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1.
In this work, we study cyclohexene oxidation by molecular oxygen on doped‐TiO 2 . The improvement of the oxidizing capacity of titanium oxide by doping with iron oxide at different molar ratios is checked. All materials with different molar ratios (Ti/Fe = 9, 4, and 2) are prepared by the sol–gel method and fully characterized by ICP , XRD , SEM , DR /UV –vis, IR , and N 2 adsorption/desorption. The results show that iron is successfully incorporated into the titanium matrix but the incorporated amount is limited. In catalytic tests, improved activity is noticed while using TiO 2 in the presence of Fe 2O 3, which is due the improved oxidation. Conversion in the range of 21–42% depending on the presence of iron oxide was obtained with excellent yield of adipic acid (97% selectivity). 相似文献
2.
The
aim of our research was to prepare yellow pigments based on structure of pseudobrookite
Fe 2TiO 5. Part of Fe was substituted
with Li and Ti from Fe 2TiO 5
to Li 0.05Fe 0.07Ti 2.44O 5.
Synthesis and pigmentary-application properties in the Li 2O–Fe 2O 3–TiO 2 system were studied for 800 and 900°C using classical ceramic
method of preparation. The main attention was aimed to usage of four different
sources of titanium compounds as raw materials. We studied the influence of
different sources of titanium compounds on the structural and the colour properties
of the prepared pigments. The thermal analysis was used for characterization
of titanium compounds and determination of their thermal stability. 相似文献
3.
Titania powders were synthesized by thermal hydrolysis of titanium tetrachloride in a mixed solvent was studied. The dielectric constant was tuned by regulating the acetone/water volume ratio (R/H ratio) and temperature of the solvent. Hydroxypropyl cellulose (HPC) was used as a steric dispersant. The synthesis were carried out at R/H ratios of 0–4, temperatures of 70–90°C, TiCl 4 concentrations of 0.05–0.2 M, HPC concentrations of 0–5 × 10 –3 g/cm 3, and synthesis times of 15–60 min. The TiO 2 particles obtained at an R/H ratio of 0, i.e., pure water system, were fine and agglomerated. In contrast, the TiO 2 particles prepared at an R/H ratio of 3 were uniform and spherical. The TiO 2 particle size increased with increasing TiCl 4 concentration. The synthesis temperature did not influence the particle size, but greatly influenced the morphologyof the TiO 2. Adding HPC to the solution yielded more uniform and spherical particles. In addition, the synthesis time should be longer than 30 min to obtain the most uniform and spherical particles. The dielectric constant of the acetone-water mixed solvent at 28 gave the most uniform and spherical TiO 2 particles. The powders prepared at the condition of 0.1 M TiCl 4, R/H ratio of 3, HPC concentration of 0.001 g/cm 3, temperature of 70°C, and synthesis time of 1 h exhibited the most uniform and spherical morphology. The as-synthesized powder was anatase and retained the phase below 400°C. It transformed to the rutile phase after calcination at 700°C. 相似文献
4.
Combinations of SiO 2–TiO 2 mixed with zeolites may open new opportunities as base supports for acid-base and oxidation reactions. These solids would endow the catalysts with specific acid sites, which may not necessarily be found in those supports with only Si-Al oxides as basic materials. Using a standard sol–gel methodology, SiO 2–TiO 2 mixtures are prepared and mixed with β, Y and ZSM-5 zeolites. By partially hydrolyzing the SiO 2 precursor at the beginning of the sol–gel procedure it is possible to maximize the number of Si–O–Ti bridges formed. FTIR and AFM analyses show that the size of sols formed depend upon the type of zeolite. Metal loading helps surface dehydroxylation of the materials, possibly indicating a good insertion of the metal into the network. 相似文献
5.
High-chromium vanadium–titanium magnetite (HCVTM) is a good valuable resource with high iron content in the form of complex iron ore which contains various valuable metal elements such as iron, vanadium, titanium, chromium. Direct reduction of HCVTM is studied based on thermodynamic analysis. Combined TG experimental verification and equilibrium calculation model was used to analyze the reaction sequence and equilibrium amount in this paper. The contents in HCVTM reduction system are simplified as 18 kinds of chemical compositions. Reductions of Fe3O4 and FeO·TiO2 are the main reduction reactions and are mainly reduced by C. The reduction reaction sequence of FeO·TiO2 is FeO·TiO2, TiO2, TiC, and Ti; the reduction reaction sequence of Fe3O4 is Fe3O4, FeO, and Fe. The minimum reduction temperature of HCVTM is 860 °C. The reduction of Cr is difficult to implement, and the minimum reduction temperature of V is above 700 °C. The gas phase in this system is mainly CO when the temperature is above 1000 °C. CO partial pressure curve of gasification reaction is in the shape of ‘S’ with increase of temperature. When the temperature is 1350 °C, C/O is 1.0 and reduction time is 30 min, HCVTM can be reduced thoroughly and the reduction degree can reach to 0.98. When C/O is lower than 1.0, FeTi2O5 is the reduction intermediate products from FeO·TiO2. When C/O is 1.0, diffraction peaks of Fe3O4 and FeO·TiO2 disappear, and they are reduced to Fe and TiO2. 相似文献
6.
A series of Zn–Al hydrotalcites with Zn/Al molar ratios of 1, 2, 3 and 6 were prepared by co-precipitation method. TG-DTG results showed that the hydrotalcites decompose in two stages, corresponding to the two endothermic peaks around 180 and 220°C. After calcination at 400°C, the samples were converted into Zn–Al mixed oxides with the only XRD pattern of ZnO, except for the sample with the ratio of 6. The Zn–Al mixed oxides possess similar surface acidity revealed by microcalorimetric adsorption of NH 3. The basicity of the samples increases with the order: ZnO>6Zn/Al>1Zn/Al>Al 2O 3.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
7.
LiFe 0.5Ti 1.5O 4 was synthesized by solid-state reaction carried out at 900 °C in flowing argon atmosphere, followed by rapid quenching of the reaction product to room temperature. The compound has been characterized by X-ray powder diffraction (XRD) and 57Fe Mössbauer effect spectroscopy (MES). It crystallizes in the space group P4 332, a = 8.4048(1) Å. Results from Rietveld structural refinement indicated 1:3 cation ordering on the octahedral sites: Li occupies the octahedral (4 b) sites, Ti occupies the octahedral (12 d) sites, while the tetrahedral (8 c) sites have mixed (Fe/Li) occupancy. A small, about 5%, inversion of Fe on the (4 b) sites has been detected. The MES data is consistent with cation distribution and oxidation state of Fe, determined from the structural data.The title compound is thermally unstable in air atmosphere. At 800 °C it transforms to a mixture of two Fe 3+ containing phases – a face centred cubic spinel Li (1+y)/2Fe (5−3y)/2Ti yO 4 and a Li (z−1)/2Fe (7−3z)/2Ti zO 5 – pseudobrookite. The major product of thermal treatment at 1000 °C is a ramsdellite type lithium titanium iron(III) oxide, accompanied by traces of rutile and pseudobrookite. 相似文献
8.
Mn/Fe mixed oxide solids doped with Al 2O 3 (0.32-1.27 wt.%) were prepared by impregnation of manganese nitrate with finely powdered ferric oxide, then treated with different amounts of aluminum nitrate. The obtained samples were calcined in air at 700-1000 °C for 6 h. The specific surface area ( SBET) and the catalytic activity of pure and doped precalcined at 700-1000 °C have been measured by using N 2 adsorption isotherms and CO oxidation by O 2. The structure and the phase changes were characterized by DTA and XRD techniques. The obtained results revealed that Mn 2O 3 interacted readily with Fe 2O 3 to produce well-crystallized manganese ferrite (MnFe 2O 4) at temperatures of 800 °C and above. The degree of propagation of this reaction increased by Al 2O 3-doping and also by increasing the heating temperature. The treatment with 1.27 wt.% Al 2O 3 followed by heating at 1000 °C resulted in complete conversion of Mn/Fe oxides into the corresponding ferrite phase. The catalytic activity and SBET of pure and doped solids were found to decrease, by increasing both the calcination temperature and the amount of Al 2O 3 added, due to the enhanced formation of MnFe 2O 4 phase which is less reactive than the free oxides (Mn 2O 3 and Fe 2O 3). The activation energy of formation (Δ E) of MnFe 2O 4 was determined for pure and doped solids. The promotion effect of aluminum in formation of MnFe 2O 4 was attributed to an effective increase in the mobility of reacting cations. 相似文献
9.
As part of a systematic study of mechanisms of response of semiconducting oxides as trace gas sensors, we have explored the behaviour of iron–titanium oxide solid solutions Fe 2−xTi xO 3 ( x = 0.1–1.4). The materials were single-phase for x = 0.1 with increasing proportions of a pseudobrookite second phase at higher degree of substitution. Unmodified, pure iron oxide does not show sensitivity to CO. A significant signal was developed for x = 0.1, that then diminished with increasing x and was lost for x = 1.4. Three effects have been deduced important for the gas response: significant surface segregation of Ti at low Ti content; grain growth inhibition and agglomeration into more massive, non-porous lumps as Ti content increased; and the appearance of a band-gap state associated with Fe(II) at higher Ti content. The effects of microstructure change have been analyzed by fitting the data to a simple 2-resistor model of gas-insensitive ‘grains’ in series with gas-sensitive ‘grain boundaries’. A Mars–van Krevelen type model for the response is presented, based on reactions at surface-segregated defect clusters, to develop and remove electrically-active surface trap states. 相似文献
10.
A platinum-lined, flowing autoclave facility was used to investigate the solubility behavior of titanium dioxide (TiO 2) in aqueous sodium phosphate, sodium hydroxide and ammonium hydroxide solutions between 17 and 288°. Baseline Ti(IV) solubilities were found to be on the order of one nanomolal, which were enhanced by the formation of anionic hydroxo- and phosphato-complexes. The measured solubility behavior was examined via a titanium(IV) ion hydrolysis/complexing reaction equilibria were obtained from a least squares analysis of the data. The existence of three new Ti(IV) ion complexes is reported for the first time: Ti(OH) 4(HPO 4) 2–, Ti(OH) 5(H 2PO 4) 2– and Ti(OH) 5(HPO 4) 3–. The triply-charged anionic complex was the dominant Ti(IV) species in concentrated, alkaline phosphate solutions at elevated temperatures. This complex is expected to exhibit C.N.=4 (i.e., Ti(OH) 2OPO
4
3–
). A summary of thermochemical properties for species in the systems TiO 2-H 2O and TiO 2-P 2O 5-H 2O is also provided. 相似文献
11.
Alumina-titania mixed oxides with nominal atomic ratios Al/Ti=25 and 2 have been synthesized by cohydrolysis of Al(OsecBu) 3 and Ti(OBu) 4. The oxides were amorphous at 500°C, showing only short range order. Ti was incorporated in alumina in a well dispersed way creating a true Al/Ti mixed oxide. The strength of surface acid sites and specific surface areas were increased at the higher Ti content. The TiO 2 anatase phase was avoided and rutile was formed directly at 900°C. 相似文献
12.
The temperature dependences of the rate of oxidation of acetone vapors by oxygen on oxide surface catalysts: V 2O 5, Co 3O 4., MoO 3 and TiO 2 (rutile), and the industrial catalyst VKSh were determined. A series of the catalytic activity of the above surface catalysts was established. The relationship between the catalytic properties of the oxides in the oxidation of acetone and their redox and acid-base characteristics was analyzed. The catalytic activity of the oxides in the oxidation reaction of acetone and methanol were compared.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 114–117, January–February, 1988. 相似文献
13.
Fine‐powdered, heterostructured, nanoporous Bi 2O 3–TiO 2 (BTO) was synthesized by a green approach using ultrasonication, with the mole ratio Bi/Ti of 1:1 and calcined at different temperatures. The physical and optical properties of the mixed oxides were investigated. The phase structure, as identified by X‐ray diffraction (XRD), showed the appearance of new phases as a function of the calcination temperature. Morphological examinations indicated the formation of a nanoporous structure with a drastic change in morphology at the calcination temperature of 850°C from a globule to a rod‐shaped structure, which further got transformed to a rocky appearance at 1200°C. Doping with Bi 2O 3 led to the lowering of the bandgap of TiO 2 from 3.25 to 2.5 eV. A BTO nanocatalyst calcined at 450°C exhibited promising photocatalytic activity for the degradation of quinalphos (QP) (92%) after a time interval of 100 min under visible light and at the optimum pH 8. The kinetics of degradation of QP showed that it follows a pseudo‐first‐order path with a rate constant 0.01267 min ?1. The synthesized BTO mixed oxide showed profound improvement in photocatalytic activity in the visible region as compared to TiO 2. 相似文献
14.
We have used thermal desorption to study the catalytic activity in CO oxidation and the state of the surface of an iron–cobalt oxide system. In the region of co-existence of the spinels CoFe 2O 4 and CoCo 2O 4, the activity and specific surface area are practically constant. We observe substantial deviation from additivity for the catalytic activity in the region of co-existence of the oxide Fe 2O 3 and the spinel CoFe 2O 4. We have established that chemisorption of CO on the surface of the oxides leads to formation of a number of stable forms of chemisorbed CO 2, among which the least strongly bound 2 form is characteristic of the most active catalysts. 相似文献
15.
The conventional impregnation method was used to prepare 15 wt% Mn-supported catalysts, which were applied to the catalytic oxidation of volatile organic compounds (VOCs; toluene, benzene, and o-xylene). The effects of calcination temperatures in the range of 500–900 °C and supports (γ-Al 2O 3, SiO 2, and TiO 2) on the property and performance of 15 wt% Mn-supported catalysts were investigated. Their physicochemical characteristics were analyzed by the BET, XRD, NH 3–TPD, H 2–TPR, and XPS. The calcination temperature greatly affected the crystalline structure and O1 s D (defect oxides)/O1 s L (lattice oxides) area ratio of the 15 wt% Mn/γ-Al 2O 3 (15 Mn/Al) catalyst. The order of the O1 s D/O1 s L area ratios of the 15 Mn/Al catalysts with respect to calcination temperature was 900 > 500 > 700 °C, which was in good agreement with that observed for the catalytic activity. In addition, the activity order of the 15 wt% Mn-supported catalysts with respect to the type of support was γ-Al 2O 3 > SiO 2 > TiO 2. The 15 wt% Mn/Al catalyst, which had a higher O1 s D/O1 s L area ratio, showed better activity than the 15 wt% Mn/SiO 2 (15 Mn/Si) and 15 wt% Mn/TiO 2 (15 Mn/Ti) catalysts. Defect oxides played a significant role in the catalytic oxidation of VOCs. The catalytic activity with respect to the type of VOC decreased in the order of benzene > toluene > o-xylene. 相似文献
16.
Mössbauer spectroscopy and X-ray diffractometry have been used to study Sm–Fe mixed oxides (with different SmFe atomic ratios) annealed at 550, 850, 1000 and 1250 °C. The room temperature Mössbauer spectra can be interpreted in terms of one, two or three sextets and in some cases by an additional doublet depending on the composition and the heat treatment. The sextets have been associated with SmFeO 3 perovskite, Sm 3Fe 5O 12 garnet and -Fe 2O 3 hematite. These results are in agreement with those of X-ray diffractometric measurements, which give a clear, evidence of the presence of these phases. 相似文献
17.
A series of mixed oxides Ce 1 ? x Fe x O 2 was prepared by a hydrothermal method. XRD and Raman spectra were measured to study the structure of the prepared materials. The temperature-programmed reduction was undertaken to estimate reducibility of the oxides. Syngas generation from methane using these materials as oxygen carriers/catalysts via a chemical-looping procedure was investigated in detail. This procedure includes catalytic oxidation and decomposition of methane to produce H 2-rich gas at the first step followed by the production of the CO-rich gas by oxidizing the carbon deposited on deactivated catalysts. The results showed that all iron ions were incorporated into the ceria lattice with the formation of oxygen vacancies in the Ce 0.9Fe 0.1O 2 sample, while isolated Fe 2O 3 particles were distributed on the surface of the Ce 0.8Fe 0.2O 2 sample. TPR measurements and the analysis of the two-step chemical-looping reactions indicated a strong interaction between the Ce and Fe species which accounts for an increased activity of the mixed oxides in the syngas generation compared to that of individual oxides. Among the several samples, the Ce 0.8Fe 0.2O 2 catalyst showed the highest activity for methane partial oxidation due to the synergetic effects caused by the interaction of surface iron entities and Ce-Fe solid solution. In addition, selective oxidation of carbon by oxygen to CO can also be found over this material since gaseous products are formed at the carbon oxidation step with the selectivity to CO reaching 91.2%. Evidence is presented that syngas can be feasibly produced from methane with high selectivity via the chemical-looping procedure over the CeO 2-Fe 2O 3 mixed oxides. 相似文献
18.
Fe 2O 3/SiO 2 nanocomposites based on fumed silica A-300 ( SBET = 337 m 2/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac) 3) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac) 3 then oxidized in air at 400–900 °C. Samples with Fe(acac) 3 adsorbed onto nanosilica and samples with Fe 2O 3/SiO 2 including 6–17 wt% of Fe 2O 3 were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe 2O 3 deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac) 3 solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac) 3 solution in carbon tetrachloride only α-Fe 2O 3 phase is formed in addition to amorphous Fe 2O 3. The Fe 2O 3/SiO 2 materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm 3 and SBET = 265–310 m 2/g. 相似文献
19.
Au/TiO 2/Ti electrode was prepared by a two-step process of anodic oxidation of titanium followed by cathodic electrodeposition of
gold on resulted TiO 2. The morphology and surface analysis of Au/TiO 2/Ti electrodes was investigated using scanning electron microscopy and EDAX, respectively. The results indicated that gold
particles were homogeneously deposited on the surface of TiO 2 nanotubes. The nanotubular TiO 2 layers consist of individual tubes of about 60–90 nm in diameter, and the electrode surface was covered by gold particles
with a diameter of about 100–200 nm which are distributed evenly on the titanium dioxide nanotubes. This nanotubular TiO 2 support provides a high surface area and therefore enhances the electrocatalytic activity of Au/TiO 2/Ti electrode. The electrocatalytic behavior of Au/TiO 2/Ti electrodes in the glucose electro-oxidation was studied by cyclic voltammetry. The results showed that Au/TiO 2/Ti electrodes exhibit a considerably higher electrocatalytic activity toward the glucose oxidation than that of gold electrode. 相似文献
20.
Photocatalytic activity of titanium(IV) oxide (TiO 2) can be enhanced through modification of its surface‐active sites. Here, iron(III) carboxylate [MIL‐53[Fe]]‐incorporated TiO 2 (as MIL‐53(Fe)/TiO 2) was prepared using a hydrothermal method. This material was then calcined at 500°C to obtain a MIL‐53(Fe)‐derived γ‐Fe 2O 3/TiO 2 photocatalyst. A photocatalytic study of MIL‐53(Fe)/TiO 2 and MIL‐53(Fe)‐derived γ‐Fe 2O 3/TiO 2 toward cationic methylene blue (MB) and anionic methyl orange (MO) showed that MIL‐53(Fe)/TiO 2 (0.25 wt%) and MIL‐53(Fe)‐derived γ‐Fe 2O 3/TiO 2 (0.75 wt%) resulted the best degree of dye degradation. The MIL‐53(Fe)‐derived γ‐Fe 2O 3/TiO 2 (0.75 wt%) composite for instance is capable of degrading almost 100% of 20‐ppm MB and MO, respectively, within 6 hr. Photocatalytic degradation of MB and MO was well fitted to the Langmuir‐Hinshelwood pseudo‐first order kinetics model, which indicates physisorption as the key partway that facilitates dye decomposition on the surface of a photocatalyst under UV‐A irradiation. This study provides new insights into the exploration of MILs/TiO 2 materials for the environmental remediation and pollution control. 相似文献
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