Cracking of light alkanes over HNaK erionites

The activity and selectivity of a series of partially exchanged HNaK erionites for cracking of n-butane and n-hexane were investigated. Only the strong Brønsted acid sites (SiOHAl groups) were concluded to be active. The turnover frequencies for both reactions increased proportionally to the positive charge at the proton of the strong Brønsted acidic OH group calculated according to the electronegativity model of Sanderson. The positive influence of the increasing charge of the protons (i.e., of their acid strength) is also evidenced in the decrease in the apparent energy of activation for the cracking reaction. The product selectivity suggests that the molecules are cracked according to the monomolecular mechanism. Dehydrogenation gains importance with increasing strength of the protons and decreasing reaction temperature.