Through DFT calculations, we have studied the MTO
conversion within cha, lta, and lev cavities assuming the same
side-chain mechanism. The cha cavity exhibits the lowest
intrinsic free-energy barriers for all of the methylation and
olefin-production steps, which agrees well with the fact that
SAPO-34 constructed by the cha cavities is one of the most
widely used catalysts for MTO conversion. Further investigations
show that the suitable confinement effect of the cha
cavity might be the reason for such low reaction barriers. The
lev and lta cavities are either too small or too large, providing
too much or too little confinement to the HP species. Our
theoretical calculations clearly demonstrate the essential role of
the confinement of zeolite cavities during MTO conversion.
Other zeolite cavities might be good candidate catalysts for
MTO conversion following the side-chain route if they are able
to provide suitable confinement to HP species such as cha does.