Hydrogen-oxygen-propene-oxide

These results led to the postulate that the bismuth component of bismuth molybdate catalysts is responsible for the abstraction of the first hydrogen from propene, but that this oxide is not capable of inserting oxygen into the reaction intermediate which forms. Instead any allyl species which form over this oxide from allyl iodide and less easily from propene, dimerize to hexadiene in the absence of a suitable source of oxygen. By contrast, allyl species do not form from propene over molybdenum oxide. However, when this oxide is exposed to a facile source of allyl species, namely allyl iodide, acrolein forms readily, consistent with the oxygen insertion and second hydrogen abstraction steps occurring over this component of the bismuth molybdate catalysts. 

When a supported copper salt, which has been pre-reduced with hydrogen, is contacted with a propene/oxygen mixture, propene oxide is initially produced. 

Direct oxidation of propene to propene oxide (PO) with high selectivity and activity is yet to be achieved in heterogeneous catalysis, as was already indicated in the description on the preparation of the Au catalysts. Obviously, the most attractive reaction is the direct oxidation with oxygen, rather than using the previously discussed mixture of oxygen and hydrogen ... 

Highly dispersed titanium oxide species on silica prepared by the sol-gel method catalyse the selective epoxidation of propene by molecular oxygen.59 This is potentially very significant as the new commercial route to propene oxide is based on the reaction of propene with hydrogen peroxide catalysed by a mixed Ti-Si oxide the direct reaction with oxygen has clear advantages. 

The fact that gold is active under very mild conditions means that its potential as a selective oxidation catalyst is high, and many selective oxidation processes are important in the chemical industry [1,2]. Papers have been published on the selective oxidation of propene to propene oxide in the presence of hydrogen, oxidation of sugars and aldehydes to acids, and the oxidation of alcohols and other hydroxyl-compounds. Au-Pd catalysts have been used to oxidize ethene to vinyl acetate in the presence of acetic acid and oxygen and this is a process used by a number of manufacturers worldwide. The selective oxidation of hydrogen to hydrogen peroxide, rather than water, is also catalyzed efficiently by supported Au-Pd catalysts [49]. 

Figure 2.5 The response of an MISiC sensor, (a) At 600°C to gas mixtures containing different hydrocarbons (butane, propene, ethane) and concentrations. (From [56]. 1997 Elsevier B.V. Reprinted with permission.) (b) To hydrogen in different oxygen concentrations at 300°C and at T> 600°C plotted versus the ratio of reducing to oxidizing species, a, as defined in (2.6). Inset the pulse response at 620°C to 0.1, 0.2, and 0.3% Hj in 0.1% Oj/Ar. (From [57]. 1 988 The Electrochemical Society. Reprinted with permission.)...

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