Partial pressure, directed metal oxidation

Catalyst deactivation includes (among other reactions) the formation of inactive Rh species, ligand decomposition, or P-C cleavage by direct oxidative insertion of the rhodium metal for formation of PDSPP (propyldi[w-sulfophenyl phosphine) acting as strong electron donor reducing the amount of active Rh catalyst. It turned out to be beneficial to control the Pni/Rh ratio and the CO partial pressure very carefully. 

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. 

For the deposition of a stoichiometric oxide film by reactive evaporation, a relatively high 02 partial pressure and a slow metal-atom condensation rate are required, so that completely oxidized metal-oxide films can be formed. The partial pressure of the reactive gas component is usually few 10 4 mbar. The significant technology of reactive evaporation [250] is applied in all cases where direct evaporation of a chemical compound is not possible because of thermal dissociation or too low a vapour pressure. In practice, oxide films are usually produced using sub-oxides or metallic starting materials. However, basically it is also possible to produce sulphides and nitrides or other compounds in this manner. 

Figure 7. Schematic of transport processes through an oxide layer growing on a metal. Two limiting cases may be distinguished. First, metal ions and electrons may migrate from the metal toward the oxide gas interface and second, oxygen ions may migrate toward the metal-oxide interface with electrons migrating in the opposite direction. In any volume element of the oxide, electrical neutrality is required. The chemical potential of oxygen is fixed at both the metalr-oxide and-the oxide-gas interface. The former is fixed by the dissociation pressure of the oxide, po/, and the latter by the ambient oxygen partial presure, po"-...

---