Palladium reaction kinetics

Palladium metal is not produced in the new reaction and the substitution of a twenty-fold excess of lithium chloride for cupric chloride prevented reaction kinetic data revealed first-order dependences upon both Pd(II) and Cu(II). The distribution of products varied in an unpredictable way with reactant concentrations. The following mechanism was proposed by Henry (X = CP or CH3CO2 )... 

Once the reaction kinetics were determined and the appropriate reaction conditions were set, the analyses of different catalysts was launched. A variety of different heterogeneous catalysts were evaluated for the deprotection of 20 mmol Cbz-glycine (1, R=-H). Catalysts composed of different platinum group metals supported on activated carbon were evaluated as well as palladium supported on alumina. Figure 5 confirms that Pd supported on activated carbon is indeed the catalyst of choice for this type of hydrogenolysis reaction. 

Engel, D. C., Versteeg, G. F., and Van Swaaij, W. P. M. (1995). Reaction Kinetics of Hydrogen and Aqueous Sodium and Potassium Bicarbonate Catalysed by Palladium on Activated Carbon. Chemical Engineering Research and Design, 73(A6), 701-706. 

The following describes results of three, relatively simple chemical reactions involving hydrocarbons on model single crystal metal catalysts that illustrate this general approach, namely, acetylene cyclotrimerization and the hydrogenation of acetylene and ethylene, all catalyzed by palladium. The selected reactions fulfdl the above conditions since they occur in ultrahigh vacuum, while the measured catalytic reaction kinetics on single crystal surfaces mimic those on reahstic supported catalysts. While these are all chemically relatively simple reactions, their apparent simplicity belies rather complex surface chemistry. 

Another important reaction, the Heck reaction catalyzed by palladium salts and complexes, has been studied as well via EXAFS [191]. The authors of the study highlight the importance of correlating structural data with reaction kinetics. Among others the authors showed that in chloride-based ionic liquids the Heck reaction shows poor reactivity until, at some point during the reaction, Pd nanoparticles form, which initiates the reaction. They pointed out that the correlation between the induction period and the nanoparticle formation was strong, and although the metal may not be the active site for the catalysis [91], the presence of Pd(0) is clearly important. 

In the present concept of styrene dehydrogenation implementation of inorganic membranes is not feasible. Application of Knudsen diffusion membranes with a low permselectivity to hydrogen leads to a considerable permeation of ethylbenzene and thus, to lower yields. Microporous and palladium membranes give better results, but worse than a conventional case, because the conversion is limited by reaction kinetics. The ratio of permeation rate to reaction rate is very important in selecting membranes in a membrane reactor process in which equilibrium shift is foreseen. 

The reaction kinetics of the vapor-phase hydrogenation of benzene was studied on ruthenium, rhodium, palladium, and platinum catalysts supported on alumina at temperatures ranging from 25 to 225° and 1 atm. pressure. 

Palladium(II) generally forms isostructures with Pt complexes, but with reaction kinetics that are 10 times faster than those of The greater lability of Pd compounds has led to some... 

Acetoxyindole derivatives have been prepared by the reaction of Af-benzylindole with (diacetoxyiodo)benzene catalysed by palladium acetate. Kinetic experiments suggest that palladation to produce intermediates, such as (60), is rate limiting. " Palladium catalysis, using a Josiphos ligand, has also been used to prepare (V-alkyltacrines, such as (61), by amination of 9-chlorotetrahydro-acridines. " ... 

Figure 16.23 A set of fundamental equations for simulating the reaction progress in the palladium membrane reactor (a) reaction kinetics of ethylhenzene dehydrogenation and (b) the simultaneous differential equations.

Nikov I, Paev K. Palladium on alumina catalyst for glucose oxidation reaction kinetics and catalyst deactivation. Catal. Today 1995f24 41-47. 

The Wacker oxidation of ethene to ethanal is an important industrial process for the oxygenation of a hydrocarbon feedstock. Essentially, the same process may be used to convert 1-alkenes to methyl ketones. The stoichiometry of the process is shown in Figure 23.23. The reaction is catalytic in both palladium and copper the ultimate oxidant is (inexpensive) molecular oxygen. A proposed mechanism is shown in Figure 23.24 the main controversy has been as to whether the attack of water on the coordinated alkene is external or via prior coordination of the water to palladium. Current thinking is that external attack predominates in high concentrations of chloride ion and internal attack when [CT] is low. Different details of mechanisms under the two conditions are supported by different reaction kinetics. 

The equilibrium is more favorable to acetone at higher temperatures. At 325°C 97% conversion is theoretically possible. The kinetics of the reaction has been studied (23). A large number of catalysts have been investigated, including copper, silver, platinum, and palladium metals, as well as sulfides of transition metals of groups 4, 5, and 6 of the periodic table. These catalysts are made with inert supports and are used at 400—600°C (24). Lower temperature reactions (315—482°C) have been successhiUy conducted using 2inc oxide-zirconium oxide combinations (25), and combinations of copper-chromium oxide and of copper and silicon dioxide (26). 

Pt(PPh3) (n = 3, 4) species [54] have been studied with profit for many years they undergo a wide range of addition reactions with attendant loss of phosphine, the kinetically active species probably being Pt(PPh3)2. (The palladium analogues generally behave similarly but are much less studied.)... 

The kinetics of hydrogenation of phenol has already been studied in the liquid phase on Raney nickel (18). Cyclohexanone was proved to be the reaction intermediate, and the kinetics of single reactions were determined, however, by a somewhat simplified method. The description of the kinetics of the hydrogenation of phenol in gaseous phase on a supported palladium catalyst (62) was obtained by simultaneously solving a set of rate equations for the complicated reaction schemes containing six to seven constants. The same catalyst was used for a kinetic study also in the liquid phase (62a). 

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