Ethane hydrogenolysis effect

In view of this complexity and the evident interrelation between reaction and self-poisoning, it is actually less surprising that the literature does not offer a clear picture of the particle size effects in the HC reactions. Hydro-genolysis of ethane by Pt and lr reveals a decrease in TON by a factor of 10-15, when the dispersion D is increased (antipathic relation) from %0.1 to 0.8 (231). An early paper on ethane hydrogenolysis by Ni reports a strong and a later paper reports a less pronounced variation of activity with D. However, in contrast to Pt and lr, this variation is always a sympathetic one (232, 233). The same holds true for Rh (234). 

The effects of the overlayer on the hydrogenation of carbon monoxide and the hydrogenolysis of ethane were examined. With increasing titania coverage, the activity of Rh for carbon monoxide hydrogenation passes through a maximum, whereas the activity for ethane hydrogenolysis decreases monotonically. 

In contrast, ethane hydrogenolysis, which is a structure sensitive reaction over bulk Ni, displayed marked structural effects on the Ni/W system (41). We have observed, as shown in Figure 5, that the specific rate, or rate per surface metal atom, but not the activation energy, is a strong function of metal coverage on the Ni/W(110) surface, suggesting that the critical... 

Figure 5.2.6 I Effect of alloy composition on the rates of ethane hydrogenolysis and cyclohexane dehydrogenation on Ni-Cu catalysts. (Figure from Catalytic Hydrogenolysis and Dehydrogenation Over Copper-Nickel Alloys by J. H.

The presence of a second metal can also have a significant impact on the selectivity of a reaction. Recall the data shown in Fig. 3.1 illustrates the effect of adding copper to a nickel catalyst used to promote both cyclohexane dehydrogenation and ethane hydrogenolysis. 39 It was found that the addition of... 

As an attempt in this direction, a hierarchy was recently developed for nickel catalysts (6). The basic idea is to monitor the chemical properties of a catalyst as probed by hydrogen chemisorption, ethane hydrogenolysis, and carbon monoxide hydrogenation. The hierarchy, originally developed for Ni/I O catalysts, was later extended to nickel supported on phosphate-containing materials and a niobia-silica surface phase oxide. In this paper the usefulness of the hierarchy will be illustrated by its ability to differentiate between support effects of niobia and phosphate, and to establish the intermediate degree of interaction of niboia-silica. 

Catalytic chemists have long suspected that the properties of the active component may be affected by contact with the support. Indeed, as we shall see. there are so many ways in which supports exert influences that it is not surprising that these were noted. It was not until recently that researchers were able to unravel some of the these effects with more sophisticated characterization methods. For example, measured areal rates of ethane hydrogenolysis showed the patterns in Table 2.4. ... 

The effect on activity for the dehydrogenation reaction is very different from that for the hydrogenolysis reaction. In the case of ethane hydrogenolysis, adding only 5 at.% copper to nickel decreases catalytic activity by three orders of magnitude. Further addition of copper continues to decrease the activity. However, the activity of nickel for dehydrogenation of cyclohexane is affected very little over a wide range of composition, and actually increases on addition of the first increments of copper to nickel. Only as the catalyst composition approaches pure copper is a marked decline in catalytic activity observed. 

Figure 3.3 The effect of hydrogen treatment temperature on the hydrogen chemisorption capacity and ethane hydrogenolysis activity of ruthenium-copper aggregates containing 1.5 at.% copper (3). (Reprinted with permission from Academic Press, Inc.)...

It is known that nature and quality of a catalyst carrier material is important to the performance of a catalyst. The carrier impacts the catalytic reaction and process by its chemical, physical or mechanical properties and/or provides co-catalytic function. An example for a typical support effect is the well-investigated standard reaction of ethane hydrogenolysis over nickel or cobalt on different support materials (Figure 1) [1] ... 

By studying a series of Rh/Ti02 catalysts of varying metal dispersion, we noticed that the deactivating effect of HTR for ethane hydrogenolysis could be better correlated with the extent of interfacial perimeter around the metal particle than with the extent of interfacial metal-support contact area. In addition, we found that the kinetics of deactivation followed a square root of time dependence, which is generally observed for diffu-... 

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