Propanol, oxidation

Figure 11. Illustration of the reaction at a ZnS colloidal particle in the presence of C02 and 2-propanol.124 Two-electron and one-hole mechanism for C02 reduction and 2-propanol oxidation, respectively, are shown in the figure.

Iyer, A., Galindo, H., Sithambaram, S., King ondu, C., Chen, C. and Suib, S.L. (2010) Nanoscale manganese oxideoctahedral molecular sieves (OMS-2) as efficient photocatalysts in 2-propanol oxidation. Applied Catalysis A General, 375, 295-302. 

Fig. 19. ATR signals as a function of time for 2-propanol oxidation at 298 K catalyzed by 5% Pd/ TiO2 immobilized on a ZnSe IRE. At time t = 20 s, the solvent flow was switched from hydrogen-saturated 2-propanol to oxygen-saturated 2-propanol. At t = 120 s, the flow was switched again to hydrogen-saturated 2-propanol. Signals associated with the oxidation product of 2-propanol, acetone, and water are shown. The signal at 1820 cm is associated with changes occurring on the metal catalyst (see text for details) (49. ...

Propanol oxidation under mild conditions takes place with high selectivity. No products other than acetone were observed in the ATR spectra recorded in situ. The situation is more complex for the oxidation of primary alcohols such as ethanol. The first oxidation step produces acetaldehyde, which is prone to further reactions, as is apparent in the ATR spectra. Figure 20, left, shows ATR spectra recorded in situ during ethanol oxidation. Figure 20, right, shows some signals as a function of time. The experiment was performed in a manner similar to that of the one... 

Identification of an adsorbate may be facilitated by simple adsorption of a precursor that resembles it, or just the adsorbate itself, such as CO (e.g., panel (c). Fig. 21). Adsorbed reaction intermediates on Pd/Al2O3 for 2-propanol oxidation were identified by using time-resolved ATR spectroscopy and quantum chemical calculations 45), as described in detail below. Reaction intermediates are usually... 

The very rapid conversion of 2-propanol to acetone under these conditions can be consistent with such a mechanism, although it conflicts with the deuterium effect for the central H-atom reported by Buiten. The high velocity of the 2-propanol oxidation, on the other hand, hampers the finding of clear evidence in favour of one of the above mechanisms. 

Biirgi T, Bieri M (2004) Time-resolved in situ ATR Spectroscopy of 2-propanol oxidation over Pd/A1203 evidence for 2-propoxide intermediate. J Phys Chem B 108 13364-13369... 

Note that a different termination step from that in the 2-propanol oxidation is responsible for the rate being independent of the substrate concentration. The absence of in equation (41) predicts the same rate for CD3OH. The observed isotope effect ( h/ d) is 1 3 which can reasonably be ascribed to a secondary effect on or an inverse effect on k (Edwards et aV ). 

Rates of 2-propanol oxidation using a Pt/Si02 catalyst at various partial pressures of 02-... 

The rates of 2-propanol oxidation were measured for reactions run over an 8% Pt/Si02 catalyst in water at 20°C. The initial rates of oxygen uptake (about 10% conversion) were determined at three fixed partial pressures of oxygen over a range of alcohol concentrations. The resulting data are listed in Table 7.1. 

Fig. 7.15. Double reciprocal plot of 2-propanol oxidations run under various partial pressures of oxygen.

The value for V, ax 27" (mole site) , is the maximum rate for this reaction when it is run under saturation conditions for both substrates. In contrast to the single type of active site found in most enzymes, there are a number of different types of sites present on the surface of the platinum catalyst used for these oxidations. It was shown in a parallel study that 2-propanol oxidation takes place over the coordinately unsaturated corner atoms, that is, the single turnover (STO) characterized M, and MH sites (see Chapter 2). It was also shown that the specific site turnover frequencies (TOF) for these sites are 5.5,7.9 and 5.0 moles O2 uptake/mole site/minute respectively. 

Chemical deactivation by adsorbed impurities or reaction products was identified as a primary cause of catalyst deactivation [42,43,45-48,50]. Deactivation of platinum catalysts in l-methoxy-2-propanol oxidation was attributed to polymeric species formed by aldol-dimerization and detected by chromatographic... 

Certain features of alcohol photo-oxidation are connected with the presence of sensitizers. As found by Backstrom [60], the rate of photooxidation of 2-propanol (with benzophenone as sensitizer) is inversely proportional the oxygen pressure. Dependence of the 2-propanol oxidation rate on alcohol concentration and on light intensity, /, (with anthraquinone as sensitizer) is expressed as... 

If >>c(oo-)o-h = 75 kcal mole-1, then q = 30 kcal mole-1. Therefore, hyroxyperoxy radicals, in contrast to alkylperoxy radicals, display a dual reactivity. They can take part both in oxidation and in reduction reactions and they would be expected to react not only with radicals but with molecules of the oxidizing agent, with quinones for example. The kinetics of 2-propanol oxidation in the presence of benzoquinone has been studied [80], Quinones are known to terminate chains in hydrocarbon oxidation only by reactions with alkyl radicals [1]. In alcohol oxidation, quinone terminates chains by reaction with hydroxyalkyl as well as with hydroxyperoxy radicals [80]. At 71°C and PQl = 760 torr, 86% of chain termination is due to the reaction >C)0H)00- + quinone. The rate coefficient is M>C(0H)00- + quinone) = 3.2 X 1031 mole-1 s-1 and kQ/kp = 1.0 X 104. Just as in the case of aromatic amines, f> 2 f= 23 for quinone, i.e. quinone is regenerated in the reactions... 

Br" ions inhibit the oxidation of alcohols if the latter do not contain H202. However, in the presence of H202, 2-propanol oxidation is accelerated by Br" [89], as the latter induces decomposition of H202 leading to free radical formation. The rate of initiation by reaction of Br" with H202 is [89]... 

When 2-propanol is oxidized in the presence of benzene, the latter is hydroxylated to form phenol [116]. Phenol is oxidized in the course of the reaction giving a resin displaying a strong inhibiting action. Hydroxyla-tion of benzene is observed in 2-propanol oxidation at temperatures of 150—200°C. Phenol accumulates in concentrations up to 0.2 mole l-1. The ratio of rate coefficients is... 

Gallardo-Amores J., Armaroli, T, Ramis, G., Finocchio, E., and Biisca, G., 1999, A study of anatase-supported Mn oxide as catalyst for 2-propanol oxidation, Appl. Catal B Environ., 22 249-259. 

We were able to observe clear evidence for the chain-type mechanism in experiments, involving acetaldehyde decomposition in the gas-phase [98], similar to those already discussed for 2-propanol. With acetaldehyde, the values exceeded the maximum value obtained for a similar film for 2-propanol oxidation (0.28) (Fig. 6). As already discussed, the latter value may be considered to be an intrinsic maximum value for this particular film. Therefore, if < > exceeds the intrinsic maximum value, it indicates that radical chain reactions are important, that is, a single photon can cause more than one photodecomposition reaction. 

Rodrigues I A, Nart FC (2006) 2-Propanol oxidation on platinum and platinum-rhodium electrodeposits. J Electroanal Chem 590 145-151... 

Fig. 2.19 Small shaped Pt nanoparticles (0.8-1 ran) and their catalytic activity for 2-propanol oxidation (adapted from ref. [59])...

Recently, Chu and Shul [128] have applied combinatorial chemistry to the screening of 66 PtRuSn-anode arrays for investigation of methanol, ethanol, and 2-propanol oxidation. The screening was performed by employing quinine as indicator of the catalytic activity, which allowed for selection of the optimum composition of electrocatalysts for DAFCs (Direct Alcohol Fuel Cells). PtRuSn (80 20 0), PtRuSn (50 0 50), and PtRuSn (50 30 20) furnished the lowest onset potential for methanol, ethanol, and 2-propanol electro-oxidation according to the CV results, respectively. The active area/composition for ethanol electro-oxidation is represented in Figure 15.8 as adapted from Ref. [128]. 

Fig. 19.9. Cyclic voltammograms for (A) ethanol oxidation and (B) 2-propanol oxidation for as-deposited diamond / Pt (dotted Une), Pt-nanoparticle-fiUed nano-honeycomb 60 x 500 nm (dot dashed line), and 400 nm x 3 un (solid line) electrolyte, 2 M ethanol or 2 M 2-propanol + 1 M H2SO4 sweep rate, 50 mV s b geometric surface area, 0.071 cm2.

In addition, 2-propanol oxidation was examined. Figure 19.4.4B shows cyclic voltammograms obtained for as-deposited diamond/Pt, 60 x 500 nm/Pt and 400 nm x 3 pm/Pt electrodes in 2 M 2-propanol in 1 M H2SO4. In this case [33], it can be seen that the oxidation currents for as-deposited diamond/Pt, 60 x 500 nm/Pt and 400 nm x 3 mm/Pt electrodes are all similar, and therefore, there was no enhancement due to the honeycomb roughness for either nanohoneycomb/Pt electrode. 

The reduction of the HPA occurred along with the oxidation of 2-propanol in the homogeneous system, whereas 2-propanol oxidation decreased under visible light in the sequence A > B >> H3PW12O40 > C. The mechanism is reported below ... 

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