Pichler-Schulz mechanism

The second proposed mechanism for the Fischer-Tropsch reaction is the Pichler-Schulz mechanism (2,16) (Scheme 2), which is characterized by chain growth by insertion of CO. This mechanism implies that the insertion step and subsequent dehydroxylation are fast compared with the chain-termination reaction. We emphasize that, according to this scenario, CO dissociation does not need to proceed rapidly. 

A characteristic of the Pichler-Schulz mechanism (presented in Scheme 2) is that the chain-growth reaction does not require high "Ci coverage but is favored by a high CO coverage. In contrast to the Biloen-Sachtler... 

To initiate chain growth, a "Ci" surface species may be required as in the Sachtler-Biloen mechanism, but the rate of formation of such species may be low. This scenario is comparable to conventional polymerization catalysis, in which initiation is usually the rate-limiting step. Assuming the generation of "Ci" species to be rate determining contrasts the Pichler-Schulz reaction scheme from the Sachtler-Biloen scheme, in which the slow step of the reaction is the termination. Because of the structure sensitivity of the CO dissociation reaction, and also because of the expected structure sensitivity of the chain-growth reaction, the Pichler-Schulz mechanism requires unique sites. The rate of CO insertion and consecutive steps should be fast compared with the rate of CO dissociation. Of course, the rate of termination should be low compared with that of chain growth. 

In summary, on the basis of the computational results, it can be concluded that the Pichler-Schulz mechanism does not contribute significantly to chain growth in the Fischer-Tropsch reaction. 

Closely related to well-known organometallic chemistry is the third mechanistic proposal, the Pichler-Schulz mechanism (1970), which proposes the migration... 

We then focus on the Pichler-Schulz CO insertion mechanism (39). This reaction has been much less investigated than the carbide mechanism. We recognize that in homogeneous catalysis, alkene hydroformyla-tion has been investigated extensively it appears that hydroformylation is much more difficult on metallic surfaces than in the presence of mononuclear cationic metal complexes (40). 

The third class of mechanisms is that originated by Pichler and Schulz in which chain growth is accomplished by direct insertion of an absorbed CO molecule into a carbon-metal bond produced by hydrogenation of a surface carbonyl (89). A complete representation of this mechanism (see... 

Pichler and Schulz [7] suggested a third mechanism, which is worth considering and seeking to verify. According to this suggestion, a carbonyl of a metal in question is formed first, which is followed by the formation of formyl (in later... 

Aikane Aicohoi, Aidehyde SCHEME 2 Fischer-Tropsch mechanism as proposed by Pichler and Schulz (2). 

The one-carbon addition schemes are typical of processes in which the growing species may be envisioned to be a chemisorbed a olefin but with a finite probability that the double bond may move to position. These schemes may be consistent with the recent mechanism of Pichler and Schulz (17). The one- and two-carbon-addition schemes are typical of the old "alcohol dehydration" mechanism, which incidentally has found no analogy in homogeneous organometallic reactions. Extension of the... 

CO insertion. The CO insertion mechanism, in which CO inserts into R-CH2 directly, was originally proposed by Pichler and Schulz. Hu and Saeys have calculated the activation barrier for the CH2-I-CO coupling step. The barrier for insertion is about 1.87 eV, being too high to... 

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