Hydrogenation catalysis kinetics

Weddle, K.S., Aikin, J.D. and Finke, R.G. (1998) Rh(0) nanoclusters in benzene hydrogenation catalysis kinetic and mechanistic evidence that a putative [(C8Hi7)3NCHj] [RhCl4]" ion-pair catalyst is actually a distribution of Cl" and [(CsH,7)3NCH3] stabilized Rh(0) nanoclusters. Journal of the American Chemical Society, 120, 5653-66. 

According to Chen et ah, alkali cation co-catalysis kinetics cannot be distinguished from classic ideas (proton instead of alkali) for the asymmetric hydrogenation of acetophenone with the Noyori-catalyst trans-RuC12[(S)-BINAP]... 

Since improvements achievable with bulky electrodes are limited by the structure of the electrode itself, sintered, porous, Teflon bonded, or phosphate-bonded Ni electrodes have been proposed [386, 391, 399, 400]. A mere increase in surface area is observed without any change in Thfel slope. The same is the case with Ni wiskers in spite of their very large surface area and small particle size [401, 402], A decisive modification of the kinetic pattern is indeed obtained as Raney Ni is used [93, 403] (see Fig. 11). This form of Ni is well known also in the field of hydrogenation catalysis. As an electrocatalyst it was proposed by Justi et al. [404] long ago. Raney Ni is obtained by allowing Ni with a component (usually Al or Zn) which is then... 

K. (2005) Noble metal water gas shift catalysis Kinetics study and reactor design. International Journal of Hydrogen Energy, 30 (11), 1259-1264. 

Mechanism p-Hydrogen Exchange Kinetic S Faster Than Order Elimination General or Specific Base Catalysis Electron Withdrawal atCP Electron release atCa Leaving- Group Isotope Effect or Element Effect... 

Key Words Direct propylene epoxidation. Propylene oxide, Gold, Titanium, Propene, Au/Ti catalysts. Catalysis by gold. Titanium silicalite, TS-1, Gold/TS-1, Hydrogen peroxide, Kinetics, Design of experiments, Deposition-precipitation, Ammonium nitrate, Selective oxidation, Alkene epoxidation, Density functional theory, DFT calculations, QM/MM calculations. 2008 Elsevier B.v. 

In addition, hydrotrope solutions have been involved in reactions concerning solid particles. As examples may be mentioned the template-free synthesis of microtubules [34], important materials in nano-technology, and the more sophisticated role of hydrotropes to concurrently optimize the interfacial tension and the colloidal stabilization of rhodium particles in biphasic liquid-liquid alkene hydrogenation catalysis [35], Finally reaction kinetics has been used as a means to follow the association of hydrotrope molecules in aqueous solutions [36],... 

S.L. Kiperman, Some Problems of Chemical Kinetics in Heterogeneous Hydrogenation Catalysis, in Catalytic Hydrogenation, L. Cerveny (eds.), 1986. 

In fact, when either chloride ion or water is added to the reaction mixture, both the rate and the product composition change markedly. For example, the rate increases by fourteen times and the product composition changes from 9% of the N-coupled diazoamino compound to 79% of the diazoamino compound when the chloride ion concentration is increased from zero to 1.4 x 10" M. The amount of the N-coupled diazoamino product also increased at all three temperatures used in the study as the amount of amine (base) increased. On the basis of the base catalysis and the hydrogen-deuterium kinetic isotope effects and their studies of other diazo coupling reactions, the authors concluded that the N-coupling and the C-coupling reactions both proceed by an S 2 mechanism with the proton transfer from the cr-complex rate-determining. The results are best explained by the mechanism presented in Scheme 3. 

It should be noted, that the examples of nanoparticulate hydrogenation catalysis in ionic liquids presented here do not represent the full list of successful, published applications. Several other groups have recently contributed details on the formation, stabilization and immobilization of nanoparticles in ionic liquids and have described the catalytic activity and reaction kinetics of these systems in different hydrogenation reactions [282]. 

C, 0.356—1.069 m H2/L (2000—6000 fU/bbl) of Hquid feed, and a space velocity (wt feed per wt catalyst) of 1—5 h. Operation of reformers at low pressure, high temperature, and low hydrogen recycle rates favors the kinetics and the thermodynamics for aromatics production and reduces operating costs. However, all three of these factors, which tend to increase coking, increase the deactivation rate of the catalyst therefore, operating conditions are a compromise. More detailed treatment of the catalysis and chemistry of catalytic reforming is available (33—35). Typical reformate compositions are shown in Table 6. 

The role that acid and base catalysts play can be quantitatively studied by kinetic techniques. It is possible to recognize several distinct types of catalysis by acids and bases. The term specie acid catalysis is used when the reaction rate is dependent on the equilibrium for protonation of the reactant. This type of catalysis is independent of the concentration and specific structure of the various proton donors present in solution. Specific acid catalysis is governed by the hydrogen-ion concentration (pH) of the solution. For example, for a series of reactions in an aqueous buffer system, flie rate of flie reaction would be a fimetion of the pH, but not of the concentration or identity of the acidic and basic components of the buffer. The kinetic expression for any such reaction will include a term for hydrogen-ion concentration, [H+]. The term general acid catalysis is used when the nature and concentration of proton donors present in solution affect the reaction rate. The kinetic expression for such a reaction will include a term for each of the potential proton donors that acts as a catalyst. The terms specific base catalysis and general base catalysis apply in the same way to base-catalyzed reactions. 

The first unequivocal evidence for the AE + DE mechanism came in three papers by Zollinger (1955 a-c) dealing with general base catalysis and primary kinetic hydrogen isotope effects in azo coupling reactions of various types. Three classes of reactions were identified i) reactions with no isotope effects (ArH/A D - 1.0) and no general base catalysis, ii) others with large isotope effects (k /k — 6.5) and (practically) linear base catalysis, and iii) intermediate cases with isotope effects of around 3.0 and less-than-linear base catalysis. 

It is important for acid-catalysed reactions to determine whether the reaction is specifically catalysed by hydrogen ions or whether general acid catalysis takes place. Specific acid catalysis has been conclusively demonstrated for the benzidine rearrangement by three different sorts of kinetic experiments. In the first, it has been shown41 by the standard test for general acid catalysis (by measuring the rate of reaction in a buffered solution at constant pH over a range of concentration... 

T.I. Politova, V.A. Sobyanin, and V.D. Belyaev, Ethylene hydrogenation in electrochemical cell with solid proton-conducting electrolyte, Reaction Kinetics and Catalysis Letters 41(2), 321-326 (1990). 

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