(703d) The Role of ABC-6 Zeolite Cavity in Methanol to Olefin Conversion

A density functional study (DFT) study is reported to investigate methanol to olefin (MTO) conversion in four ABC-6 zeolite cavities (cha, avl, aft and h1) differing in shape and size. The reaction barriers and energies of methylations, deprotonations and eliminations based on the side-chain of hydrocarbon pool (HP) mechanism are calculated in these cavities. By comparing their catalytic performance, we find that cha with low barriers in methylations and eliminations exhibits a stronger confinement effect due to its elliptical shape and small size. Avl and aft have low barriers in the first and second methylations, and the elimination barriers similar to cha for producing olefins. With a slightly wider dimension, aft shows high stability for HP species, especially the charged HP species due to long-range interaction with zeolite framework. These results demonstrate that the activity and selectivity of MTO conversion depend strongly on the size and shape of zeolite cavity, which is highly controlled by the confinement effect of zeolite framework. Our calculations also predict a candidate zeolite with aft cavity might perform well in MTO conversion. This theoretical study reveals the relationship between zeolite structure and activity performance, and provides an efficient approach to design and screen ideal zeolites for MTO conversion.