Hydrogenolysis compensation effect

The support induced changes in hydrogenolysis reactions of alkanes can be explained to a large extent by support induced changes in the Pt-H bond strength and hydrogen adsorption site on Pt. This can easily explain the well-known compensation effect found in the kinetics of the hydrogenolysis of alkanes catalyzed by supported metal catalysts. 

In addition to the correlation between the order in Ph2 and Eapp, the compensation effect is regularly observed for hydrogenolysis reactions48 50. The compensation effect denotes a linear relationship between the apparent activation energy and the pre-exponential factor. This relationship is also called the Constable-Cremer relation51 ... 

These new results can explain the compensation effect and the negative order in the partial pressure of hydrogen found for the hydrogenolysis of neopentane catalyzed by supported Pt particles. The kinetics of the catalytic reaction is driven by the mode of the adsorption of hydrogen on the Pt surface. 

Figure 7.5. Compensation effect for the hy-drogenolysis reaction. The logarithm of the preexponential factor is plotted against the apparent activation energy, A , for this reaction over several transition-metal catalysts. The squares, triangles, and circles represent values for ethane, methylamine, and methyl chloride hydrogenolysis, respectively [1881.

Figure 14.13. Compensation effects for the Arrhenius parameters of MCP hydrogenolysis on R/Ti02 variously pretreated (see text) , 2-methylpentane A, 3-methylpentane v> n-hexane O, C1-C5 alkanes.

Figure 14.6. Arrhenius parameters for hydrogenolysis of n-hexane on Pd/Al203 shown as a compensation plot effect of various metal loadings and pre-treatments (see text). The parallel Unes delineate the zone that contains the points for lower alkanes on catalysts in Figure 13.3 the broken line is that for EUROPT-1. O, 0.3% Pd , 0.6% Pd A, 2.8% Pd. Open points, LTR half-filled points, HTR filled points, regenerated.

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