A density functional theory study of hydrogen recombination and hydrogen-deuterium exchange on Ga/H-ZSM-5

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.     

Revisiting Ga2O3/H-ZSM-5 propane aromatization catalysts

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.     

Carbenium ion properties of octene-1 adsorbed on zeolite H-ZSM-5

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.     

Zeolite ZnY catalysts prepared by solid-state ion exchange

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.     

Catalysis at the toluene/water interface: shape-selective hydrolysis of esters having some rings and lactones promoted by octadecyl immobilized H-ZSM-5 catalyst

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.     

Acid-Base Properties of Alumina-Supported M2O3 (M=B, Ga, In) Catalysts

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.     

Side-by-Side In(OH)<Subscript>3</Subscript> and In<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanotubes: Synthesis and Optical Properties

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.     

Ir/H-ZSM-5 Catalysts in the Selective Reduction of NOx with Hydrocarbons

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.     

Effects of the starting materials and mechanochemical activation on the properties of solid-state reacted Li4Ti5O12 for lithium ion batteries

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.     

Nanocrystalline Nd2O3: Preparation,phase evolution,and kinetics of thermal decomposition of precursor

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.     

Characterization of photovoltaics with In2S3 nanoflakes/p-Si heterojunction

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%.     

The Remarkable Effect of In2O3 on the Catalytic Activity of In/HZSM-5 for the Reduction of NO with CH4

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.     

The use of the Nb-Nb2O5 as an oxide ion indicator electrode in fused salts

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.     

13C solid state NMR evidence for the existence of isobutyl carbenium ion in the reaction of isobutyl alcohol dehydration in H-ZSM-5 zeolite

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.     

A Flower-like In2O3 Catalyst Derived via Metal–Organic Frameworks for Photocatalytic Applications

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.     

Preparation and electrochemical performance of Li4Ti5O12/carbon/carbon nano-tubes for lithium ion battery

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.     

Coating Gd2O3:Eu phosphors with silica by solid-state reaction at room temperature

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.     

Photocatalytic Study of Bi-ZSM-5 and Bi2O3/HZSM-5 for the Treatment of Phenolic Wastes

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.     

Selective Catalytic Reduction of NOx over H-ZSM-5 Under Lean Conditions Using Transient NH3 Supply

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.