Reaction kinetics ethane hydrogenolysis

Table 5. Ethane hydrogenolysis reaction rates and kinetic parameters for both series of Pt/SBA-15 catalysts [13,16].

The first reported work on the kinetics of hydrogenolysis reactions of simple hydrocarbons appears to be that of Taylor and associates at Princeton (2-4, 14, 15), primarily on the hydrogenolysis of ethane to methane. The studies were conducted on nickel, cobalt, and iron catalysts. More recently, extensive studies on ethane hydrogenolysis kinetics have been conducted on all the group VIII metals and on certain other metals as well (16,28-83). 

The hydrogenolysis of neopentane occurs primarily by breaking of a single C—C bond to produce methane and isobutane as the major reaction products Small amounts of ethane and propane were also produced. The reaction kinetics were similar on the two surfaces, indicating a similar mechanism for both surfaces. 

The kinetics of alkane hydrogenolysis, that is, the dependence of rate on reactant concentration, have been the subject of numerous studies, and much effort has been devoted to devising rate expressions based on the Langmuir-Hinshelwood formalism to interpret them. Reactions of ethane, propane, and n-butane with H2 on EUROPT-3 and -4 have been carefully studied, with the surfaces in either as clean a state as possible, or deliberately carbided [21, 22] kinetic measurements at different temperature permitted adsorption heats and true activation energies to be obtained. There were two surprises (but like all surprises they were obvious afterwards) ... 

The chemical behavior of monolayer coverages of one metal on the surface of another, i.e., Cu/Ru, Ni/Ru, Ni/W, Fe/W, Pd/W, has recently been shown to be dramatically different from that seen for either of the metallic components separately. These chemical alterations, which modify the chemisorption and catalytic properties of the overlayers, have been correlated with changes in the structural and electronic properties of the bimetallic system. The films are found to grow in a manner which causes them to be strained with respect to their bulk lattice configuration. In addition, unique electronic interface states have been identified with these overlayers. These studies, which include the adsorption of CO and H2 on these overlayers as well as the measurement of the elevated pressure kinetics of the methanation, ethane hydrogenolysis, cyclohexane dehydrogenation reactions, are reviewed. 

TABLE 3.3. Kinetic Parameters of the Ethane Hydrogenolysis Reaction in Terms of the Power Rate Law r = k [C2H6] [H2]" ... 

The adsorbed species discussed above are simplified representations of the actual surface complexes since the number of participating surface metal atoms and the number of bonds between the molecule and the surface are not known. Hydrogenolysis reactions, however, are believed to take place on multiple surface sites, specifically, on a certain ensemble of atoms. For example, on the basis of kinetic data, Martin concluded273 that at least 12 neighboring nickel atoms free from adsorbed hydrogen are required in the complete cleavage of ethane ... 

It is appropriate to discuss this pattern of kinetic behavior, and the interpretation offered here, with reference to problems that arise in the elucidation of the mechanisms of cracking reactions of hydrocarbons on nickel. The hydrogenolysis of ethane has been the subject of many studies and it is believed by (inter alia) Sinfelt (74), Tetenyi (87, 123), Shopov (124), and their co-workers that the rate-limiting step is carbon-carbon bond rupture. In... 

Hydrogenolysis of alkanes and related reactions on these catalysts have been studied by a number of groups [18, 19, 21-23], Kinetic parameters for ethane, propane, and n-butane on both catalysts are summarized in Table 3. With propane, selectivities to ethane on... 

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