Olefins hydrogenation kinetics

The catalytic system studied by Rennard and Kokes was in fact very complex. It can be expected that the satisfactory prolongation of the reaction should, however, result in a deviation from the formulated kinetics. Unfortunately no investigation comparable to that of Scholten and Kon-valinka has been done in the case of olefin hydrogenation. Such a study of the catalytic activity of the pure /3-phase of palladium hydride in comparison with the a- or (a + /3)-phases would supplement our knowledge concerning catalytic hydrogenation on palladium. 

Kinetic analyses and deuterium-labeling experiments have demonstrated that, remarkably, the reductive elimination of TEA and the formation of intermediate C is the rate-determining step in the (de)hydrogenation cycle. Accordingly, hydrogenation of the acceptor appears to be slower than dehydrogenation of the alkane substrate. This contrasts with the fact that catalytic olefin hydrogenation is well-established in transition-metal-mediated chemistry [10]. 

In this autocatalytic mechanism the olefin hydrogenation step is considered faster than the nucleation and growth steps. When the olefin hydrogenation is a rapid process, the equations can be deduced in terms of the two constants, ki and lc2, the values of which can be obtained from kinetic Equation 15.1 ... 

The initial limitations of the book are still largely present in the third edition. First the book applies primarily to clathrate hydrates of components in natural gases. Although other hydrate formers (such as olefins, hydrogen, and components larger than 9 A) are largely excluded, the principles of crystal structure, thermodynamics, and kinetics in Chapters 2 through 5 will still apply. 

The formation of halohydrins can be promoted by peroxidase catalysts.465 Recently 466 it has been shown that photocatalysis reactions of hydrogen peroxide decomposition in the presence of titanium tetrachloride can produce halohydrins. The workers believe that titanium(IV) peroxide complexes are formed in situ, which act as the photocatalysts for hydrogen peroxide degradation and for the synthesis of the chlorohydrins from the olefins. The kinetics of chlorohydrin formation were studied, along with oxygen formation. The quantum yield was found to be dependent upon the olefin concentration. The mechanism is believed to involve short-lived di- or poly-meric titanium(IV) complexes. 

Experimental results are described accurately without the need for multiple chain growth sites, secondary hydrogenation functions, or a-olefin readsorption kinetics that depend on chain size. The model also predicts... 

The opposing reactant contactor mode applies to both equilibrium and irreversible reactions, if the reaction is sufficiently fast compared to transport resistance (diffusion rate of reactants in the membrane). This concept has been demonstrated experimentally for reactions requiring strict stoichiometric feeds, such as the Claus reaction, or for kinetically fast, strongly exothermic heterogeneous reactions, such as partial oxidations. Triphasic (gas/liquid/solid) reactions, which are limited by the diffusion of the volatile reactant (e.g., olefin hydrogenation), can also be improved by using this concept. 

Beck and Gerischer (34) used also the potentiometric method to study the kinetics of reduction of various simple-chain and cyclic olefins. Hydrogenation on a vibrating platinized platinum electrode was zero order in alkene and independent of pH in the region 2-8. In the presence of halide ions, specific catalyst poisoning caused decline of the reduction rate. 

The olefin hydrogenation by the lr(0) NPs in ILs follows the classical monomo-lecular surface reaction mechanism v= fecK[S]/l -i- K[Sj. The reaction rate is a mass controlled process under hydrogen pressure <4 atm. The catalytic kinetic constant... 

Substrate limitations have been documented and quantitatively described ( U, 2, 17 ). Dooley et al. (11) present an excellent description of modeling a reaction in macroreticular resin under conditions where diffusion coefficients are not constant. Their study was complicated by the fact that not all the intrinsic variables could be measured independently several intrinsic parameters were found by fitting the substrate transport with reaction model to the experimental data. Roucls and Ekerdt (16) studied olefin hydrogenation in a gel-form resin. They were able to measure the intrinsic kinetic parameters and the diffusion coefficient independently and demonstrate that the substrate transport with reaction model presented earlier is applicable to polymer-immobilized catalysts. Finally, Marconi and Ford (17) employed the same formalism discussed here to an immobilized phase transfer catalyst. The reaction was first-order and their study presents a very readable application of the principles as well as presents techniques for interpreting substrate limitations in trlphase systems. 

Olefin polymerization kinetics are considered and discussed in many reviews [ 1-6]. In this section, the influence of the main parameters such as the concentrations of catalysts and cocatalysts and time of polymerization on polymerization rate, and the main reactions in the olefin polymerization process will be briefly reviewed. We also consider the problems of deviation from the linear law of polymerization rate with changing monomer concentration, the effect of hydrogen in the ethene and propene polymerizations, as well as the nature of the comonomer effect, which are under discussion in the literature and the natures of which are not yet completely clear. 

Kinetics of the olefin hydrogenation reaction were investigated most accurately in the case of cyclohexene and styrene with the application of Wilkinson s catalyst [RhCl(PPh3)3]. 2"-"" ... 

Halpern s proposed mechanism (13.28) is similar in nature. Although his main steps are analogous to the those in the mechanism proposed by Wilkinson, Petit, and de Croon, the kinetic equations for the olefin hydrogenation reaction are considerably different for the latter authors ... 

In the case of dejin hydrogenation the oxidative addition of hydrogen happens directly to the Rh-alkyl complexes n-II or iso-II. Hydrogen transfer and reductive ehmination results in the same saturated alkane product from both regioisomers of the catalyst. Thus, olefin hydrogenation is a favored side reaction for all catalyst complexes that favor the kinetics of oxidative hydrogen addition over CO association and insertion. Olefin hydrogenation is, for example, much more relevant for Co hydroformylation catalysts compared to their Rh counterparts. 

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