Manganese kinetic rate constants

On the contrary, for 0.6Mn2 supported samples, with lower values of the kinetic rate constant, the catalytic activity increases with the calcination temperature. This can be correlated with the increase of the surface area and a possible explanation is the migration of manganese leading to a better dispersion. 

In the presence of manganese and cobalt acetates the reaction becomes very fast, and the intermediate AMP cannot be detected. The kinetics of these reactions were studied in a flow reactor, and the results gave a good second-order fit (first order in peracetic acid and first order in acetaldehyde) at different catalyst concentrations. The plot of [acetaldehyde] vs. [peracetic acid] was linear with a slope of 1, indicating that equimolar quantities of the two substances are reacting. A plot of the experimental second-order rate constants (k Co) as a function of catalyst concentration gave a very good first-order fit for cobalt acetate... 

Values of the ratio of the rate constants, a kj2/ 13, are plotted as a function of temperature in Figure 2. It is seen that (1) the a-values decrease with temperature as expected theoretically and (2) the kinetic isotope effects are not the same for the different oxidants. There appears to be one trend for hematite and anhydrite and another for cupric oxide and manganese dioxide. 

An increase was reported in the rate constants of PPhj-promoted formation (32.0°C, hexane) of the acyl derivative of manganese(I) Mn(COR)(CO)j, as a function of the length of the linear alkyl group R [reaction (b)] for n = 1-3 (from the methyl to the n-propyl derivative), followed by an abrupt decrease up to n = 7 (n-heptyl) the kinetics slowly decrease from n = 7 to n = 18. 

Manganese is present in both the colloidal and noncolloidal particle-size fractions of freshwater sediments (Oscarson et al., 1981b). The depletion (oxidation plus sorption) of As(III) by the sediments involves at least two rates one rate before (dashed lines) and one after 30 min (Fig. 8-2). However, because of experimental limitations involved in obtaining accurate, meaningful data for the time period < 30 min, rates and energies of depletion of As(III) were not evaluated for this time period. The depletion of As(III) by sediments after 30 min follows first-order kinetics. The rate constant increases with increasing temperature from 278 to 298 K (Table 8-3). The heat of activation for the process varies from 13.8 to 35.6 kJ mol for the sediments, indicating that the depletion of As(III) is predominantly a diffusion-controlled process. 

Highly Catalyzed Experiments. In conjunction with experiments in which the manganese concentration was 2000 ppm, the model was first used to determine the mass transfer coefficient of calcium sulfite (T=40°C, pH=5.0). A reaction order of 1.5 was obtained from previous liquid phase kinetic studies with a rate constant of 85 1 ° 5 mol 0,5 sec-1 (25). Computer curves were generated using a series of mass transfer coefficients and plotted along with the experimental kinetic results on Figure 7. A mass transfer coefficient of 0.015 cm/sec most closely fits the data. The bulk pH drops quickly during the initial several seconds and then stays around 2.9, but the surface pH remains almost constant at 5.15 which implies that the oxidation only has small influence on the surface conditions. 

In contrast the manganese superoxide dismutase appears to exhibit complex kinetics. The simple scheme of one electron reduction and oxidation of the metal appears not to be applicable. Pick et al. (1974) investigating the manganese superoxide dismutase from . coli suggested that not two but four oxidation-reduction reactions are involved and that each reaction is characterized by a different second-rate constant ... 

The kinetics and mechanism of oxygen transfer in the reaction of p-cyano-N,N-dimethylaniline N-oxide with the manganese(III) complex of the me50-tetrakis(2,6-dimethylphenyl)porphinato dianion have been investigated in the presence of imidazole.From the dependence of the pseudo first-order rate constants upon [ImH], and a knowledge of the equilibrium constants for imidazole ligation, second-order rate constants of = 3.3 x 10 s 2 = 5.53 s and —... 

Firstly, Che kinetics and mass transfer effects of catalyst synthesis via deposition precipitation onto pre-shaped and powder carriers have been studied under pseudo-stationary conditions. The precipitation of manganese hydroxide onto silica by urea hydrolysis has been used as a model reaction. The overall disappearance of manganese ions from the aqueous solution could be described as a first-order process. The rate-determining step for Mn deposition is related -as expected - to the urea hydrolysis. From the distribution of Mn over the silica granules after precipitation the rate constant for the surface deposition process has been determined. The latter process has a much higher rate constant than the rate—determining hydrolysis reactions. The surface reaction appears to determine the ultimate distribution by a combined process of reaction and diffusion. The consequences of this study for the viability of deposition precipitation onto pre-shaped carriers for practical application are addressed. 

The processes described and their kinetics is of importance in the accumulation of trace metals by calcite in sediments and lakes (Delaney and Boyle, 1987) but also of relevance in the transport and retention of trace metals in calcareous aquifers. Fuller and Davis (1987) investigated the sorption by calcareous aquifer sand they found that after 24 hours the rate of Cd2+ sorption was constant and controlled by the rate of surface precipitation. Clean grains of primary minerals, e.g., quartz and alumino silicates, sorbed less Cd2+ than grains which had surface patches of secondary minerals, e.g., carbonates, iron and manganese oxides. Fig. 6.11 gives data (time sequence) on electron spin resonance spectra of Mn2+ on FeC03(s). 

In systems where such radicals appear (alcohols, amines, some unsaturated compounds), variable-valence metal ions manifests themselves as catalysts for chain termination (see Chapter 11). The reaction of the ions with peroxyl radicals appears also in the composition of the oxidation products, especially at the early stages of oxidation. For example, the only primary oxidation product of cyclohexane autooxidation is hydroperoxide the other products, in particular, alcohol and ketone, appear later as the decomposition products of hydroperoxide. In the presence of stearates of such metals as cobalt, iron, and manganese, all three products (ROOH, ROH, and ketone) appear immediately with the beginning of oxidation and in the initial period (when ROOH decomposition is insignificant), they are formed in parallel with a constant rate. The ratio of rates of their formation is determined by the catalyst. The reason for this behavior is evidently related to the fast reaction of R02 with the catalyst. Thus, the reaction of peroxyl radicals widi variable-valence ions manifests itself in the kinetics as well (the induction period appears imder certain conditions), and alcohol and ketone are formed in parallel with ROOH from R02 among the oxidation products. 

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