Hydrogen reduction kinetics

The kinetics of NO reduction by hydrogen and CO was studied by Ayen and Peters. Hydrogen reduction of NO over oxides of copper, zinc, and chromium was studied at 375-425°C. The products formed include... 

The NO reduction over Cu-Ni-Fe alloys has been studied recently by Lamb and Tollefson. They tested copper wires, stainless steel turnings, and metal alloys from 378 to 500°C, at space velocities of 42,000-54,000 hr-1. The kinetics is found to be first order with respect to hydrogen between 400 and 55,000 ppm, and zero order with respect to NO between 600 and 6800 ppm 104). The activation energies of these reactions are found to be 12.0-18.2 kcal/mole. Hydrogen will reduce both oxygen and NO when they are simultaneously present. CO reduction kinetics were also studied over monel metals by Lunt et al. 43) and by Fedor et al. 105). Lunt speculated that the mechanism begins by oxidant attack on the metal surface... 

Table 4.2 lists the same catalytic systems but now grouped in terms of different reaction types (oxidations, hydrogenations, reductions and others). In this table and in subsequent chapters the subscript D denotes and electron donor reactant while the subscript A denotes an electron acceptor reactant. The table also lists the temperature and gas composition range of each investigation in terms of the parameter Pa/Pd which as subsequently shown plays an important role on the observed r vs O global behaviour. Table 4.3 is the same as Table 4.2 but also provides additional information regarding the open-circuit catalytic kinetics, whenever available. Table 4.3 is useful for extracting the promotional rules discussed Chapter 6. 

PdClJ , Rh(III) and Ru(III) act as homogeneous catalysts for reduction of FeClj by molecular hydrogen ° °. The kinetics of all three activation reactions fall into Class I. The Arrhenius parameters are... 

Maintaining the hydrogenation under kinetic control provides limited alcohol formation and avoids over reduction of product C. The performance of a hydrogenator depends on the gas-liquid mass transfer characteristics Kla (8). Possible operating scenarios with their observed impurity profiles are summarized in Table 5. 

Kim et al. (2004) CuO, Cu20 Reduction kinetics, intermediate phases + + + Reductive activation with hydrogen... 

The kinetics of the hydrogen reduction reaction have received a great deal of attention by many investigators. It may be noted, however, that - as in the case of oxygen - the exchange current density (i0)jj is very low on most metals so... 

Rekoske and Barteau (68) used TEOM in scaling-up to higher pressure surface-science results dealing with solid reactions related to redox cycles. These authors investigated reduction kinetics and reaction on titanium oxide (69,70). Recent applications also include the investigation of carbon nanofibers (9) and hydrogen adsorption properties of single-walled carbon nanotubes (71). 

The electroless deposition of metals on a silicon surface in solutions is a corrosion process with a simultaneous metal deposition and oxidation/dissolution of silicon. The rate of deposition is determined by the reduction kinetics of the metals and by the anodic dissolution kinetics of silicon. The deposition process is complicated not only by the coupled anodic and cathodic reactions but also by the fact that as deposition proceeds, the effective surface areas for the anodic and cathodic reactions change. This is due to the gradual coverage of the metal deposits on the surface and may also be due to the formation of a silicon oxide film which passivates the surface. In addition, the metal deposits can act as either a catalyst or an inhibitor for hydrogen evolution. Furthermore, the dissolution of silicon may significantly change the surface morphology. 

Electroless metal deposition at trace levels in the solution is an important factor affecting silicon wafer cleaning. The deposition rate of most metals at trace levels depends mainly on the metal concentration and some may also depend on the interaction with other species as well. For copper the deposition rate at trace levels in HF solutions is different for n and p types. It depends on illumination for p-Si but not for n-Si. It is also different in HF and BHF solutions. In a HF solution the deposition process is controlled by both the supply of minority carriers and the kinetics of cathodic reactions. Thus, a high deposition rate occurs on p-Si only when both and illumination are present. In the BHF solution, the corrosion process is limited by the supply of electrons for p-Si whereas for n-Si it is limited by the dissolution of silicon because the reaction rate is indepaidmt of concentration and illumination. The amount of copper deposition does not correlate with the corrosion current density, which may be attributed to the chemical reactions associated with hydrogen reduction. More information on trace metal deposition can be found in Chapters 2 and 7. 

The complexes of ruthenium of the formula RUCI3L2 Where L is benzimidazole (BzlH), 2-Methylbenzimidazole (2-MebzlH), 2-Ethylbenzimidazole (2-EtbzlH) and 2-propyl benzimidazole (2-PrbzlH) acts as homogeneous catalysts in dimethylformamide in the presence of sodiumborohydride for the reduction of Schiff bases to secondary amines. The reactions were carried out at 30 C and 1 atmosphere of hydrogen pressure. Kinetic studies reveal that the reaction has depencence on [Catalyst] and [Schiff base] in the concentration ranges studied. 

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