(2)where E ads is the alkane adsorption energy at the reaction site and E int is the intrinsic activation energy. (9) This mechanism represents the direct protonation of the alkane at the Brønsted acid site, (11) creating a carbocation intermediate, which then dissociates into a shorter alkene and alkane: (10) The alternative monomolecular Haag-Dessau mechanism is preferred at high temperature ( T > 600 K) and low partial alkanes pressure. This mechanism involves a chain of reactions propagated by the carbenium ions. (9) The bimolecular mechanism dominates at low temperatures, high partial alkanes pressure, and high conversion. (8) The mechanism of cracking depends on the reaction conditions. Fluid catalytic cracking is a key process in the conversion of crude oil to transportation fuels and petrochemical feedstock. (1−7) In addition to acidity and microporosity, the high thermal stability and low production cost facilitate the use of zeolites in many industrial processes. Guest-site congruity imparts differences in the stability of reactive species, transition states, and intermediates, giving rise to shape selectivity. For any particular zeolite cage, the specific geometric structure of the Brønsted acid sites affects their ability to accommodate guest species. When the negative charge on the AlO 4 – site is compensated by a proton, a (≡Al–OH–Si≡) Brønsted acid site is formed. Zeolites are microporous materials composed of corner-sharing AlO 4 – and SiO 4 tetrahedra linked in a superlattice of cages and channels.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
December 2022
Categories |