Binary catalyst-oxidant systems

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

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. ... 

In contrast to the aforementioned binary oxides, V2Os has a stronger oxidation power and is able to attack hydrogen attached to the aromatic nucleus. Sometimes attention is drawn to the importance of a layer structure in the catalyst or to geometric factors (e.g. Sachtler [270]). Unexpectedly, however, very effective vanadium-based catalysts exist which operate in the molten state, indicating that a fixed structure is not important. The catalytic activity of molten oxide phases seems to occur exclusively in the oxidation of aromatic hydrocarbons over V2Os-based catalysts, such systems have not been reported for the selective oxidation of olefins. 

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]. 

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

Aside from the recently described Cu/Th02 catalysts, copper on chromia and copper on silica have been reported to catalyze methanol synthesis at low temperatures and pressures in various communications that are neither patents nor refereed publications. It is not feasible to critically review statements unsupported by published data or verifiable examples. However, physical and chemical interactions similar to those documented in the copper-zinc oxide catalysts are possible in several copper-metal oxide systems and the active form of copper may be stabilized by oxides of zinc, thorium, chromium, silicon, and many other elements. At the same time it is doubtful that more active and selective binary copper-based catalysts than... 

Ir02 and Ru02 are mutually soluble in one another and consequently the Ir02-Ru02 binary oxide system [244] along with the ternary systems (Ir, Ru, Ta)Ox [245] and (Ir, Ru, [246] have been investigated as catalysts for... 

Source of Activity in other Strongly Acidic Oxides.—While surface acidity is found to some degree in many oxides, relatively few show strong acidity comparable with that of the various siliceous materials considered above. Earlier work on these oxide systems has been reviewed by Tanabe and he later proposed a general model for acidic binary oxide catalysts. 

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. 

In this work a modified hydrolytic sol-gel technique has been applied to synthesize binary and ternary systems based on Nb, Mo and V, as potential catalysts for the selective oxidation of propane to acrolein and/or acryhc acid. Crystalline mixed oxide phases were obtained and investigated by XRD, Raman and UV-VIS spectroscopy. 

The ammoxidation of propylene is carried out by feeding the olefin, air, ammonia and steam over a fixed or fluidized bed of catalyst at between 420 and 500°C. Several binary oxide systems, Bi-Mo, U-Sb (Sohio) and Sn-Sb (BP Chemicals), form the basis of commercial catalysts. Selectivities are now about 70% on propylene, with acetonitrile and HCN as byproducts. 

In the case of these binary catalysts it was found that the Lewis acid-oxidant ratio had an important effect on benzene polymerization. With the AICI3-CUCI2 system the polymer yield increased considerably as the... 

Oxidation of Methanoi The oxidation of methanol via a binary catalyst will be discussed for PtRu combinations as a model system. As known from early investigations [59, 63] and already demonstrated here with the IR results of Fig. 16, PtRu surfaces are strongly enhancing the oxidation of methanol. In order to approach the behavior in the stationary case, we analyze the activity mainly in the form ofi(f)-curves. 

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