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1.
Hexagonal Al-doped zinc oxide (ZnO) powders with a nominal composition of Zn1-xAlxO (0≤x≤0.028) were synthesized by the co-precipitation method. The contents of the Al element in the samples were measured by the inductively coupled plasma-optical emission spectroscopy (ICP-OES) technique. The structures of the Zn1-xAlxO (0≤x≤0.028) compounds calcined at 1000 and 1200℃ have been deter- mined using the Rietveld full-profile analysis method. Rietveld refinements of the diffraction data indi- cated that the addition of Al initially has a considerably positive effect on the decreasing of the lattice parameters a and c of Zn1-xAlxO, but the effect becomes very slight and even negative with the further increase of the Al content. The solid solubility limit of Al in ZnO (mole fraction y) is 2.2l%, resulting in Zn0.978Al0.22O. It seems that when the Al content is excessive, Al prefers to form a ZnAl2O4 compound with ZnO, but not to incorporate into the ZnO lattice to occupy the Zn2 cites. Two phases, [ZnO] (or Al-doped ZnO) and [ZnAl2O4], are obviously segregated in Zn1-xAlxO while the value of x is larger than 0.024. The UV-Vis absorption spectra show that the Al-doped ZnO exhibits a red-shift in the absorption edge without reduced transmission compared with pure ZnO, which also confirms that Al ions enter the ZnO lattice and form a Zn1-xAlxO solid solution.  相似文献   

2.
Sn1-2xFexNbxO2(0.45≤x≤0.50) samples were prepared at 1000 ℃ via a simple chemical co-precipitation method.The effects of the concentrations of Sn doped on the structures and magnetic properties of the samples have been investigated.A systematic variation from monoclinic to orthorhombic FeNbO4 structure was observed with increasing Sn content.The phase evolutions were observed from monoclinic structure with x=0.50 to the coexistence of monoclinic and orthorhombic structures with x=0.48,0.47,0.46,and then to orthorhombic structure with x=0.45.Antiferromagnetic behavior was observed for all the samples,and the magnetic ordering temperatures decrease with increasing Sn concentration,which further indicated the sequence of phase transitions.The results suggest that the incorporation of Sn can stabilize the orthorhombic FeNbO4.  相似文献   

3.
Ce6-xHoxMoO15-δ(0.0≤x≤1.2) was synthesized by modified sol-gel method and characterized by diffe-rential X-ray diffraction(XRD), Raman, and X-ray photoelectron spectroscopy(XPS) methods. The oxide ionic con-ductivity of the samples was investigated by AC impedance spectroscopy. It shows that all the samples are single phase with a cubic fluorite structure. The solid solution Ce6-xHoxMoO15-δ(x=0.6) was detected to be the best con-ducting phase with the highest conductivity(σt=1.05×10-2 S/cm) at 800 ℃ and the lowest activation energy(Ea=1.09eV). These properties suggest that this kind of material has a potential application in intermediate-low temperature solid oxide fuel cells.  相似文献   

4.
ZHU  Ying-Hong LOU  Hui 等 《中国化学》2002,20(4):346-351
K2NiF4 type compounds Sm2-xSrxCuO4(0≤x≤1.2)were prepared.Rietveld refinement of powder diffraction data shows that the crystal system of these compounds belongs to T′ type tetragonal structure of space group I4/mmm,and the addition of Sr causes a dramatic shift of the O(I) ions along the c axis from Sm(Sr) toward Cu while scarcely affecting the Cu-O(Ⅱ)bond in basal CuO4 phane.From XRD data,it can be seen that when 0.0≤x≤0.6,Sm2-xSrxCuO4 belongs to a singlephase K2NiF4 type structure,while at x≥0.7,both the free SrO phase and the CuO phase exist in these compounds.From the results of XPS and rietveld refinement,it can be seen that after replacing Sm^3 with Sr^2 of lower valence,the valence of Cu and Sm does not change apparently,and thus some defect must be formed at the oxygen ion positions and/or position A on A2BO4 to keep charge balance and to stabilize the structure.  相似文献   

5.
The structural and the optical properties of ZnO films with high quality grown via plasma-enhanced met-al-organic chemical vapour deposition(MOCVD) on C-plane sapphire substrate were studied. The crystallini-ty and the optical properties of the films are greatly improved having been annealed in oxygen plasma atmo-sphere. The structure, the band gap and the binding energy of O1s electrons, and the molar ratio of O to Zn were determined by X-ray diffraction (XRD), photoluminescence (PL) and X-ray photoelectron scan meth-ods. For both the annealed and the as-grown films, the exciton peak features were observed at room temper-ature. The band-edge photolof the annealed film is much stronger than that of the as-grown film, and the exciton peak relating to the deep level at 439 nm disappears. The molar ratio of O to Zn in the annealed film is 0. 91, while it is 0. 78 for the as-urown film.  相似文献   

6.
Aiming to improve the reactive adsorption desulfurization(RADS) performances of Ni/Zn O adsorbents,ZnxAly(OH)2(CO3)z·x H2 O precursor is synthesized by coprecipitation of Zn2+,AlO-2,and CO2-3; the Zn OZn6Al2O9 composite oxides are obtained by the calcination of ZnxAly(OH)2(CO3)z·x H2 O precursor,and the Ni/Zn O-Zn6Al2O9(6.0 wt% Ni O) adsorbents are prepared by wetness impregnation method. The phase,acid strength,acid type and quantity,morphology,and thermal properties were characterized by X-ray diffraction,temperature-programmed desorption of ammonia,pyridine-adsorbed infrared spectrum,high-resolution transmission electron microscopy,and Thermo Gravimetry-Derivative Thermo Gravimetry(TG-DTG),respectively. The breakthrough sulfur capacities of six adsorbents are between 34.2 and 47.9 mg/gcat. The kinetic studies indicated that the active energy of RADS(49.4 k J/mol) could reach nano-sized Zn O,the particle size of is about 12.0 nm. All the excellent RADS performances can be due to the high SBET. Also,there are some extents of aromatization reactions that occur,which can be contributed to the B?nsted acid rooted in Zn6Al2O9 composite oxide,and the octane number of products can be preserved well.  相似文献   

7.
A series of ternary perovskite type oxides LaNi1-xCuxO3(x = 0.2,0.4,0.6,0.8,and 1.0) were synthesized via the sol-gel method in propionic acid.Partial substitution of Ni by Cu showed higher activities and selectivities towards syngas products.LaNi0.8Cu0.2O3 was the most active toward the CH4 and CO2 conversions,and was selective for syngas products.Temperature-programmed reduction results showed that the addition of Cu facilitates the reduction of Ni3+ to Ni0,which is the main reason for the higher performance of this catalyst.  相似文献   

8.
A series of Cu/Zn based catalysts with and without Ni, prepared by the co-precipitation method, has been studied for methanol decomposition. CO and H2 are the major products. The Cu/Zn catalysts show a low initial activity and a poor stability. The formation of the CuZn alloys was observed in the deactivated Cu/Zn catalysts which were used for methanol decomposition at 250 . When small amounts of Ni were added in the catalyst, the Cu/Zn/Ni(molar ratio 5/4/ x) catalysts showed a high activity at a low temperature. The activity and the stability of the catalyst depend on the nickel content. The activity of the Cu/Zn/Ni catalysts was maintained at a. relatively stable value of 78% conversion of methanol with 95% selectivity of H2, 93% selectivity of CO, and a more than 70% yield of hydrogen was obtained at 250 C when x >1. The stability of the Cu/Zn/Ni (molar ratio 5/4/x) catalysts showed the maximum (ca 88%) when x=1. The stabilization effect of nickel on the Cu/Zn based catalysts may lead to the increasin  相似文献   

9.
纳米分子筛ZSM-5的热稳定性研究   总被引:5,自引:0,他引:5  
Nanosized ZSM 5 zeolite was synthesized by hydrothermal method and characterized by XRD and TEM techniques. The specific heat of the nanosized ZSM 5 zeolite was measured in the temperature range from 79 to 370 K, and its enhancement in specific heat was observed as compared with the corresponding microsized zeolite, indicating that the nanosized ZSM 5 zeolite possesses higher surface activity. The thermostability of the samples was determined by differential scanning calorimetric (DSC) and thermogravimetric (TG) techniques. The DSC results showed that, for the nanosized ZSM 5, a broad exothermic peak is observed from 1?300 K; for the microsized ZSM 5, the corresponding exothermic peak begins at 1?400 K, and a distinct phase transition can be observed at 1?620 K. The TG results showed that, for the nanozised ZSM 5, the maximum mass loss ratio is 6 9%, and two mass loss stages can be observed in the temperature ranges of 298~663 K and 923~ 1?273 K, respectively; for the microsized ZSM 5, the maximum mass loss ratio is 6 5% and it is more stable than the nanosized ZSM 5.  相似文献   

10.
(La_(1-x)Mg_x)_2(Ni_(0.8)Co_(0.2))_7(x = 0.125, 0.25, 0.5) alloys were synthesized from the sintered mixture of La_2O_3+ Ni O + Co O + Mg O in the molten CaCl_2 electrolyte at 750 °C and the electrochemical hydrogen storage capacities of the synthesized alloys were measured. Non-hygroscopic LaNiO_3 phase formed during sintering(at 1200 °C for 2 h) as a result of the reaction of hygroscopic La_2O_3 with NiO. Another sinter product was Mg_(0.4)Ni_(0.6)O phase. Both mixed oxide sinter products facilitated the La-Ni and Mg-Ni phase formations. X-ray diffraction peaks indicated that the first stable phase appeared in the alloy structure was LaNi_5 which formed upon reduction of La_2NiO_4 phase. Increase in Mg content caused formation of La_(1.5)Mg_(0.5)Ni_7 phase in the alloy structure and the presence of this phase improved the hydrogen storage performance of the electrodes. It was observed that(La_(1-x)Mg_x)_2(Ni_(0.8)Co_(0.2))_7(x = 0.125, 0.25, 0.5) alloys have promising discharge capacities change between 319 m Ah/g and 379 m Ah/g depending on the alloy Mg content.  相似文献   

11.
In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.  相似文献   

12.
Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.  相似文献   

13.
KMnO4-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.  相似文献   

14.
The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.  相似文献   

15.
The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.  相似文献   

16.
A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.  相似文献   

17.
18.
A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.  相似文献   

19.
An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.  相似文献   

20.
Quercetin, the polyphenolic compound, which has the highest daily intake, is well known for its protective effects against aging diseases and has received a lot of attention for this reason. Both quercetin 3-O-β-d-glucuronide and quercetin 3′-O-β-d-glucuronide are human metabolites, which, together with their regioisomers, are required for biological as well as physical chemistry studies. We present here a novel synthetic route based on the sequential and selective protections of the hydroxyl functions of quercetin allowing selective glycosylation, followed by TEMPO-mediated oxidation to the glucuronide. This methodology enabled us to synthesize the five O-β-d-glucosides and four O-β-d-glucuronides of quercetin, including the major human metabolite, quercetin 3-O-β-d-glucuronide.  相似文献   

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