Influence of acidity on the H-Y zeolite performance in n-decane catalytic cracking: evidence of a series/parallel mechanism

In this work, n-decane cracking, taken as a model reaction for the catalytic cracking of Fischer–Tropsch naphta fraction, was carried out at 350 °C over various H-Y zeolites, with different Si/Al ratios and, thus, different acid strength distributions. It was observed that the catalytic activity does not decrease gradually with the contact time for the catalysts under study, notably for the zeolite samples having lower activity (hence lower total acidity as well) but, in fact, the catalytic activity first increases with contact time and then decreases. This behavior was successfully interpreted by resorting to the fundamental view of the catalytic cracking mechanism as a series/parallel scheme. The authors combined the bi-molecular process involving a carbenium-chain mechanism and the protolytic process involving the formation of carbonium ions to construct a simple model to predict, in as much detail as possible, the zeolite catalytic performance of the different catalysts that were used.