Alkane dehydrogenations reaction

Theoretical studies of catalytic alkane-dehydrogenation reactions by [(PCP )IrH2], PCP rf-C6H3(CH2P112)2-l, 3 and [cpIr(PH3)(H)]+, suggest that they proceed through similar steps in both cases namely (i) alkane oxidation, (ii) dihydride reductive elimination, (iii) /3-II transfer from alkyl ligand to metal, (iv) elimination of olefin.402 The calculated barriers to steps (i), (ii), and (iv) are more balanced for the PCP system than for cp(PH3). 

The thermodynamic parameters for the alkane dehydrogenation reaction are calculated for both the pincer and anthraphos iridium(III) complexes. The mechanism of the transfer reaction, and the associative, dissociative and interchange mechanisms for the acceptorless reactions are discussed and compared. As these reactions typically occur at conditions very different from STP, important corrections for high temperature, high reactant (alkane) concentration and low product (H2, olefin) concentration are important. 

From the outset, iridium compounds have played an important role in the better understanding of the C—H activation process, and consequently in the development of efficient alkane dehydrogenation reactions [8]. Hence, in this chapter we will review the participation of iridium complexes in the optimization of chemical processes for C—H activation which, today, have led to some highly promising... 

Alkane dehydrogenation reactions were studied at reaction temperatures between 573 and... 

The simplest paraffin (alkane) and the most widely used feedstock for producing ethylene is ethane. As mentioned earlier, ethane is obtained from natural gas liquids. Cracking ethane can be visualized as a free radical dehydrogenation reaction, where hydrogen is a coproduct ... 

In contrast to the results obtained for dehydrogenation reactions, kinetic energy release distributions for alkane elimination processes can usually be fit with phase space theory. Results for the loss of methane from reaction 9 of Co + with isobutane are shown in Figure 10b. In fitting the... 

The success of derivatives of 1 and 2 as dehydrogenation catalysts has led to the investigation of numerous different pincer ligands for iridium-catalyzed alkane dehydrogenation. The Anthraphos pincer iridium complex (3-H2) was expected to afford even greater thermal stability (Eig. 1), and indeed, the catalyst can tolerate reaction temperatures up to 250°C [42]. The catalytic activity of 3-H2, however, is much less than that of I-H2 under comparable conditions. 

Hydrogenation dehydrogenation reactions. The end products of the F-T process are a mixture of higher alkanes and alkenes. The promoter elements could show under F-T conditions some activities for hydrogenation or dehydrogenation reactions leading to a shift in the relative ratio of alkanes to alkenes. 

The data presented above showed that the oxidative dehydrogenation reactions of the various alkanes share many common features. Thus it is tempting to discuss selectivity for alkane oxidative dehydrogenation with a common scheme. The reaction scheme for ethane oxidation [Eqs. (5)-(7)] provides a useful basis for such a discussion. It shows that the primary reaction of alkane oxidation can take on three different pathways depending on the reaction temperature (Scheme I). The first step in all three pathways is breaking a C—H bond, which is the rate-limiting step. The three pathways are described below. 

These reactions are both endothermic by a nearly constant 5 kJmol"1, (5.0 1.3) and (5.3 2.8), respectively. By contrast, the sequential oligomerization/dehydrogenation reactions of saturated alkanes (equations 10a and 10b)... 

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