Transition Metal Oxides And Oxoions

Most industrially desirable oxidation processes target products of partial, not total oxidation. Well-investigated examples are the oxidation of propane or propene to acrolein, butane to maleic acid anhydride, benzene to phenol, or the ammoxidation of propene to acrylonitrile. The mechanism of many reactions of this type is adequately described in terms of the Mars and van Krevelen model31 A molecule is chemisorbed at the surface of the oxide and reacts with one or more oxygen ions, lowering...

Chemical Anchoring And Deanchoring

For metal atoms the state of lowest Gibbs Free Energy is achieved when they are organized in a macroscopic polyhedron. High dispersion on a support requires strong chemical interaction between metal and support, conventionally called chemical anchoring. The formation of solid particles either from the vapor or from an adsorbed precursor is dominated by two kinetic processes The interplay of these two basic rates determines the size of the resulting particles. For instance, the reason that snow...

Thermodynamic and Kinetic Properties ofWOx Reactions

Based on the standard Gibbs free energy of the various oxides, three triple points can be calculated WO2.72, WO2.9, WO2 at about 600 C, WO29, WO3, WO2 at about 270 C, and WO2, WO2.72, W at 1480 C. Using this data, a phase diagram can be constructed. The stability of the various oxides is shown in Fig. 8.2 with respect to the partial pressures of H2O and H2, and temperature. Because all of these compositions are equilibrium compositions, any of them can be produced simply by annealing W or WO3...

Dendrimer Templated Heterogeneous Catalysts

Silica supported Pt catalysts have been examined in the most depth to identify appropriate activation conditions. The first study with these materials involved catalysts prepared from G5-OH(Pt50) and G5-OH(Pt100), calcined under O2 at 300 C for four hours and reduced at 300 C for two hours.53 The resulting catalysts are active for both oxidation and hydrogenation reactions. The turnover requencies (TOFs) for catalytic CO oxidation (see Fig. 7.4) and toluene hydrogenation (at 60 C) by the Pt100...

Self Driven Methods for Movement

Surface Energy Driven Phenomena. Camphor boats at the water-air interface were one of the first well-studied systems that move autonomously.5 The motion of a camphor boat is accredited to the dissolution of camphor which lowers the interfacial tension of the surrounding water and moves the object until it is completely dissolved. Interfacial tension gradients are not exclusive to camphor boats in water. Another system where interfacial tension gradients are responsible for the...

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1 Trimethylpentane. ' Dimethylhexane. 1 Trimethylpentane. ' Dimethylhexane. The 1-butene conversion and product distribution obtained at 25 C after 1 h of alkylation reaction of isobutane on JML-150 and Beta catalysts are summarized in Table 6.1. The conversion 97 with JML- o catalyst is higher than that 86 with zeolite Beta. The primary products with the above catalysts are C8 compounds 59.9 with JML-150 and 62 with Beta . The C8 products mainly consist of trimethylpentanes TMPs , 58.7 for...

Uv Absorption Of Zro2

Vis Doped Ceo2

Surface OH groups Scheme 11.1 .30 IR peak positions of different hydroxyl groups for CeO2 sample are also given in Scheme 11.1. After passing hydrogen and then water at 873 K, the sample was evacuated and the IR spectrum was measured. The intensity of the OH groups on different supports increased in the order Al2O3 lt CeO2-ZrO2 Al2O3 lt NiO 20 -Al2O3 20 -CeO2 6 -ZrO2 54 . Significant amount of surface OH groups were present under reaction conditions. In addition to...

Oxidation and Reduction of Tungsten and Tungsten Oxides

The chemistry of tungsten and its oxides is well understood for a few compounds, but due to the richness and complexity of the tungsten-oxygen system, this knowledge is far from comprehensive. The complexity of the tungsten-oxygen system is shown in tree representation of the various classes of oxides in Fig. 8.1. In most of these oxides, tungsten is predominately in the W 6 oxidation state, with 6 oxygen atoms FIGURE 8.1. A summary of the tungsten-oxygen system. From Lassner and Schubert....

Supported Metal Clusters

A crucial invention was made in 1947 by V. Haensel and his associates at Universal Oil Products. They developed a catalyst for the conversion of predominantly straight chain paraffinic hydrocarbons to high octane gasoline.5 Their catalyst converted 90 of a low octane gasoline into a product with an octane rating above 80 and had an astonishingly long life. The support was alumina presumably this was the first bifunctional catalyst, exposing both platinum atoms and acid sites. It was soon found...

Tungsten Oxide as a Catalyst

Because of their electronic properties, particularly their visible-ultraviolet band gap, tungsten oxides have been the focus of a number of catalysis studies. Kohler and Gopel examined the electrocatalytic properties of WO2 72 using spectroscopic surface analytical techniques.43 This method allowed them a detailed account of the chemical states present at the surface of WO2 72 during aqueous reductions. They found that OH-ions adsorb to the surface of the material and donate their electron to...

Monoatomic Platinum In Zeolites

Monoatomic Platin

The extreme case of an ultrananoparticle consists of one single atom. Such mono-atomic Pt sites have been realized in Pt H-zeolites that are prepared at low temperature. They are identified by their unique selectivity in catalyzing the H D exchange between cyclopentane and D2. Numerous data in the literature show that over conventional Pt FIGURE 9.4. Distribution patterns of deuteron cyclopentanes Multiple exchange after H D exchange over conventional Pt catalysts with Ptn particles. Abscissa...

Electro Optical Properties and Quantum Confinement

A number of unique properties result from these characteristics. Some of the more exciting effects involve the nanorods' electrical and optical properties. Park's group noticed that little research had been done on the photoluminescence of nanostructured tungsten oxides.24 They found that the strongest peaks occur at slightly different wavelengths for different nanorod lengths, with shorter nanorods emitting at shorter wavelengths. These photoluminescence spectra are shown in Fig. 8.8. The...

Introduction

In recent decades, direct alcohol fuel cells DAFCs have been extensively studied and considered as possible power sources for portable electronic devices and vehicles in the near future.1 The application of methanol is limited due to its high volatility and toxicity,2'3 although it is relatively easily oxidized to CO2 and protons. So other short chain organic chemicals especially ethanol, ethylene glycol, propanol, and dimethyl a Graduate School of the Chinese Academy of Sciences, Beijing...

Crystal Structure And Growth

Though the synthetic routes vary greatly among these three groups, they do all agree on the crystal structure and growth direction of the nanorods. All three identify their nanorods as WO2.72, citing X-ray diffraction XRD data that confirms the crystals' monoclinic dimensions in agreement with the literature.10'12'24 Furthermore, Park compares the intensities of the 010 and 014 peaks to bulk WO272. Because the intensity of the peak resulting from 010 in the nanorods has increased by 2.25 times...

Ir Spectroscopy No3-

TGA and DTA curves of the Ag SiO2 sample prepared by two-step method. 6.2.2.2. Characterization. IR spectra of the samples were recorded on Nicolit AVATAR360 spectrometer. The TEM images were obtained on Hitachi H-8100IV electron microscope. TGA and DTA analyses were carried out in Du pont 9900 Thermal Analysis System. X-ray diffraction XRD measurement was conducted on a Siemens D5005 diffractometer using Cu Ka radiation X 1.54 A . Thermogravimetric analysis TGA and differential...

Ethyne Hydrochlorination

In the early 1980s one of the routes to the synthesis of vinyl chloride was based on ethyne hydrochlorination using mercuric chloride supported on carbon as a catalyst. This catalyst suffers from deactivation due to sublimation of the active component and so a replacement catalyst that was more stable was an important research goal. Based on a detailed study by Shinoda21 it was observed that a range of metal chlorides supported on carbon could give a spectrum of activities for this reaction...