Isobutane Cracking over Y-Zeolites. I. Development of a Kinetic Model

Article abstract of DOI:10.1006/jcat.1995.1107

We have developed a kinetic model for isobutane cracking over calcined and steamed Y-zeolite catalysts based on carbo-cation surface chemistry.The model utilized 21 reaction steps, including initiation, oligomerization, β-scission, olefin desorption, isomerization, and hydride ion transfer, which adequately described the formation of all major products.We estimated kinetic parameters using transition state theory, the Evans-Polanyi correlation, and gas phase thermodynamic data.In order to relate the gas phase calculations to the catalyst surface, we introduced a parameter ΔH₊, which is the heat of stabilization of a carbenium ion relative to the heat of stabilization of a proton in the zeolite framework.The model provided a good description of the experimental data for calcined and steamed catalyst with physically realistic kinetic parameters.The main difference between the two catalysts was the higher ΔH₊ for the steamed catalyst.This indicates that steaming decreased the Broensted acid strength of the catalyst.