Thermal decomposition, metallic surfaces

The reaction is carried out over a supported metallic silver catalyst at 250—300°C and 1—2 MPa (10—20 bar). A few parts per million (ppm) of 1,2-dichloroethane are added to the ethylene to inhibit further oxidation to carbon dioxide and water. This results ia chlorine generation, which deactivates the surface of the catalyst. Chem Systems of the United States has developed a process that produces ethylene glycol monoacetate as an iatermediate, which on thermal decomposition yields ethylene oxide [75-21-8]. 

Vacuum Deposition-also vapor deposition or gas plating the deposition of metal coatings by means of precipitation (sometimes in vacuum) of metal vapor onto a treated surface. The vapor may be produced by thermal decomposition, cathode sputtering or evaporation of the molten metal in air or an inert gas. 

The segregation process of graphite on the surface of a metal particle is similar to that proposed by Ober-lin and Endo[35] for carbon fibers prepared by thermal decomposition of hydrocarbons. Flowever, the... 

Fibers of titanium diboride can be prepared by reaction (a) at 400°C in an electrical discharge. Adherent layers of certain metal borides on metal substrate surfaces are obtained by thermal decomposition of metal (Mo, W, Nb, Ta) halides and BBr3 on a metallic substrate using a solar furnace or induction heating ... 

Two different methods were used to produce Iron oxide (Fe203) particles on Grafoll. One method was a simple Impregnation-calcination based on the method of Bartholomew and Boudart (20). The exact method used 1s described elsewhere (27). The second method used was a two step process. First, metallic iron particles were produced on the Grafoll surface via the thermal decomposition of Iron pentacarbonyl. This process Is also described in detail elsewhere (25). Next, the particles were exposed to air at room atmosphere and thus partially oxidized to 2 3 Following the production of Iron oxide particles (by... 

Zinc oxide is made either by the oxidation of the metal in oxygen (the indirect, IP, or French process), by the direct decomposition of zinc ores in air (the direct or American process) or by the thermal decomposition of zinc salts (TD zinc oxide). IP zinc oxides differ from TD zinc oxides in that their surfaces do not contain absorbed water. Also, whereas TD zinc oxide reacts with plain eugenol, IP zinc oxide hardly reacts unless activated by an acetic add or zinc acetate accelerator (Table 9.2). 

Analysis of thermal decomposition of molecules on hot surfaces of solids is of considerable interest not only for investigation of mechanisms of heterogeneous decomposition of molecules into fragments which interact actively with solid surfaces. It is of importance also for clarifying the role of the chemical nature of a solid in this process. Furthermore, pyrolysis of molecules on hot filaments made of noble metals, tungsten, tantalum, etc., is a convenient experimental method for producing active particles. Note that it allows continuous adjustment of the intensity of the molecular flux by varying the temperature of the filament [8]. 

For technical purposes (as well as in the laboratory) RuOz and Ru based thin film electrodes are prepared by thermal decomposition techniques. Chlorides or other salts of the respective metals are dissolved in an aqueous or alcoholic solution, painted onto a valve metal substrate, dried and fired in the presence of air or oxygen. In order to achieve reasonable thicknesses the procedure has to be applied repetitively with a final firing for usually 1 hour at temperatures of around 450°C. A survey of the various processes can be found in Trasatti s book [44], For such thermal decomposition processes it is dangerous to assume that the bulk composition of the final sample is the same as the composition of the starting products. This is especially true for the surface composition. The knowledge of these parameters, however, is of vital importance for a better understanding of the electrochemical performance including stability of the electrode material. 

Metallic powders are made several different ways. They can be prepared by reducing salts in a stream of a reducing gas, such as hydrogen chlorides of metals are commonly used but oxides are used too. Thermal decomposition in a vacuum of metal carbonyls or metal salts of organic acids, such as formates, produces metal powders. Surface areas of such powders are around 1.5 m2/g. Powders can also be made from electrolytic reduction of salts in organic solvents and by atomization of the metal. 

The flexibility in composition of LDHs has led to an increase in interest in these materials. As a result of their relative ease of synthesis, LDHs represent an inexpensive, versatile and potentially recyclable source of a variety of catalyst supports, catalyst precursors or actual catalysts. In particular, mixed metal oxides obtained by controlled thermal decomposition of LDHs have large speciflc surface areas (100-300 m /g), basic properties, a homogeneous and thermally stable dispersion of the metal ion components, synergetic effects between the elements, and the possibility of structure reconstruction under mild conditions. In this section, attention is focused on recently reported catalytic applications in some flelds of high industrial and scientific relevance (including organic chemistry, environmental catalysis and natural gas conversion). 

Activation by Thermal Decomposition of Metallic Oxides. The surface of alumina, AI2O3, may be activated by employing laser or ultraviolet irradiation to decompose AI2O3 (68). Decomposition of AI2O3 results in the generation of aluminum particles that are catalytic for electroless deposition of Cu (the first reaction probably is displacement deposition). 

Subsequent thermal decomposition under vacuum or an inert atmosphere gives complex surface reactions and Ru(II) dicarbonyl species and ruthenium metal particles sized 1-1.5 nm form [92]. 

Early studies of the interaction of lr4(CO)i2 with a silica surface indicate that physisorption of the cluster takes place. Although the cluster can sublime during thermal treatments after impregnation [198], the loss of metal carbonyl can be avoided by mild thermal treatments that produce a redispersion of the physisorbed lr4(CO)i2 onto the silica surface [199]. An XPS and FTIR study of the evolution of physisorbed lr4(CO)i2 under different conditions pointed to the formation of metallic particles by mild thermal decomposition under Ar or H2, with the particle size increasing with increasing temperature [200]. 

For a long time, conventional alkaline electrolyzers used Ni as an anode. This metal is relatively inexpensive and a satisfactory electrocatalyst for O2 evolution. With the advent of DSA (a Trade Name for dimensionally stable anodes) in the chlor-alkali industry [41, 42[, it became clear that thermal oxides deposited on Ni were much better electrocatalysts than Ni itself with reduction in overpotential and increased stability. This led to the development of activated anodes. In general, Ni is a support for alkaline solutions and Ti for acidic solutions. The latter, however, poses problems of passivation at the Ti/overlayer interface that can reduce the stability of these anodes [43[. On the other hand, in acid electrolysis, the catalyst is directly pressed against the membrane, which eliminates the problem of support passivation. In addition to improving stability and activity, the way in which dry oxides are prepared (particularly thermal decomposition) develops especially large surface areas that contribute to the optimization of their performance. 

Thermal decomposition of metal acetates in the presence of PVP was proposed by Bradley et al. (30), where the preparative procedure of Esumi et al. (31) was modified. Thus, heating of palladium and copper acetates in a solvent with a high boiling point (ethoxyethanol) provides PVP-stabilized Pd/Cu bimetallic nanoparticles. In this method, not only thermal decomposition but also reduction by ethoxyethanol could be involved. However, the Bradley method can provide Cu/Pd bimetallic nanoparticles that contain less than 50 mol% of Cu, while our method mentioned earlier can provide fine particles with 80 mol% of Cu. In Esumi s original procedure, methyl iso-butyl ketone (MIBK) was used as a solvent without a stabilizer. In his method, Cu" was not completely reduced to Cu°, but Cu20 was involved in the bimetallic nanoparticles. Probably, thanks to Cu1 species in the surface of the particles, no stabilizer is necessary for the stable dispersion. 

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