STRUCTURE-SENSITIVE AND STRUCTURE-INSENSITIVE CATALYTIC REACTIONS AND THEIR NEW CHARACTERISTICS, DEMONSTRATED WITH COPPER-SUPPORTED CATALYSTS

A new type of structure sensitivity for copper deposited on silica, alumina, or magnesia catalysts has been observed for the partial hydrogenation of cyclopentadiene. Whereas in the case of the conventional definition of the structure sensitivity the rate of a reaction per gram of metal increases first linearly when the metal surface area per gram of metal increases (structure insensitivity) and then increases more than linearly (structure sensitivity), in the case of copper catalysts this rate is constant for each family of catalysts when the surface area of the metal increases in each family, but varies from one family to the other. This behavior is explained by the interaction between the metal and the carrier which changes, for each family, the catalytic quality of copper per unit surface of copper. Conversely, for the hydrogenation of ethylene the same catalysts behave in a conventional way (structure sensitivity) but a compensation effect between the preexponential factor and the activation energy for all families of catalysts is detected. For this reason an isokinetic temperature may be observed for these catalysts where the rate of the reaction is the same for all catalysts and the reaction is apparently structure insensitive. It therefore appears that the criterion which allows the classification of a reaction as structure sensitive or insensitive should also include the temperature or the range of temperatures if the compensation effect is simultaneously observed. © 1979.