Correlation of the cracking activity with solid acidity and adsorption property on zeolites

Activities for catalytic cracking of octane and hexane were measured on various zeolites, and the dependence of the turnover frequency and the activation energy on the characterization parameters was studied. The heats of ammonia and alkanes adsorption were measured to be correlated with the catalytic activities. From the relations between the heats of alkane and ammonia adsorption, zeolites were divided into two Groups I and II In the zeolites of Group I on which a close relation between heats of alkane and ammonia adsorptions was observed, a compensation relation between the heat of alkane adsorption and activation energy was observed, but the so-called constant intrinsic activation energy was not confirmed. In the zeolites of Group II on which the relation between the heats of adsorption was not observed, the compensation relation did not exist. Thus, the dependence of the cracking activity upon characterization parameters was summarized: i.e., the heat of alkane adsorption cannot be utilized as a parameter to elucidate the activities of a few zeolites in Group II: on the other hand, the heat of ammonia adsorption can be totally correlated with these activities. Thus, the prevailing role of the solid acidity in the alkane cracking is proven. Finally, the cracking activity is discussed based on the solid acidity. (C) 2009 Elsevier B.V. All rights reserved.