Oxidation binary catalyst

Quantitative and qualitative changes in chemisorption of the reactants in methanol synthesis occur as a consequence of the chemical and physical interactions of the components of the copper-zinc oxide binary catalysts. Parris and Klier (43) have found that irreversible chemisorption of carbon monoxide is induced in the copper-zinc oxide catalysts, while pure copper chemisorbs CO only reversibly and pure zinc oxide does not chemisorb this gas at all at ambient temperature. The CO chemisorption isotherms are shown in Fig. 12, and the variations of total CO adsorption at saturation and its irreversible portion with the Cu/ZnO ratio are displayed in Fig. 13. The irreversible portion was defined as one which could not be removed by 10 min pumping at 10"6 Torr at room temperature. The weakly adsorbed CO, given by the difference between the total and irreversible CO adsorption, correlated linearly with the amount of irreversibly chemisorbed oxygen, as demonstrated in Fig. 14. The most straightforward interpretation of this correlation is that both irreversible oxygen and reversible CO adsorb on the copper metal surface. The stoichiometry is approximately C0 0 = 1 2, a ratio obtained for pure copper, over the whole compositional range of the... 

Cu-Mn mixed-oxide binary spinel catalysts (CuxMn3 x04, where x = 0, 0.25, 0.5, 0.75 and 1) prepared through co-precipitation method exhibit phenol methylation activity imder vapor phase conditions [75]. All of the catalysts, irrespective of the compositions, produced only C-methylated phenols. However, a total ortho selectivity of 100% with 2,6-xylenol selectivity of 74% was observed over x = 0.25 compositions at 400°C. This composition was found to be relatively stable under reaction conditions compared with the other compositions studied. The catalysts with high copper content suffered severe reduction under methylation conditions whereas, catalysts with low copper content had a hausmannite phase (Mu304) that sustained... 

Lu and coworkers have synthesized a related bifunctional cobalt(lll) salen catalyst similar to that seen in Fig. 11 that contains an attached quaternary ammonium salt (Fig. 13) [36]. This catalyst was found to be very effective at copolymerizing propylene oxide and CO2. For example, in a reaction carried out at 90°C and 2.5 MPa pressure, a high molecular weight poly(propylene carbonate) = 59,000 and PDI = 1.22) was obtained with only 6% propylene carbonate byproduct. For a polymerization process performed under these reaction conditions for 0.5 h, a TOF (turnover frequency) of 5,160 h was reported. For comparative purposes, the best TOF observed for a binary catalyst system of (salen)CoX (where X is 2,4-dinitrophenolate) onium salt or base for the copolymerization of propylene oxide and CO2 at 25°C was 400-500 h for a process performed at 1.5 MPa pressure [21, 37]. On the other hand, employing catalysts of the type shown in Fig. 12, TOFs as high as 13,000 h with >99% selectivity for copolymers withMn 170,000 were obtained at 75°C and 2.0 MPa pressure [35]. The cobalt catalyst in Fig. 13 has also been shown to be effective for selective copolymer formation from styrene oxide and carbon dioxide [38]. 

Enantiomer-differentiating co-polymerization of terminal epoxides is achieved by chiral chromium and cobalt complexes. Jacobsen etal. reported the co-polymerization of 1-hexene oxide with GO2 by using complex 35a. The reaction proceeds with kinetic resolution at 90% conversion, the unreacted epoxide is found to be enriched in the (i )-enantiomer of 90% ee. Detailed information about the resultant polymer, however, is not described. As discussed in the previous section, chiral cobalt-salen complex 34c co-polymerizes PO and GO2 (Table 3). When 34c with /r<3 / j--(li ,2i )-diaminocyclohexane backbone is applied to the co-polymerization, (A)-PO is consumed preferentially over (i )-enantiomer with a of 2.8 to give optically active PPG (Equation (8)). In a similar manner, a binary catalyst system, 34d/Bu4NGl, preferentially consumes (A)-PO over R)-PO with = 2.8-3.5. ... 

Another successful iron-catalyzed reaction is sulfoxidation, consisting of the use of the binary catalyst Fe(N03)3 -9H20-FeBr3.This system was able to catalyze efficiently the oxidation of sulfides at room temperature in MeCN under air (Table 3.8) [159]. 

As a consequence of the experimental results for catalyst Sets A and B, appropriate rhodium-containing catalysts were tested as Set C. Figure 3.38 shows the reactor outlet concentration for propylene oxide, acrolein and acetone. A large number of the catalysts tested produce high concentrations of propylene oxide of up to 2000 ppm at 1% conversion of propylene. The combinations Rh-Sn and Rh-In are very effective for propylene oxide formation. In most cases the binary catalysts have higher activity at lower propylene loading. In Figure 3.38, it can also be seen... 

Figure 3.37 Reactor exit concentrations of propylene oxide for the binary catalyst Set A. Feed gas, 20 000 tr1 GHSV propylene oxygen ratio, 4 1 temperature, 250 °C 40% propylene [40] (by courtesy of Elsevier Ltd.).

Ai, M. Oxidation activity and acid-base properties of Sn02-based binary catalysts. 1. Sn02-V205 system. J. Catal., 1975, 40, 318-326. 

The electronic interaction between the catalyst components is best exemplified by its color and optical spectra. For example, the very active binary catalyst Cu/ZnO = 30/70 has a pitch black color and although it is composed of crystallographically identifiable copper and zinc oxide, its optical spectrum is not a superposition of the spectrum of copper metal and zinc oxide, but rather comprises a very intense continuous absorption band in the visible part of the spectrum that contains no trace of the characteristic... 

Fig. 8. (a) Transmission electron micrograph of a Cu/ZnO = 30/70 binary catalyst (40) 60 A copper spheres are placed on crystalline zinc oxide network, (b) Dark field image of the copper crystallites in the area shown in the bright field image (a) obtained using the [111] reflection of copper. [Adapted with permission from J. Catal. 57, 339 (1979). Copyright (1979) Academic Press, New York.]... 

As mentioned above, direct methanol oxidation and reformate tolerance represent two very challenging but significantly different electrocatalytic issues. This is despite the fact that poisoning by CO (or similar Ci moieties) is one of the critical aspects for both fuels. Binary catalysts such as PtSn, PtMo or PtRu offer superior performance but the precise reason for this is not known. At least 3 different mechanisms have been proposed, whereby the alloying M element ... 

These results clearly confirm that modifying a conducting polymer with metallic particles containing Pt, Ru, and Mo leads to enhanced catalytic performances versus the oxidation of methanol in comparison to the behavior of binary catalysts (Pt-Ru). 

Sulfoxides. The air oxidation of sulfides can use BiBrj-BilNOj) as a binary catalyst. 

Effect of Redox Treatment on Methane Oxidation over Binary Catalyst. 

In this work the oxidative transformations of methane were studied with a catalyst system that combines an oxide and a metal component. The presence of both components gave rise to complex oscillation phenomena. The influence of pretreatment and reaction conditions over a wide range of parameters (temperature, total pressure, and oxygen concentration) on the oscillatory process was studied. The possible role of mass transfer and the balance of heat in the reactor were analyzed, and a model for the role of the components in the binary catalyst system is suggested. 

Oxidation of methane in the presence of such a binary oxide-metal catalyst proceeds in an oscillatory regime, and both temperature and concentration oscillations take place. Oscillations arise at the temperature at which the rate of reaction over the oxide component becomes noticeable ( 500°C). As temperature increases, the oscillation amplitude passes through a maximum. The oscillatory behavior disappears when complete conversion of oxygen is reached. In other words, the range of temperatures in which the oscillations are observed covers the range of oxygen conversions from 0 to 100%. 

Effects on oscillatory behavior of the treatment of the binary oxide-metal catalyst bed in different gases are presented in Fig.5. If the binary catalyst was treated in inert gas, the sharp increase of temperature begins immediately after the reactants are supplied to the reactor, and then the process proceeds in the regular oscillatory manner, despite a phase of oscillation in which the flow of reactants was switched to the inert gas flow. 

Effects of the treatment of the binary oxide-metal catalyst in oxidizing and reducing gases on the oscillatory behavior provide further evidence for this conclusion. As is shown elsewhere [5], the treatment of oxide OCM catalyst in oxygen and hydrogen leads to a sharp increase and decrease in their activity, respectively. However, this effect is of short duration after few minutes the rate of reaction undergoes a relaxation to a steady-state level which is the same in all cases, i.e., if the treatment in hydrogen has an irreversible effect on oscillatory behavior, this can be explained by its influence on the metal component. 

Since the metal filament is inert in both methane and ethane activation, but active in the binary catalyst, this effect is likely due to reactions involving some intermediates. In the absence of the metal filament, the oxide component is a very efficient catalyst for the OCM process, which is well-known to proceed via the formation and recombination of free methyl radicals [6] ... 

The data presented above indicate that, although the metal component is not able to activate saturated hydrocarbon molecules, it is very active as a trap for free radicals generated by the oxide catalyst. As a result, reaction (5) competing with (4) leads to the apparent increase in activity of the binary catalyst, and the selectivity of the overall process is determined by the competition between reactions (3) and (5). On the other hand, the treatment in hydrogen flow causes exhaustion of this oxygen buffer , which cannot be restored in the presence of both reactants in the reaction mixture due to the high reducing activity of methyl radicals. 

Binary vanadium-titanium oxide catalysts with various ratios of vanadium oxide and titania, as well as individual oxides of vanadium and titanium were examined in oxidation of P-picoline. Nicotinic acid, 3-pyridinecarbaldehyde, and CO2 were the reaction products over all the catalysts. The binary catalysts and individual vanadium oxide were highly selective for nicotinic acid, the most effective in P-picoline oxidation were the samples containing 20% and more of vanadium pentoxide. A regular stacking of crystallites of V2O5 and Ti02 was found to be the characteristic feature of the structure of the most effective compositions. 

IR spectrum of individual titania and the IR spectra of the binary catalysts coincide well with the spectrum of anatase [8] at 200-1300 cm". However in the spectra recorded for individual Ti02 and the sample containing 5% of vanadium oxide, the maxima of broad absorption bands (a.b.) at 540 and 342 cm", which are characteristic of anatase, are shifted downfield to 517 and 332 cm , at the same time a.b. at 965 and 1050 cm with 1070 and 1125 cm shoulders, respectively, are observed, that indicates the presence of sulfate-ion... 

All the binary vanadium-titania catalysts and vanadium oxide are selective for oxidation of P-picoline to nicotinic acid. The only by-product is carbon dioxide. The selectivity for CO2 is no more than 10% even at high conversions observed for all of the binary catalysts and individual vanadium pentoxide. However we can distinguish the most effective compositions... 

We can conclude that the formation of the interface between the crystallites of anatase and vanadium pentoxide, which is likely to produce the states of vanadium and oxygen other than those in the individual oxides, can be responsible for a higher efficiency of the binary catalysts. 

On a pure Pt electrode, H20ads(Pt) dissociation is difficult [6,7] and relatively high positive electrode potentials are needed to activate H2O. Nanoscale binary Pt-M catalysts are often employed to increase the efficiency of CO electro-oxidation to combine the catalytic effects of both metals. The binary catalysts may be alloys or segregated metal particles. Pt-Ru and Pt-Sn alloys have received considerable attention as promising catalysts for the direct electro-oxidation of methanol (EOM) it has been shown that the catalytic activity of Pt for EOM can be enhanced by alloying with Ru or Sn. Other metals, e.g. Mo [17-21], Re [22], and Rh [23], have also been used as allo5dng metals. 

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