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1.
Experimental data on the sol–gel synthesis of manganese oxides formed during the reduction of potassium permanganate by polyvinyl alcohol in an aqueous medium are presented. The physicochemical properties of the obtained manganese oxide systems that depend on the conditions of the synthesis are studied by means of DTA, XRD, SEM, and the low temperature adsorption–desorption of nitrogen. It is found that the obtained samples have a mesoporous structure and predominantly consist of double potassium–manganese oxide K2Mn4O8 with a tunnel structure and impurities of oxides such as α-MnO2, MnO, α-Mn2O3, and Mn5O8. It is shown that the proposed method of synthesis allows us to regulate the size and volume of mesopores and, to a lesser extent, the texture of the obtained oxides, which can be considered promising sorbents for the selective extraction of strontium and cesium ions from multicomponent aqueous solutions.  相似文献   

2.
We prepared Pd catalysts supported on various metal oxides, viz. γ-Al2O3, α-Al2O3, SiO2–Al2O3, SiO2, CeO2 and TiO2 by an incipient wetness method and applied them to propane combustion. Several techniques: N2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), CO chemisorption, temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO) were employed to characterize the catalysts. Pd/SiO2–Al2O3 showed the least catalytic activity at high temperatures among Pd catalysts supported on irreducible metal oxides, viz. SiO2, Al2O3 and SiO2–Al2O3. Pd/γ-Al2O3 was much superior for this reaction to Pd/α-Al2O3. The Pd catalyst supported on reducible metal oxides (CeO2 and TiO2) with a less specific surface area showed the higher catalytic activity compared with that supported on reducible metal oxides with a higher specific surface area, even though the former had a less Pd dispersion than the latter. In the case of Pd/SiO2–Al2O3, the initially reduced Pd catalyst was superior to the fully oxidized one. The oxidation of metallic Pd occurred in the presence of O2 with increasing reaction temperature, which resulted in the change in the catalytic activity.  相似文献   

3.
TG experiments on the hydrogen reduction of α-Fe2O3 were carried out to elucidate the influence of the preparation history of the oxide on its reactivity. α-Fe2O3 samples were prepared by the thermal decomposition of seven iron salts in a stream of oxygen, air or nitrogen at temperatures of 500–1200°C for 1 h. Thirteen metal ions such as Cu2+, Ni2+, etc. were used as doping agents. The reactivity of the oxide was indicated by the initial reduction temperature (Ti. α-Fe2O3 prepared at lower temperatures showed lower Ti values and the reduction proceeded stepwise (Fe2O3 → Fe3O4 → Fe). Ti values increased with the rise in the preparation temperature of the oxide. The oxides prepared at higher temperatures showed that two reduction steps (Fe2O3 → Fe3O4 → Fe) proceed simultaneously. the preparation in oxygen gave higher Ti than that in air or nitrogen. The doping by metal ions, except Ti4+, lowered the Ti of α-Fe2O3. The Cu2+ ion showed the lowest Ti, while Ti4+ showed the highest Ti and the inhibition effect.The reduction process was expressed by two equations; Avrami—Erofeev's equation for α-Fe2O3 → Fe3O4 and Mampel's equation for Fe3O4 → Fe.  相似文献   

4.
《Comptes Rendus Chimie》2015,18(4):379-384
In this report, fructose-derived carbonaceous spheres were utilized as sacrificial templates for the fabrication of metal oxide hollow spheres (MOHSs) by a facile hydrothermal approach. Hollow spheres of a series of crystalline metal oxides (α-Fe2O3, Cr2O3, Co3O4, NiO, and ZnO) have been fabricated, utilizing the metal chloride as the oxide precursors. Heating of an aqueous solution of the metal chloride and fructose to moderate temperature in an autoclave affords a spherical composite consisting of a metal precursor shell sheathing a carbonaceous core. Subsequent removal of the interior carbonaceous cores by thermal treatment through oxidation in air produces free-standing crystalline oxides hollow spheres. The MOHSs were characterized by means of SEM, TEM, XRD, IR spectroscopy, energy dispersive X-ray (EDX) and sorption measurements. The results show convincingly that using fructose as a sacrificial template after application of a hydrothermal synthesis route could be a favourable sacrificial template for the fabrication of various MOHSs.  相似文献   

5.
Metal oxides are stable and highly durable catalysts for the selective catalytic reduction (SCR) of NO by hydrocarbons and potential candidates for practical use. This review focuses on the development as well as the fundamental understanding of metal oxide based catalysts for selective reduction of NO by hydrocarbons. Our studies on the SCR-deNOx properties of Ga2O3/Al2O3, Cu-Al2O3, and Ag-Al2O3 catalysts are presented and it is attempted to demonstrate the advantages of this type of catalysts. On the basis of several spectroscopic characterizations, the effect of important factors, such as dispersion, coordination, and the electronic states of the metal cation, on the intrinsic catalytic activity are quite well clarified. From the in situ FTIR results, the reaction mechanism is understood in terms of formation and reaction of surface molecules. The structural and kinetic information obtained at the molecular level provides a useful strategy for designing better deNOx catalysts using metal oxides.  相似文献   

6.
Metal oxides are stable and highly durable catalysts for the selective catalytic reduction (SCR) of NO by hydrocarbons and potential candidates for practical use. This review focuses on the development as well as the fundamental understanding of metal oxide based catalysts for selective reduction of NO by hydrocarbons. Our studies on the SCR-deNOx properties of Ga2O3/Al2O3, Cu-Al2O3, and Ag-Al2O3 catalysts are presented and it is attempted to demonstrate the advantages of this type of catalysts. On the basis of several spectroscopic characterizations, the effect of important factors, such as dispersion, coordination, and the electronic states of the metal cation, on the intrinsic catalytic activity are quite well clarified. From the in situ FTIR results, the reaction mechanism is understood in terms of formation and reaction of surface molecules. The structural and kinetic information obtained at the molecular level provides a useful strategy for designing better deNOx catalysts using metal oxides.  相似文献   

7.
Catalytic transfer hydrogenation of 2-butanone with 2-propanol was studied in gas phase over a series of oxides of different acid-base properties. Although the basic oxides (MgO, La2O3) gave high initial conversions, these oxides underwent deactivation during the reaction. This deactivation could be partially prevented by a previous treatment with chloroform of the oxide. The amphoteric oxides (TiO2, ZrO2, Al2O3) were also active in this reaction. Increasing the acidic character of the catalyst (Nb2O5, WO3) led to a pronounced dehydration of 2-propanol. The results obtained over a series of rare earth oxides (La2O3, Sm2O3, Gd2O3, Dy2O3, Er2O3) revealed that beside the role of basic and acid sites a correlation seems to exist between the number of unpaired electrons of the metal ion and the catalytic activity, indicating the role of one electron donor sites.  相似文献   

8.
Various metal oxides with 0.1 wt% Ag loaded as a cocatalyst were prepared by an impregnation method and examined their photocatalytic activity for CO2 reduction with water. Among all the prepared Ag-loaded metal oxides, Ga2O3, ZrO2, Y2O3, MgO, and La2O3 showed activities for CO and H2 productions under ultraviolet light irradiation. Thus, metal oxides involving metal cations with closed shell electronic structures such as d0, d10, and s0 had the potential for CO2 reduction with water. In situ Fourier transform infrared measurement revealed that the photocatalytic activity and selectivity for CO production are controlled by the amount and chemical states of CO2 adsorbed on the catalyst surface and by the surface basicity, as summarized as follows: Ag/ZrO2 enhanced H2 production rather than CO production due to very little CO2 adsorption. Ag/Ga2O3 exhibited the highest activity for CO production, because adsorbed monodentate bicarbonate was effectively converted to bidentate formate being the reaction intermediates for CO production owing to its weak surface basicity. Ag/La2O3, Ag/Y2O3, and Ag/MgO having both weak and strong basic sites adsorbed larger amount of carbonate species including their ions and suppressed H2 production. However, the adsorbed carbonate species were hardly converted to the bidentate formate.  相似文献   

9.
Catalytic activities for oxygen reduction of some transition metal oxides with metallic conductivity such as LaTiO3, SrFeO3, SrVO3, SrRuO3, V0.2Ti1.8O3 and La1-xSrxMnO3 were investigated, and they as well as the activities of other oxides reported already were compared with the nature of their conduction bands. It was found that the catalytic activity of oxides having a σ* conduction band was high. The conclusion is drawn that in order for a transition metal oxide to have a high catalytic activity, (1) it must have a σ* band and (2) the band must contain electrons. This conclusion will be useful to predict the catalytic activity for oxygen reduction of transition metal oxides.  相似文献   

10.
The effects of coenzyme Q0, ascorbic acid, and 2-O-α-D-glucopyranosylascorbic acid on the radiation-induced dephosphorylation of 1-glycerophosphate, glucose-1-phosphate, and glucose-6-phosphate in deaerated aqueous solutions at pH 7 were studied by means of continuous radiolysis. It was found that the test compounds efficiently suppressed the radiation-induced dephosphorylation of organic phosphates in equimolar concentrations by interactions with water radiolysis products. At an organic phosphate to additive concentration ratio of 100: 1, ascorbic acid and coenzyme Q0 can suppress the radiation-induced dephosphorylation of the initial substances in aqueous solutions by the reduction and oxidation of hydroxyl-containing carbon-centered radicals, respectively.  相似文献   

11.
The following rare earth oxides, which were prepared by the precipitation of hydroxides, were studied as catalysts for the reaction of complete methane oxidation: CeO2, a hydrated phase of La2O3, Pr6O11, Tb4O7, and Gd2O3. The catalytic activities of the oxides were compared in terms of first-order reaction rate constants per unit surface area of the catalyst. With consideration for data on the reduction of CeO2, Pr6O11, and Tb4O7, the previously proposed redox reaction mechanism on transition metal oxides was supported. The high activity of hydrated La2O3 was found, and it was hypothesized that, in this case, the process occurred by the mechanism of oxidative methane condensation followed by the rapid oxidation of the resulting intermediate products.  相似文献   

12.
姚小江  高飞  董林 《催化学报》2013,34(11):1975-1985
探讨负载型金属氧化物催化剂的表面组分与载体之间的相互作用, 有助于理解相关催化剂的催化作用本质. 近年来, 我们对单组分CuO以及双组分CuO-Mn2O3, CuO-CoO等金属氧化物在γ-Al2O3载体表面的分散行为和存在状态, 及其物理化学性质和催化性能(CO+O2和NO+CO模型反应)进行了研究. 结果表明, 这些金属氧化物在γ-Al2O3载体表面的分散行为和所得负载型催化剂样品的一些物理化学性质及其催化性能均可参照“嵌入模型”来解释. 在此基础上, 我们讨论了这些样品的“组成-结构-性质”间的关系, 并针对表面负载双组分金属氧化物样品提出了表面协同氧空位参与的NO+CO反应机理.  相似文献   

13.
Photoredox catalysis provides opportunities in harnessing clean and green resources such as sunlight and O2, while the acid and base surface sites of metal oxides are critical for industrial catalysis such as oil cracking. The contribution of metal oxide surfaces towards photocatalytic aerobic reactions was elucidated, as demonstrated through the hydroxylation of boronic acids to alcohols. The strength and proximity of the surface base sites appeared to be two key factors in driving the reaction; basic and amphoteric oxides such as MgO, TiO2, ZnO, and Al2O3 enabled high alcohol yields, while acidic oxides such as SiO2 and B2O3 gave only low yields. The reaction is tunable to different irradiation sources by merely selecting photosensitizers of compatible excitation wavelengths. Such surface complexation mechanisms between reactants and earth abundant materials can be effectively utilized to achieve a wider range of photoredox reactions.  相似文献   

14.
New methods have been adopted for the anodic deposition of the different manganese and cobalt oxides. The deposition of the diferent oxides is usually carried out from their metal salt solutions in presence of a reducing agent. The oxides deposited are as follows: Mn2O3 from manganous sulphate in presence of boric, acid and formaldehyde at pH=5.5, Mn3O4 from manganous sulphate in presence of formic acid at pH=5.0 MnO from manganous sulphate-ammonium chloride solution in presence of telluric acid, Co2O3 from cobalt chloride in presence of telluric acid and sodium fluoride, Co3O4 from cobaltite in presence of formaldehyde and potassium chloride and finally CoO from cobalt chloride in presence of alcohol. The results of chemical analysis revealed that the purity of the oxides is 99.99% and their molecular formulae are MnO1.5, MnO1.33, MnO, CoO1.5, CoO1.33 and CoO respectively.  相似文献   

15.
利用溶胶-凝胶法,采用三种酸性金属氧化物(氧化铌、氧化钨和氧化钼)对锰铈复合氧化物催化剂进行了改性. 测试了催化剂的氮氧化物选择性催化还原(SCR)活性,以筛选对应不同温度窗口的合适酸性氧化物改性剂. 同时评价了催化剂的NO氧化和NH3氧化活性. 利用X射线衍射、BET比表面积测试、H2程序升温还原、NH3/NOx程序升温脱附和NH3/NOx吸附红外光谱等手段对催化剂进行了表征. MnOx-CeO2催化剂表现出良好的低温(100-150 ℃)活性. 酸性金属氧化物的添加削弱了催化剂的氧化还原特性,从而抑制了NH3的活化和NO2辅助的快速SCR反应. 与此同时,相对高温(250-350 ℃)区NH3的氧化也受到了抑制,B酸和L酸上的NH3吸附得以增强. 因此,催化剂的SCR脱硝温度窗口向高温移动,改性效果Nb2O5 < WO3 < MoO3.  相似文献   

16.
The applicability of IR spectroscopy in studies of the structural characteristics of the ferrite spinel phase was shown for Zn0.5Mn0.5Fe2O4 samples prepared by the pyrolysis of aerosols of aqueous solutions of metal nitrates. The IR spectra of synthesized (ZnMn)Fe2O4 ferrites, Fe2O3, ZnO, MnO, and Mn2O3 pure oxides, and mixtures of these oxides in the region of characteristic M-O stretching vibration and M-O-H bending vibration frequencies were compared to determine the degree of concentration and structural uniformity of the ferrite spinel phase.  相似文献   

17.
The effect of ascorbic acid, 5,6-O-isopropylidyl-2,3-O-dimethylascorbic acid, and 2-O-glucopyranosylascorbic acid on the formation of main radiolysis products of ethanol and aqueous ethanol, ethylene glycol, α-methylglucopyranoside, and maltose solutions was studied by means of continuous radiolysis. The obtained results indicate that ascorbic acid effectively reacts with the carbon-centered hydroxyl-containing radicals derived from the substrates, thus decreasing the yield of their recombination and fragmentation products. It was found that the interaction of ascorbic acid and its derivatives with the carbon-centered radicals during the radiolysis of deaerated ethanol and its aqueous solutions may occur via both reducing and oxidizing mechanisms and that ascorbic acid in the aerated solutions acts as a hydrogen donor, reducing mainly the HO 2 · radical to hydrogen peroxide.  相似文献   

18.
A simple oxide classification has been proposed on the basis of correlation between electronic polarizabilities of the ions and their binding energies determined by XPS. Three groups of oxides have been considered taking into account the values obtained on refractive-index- or energy-gap-based oxide ion polarizability, cation polarizability, optical basicity, O 1s binding energy, metal (or nonmetal) binding energy, and Yamashita-Kurosawa's interaction parameter of the oxides. The group of semicovalent predominantly acidic oxides includes BeO, B2O3, P2O5, SiO2, Al2O3, GeO2, and Ga2O3 with low oxide ion polarizability, high O 1s binding energy, low cation polarizability, high metal (or nonmetal) outermost binding energy, comparatively low optical basicity, and strong interionic interaction, leading to the formation of strong covalent bonds. Some main group oxides so-called ionic or basic such as CaO, In2O3, SnO2, and TeO2 and most transition metal oxides show relatively high oxide ion polarizability, O 1s binding energy in a very narrow medium range, high cation polarizability, and low metal (or nonmetal) binding energy. Their optical basicity varies in a narrow range and it is close to that of CaO. The group of very ionic or very basic oxides includes CdO, SrO, and BaO as well as PbO, Sb2O3, and Bi2O3, which possess very high oxide ion polarizability, low O 1s binding energy, very high cation polarizability, and very low metal (or nonmetal) binding energy. Their optical basicity is higher than that of CaO and the interionic interaction is very weak, giving rise to the formation of very ionic chemical bonds.  相似文献   

19.
Vanadium oxide catalysts of the monolayer type have been prepared by means of chemisorption of vanadate(V)-anions from aqueous solutions and by chemisorption of gaseous V2O3(OH)4. Using Al2O3, Cr2O3, TiO2, CeO2 and ZrO2, catalysts with an approximately complete monomolecular layer of vanadium(V) oxide on the carrier oxides can be prepared, if temperature is not too high. Divalent metal oxides like CdO and ZnO may already form threedimensional surface vanadates at moderate temperature. The thermal stability of a monolayer catalyst is related to the parameter z/a, i. e. the ratio of the carrier cation charge to the sum of ionic radii of carrier cation and oxide anion. Thus, monolayer catalysts will be thermally stable only under the condition that z/a is not too high (aggregated catalyst) nor too small (ternary compound formation).  相似文献   

20.
This paper reports the chitosan-mediated synthesis of porous hematite nanoparticles with FeCl3 as the precursor via a hydrothermal approach at 160 °C. A series of porous chitosan/iron oxide hybrid nanoparticles were obtained via changing the ratio of chitosan to FeCl3, FeCl3 concentration and pH value of the reaction solution, and producing porous iron oxide nanoparticles after calcination. The as-prepared samples were characterized by means of X-ray diffraction, transmission electron microscopy, thermal gravimetric analysis, Fourier transform infrared, and N2 sorption. The particle sizes of these metal oxides were less than 100 nm, and the pore sizes were in the range of 2–16 nm. It was demonstrated that chitosan played a key role in the formation of the porous structures. The resultant α-Fe2O3 nanoparticles were used as the support to immobilize Au or Pd nanoparticles, producing Au/α-Fe2O3 or Pd/α-Fe2O3 nanoparticles. The as-prepared α-Fe2O3 nanocatalyst exhibited high selectivity towards cyclohexanone and cyclohexanol for catalyzing cyclohexane oxidation with O2 at 150°C.  相似文献   

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