Model ethylene partial oxidation

This has in turn been related to the relative stability of the OMME compared to the ethylene reactant and the epoxide product [11]. It has been argued that the relative instability of the OMME intermediate on Ag compared to Group VIII metals is the main origin of the unique activity of Ag as an effective epoxidation catalyst. Whether this simple interpretation is correct remains to be seen and will require considerable further investigations. In our current studies, we propose to shed light on the competitive partial oxidation and total oxidation channels with ab initio derived microkinetic modeling [61]. 

In the kinetic models discussed so far, the catalyst surface was assumed to be uniform and to have constant activity. In practice, catalysts often show a decline in activity with time, because of poisoning or fouling these changes are discussed later. Catalysts may also change activity because of reactions that alter the chemical composition of the surface. One example of this is the supported silver catalyst used for the partial oxidation of ethylene. Kinetic data suggest that the active catalyst is a partial layer of silver oxide and not metallic silver. But a modified form of the Langmuir-Hinshelwood model can still be used to correlate the data, as shown in the following example. 

This reactor, sketched in Figure 24.2g, was developed especially to prevent slip in reactions required to be strictly stoichiometric. Modeling of a CNMR-E has been attempted for both fast irreversible and reversible reactions (Sloot et al., 1990, 1992 Zaspalis et al., 1991 Veldsink et al., 1992), notably the Claus reaction 2H2S -I- SO2 —> (3/8)Sg + 2H2O. This concept can also be used in partial oxidations in organic technology, for example, partial oxidation of ethylene to acetaldehyde (Harold et al., 1992). The stoichiometry of this reaction can be represented as... 

Propene epoxidation. Stoukides and Vayenas have studied the epoxi-dation of propene over silver catalysts.71 73 A Langmuir-Hishelwood type model was used to explain the results of work performed between 290 and 400°C.71 As with the work on ethylene oxidation, two types of oxygen were proposed to be involved, molecular and atomic oxygen responsible for partial and total oxidation respectively. 

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