Pressure, directed metal oxidation

Fatty alcohols are obtained by direct hydrogenation of fatty acids or by hydrogenation of fatty acid esters. Typically, this is performed over copper catalysts at elevated temperature (170°C-270°C) and pressure (40-300 bar hydrogen) [26], By this route, completely saturated fatty alcohols are produced. In the past, unsaturated fatty alcohols were produced via hydrolysis of whale oil (a natural wax occurring in whale blubber) or by reduction of waxes with sodium (Bouveault-Blanc reduction). Today, they can be obtained by selective hydrogenation at even higher temperatures (250°C-280°C), but lower pressure up to 25 bar over metal oxides (zinc oxide, chromium oxide, iron oxide, or cadmium oxide) or partially deactivated copper chromite catalysts [26],... 

The direct catalytic, oxidation method of ethylene is described in Ref 17, pp 77—87 Explosibility. Liquid ethylene oxide is stable to detonating agents, but the vapor will undergo explosive decomposition. Pure ethylene oxide vapor will decompose partially however, a slight dilution with air or a small increase in initial pressure provides an ideal condition for complete decomposition. Copper or other acetylide-forming metals such as silver, magnesium, and alloys of such metals should not be used to handle or store ethylene oxide because of the danger of the possible presence of acetylene. Acetylides detonate readily and will initiate explosive decomposition of ethylene oxide vapor. In the presence of certain catalysts, liquid ethylene oxide forms a poly-condensate. 

In preparing fine particles of inorganic metal oxides, the hydrothermal method consists of three types of processes hydrothermal synthesis, hydrothermal oxidation, and hydrothermal crystallization. Hydrothermal synthesis is used to synthesize mixed oxides from their component oxides or hydroxides. The particles obtained are small, uniform crystallites of 0.3-200 jim in size and dispersed each other. Pressures, temperatures, and mineralizer concentrations control the size and morphology of the particles. In the hydrothermal oxidation method, fme oxide particles can be prepared from metals, alloys, and intermciallic compounds by oxidation with high temperature and pressure solvent, that is, the starting metals are changed into fine oxide powders directly. For example, the solvothermal oxidation of cerium metal in 2-mcthoxycthanol at 473-523 K yields ultrafine ceria particles (ca 2 nm). 

Already in 1929 it was proposed by Schwab and Pietsch that the catalytic reaction on supported metal catalysts often takes place at the metal-oxide interface. This effect is known as adlineation, however, up to the present there is only little direct experimental evidence. In one example, the oxidation of CO on nanoscale gold, it is presently discussed whether the catalytic action takes place at the particle upport interface. Adlineation is strongly related to the effect of reverse spillover, where the effective pressure of the reactants in a catalytic process is enhanced by adsorption on the oxide material within the so-called collection zone and diffusion to the active metal particle (see Fig. 1.55 and also The Reactivity of Deposited Pd Clusters). The area of the collection zone and thus the reverse spillover are dependent on temperature, on the adsorption and diffusion properties of the reactants on the oxide material, as well as on the cluster density. 

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