Catalytic cycle representation

Fig. 18. Schematic representation of the catalytic cycle for ammoxidation of propylene and related reactions. and M2 represent the two metals in a...

Figure 9.6. Schematic representation of the catalytic cycle for the hydrodesulfurization of a sulfur-containing hydrocarbon (ethane thiol) by a sulfur vacancy on M0S2 The C2H5SH molecule adsorbs with its sulfur atom towards...

Figure 8.1 Representation of proposed catalytic cycle for reaction to produce CsHgO (Chong and Sharpless, 1977)...

Figure 1.1 Schematic representation of a well known catalytic reaction, the oxidation of carbon monoxide on noble metal catalysts CO + Vi 02 —> C02. The catalytic cycle begins with the associative adsorption of CO and the dissociative adsorption of 02 on the surface. As adsorption is always exothermic, the potential energy decreases. Next CO and O combine to form an adsorbed C02 molecule, which represents the rate-determining step in the catalytic sequence. The adsorbed C02 molecule desorbs almost instantaneously, thereby liberating adsorption sites that are available for the following reaction cycle. This regeneration of sites distinguishes catalytic from stoichiometric reactions.

Fig. 10.6. Simplified representation of the postulated catalytic cycle of microsomal and cytosolic epoxide hydrolases, showing the roles played by the catalytic triad (i.e., nucleophile, general base, and charge relay acid) and some other residues, a) Nucleophilic attack of the substrate to form a /3-hydroxyalkyl ester intermediate, b) Nucleophilic attack of the /Thydroxyal-kyl ester by an activated H20 molecule, c) Tetrahedral transition state in the hydrolysis of the /f-hydroxyalkyl ester, d) Product liberation, with the enzyme poised for a further catalytic... 

Fig. 12.1 Schematic representations of the reaction A + B = C I is a simple stoichiometric reaction, involving rate-limiting breakdown of an intermediate INT II is a catalysed reaction in which there are four intermediates-the major concentration is the resting state (RS) located before turnover-limiting breakdown to give C III is the same as II except that the resting state is now off cycle and the release of this component into the catalytic cycle controls the global rate.

Figure 3.30 a The three stoichiometric redox reactions and b the net reaction of the Wacker oxidation system c a simplified representation of the Pd and the Cu catalytic cycles (the reverse reaction arrows are omitted, for clarity). 

Figure 8.16 Schematic representation of (a) the preparation of the immunosensing layer and (b) the electrochemical-chemical catalytic cycle amplified detection of mouse IgG or prostate specific antigen (PSA).75 (Reprinted with permission torn J. Das et al., J. Am. Chem. Soc. 2006,128, 16022-16023. Copyright 2006 American Chemical Society.)...

Fig. 5.2 Generic peroxidase catalytic cycle. The square of four nitrogens around the iron atom is a representation of the prosthetic heme group of the peroxidase...

Fig. 5.14 Schematic representation of the catalytic cycle in the photo-Fenton reaction using ferrioxalate (following Hislop and Bolton, 1999).

Figure 6 Schematic representation of the proposed catalytic cycle. One fragment of the polymer is shown.

Fig. 1.67. Schematic representation of the gas-phase catalytic cycle for oxidation of carbon monoxide by gold dimer anions based on the reaction mechanism determined by kinetic measurements in conjunction with first-principles simulations. The numbers denote calculated energy barriers in eV. Also displayed are geometric structures of reactants and intermediate products according to the calculations (large, grey spheres, Au small gray spheres, C dark spheres, O) [33]...

In the case of HDN, an additional interesting possibility also consistent with the heterolytic mechanism arises, since substrates like the pyridines -or intermediate alkyl or aryl amines- are sufficiently basic to promote the activation of hydrogen so as to form a metal hydride plus a protonated base (e.g. a pyridinium or an alkylammonium cation). Furthermore, some of the most widely accepted amine HDN mechanisms include the initial protonation of the amine nitrogen, followed by elimination of ammonia from the ammonium cation. Therefore, it is very easy to combine the idea of a heterolytic hydrogen activation promoted by, say n-pentylamine, with a subsequent degradation by a Hoffmann mechanism, to conform a reasonable HDN catalytic cycle. A simplified representation of this idea is given in Fig. E4. 

Figure 12 Diagrammatic representation of the catalytic cycle of DMSO reductase in...

MnSOD catalyzes the dismutation of H02 into dioxygen and hydrogen peroxide. As a redox enzyme, it shuttles between the Mn" and the Mn111 oxidation states (77). This process has been studied, and the enzyme has been shown to catalyze this reaction at a rate of 1-2.2 X 109 M s-1, which is at the diffusion limit (52). A representation of the proposed catalytic cycle is shown in Scheme 3 (78). Several studies on MnSOD kinetics have been published (78-82). Early studies on the reaction of MnSOD from Escherichia coli and Bacillus thermophilus indicated evidence for a four-step process involving two fast and... 

Fig. 28.22 (a) Schematic representation of the active site in human carbonic anhydrase II (CAII). (b) The catalytic cycle for the hydration of CO2 catalysed by CAII. 

Fig. 3. Schematic representation of the catalytic cycle of a 5 -deoxyadenosylcobalamin-requiring enzyme. See text for descriptions of the individual steps.

Schematic representation of two coupled catalytic cycles in the isomerization of n-pentane to i-pentane on a bifunctional catalyst consisting of platinum supported on acidic alumina...

The first indication of selective substitution reactions came from experiments with 1 and 2 as catalysts for alkene epoxidation. NMR experiments have shown that both compounds catalyze the epoxidation of cyclohexene with t-butyl hydroperoxide (TBHP). The catalytic activity is comparable to that of the model compound Hex7Si70i2Ti(0 Pr). " The measured turn over numbers indicate that all four Ti centers are involved in the catalytic process. The catalysts could be recovered quantitatively, a proof of core-functionalization and for the core stability during many catalytic cycles. A more detailed catalytic study has recently been performed with the cubic titanasiloxane [(2,6- Pr2C6H3) (Me3Si)NSi]40i2[Ti0 Bu]4 (12). This compound was prepared by the reaction of 9 with t-butanol and catalyzes the epoxidation of cyclohexene with TBHP. The titanium butylperoxo intermediate could be isolated after a stoichiometric reaction with TBHP. This intermediate then reacted with cyclohexene to produce cyclohexene oxide. A schematic representation of the catalytic process is given in Figure 28.4. 

Scheme 3 Schematic representation of the catalytic cycle for ATP hydrolysis by the chemo-sensor 5 following the nucleophilic pathway...

The main emphasis here is on mechanisms, and few process details are included (see Chapter 12 for the latter). Whenever possible, related homogeneous and heterogeneous catalytic processes have been brought together for comparison. However, many of the mechanistic equations, diagrammatic representations and catalytic cycles have been greatly simplified, and details often continue to attract considerable debate. 

Fig. 4.1 Schematic representation of the cytochrome P450 catalytic cycle. The [Fe ] represents the ferric heme of the enzyme and RFl a substrate molecule. The brackets stand for the heme and substrate-binding sites. The changes occurring at the heme iron and porphyrin framework during the catalytic cycle are indicated. The electrons (e") required for the catalytic cycle are provided by electron...

In heterogeneous catalysis, the simplest mechanism of a catalytic cycle is the two-step Temkin-Boudart mechanism. A particular case of this mechanism is the two-step mechanism of the water-gas shift (WGS) reaction (see Table 3.3). Table 3.4 shows a general representation of the... 

Fig. 8.7 Schematic representation of catalytic cycle for NO oxidation reaction over metal-exchanged zeolite catalysts. Redox sites are associated with oxo-metal (isolated or binuclear) ion-exchanged sites...

Fig. 8.20 Schematic representation of catalytic cycle for standard SCR reaction over vanadium-based catalyst. Acidic site and redox site are associated with V +-OH and V +=0, respectively...

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