Selective oxidation of propene

The heterogeneously catalyzed gas-phase oxidations of unsaturated hydrocarbons are large-scale industrial processes. The best known processes are  

Economic operation of these processes requires a selectivity of at least 60 %. In the last few decades the industrial oxidation catalysts have been so much improved 

Selective oxidation still offers interesting development possibihties for the chemical engineer [8]. Here we shall consider the oxidation and anunoxidation of propene, which both proceed by a similar mechanism, in more detail. 

The catalytic oxidation of propene leads preferentially to formation of acrolein (Eq. 8-7). 

Carbon dioxide, acetaldehyde, and acrylic acid are formed as side products. A technical breakthrough was achieved by Standard Oil of Ohio (SOHIO) with the discovery of the bimetallic bismuth molybdate and bismuth phosphomolybdate catalysts. Propene is oxidized with air on a Bi203/Mo03 catalyst at 300-400 °C and 1-2 bar in a fixed-bed tubular reactor, which allows effective removal of heat from the exothermic reaction [15]. 

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In an experiment (Williams, 1996) to evaluate a catalyst for the selective oxidation of propene (C3H6) to various products, 1 g of catalyst was placed in a plug-flow reactor operated at 450°C and 1 bar. The feed consisted of propene and air (21 mole % 02,79% N2 (inert)). GC analysis of the inlet and outlet gas gave the following results, the outlet being on a water-free basis (H20 is formed in the oxidation) ... 

Structure Sensitivity in Selective Oxidation of Propene over CU2O Surfaces... 

Selective oxidation of propene to acrolein was carried out in a dynamic differential microreactor containing 40 to 60 mg of catalyst as described previously (12). Reaction conditions were as follows propene/02/N2 (diluting gas) = 1/1.69/5 total flow rate 7.2 dm. h-i total pressure 10 Pa and reaction temperature 380 °C. 

The selective oxidation of propene to acetone can be effected by two entirely different types of catalysts metal oxide combinations, which contain Mo03 as the essential component, and catalysts based on palladium. 

The conversion of isobutene to methacrolein is closely related to the selective oxidation of propene to acrolein and demands similar catalysts. It has been verified that the same mechanism applies, involving a symmetrical allylic intermediate, viz. 

Wise [350] investigated the parallel between ammoxidation and oxidation of ammonia over bismuth molybdates. It was shown that the rate of conversion to nitrogen is first order in NH3 and independent of oxygen concentration, analogous to the selective oxidation of propene. Under conditions in which propene combusts, NH3 is converted to nitrogen oxides. 

Table 8.1 Selected results for the selective oxidation of propene on titania- and silica-titania catalysts.

The selective oxidation of propene to acrolein on supported vanadia catalysts was recently investigated by combined Raman, IR, and UV-vis DR spectroscopies (Zhao and Wachs, 2006). The surface vanadia species became more reduced under these reaction conditions as compared to those of alkane ODH (vide supra) because of the greater reducing power of alkenes relative to alkanes. Consequently, the reaction rates were dependent on the O2 partial pressures, because the surface vanadia sites were... 

Bismuth molybdates having a Bi/Mo ratio in the range of 0.67 2.0 catalyze the selective oxidation of propene to acrolein, and the ammoxidation of propene to acrylonitrile (equations 5 and 6). Both reactions proceed through an aUyhc intermediate. Three typical active phases o -Bi2Mo30i2,... 

Figure 1 Mechanism for the selective oxidation of propene to acrolein over bismuth molybdate catalysts...

Several oxidation reactions (Section 5.5) have been selected. Selective oxidation of propene Section 5.5.1) is a key example of the use of oxides in oxidation catalysis. 

It is partially contained in the technical blue oxide and acts in pure form as an important catalyst in industrial chemical syntheses (see Chapter 10). Similar to WO2.72, it catalyzes the decomposition of N2O and the selective oxidation of propene oxygen mixtures to acroleine. 

Various catalysts based on molybdates have been used both for selective oxidation of propene to acrolein... 

This result indicates that the main reaction site is not inside the YSZ film, but its surface. Therefore, it is likely that the selective oxidation of propene occurred at the Au-YSZ-gas triple phase boundary by the oxygen species pumped electrochemicaUy through the SDC and then the YSZ, as shown in Figure 5. However, it was found that acrylaldehyde selectivity in the case of using YSZ I SDC or YSZ i GDC was stiU lower than that obtained with an electrochemical reactor constructed from YSZ alone, as shown in Table 1. Accordingly, a possible occurring of the propene oxidation at the surface of SDC and/or at the triple phase boundary between Au-SDC-gas cannot be denied in this study. 

Figure 5. Mechanism of the selective oxidation of propene using an electrochemical membrane reactor.

An electrochemical cell system with ceria-based solid electrolyte coated wdth YSZ prepared by the spin coating method showed higher selectivity to acrylsildehyde than that with ceria-based solid electrol5rte alone. This may be due to the fact that a film of YSZ on the ceria-based solid electroljde to suppress the complete oxidation of propene. When the YSZ SDC disk was used as an electrolyte membrane, selectivity of the oxidation products did not depend on the thickness of YSZ. This indicates that the selective oxidation of propene occurred at the Au-YSZ-gas triple phase boundary by the oxygen species pumped electrochemicaUy through the ceria-based solid electrolyte and the YSZ. 

The allyl radical, CsHs, is an intermediate in the selective oxidation of propene to acrolein with oxygen, catalysed by bismuth molybdate and iron antimonate [69,91]... 

In the final example, we will continue with the subject of selective oxidation of propene to PO, but this time using advanced CaCOs supported Ag catalysts. The focus is directed towards a novel synthesis procedure, in which La incorporation is shown to have a significant effect on the alkali content of the catalyst and thus on the resulting catalyst performance. 

Selective oxidation of propene to acetone was achieved with Si02-grafted catalysts prepared from [ / -C4H7)2Rh 2(V40i2)] (2) and [(Cp Rh)4V60i9] (Scheme... 

In the selective oxidation of propene, metal oxides are mainly used as catalysts, and many different products are obtained (Scheme 8-5), depending on the catalyst used [19]. 

Oscillations were also found in other reactions, catalysed by copper or copper oxides, e. g. town gas combustion over supported Cu (9) selective oxidation of propene to acrolein over Cu oxides [10, 11] hydrogenation of PhN02 (supported Cu [12]) and CO oxidation, catalysed by supported CuO [13]. 

Selective Oxidation of Propene Acetone is the main product with Ti02/Si02 with the selectivity of 95 % [4]. 

Botella, P., Garcia-Gonzalez, E., Solsona, B. etal. (2009). Mo-Containing Tetragonal Tungsten Bronzes. The Influence of Tellurium on Catalytic Behaviour in Selective Oxidation of Propene, J. Catal, 265, pp. 43—53. 

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