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1.
Density functional theory calculations have been carried out to determine the thermodynamic stability of various Ga species in gallium-exchanged ZSM-5, the thermodynamics of H2 adsorption, and the most favorable pathway for H2/D2 exchange. The portion of the zeolite associated with Ga was represented by a cluster containing 7, 21, or 33 atoms. The B3LYP hybrid method was used to account for the effects of electron exchange and correlation. The most likely form of Ga expected in freshly exchanged and calcined ZSM-5 is ZGa(OH)2. H2 reduction of this species is projected to produce ZGa(H)(OH) and ZGa(H)2. While the thermodynamics of H2 desorption from ZGa(H)2 are favorable, the process is projected to be slow because of a high activation barrier. The most favorable pathway for H2/D2 exchange over ZGa(H)2 proceeds via Z(D)(Ga(H)2(D)) as an intermediate. Similar calculations have been carried out for H2/D2 exchange over H-ZSM-5. This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Oxidative or reducing treatments at 873 K of Ga2O3/H-ZSM-5 (Si/Al = 13 or 60) cause a change in H+ concentration as evidenced by IR spectroscopy of OH groups at 3610 cm–1; this change is nicely correlated to the variation ofm-xylene isomerisation rate. 相似文献
3.
Alexander G. Stepanov Mikhail V. Luzgin Vaycheslav N. Romannikov Kirill I. Zamaraev 《Catalysis Letters》1994,24(3-4):271-284
It is shown that octene-1 adsorbed on zeolite H-ZSM-5 at ambient temperature exhibits carbenium ion properties. Namely: (1) According to2H NMR, the proton of the acidic Al-OH-Si group of the zeolite is transferred into the CH2= group of the octene-1 molecule. (2) According to13C NMR the13C label inserted into the terminal CH2= group of the octene-1 molecule is scrambled over its hydrocarbon skeleton. Thermodynamic and kinetic parameters for carbon scrambling are measured within the temperature range 290–343 K. The zeolite framework is shown to favour the formation of the linear rather than branched carbeniumion. 相似文献
4.
Zeolites ZnY with various overall zinc contents were prepared from mixtures of zeolite NH4Y and crystalline zinc chloride by solid-state ion exchange. The obtained materials were investigated with carbon monoxide, xenon, and nitrogen adsorption as well as with 129Xe NMR and XRF spectroscopy. From the results of these measurements, the zinc cation distributions between the different types of cages of the faujasite framework as well as between the crystallographic positions SIII and SII within the large voids (supercages) were quantitatively determined. The concentrations of zinc cations in the supercages of the presently prepared zeolites are considerably higher than in materials obtained from NaY by conventional wet ion exchange using aqueous zinc salt solutions. Experimental evidence is provided for salt inclusion under certain conditions of preparation. This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
Shape-selective properties of octadecyltrichlorosilane-treated H-ZSM-5, abbreviated as H-ZSM-5-C18, have been observed in the hydrolysis of esters having some rings and lactones in toluene-water solvent system. The shape-selectivity for the reaction has been evaluated by the ratio
of the relative rate constants in comparison with the rate constant of methyl acetate. The selectivity became higher with increase in bulkiness of the substrate. Substrates having the minimum diameter larger than 6.5 Å, significantly larger in size than the pore openings of ZSM-5, could not react in this system. 相似文献
6.
The acid-base properties of -Al2O3 and alumina-supported B2O3, Ga2O3 and In2O3 have been determined by microcalorimetry of ammonia and sulfur dioxide adsorption. From the adsorption of NH3, it was found that the addition of B2O3 on alumina leads to an increase of the number of acid sites, while Ga2O3 and In2O3 additives caused a decrease in the acidity of alumina. Using SO2 as a probe molecule to study the basicity, the number of surface basic sites on alumina was found to be strongly decreased by the addition of boron oxide, while it was only slightly affected by the addition of gallium oxide and decreased by the addition of indium oxide. The differential heats of adsorption are discussed as a function of the coverage by the probe molecules. The electronic properties of the oxides are examined in order to explain the acid-base properties of the supported oxides. 相似文献
7.
A simple and mild wet-chemical approach was developed for the synthesis of one-dimensional (1D) In(OH)3 nanostructures. By calcining the 1D In(OH)3 nanocrystals in air at 250 °C, 1D In2O3 nanocrystals with the same morphology were obtained. TEM results show that both 1D In(OH)3 and 1D In2O3 are composed of uniform nanotube bundles. SAED and XRD patterns indicate that 1D In(OH)3 and 1D In2O3 nanostructures are single crystalline and possess the same bcc crystalline structure as the bulk In(OH)3 and In2O3, respectively. TGA/DTA analyses of the precursor In(OH)3 and the final product In2O3 confirm the existence of CTAB molecules, and its content is about 6%. The optical absorption band edge of 1D In2O3 exhibits an evident blueshift with respect to that of the commercial In2O3 powders, which is caused by the increasing energy gap resulted from decreasing the grain size. A relatively strong and broad
purple-blue emission band centered at 440 nm was observed in the room temperature PL spectrum of 1D In2O3 nanotube bundles, which was mainly attributed to the existence of the oxygen vacancies. 相似文献
8.
Three different Ir catalysts supported on H-ZSM-5 were prepared and tested for the selective catalytic reduction of NO under net oxidizing conditions using propene as reducing agent. The preparation of highly active Ir catalysts and the elaboration of a procedure for enhancing activity by on stream conditioning was targeted. Structural changes of the catalyst during conditioning were investigated by means of XRD, TEM and activity measurements. Under reaction conditions Ir was present as Ir0 and IrO2. The presence of Ir0 was essential for high DeNOx activity. The ratio of Ir0/Ir4+ was found to depend on the size of Ir-containing crystallites. Larger crystallites contained predominantly Ir0. Crystallite size and oxidation state of Ir have been identified to be crucial for the NO reduction behaviour of Ir/H-ZSM-5. 相似文献
9.
Chang-Hoon HongAlfian Noviyanto Ji Heon RyuJaemyung Kim Dang-Hyok Yoon 《Ceramics International》2012,38(1):301-310
Li4Ti5O12 was synthesized by a solid-state reaction between Li2CO3 and TiO2 for applications in lithium ion batteries. The effects of the TiO2 phase and mechanochemical activation on the Li4Ti5O12 particles as well as the corresponding electrochemical properties were investigated. Rutile TiO2 was more desirable in acquiring high purity Li4Ti5O12 than anatase due to the anatase to rutile phase transformation, which was found to be more rigid in the solid-state reaction than the intact rutile phase. Mechanochemical activation of the starting materials was effective in decreasing the reaction temperature and particle size as well as increasing the Li4Ti5O12 content. The specific capacity depended significantly on the Li4Ti5O12 content, whereas the rate capability improved with decreasing particle size due to the enhanced contact area and reduced diffusion path. Overall, a 200 nm-sized Li4Ti5O12 powder with a specific capacity of 165 mAh/g could be synthesized by optimizing the milling method and starting materials. 相似文献
10.
Nd2O3 was synthesized by calcining Nd2(C2O4)3·10H2O in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray powder diffraction, and scanning electron microscopy. The results showed that high-crystallized Nd2O3 with hexagonal structure was obtained when the precursor was calcined at 1223 K in air for 2 h. The crystallite size of Nd2O3 synthesized at 1223 K for 2 h was about 48 nm. The thermal decomposition of the precursor in air experienced three steps, which are first, the dehydration of 10 crystal water molecules; then, the decomposition of Nd2(C2O4)3 into Nd2O2CO3; and last, the decomposition of Nd2O2CO3 into hexagonal Nd2O3. Based on the KAS equation, the values of the activation energies associated with the thermal decomposition of Nd2(C2O4)3?10H2O were determined. 相似文献
11.
Yu-Jen Hsiao Chung-Hsin Lu Liang-Wen Ji Teen-Hang Meen Yan-Lung Chen Hsiao-Ping Chi 《Nanoscale research letters》2014,9(1):32
We demonstrate that heterojunction photovoltaics based on hydrothermal-grown In2S3 on p-Si were fabricated and characterized in the paper. An n-type In2S3 nanoflake-based film with unique ''cross-linked network’ structure was grown on the prepared p-type silicon substrate. It was found that the bandgap energy of such In2S3 film is 2.5 eV by optical absorption spectra. This unique nanostructure significantly enhances the surface area of the In2S3 films, leading to obtain lower reflectance spectra as the thickness of In2S3 film was increased. Additionally, such a nanostructure resulted in a closer spacing between the cross-linked In2S3 nanostructures and formed more direct conduction paths for electron transportation. Thus, the short-circuit current density (Jsc) was effectively improved by using a suitable thickness of In2S3. The power conversion efficiency (PCE, η) of the AZO/In2S3/textured p-Si heterojunction solar cell with 100-nm-thick In2S3 film was 2.39%. 相似文献
12.
In/HZSM-5/In2O3 catalyst that contained two different kinds of In induced by the impregnating and the physical mixing method respectively has shown remarkable activity for the CH4-SCR of NO
x
comparing with In/HZSM-5. The addition of In2O3 into In/HZSM-5 improved the NO conversion through enhancing the adsorption of NO
x
over In/HZSM-5. 相似文献
13.
A.A Attia 《Electrochimica acta》2002,47(8):1241-1248
The use of the Nb-Nb2O5 electrode as an oxide ion indicator electrode in potentiometric titrations between acids and bases in fused salts was investigated. Two oxide ion acceptors (acids), NaPO3 and Na4P2O7 were titrated with oxide ion donors (bases) in fused KNO3. The reaction was carried out at 625 K and the bases used in these titrations are K2CO3 and Na2O2. The electrode was found to serve as an excellent indicator for acid base potentiometric titrations in fused salts. It serves also as an oxide ion indicator for the titration of mixtures of acids in which chemical transformations are taking place during the course of titration. The experimental results were discussed in terms of the potential arrests and potential shifts upon the addition of the oxide ion donor to the acid. 相似文献
14.
Using two-dimensionalJ-resolved and CP/MAS13C NMR, the pathway for the transfer of the13C label from the CH2 group of isobutyl alcohol into the hydrocarbon skeleton of butene oligomers has been elucidated in the course of isobutyl alcohol dehydration inside H-ZSM-5 zeolite. First, the label is transferred selectively into the CH2 group of the isobutyl silyl ether reaction intermediate (IBSE), and then into the CH and CH3 groups of the isobutyl fragment (-CH2CH(CH3)2) of IBSE and/or butene oligomers. Finally, it is scrambled over the carbon skeleton of the oligomers. The obtained data suggest that isobutyl carbenium ion is formed as a reaction intermediate or transition state during the transformation of isobutyl silyl ether into butene oligomers. 相似文献
15.
Maniyazagan Munisamy Hyeon-Woo Yang Naveenkumar Perumal Nayoung Kang Woo Seung Kang Sun-Jae Kim 《International journal of molecular sciences》2022,23(8)
The most pressing concerns in environmental remediation are the design and development of catalysts with benign, low-cost, and efficient photocatalytic activity. The present study effectively generated a flower-like indium oxide (In2O3-MF) catalyst employing a convenient MOF-based solvothermal self-assembly technique. The In2O3-MF photocatalyst exhibits a flower-like structure, according to morphology and structural analysis. The enhanced photocatalytic activity of the In2O3-MF catalyst for 4-nitrophenol (4-NP) and methylene blue (MB) is likely due to its unique 3D structure, which includes a large surface area (486.95 m2 g−1), a wide spectrum response, and the prevention of electron–hole recombination compared to In2O3-MR (indium oxide-micro rod) and In2O3-MD (indium oxide-micro disc). In the presence of NaBH4 and visible light, the catalytic performances of the In2O3-MF, In2O3-MR, and In2O3-MD catalysts for the reduction of 4-NP and MB degradation were investigated. Using In2O3-MF as a catalyst, we were able to achieve a 99.32 percent reduction of 4-NP in 20 min and 99.2 percent degradation of MB in 3 min. Interestingly, the conversion rates of catalytic 4-NP and MB were still larger than 95 and 96 percent after five consecutive cycles of catalytic tests, suggesting that the In2O3-MF catalyst has outstanding catalytic performance and a high reutilization rate. 相似文献
16.
A Li4Ti5O12/carbon/carbon nano-tubes (Li4Ti5O12/C/CNTs) composite was synthesized by using a solid-state method. For comparison, a Li4Ti5O12/carbon (Li4Ti5O12/C) composite and a pristine Li4Ti5O12 were also synthesized in the present study. The microstructure and morphology of the prepared samples are characterized by XRD and SEM. Electrochemical properties of the samples are evaluated by using galvanostatic discharge/charge tests and AC impedance spectroscopy. The results reveal that the Li4Ti5O12/C/CNTs composite exhibits the best rate capability and cycling stability among the samples of Li4Ti5O12, Li4Ti5O12/C and Li4Ti5O12/C/CNTs. At the charge-discharge rate of 0.5 C, 5.0 C and 10.0 C, its discharge capacities were 163 mAh/g, 148 mAh/g and 143 mAh/g, respectively. After 100 cycles at 5.0 C, it remained at 146 mAh/g. 相似文献
17.
Silica coating on Gd2O3:Eu particles was obtained by a simple method, e.g. solid-state reaction at room temperature. The urea homogeneous precipitation method was used to synthesize the Gd2O3:Eu cores. Transmission electron microscopy (TEM) shows that the core particles are spherical with submicrometer size which is the soft agglomerates with nanometer crystallites. The TEM morphology of coated particles shows that a thin film is coated on the surface of Gd2O3:Eu cores. Scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS) analysis indicate that the coating of silica can be used to avoid agglomeration of Gd2O3:Eu particles to obtain smaller particles. X-ray photoelectron spectra (XPS) show that silica is coated on the surface of core particles by forming the chemical bond. Photoluminescence (PL) spectra conform that Gd2O3:Eu phosphors remain well-luminescent properties by the silica coating. 相似文献
18.
19.
Jakkidi Krishna Reddy Kannekanti Lalitha Valluri Durga Kumari Machiraju Subrahmanyam 《Catalysis Letters》2008,121(1-2):131-136
Bi-ZSM-5 and Bi2O3/HZSM-5 with varying amounts of (1, 3, and 5 wt.%) of Bi2O3 were prepared by impregnation and solid state dispersion (SSD) methods. These catalysts were characterized by XRD, UV–Vis
DRS, XPS, and BET surface area techniques. Characterization of these catalysts by DRS clearly shows a blue shift of >100 nm
in the absorption band edge of Bi2O3 (band gap shift from 2.75 to 3.5 eV) in the samples prepared by impregnation and a blue shift of 50 nm in the samples prepared
by SSD methods indicating that Bi2O3 is in interaction with the support in impregnated samples. XPS studies are also in favor of this observation. The photocatalytic
activities of these systems were evaluated in the degradation of phenol under UV irradiation. Catalysts prepared by impregnation
method are showing good photocatalytic activity compared to catalysts prepared by SSD method. Based on the characterization
and photodegradation activity of the Bi-ZSM-5 catalysts a structure–activity correlation has been established for the effective
treatment of phenolic wastes. 相似文献
20.
Mikaela Wallin Carl-Johan Karlsson Anders Palmqvist Magnus Skoglundh 《Topics in Catalysis》2004,(1):107-113
The selective catalytic reduction (SCR) of NO
x
over zeolite H-ZSM-5 with ammonia was investigated using in situ FTIR spectroscopy and flow reactor measurements. The adsorption of ammonia and the reaction between NO
x
, O2 and either pre-adsorbed ammonia or transiently supplied ammonia were investigated for either NO or equimolar amounts of NO and NO2. With transient ammonia supply the total NO reduction increased and the selectivity to N2O formation decreased compared to continuous supply. The FTIR experiments revealed that NO
x
reacts with ammonia adsorbed on Brønsted acid sites as NH4
+ ions. These experiments further indicated that adsorbed -NO2
– is formed during the SCR reaction over H-ZSM-5. 相似文献