing at 1100–1325 °C. The incorporation of 30 at.% Cu to the yttrium manganite induces the formation of a perovskite-type phase, with orthorhombic symmetry. Increase of the Cu amount do not appreciably affects the orthorhombicity factor b/a, up to an amount of 50 at.% Cu. Above this Cu amount, a multiphase system has been observed, with the presence of unreacted-Y2O3, YMnO3 and Y2Cu2O5, along with a perovskite phase. DC electrical conductivity measurements have shown a semiconducting behaviour for all the solid solutions with perovskite-type structure. The room temperature conductivity increases with Cu until 33 at.% Cu, and then decreases. Thermally activated small polaron hopping mechanism, between Mn3+ and Mn4+ cations, controls the conductivity in these ceramics. Results are discussed as a function of the Mn3+/Mn4+ ratio for each composition. 相似文献
12.
This study focuses on the direct sulfur recovery process (DSRP), in which SO2 can be directly converted into elemental sulfur using a variety of reducing agents over Ce1−xZrxO2 catalysts. Ce1−xZrxO2 catalysts (where x = 0.2, 0.5, and 0.8) were prepared by a citric complexation method. The experimental conditions used for SO2 reduction were as follow: the space velocity (GHSV) was 30,000 ml/g-cat h and the ratio of [CO (or H2, H2 + CO)]/[SO2] was 2.0. It was found that the catalyst and reducing agent providing the best performance were the Ce0.5Zr0.5O2 catalyst and CO, respectively. In this case, the SO2 conversion was about 92% and the sulfur yield was about 90% at 550 °C. Also, a higher efficiency of SO2 removal and elemental sulfur recovery was achieved in the reduction of SO2 with CO as a reducing agent than that with H2. In the reduction of SO2 by H2 over the Ce0.5Zr0.5O2 catalyst, SO2 conversion and sulfur yield were about 92.7% and 73%, respectively, at 800 °C. Also, the reduction of SO2 using synthetic gas with various [CO]/[H2] molar ratios over the Ce0.5Zr0.5O2 catalyst was performed, in order to investigate the possibility of using coal-derived gas as a reducing agent in the DSRP. It was found that the reactivity of the SO2 reduction using the synthetic gas with various [CO]/[H2] molar ratios was increased with increasing CO content of the synthetic gas. Therefore, it was found that the Ce1−xZrxO2 catalysts are applicable to the DSRP using coal-derived gas, which contains a larger percentage of CO than H2. 相似文献
13.
P. Bazin O. Saur F.C. Meunier M. Daturi J.C. Lavalley A.M. Le Govic V. Harl G. Blanchard 《Applied catalysis. B, Environmental》2009,90(3-4):368-379
The nature, concentration and reducibility by H2 of sulfate species formed from SO2 oxidation were studied over a range of Pt/CexZr1−xO2 catalysts using infrared spectroscopy and thermogravimetry. Ionic sulfates were formed over ceria and Ce-containing catalysts, even at high Zr content. The sample-specific surface area, the presence of platinum and the zirconium proportion affected the rate and extent of formation of sulfate in the bulk of the materials. Sulfate reduction by H2 first occurred at the CexZr1−xO2 surface. Bulk-like S-containing species subsequently migrated towards the surface to continuously replace surface sulfates removed by the reduction. The temperature required for sulfate migration as well as that necessary for sulfate reduction increased with the Zr content. The amount of stored sulfur is closely linked to the specific surface area of the sample. Finally, we have clearly shown that thermogravimetry was an appropriate technique for evaluating the oxygen storage capacity (OSC) of sulfated ceria–zirconia mixed oxides, despite the additional complexity due to the presence of sulfate compounds and various reduced S-species that can be formed during sample reduction. 相似文献
14.
15.
Macro Daturi Laurent Savary Guylene Costentin Jean-Claude Lavalley 《Catalysis Today》2000,61(1-4):231-236
Two CdMoxW1−xO4 solid solutions with the scheelite and the wolframite structures were synthesised via different techniques and their structures were determined from powder refinements. The limit of the reciprocal solubility of Mo in CdWO4 has been checked. Several compositions of the solid solutions have been tested in the catalytic mild oxidation of propane or propene and relations between the structures and the catalytic activity are proposed. 相似文献
16.
Electrocatalysts of the general formula IrxRu1−xO2 were prepared using Adams’ fusion method. The crystallite characterization was examined via XRD, and the electrochemical properties were examined via cyclic voltammetry (CV) in, linear sweep voltammetry (LSV) and chronopotentiometry measurements in 0.5 M H2SO4. The electrocatalysts were applied to a membrane electrode assembly (MEA) and studied in situ in an electrolysis cell through electrochemical impedance spectroscopy (EIS) and stationary current density–potential relations were investigated. The IrxRu1−xO2 (x = 0.2, 0.4, 0.6) compounds were found to be more active than pure IrO2 and more stable than pure RuO2. The most active electrocatalyst obtained had a composition of Ir0.2Ru0.8O2. With an Ir0.2Ru0.8O2 anode, a 28.4% Pt/C cathode and the total noble metal loading of 1.7 mg cm−2, the potential of water electrolysis was 1.622 V at 1 A cm−2 and 80 °C. 相似文献
17.
Tiziano Montini Loredana De Rogatis Valentina Gombac Paolo Fornasiero Mauro Graziani 《Applied catalysis. B, Environmental》2007,71(3-4):125-134
Rh(1%)@CexZr1−xO2–Al2O3 nanocomposites have been investigated as active and thermally stable catalysts for ethanol steam reforming. Preformed Rh nanoparticles have been efficiently protected from deactivation/sintering by a porous layer of nanocomposite oxides. Chemisorption and activity data confirm the good accessibility of the metal phase to the reaction mixture. No appreciable deactivation is observed after 160 h of reaction at 873 K. The ceria–zirconia mixed oxides favour reforming reactions, reduce coke formation and facilitate its removal. The alumina component is important to stabilize the ceria–zirconia mixed oxides, preventing their sintering. 相似文献
18.
The effect of sulphate on the catalytic properties of V2O5/TiO2 and WO3/TiO2 in the selective reduction of NO with NH3 has been investigated. For both catalytic systems, the presence of sulphate results in the enhancement of catalytic activity without reduction of selectivity to nitrogen. The rate of NO reduction depends on the sulphate content, which is affected by the original composition of titania, the method of catalyst preparation and the metal oxide loading. 相似文献
19.
J.A. Anderson R.A. Daley S.Y. Christou A.M. Efstathiou 《Applied catalysis. B, Environmental》2006,64(3-4):189-200
Pt-Rh/CexZr1−xO2-Al2O3 with 0.6 and 1.0 wt.% noble metal loadings were prepared and characterized for their metal dispersion with respect to CexZr1−xO2-free Pt-Rh/Al2O3 in fresh, thermally aged and oxychlorinated states. Thermal ageing at 973 K led to loss of metal dispersion in all cases but to negligible effect on the dispersion of the CexZr1−xO2 component where present. Oxychlorination was able to fully recover metal dispersion in all cases but led to different effects on the redox properties of CexZr1−xO2 which appeared to be related to the metal loadings. Despite showing improved dispersion following regeneration, higher loaded catalyst showed no improvement in light-off performance for either NO reduction or CO oxidation and showed poorer oxygen storage (OSC) ability, particularly at higher temperatures. Lower loaded catalyst showed improved dispersion, improved OSC and reduced light-off temperatures for NO reduction and CO oxidation after oxychlorination compared to that in the thermally aged state. 相似文献
20.
A BaTiO3 powder has been prepared by the sol-gel process from the hydrolysis of a solution of barium acetate and titanium ethylate in the presence of acetic acid as a catalyst. Supplementary constituents in the form of Ca(CH3COO)2, Zr(OC3H7)4, Sr(NO3)2 also can be used. Intermediate phases of barium acetate and barium carbonate have been identified by differential thermal analysis, X-ray diffraction, infra-red and scanning electron microscopy. BaTiO3 with perovskite structure synthesizes in the temperature range from 600 to 1000°C. 相似文献