Significance of Acid Strength

While average deprotonation energy is a good measure of the intrinsic Bronsted acid strength of a zeoHte, it is the extrinsic acidity, also impacted by the chemical interaction between the protonated basic probe molecule and the deprotonated zeoHte, that really counts for catalysis. 

In the case of alkenes, 1-pentene reactions were studied over a catalyst with FAU framework (Si/Al2 = 5, ultrastable Y zeoHte in H-form USHY) in order to establish the relation between acid strength and selectivity [25]. Both fresh and selectively poisoned catalysts were used for the reactivity studies and later characterized by ammonia temperature programmed desorption (TPD). It was determined that for alkene reactions, cracking and hydride transfer required the strongest acidity. Skeletal isomerization required moderate acidity, whereas double-bond isomerization required weak acidity. Also an apparent correlation was established between the molecular weight of the hard coke and the strength of the acid sites that led to coking. 

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