Cracking activity, influencing factors

The CF and GF represent the coke- and gas-forming tendencies of an E-cat compared to a standard steam-aged catalyst sample at the same conversion. The CF and GF are influenced by the type of fresh catalyst and the level of metals deposited on the E-cat. Both the coke and gas factors can be indicative of the dehydrogenation activity of the metals on the catalyst. The addition of amorphous alumina to the catalyst will tend to increase the nonselective cracking, which forms coke and gas. 

Tphe excellent catalytic activity of lanthanum exchanged faujasite zeo-A lites in reactions involving carbonium ions has been reported previously (1—10). Studies deal with isomerization (o-xylene (1), 1-methy 1-2-ethylbenzene (2)), alkylation (ethylene-benzene (3) propylene-benzene (4), propylene-toluene (5)), and cracking reactions (n-butane (5), n-hexane, n-heptane, ethylbenzene (6), cumene (7, 8, 10)). The catalytic activity of LaY zeolites is equivalent to that of HY zeolites (5 7). The stability of activity for LaY was studied after thermal treatment up to 750° C. However, discrepancies arise in the determination of the optimal temperatures of pretreatment. For the same kind of reaction (alkylation), the activity increases (4), remains constant (5), or decreases (3) with increasing temperatures. These results may be attributed to experimental conditions (5) and to differences in the nature of the active sites involved. Other factors, such as the introduction of cations (11) and rehydration treatments (6), may influence the catalytic activity. Water vapor effects are easily... 

Based on experiments with pure hydrocarbons and synthetic silica-alumina catalyst, it has been estimated that the cracking-rate constant at 932°F. should decrease by a factor of to when particle diameter is increased from about 0.5 mm. to 4 mm. (74). The influence of particle size on effective activity is especially pronounced at very high cracking temperatures (49). This behavior is in line with predictions because, with increasing temperature, reaction rate on the catalyst surface increases more rapidly than the rate of diffusion of reactants into the pores. Cracking of unsymmetrical diarylethanes is an exceptional case in which the reaction appears to depend entirely upon the number of collisions of the hydrocarbon with the external area of the catalyst particles (208). 

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