Oxidation zeolitic

NO -laden fumes are preheated by effluent from the catalyst vessel in the feed/effluent heat exchanger and then heated by a gas- or oil-fired heater to over 600° F. A controlled quantity of ammonia is injected into the gas stream before it is passed through a metal oxide, zeolite, or promoted zeolite catalyst bed. The NO is reduced to nitrogen and water in the presence or ammonia in accordance with the following exothermic reactions ... 

Catalysts may be metals, oxides, zeolites, sulfides, carbides, organometallic complexes, enzymes, etc. The principal properties of a catalyst are its activity, selectivity, and stability. Chemical promoters may be added to optimize the quality of a catalyst, while structural promoters improve the mechanical properties and stabilize the particles against sintering. As a result, catalysts may be quite complex. Moreover, the state of the catalytic surface often depends on the conditions under which it is used. Spectroscopy, microscopy, diffraction and reaction techniques offer tools to investigate what the active catalyst looks like. 

Finally, we mention here recent progress made in the Bayer-Villiger oxidation. Zeolite Sn-Beta (1.6 wt.% Sn) was found to be an excellent catalyst [25], Thus, the monoterpene dihydrocarvone gives - with Sn-Beta and H202 - exclusively the lactone (Scheme 5.7), whereas m-chloroperbenzoic acid and Ti-Beta/H202 give the epoxide as the main product. 

Application of transmission electron microscopy (TEM) techniques on heterogeneous catalysis covers a wide range of solid catalysts, including supported metal particles, transition metal oxides, zeolites and carbon nanotubes and nanofibers etc. 

Isomerization of olefins or paraffins is an acid-catalyzed reaction that can be carried out with any number of strong acids, including mineral acids, sulfated metal oxides, zeolites and precious metal-modified catalysts [10]. Often the catalyst contains both an acid function and a metal function. The two most prevalent catalysts are Pt/chlorided AI2O3 and Pt-loaded zeolites. The power of zeoHtes in this reaction type is due to their shape selectivity [11] and decreased sensitivity to water or other oxygenates versus AICI3. It is possible to control the selectivity of the reaction to the desired product by using a zeoHte with the proper characteristics [12]. These reactions are covered in more detail in Chapter 14. 

Alkali metal ion-exchanged zeolites and occluded alkali metal oxide zeolites have been investigated extensively and applied as basic catalysts for a variety of organic transformations (1,41,221,222). Zeolites modified with alkaline earth compounds have been applied much less frequently as base catalysts for organic reactions. 

A comparable paradigm of success is still to be established for more complex catalytic materials e.g., finite metal/compound clusters, mixed oxides, zeolites), many of which are highly important technological catalysts and often contain multiple active centers that are required to achieve a series of specific transformations. The local structures of these catalysts and... 

Immobilized nitrile hydratase Mixed metal oxides Zeolites, SAPO Zeolite... 

Current polymeric materials are inadequate to fully meet all requirements for the various different types of membranes (cf. Section 2.2) or to exploit the new opportunities for application of membranes. Mixed-matrix membranes, comprising inorganic materials (e.g., metal oxide, zeolite, metal or carbon particles) embedded in an organic polymer matrix, have been developed to improve the performance by synergistic combinations of the properties of both components. Such improvement is either with respect to separation performance (higher selectivity or permeability) or with respect to membrane stability (mechanical, thermal or chemical). 

De Vos, Sels, and Jacobs illustrate strategies of immobilizing molecular oxidation catalysts on supports. The catalysts include complexes of numerous metals (e.g., V, Cr, Mn, Fe, Co, and Mo), and the supports include oxides, zeolites, organic polymers, and activated carbons. Retention of the catalyt-ically active metal species on the support requires stable bonding of the metal to the support at every step in the catalytic cycle, even as the metal assumes different oxidation states. Examples show that catalysts that are stably anchored and do not leach sometimes outperform their soluble analogs in terms of lifetimes, activities, and selectivities. 

With simple probe molecules, such as H2, information about the number of surface metal atoms is readily obtained by using adsorption measurements. However, even with such simple probe molecules further information about the heterogeneity of a surface may be obtained by performing temperature-programmed desorption measurements. With probe molecules which are chemically more specific (e.g., NH3 and organic amines, H2S and organic sulfides) it may be possible to obtain information about the number and nature of specific types of surface sites, for example, the number and strength of Lewis or Bronsted acid sites on oxides, zeolites or sulfides. 

There have been few Raman investigations of catalyst preparation (of oxides, zeolites, or metals). Such experiments deliver information about molecular structures, and the formation of crystalline phases is detected at earlier stages by Raman spectroscopy than by XRD. Moreover, cells that allow for variable conditions are easily constructed. 

These results indicate that the high activity of the charge-transfer excited state (TP -O ) of the tetrahedral titanium oxide species plays a significant role in the photocatalytic reduction of CO2 with H2O on the titanium oxide/ zeolite catalysts. 

Water, although it is the solvent with respect to which all oxide zeolites are defined, greatly complicates the ion-exchange process because of its ability to dissociate. Yet no other solvent is known, with the possible exception NH3(f), which is as successful for ion exchange. ... 

Surface organometallic chemistry is at a very preliminary stage. From an organo-metallic standpoint, it now seems possible to develop on surfaces of oxides, zeolites, or metals a unique chemistry which leads to expected, and sometimes very... 

The future of Raman spectroscopy in the research and the development of catalysts appears to be extremely promising. The recent revolution in Raman instrumentation has dramatically increased the ability to detect weak Raman signals and to collect the data in very short times. Thus, it is now possible to perform real-time Raman analysis and to study many catal) c systems that give rise to unusually weak Raman signals. The enormous strides in Raman instrumentation now allow for the characterization of a wide range of catalytic materials bulk mixed oxides, supported metal oxides, zeolites, supported metal systems, metal foils, as well as single crystal surfaces. Few Raman studies have been reported for sulfides, nitrides, or carbides, but these catalytic materials also give rise... 

Thermodynamic aspects of ionic reactions on inorganic soil constituents (clays, oxides, zeolites, and minerals) have received considerable attention over the years. These studies allow quantification of interactive phenomena, but fail to provide insight into the dynamics, mechanisms, and facets of great importance for construction of effective models. 

It is common practice in soil science to use kinetic theory of homogeneous reactions as an approximation for reactions occurring in soil-solution systems. The rationale is that the very fine subdivision of the soil particles (clays, minerals, oxides, zeolites, humic acids, etc.) allows the system to appear homogeneous except on a very small scale. 

An important requirement for all homogeneous catalytic processes is that the dissolved catalyst must be separated from the liquid product and recycled to the reactor without significant catalyst loss the need is acute when the metal is as expensive as rhodium. One approach to aid this separation process is to immobilize (anchor) the soluble catalyst on a solid support in order to confine the catalyst to the reactor and overcome the need for a catalyst recycle step. A number of types of solid support have been employed to anchor rhodium catalysts for use in methanol carbon-ylation with liquid- or gas-phase reactants. These were reviewed by Howard et al. in 1993 [8] and include activated carbon, inorganic oxides, zeolites, and a range of polymeric materials. 

Solid-state ion exchange may be carried out in stoichiometric mixtures of salts (or oxides) and zeolites, related to the Al content (in case of aluminosilicates) of the framework. However, it also works with under-stoichiometric mixtures or mixtures containing an excess of the in going cation. In the latter case, the excess may be removed by brief extraction of the solid-state reaction product with water also, salt occlusion may occur during heat treatment [2-3]. Thus, with many important salt(oxide)-zeolite... 

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