Rate constants of Co

One notes that the coverage of Cads depends on two important parameters the ratio p of the rate of hydrogenation of Cads to give methane and the rate constant of CO dissociation ... 

The rate of dissociation of CO is given by the product of the elementary rate constant of CO dissociation A. ... 

Due to the identical racemization mechanisms for both substrate enantiomers in the presence of an achiral catalyst, some simplifications can be made. First, the rate constant for CO abstraction from (R) to form I is equal to the rate constant of CO abstraction from (S), ie, k+i =k-2- Analogously, k = k+2- Both species (R) and (S), as well as the (R)- and (S)-alcohols, have similar energies thus, k+3 = k-3. 

Figure A3.10.25 Arrhenius plots of CO oxidation by O2 over Rli single crystals and supported Rli/Al203 at PCO = PO2 = 0.01 atm [43]. The dashed line in the figure is the predicted behaviour based on the rate constants for CO and O2 adsorption and desorption on Rli under UHV conditions.

Equilibrium constants and second-order rate constants for Co, Ni, Cu and Zn catalysed of the... 

Figure 2.6. Hammett plots for the equilibrium constant of binding of 2.4 to Co, NL, Cu and (open symbols), and for the rate constants of reaction of the metal-ion - 2.4 complex with 2.5 (solid symbols).

Further evidence for an increased efficiency of complexation in the presence of micellar aggregates with bivalent metal counterions is presented in Table 5.4. The apparent rate constants of the reaction of 5.1c with 5.2 in the presence of micelles of Co(DS)2, Ni(DS)2, Cu(DS)2 and Zn(DS)2 are compared to the rate constants for the corresponding bivalent metal ion - dienophile complexes in the absence of micelles. The latter data are not dependent on the efficiency of the formation of the catalyst - dienophile complex whereas possible incomplete binding will certainly be reflected in the former. The good correlations between 1 and and the absence of a correlation between and... 

The origin of the isotope effect is the dependence of coq and co on the reacting particle mass. Classically, this dependence comes about only via the prefactor coq [see (2.14)], and the ratio of the rate constants of transfer of isotopes with masses mj and m2 m2 > mj) is temperature-independent and equal to... 

Diffusion effects can be expected in reactions that are very rapid. A great deal of effort has been made to shorten the diffusion path, which increases the efficiency of the catalysts. Pellets are made with all the active ingredients concentrated on a thin peripheral shell and monoliths are made with very thin washcoats containing the noble metals. In order to convert 90% of the CO from the inlet stream at a residence time of no more than 0.01 sec, one needs a first-order kinetic rate constant of about 230 sec-1. When the catalytic activity is distributed uniformly through a porous pellet of 0.15 cm radius with a diffusion coefficient of 0.01 cm2/sec, one obtains a Thiele modulus y> = 22.7. This would yield an effectiveness factor of 0.132 for a spherical geometry, and an apparent kinetic rate constant of 30.3 sec-1 (106). 

Figure 6.3. Examples for the four types of global electrochemical promotion behaviour (a) electrophobic, (b) electrophilic, (c) volcano-type, (d) inverted volcano-type, (a) Effect of catalyst potential and work function change (vs I = 0) for high (20 1) and (40 1) CH4 to 02 feed ratios, Pt/YSZH (b) Effect of catalyst potential on the rate enhancement ratio for the rate of NO reduction by C2H4 consumption on Pt/YSZ15 (c) NEMCA generated volcano plots during CO oxidation on Pt/YSZ16 (d) Effect of dimensionless catalyst potential on the rate constant of H2CO formation, Pt/YSZ.17 n=FUWR/RT (=A(D/kbT).

This was proved by showing that the reciprocal of the life-time of the pivaloyl ion, t5co+> is independent of the concentration of t-butyl ion. A mechanism based on equation (7) would have resulted in t5,co+ being proportional to [t-C4H ]. The rate constant of decarbonylation of t-C4H9CO+ in HF—SbFg (equimolar) and in FHSO3—SbFs (equimolar) was determined to be sec. This... 

Calculation of the second-order rate constant of carbonylation, kg, and the equilibrium constant, K = [t-C4H9CO+]/[t-C4H ][CO] = A c/fcD> requires knowledge of the concentration of CO. The constant a in Henry s law Pco = [CO] was determined to be 5-3 litre mole atm in HF—SbFs (equimolar) and 53 litre mole atm in FHSOs—SbFs (equimolar) at 20°C. From the ratio [t-C4HBCO+]/[t-C4HJ"] at a known CO pressure, values for k and K were obtained. The data are listed in Table 1, which includes the values for the rate and equilibrium constants of two other tertiary alkyl cations, namely the t-pentyl and the t-adamantyl ions (Hogeveen et al., 1970). 

From the product distribution at various CO—C2H6 ratios it was concluded that the dimerization step (21) has a rate constant of the same order of magnitude as that of the carbonylation step (20). 

The donor-acceptor complexes [Ir(/r-dmpz)(CO)(PPh2 0(CH2)2R )]2 exhibit photo-induced electron-transfer rate constants of 1012s—1 and charge recombination rates slower than 2 x 10los-1 when R = pyridine and 4-phenylpyridine.534 Further studies on these complexes revealed that recombination reactions were temperature dependent and slower for the deuterated acceptors.535... 

In contrast to the reactions shown in Scheme 3, the complex OsHCl(CO)(P Pr3)2 reacts with cyclohexylacetylene at room temperature to give the hydride-vinylidene derivative OsHCl(C=CHCy)(CO)(P Pr3)2 in 70% yield (Scheme 8).37 Kinetic measurements yield a second-order rate constant of (6.0 0.2) x 10 3 at... 

Cramer and co-workers (1967) have recently measured rate constants as well as equilibrium constants for the association of p-nitrophenol and a series of azo dyes with cydohexaamylose. The general structure of the dyes employed in this study is illustrated in Fig. 4. p-Nitrophenol and p-nitro-phenolate bind to cydohexaamylose with rate constants of about 108 M l sec-1, near the diffusion-controlled limit. Within the series of dyes, however, binding rates decrease by more than seven orders of magnitude as the steric bulk of the dye is increased. Equilibrium constants, on the other hand, are roughly independent of the steric nature of the substrate, indicating that association and dissociation rates are affected by similar... 

IR kinetic measurements on Cr(CO)5(N2) were a particular technological triumph (99) because not only were the strong vc—o bands observed but also the very weak (2240 cm J) and natural abundance vnCo bands were detected. The compound Cr(CO)5(N2) decayed at 25°C with a pseudo-first order rate constant of 1.7 second-1. Thus, Cr(CO)5(H2) and Cr(CO)5(N2) have similar thermal stabilities, and it has been one of the great surprises of the Miilheim work (96-99) to find how long-lived unstable molecules can be. 

The rate constant for the exponential relaxation of the latter system to the starting system was calculated to be 1.4 x 10 s . From this value, an approximate second order rate constant of 1.0 x 10 L mol" -s"l was calculated for the reaction between IV and CO. Given the above determination of the limiting rate constant for CO dissociation... 

We now turn to the addition of hydrogen to 3Fe(CO)3. This is hypothesized to be the process that leads to the short-lived species formed in sc Ar upon photolysis of iron pentacarbonyl in the presence of H2 (24). It is however possible that Fe(CO)3 is present instead in the form of the weakly bound 3Fe(CO)3(Ar) species under these conditions. However, the reaction has also been studied in the gas phase, where a room-temperature rate constant of 2.7 x 10 11cm3molecule 1s 1 was reported (49,55), again corresponding to a very large, near collision-limit value. 

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