The role of zeolite topology in the stepwise methylation of ethene by surface methoxides was investigated. Density functional theory was employed in the determination of reaction mechanisms and energy barriers. Elementary steps were studied across multiple frameworks (i.e., BEA, CHA, FER, MFI, and MOR) constituting a wide variety of confinement environments. Surface methoxides were found to react with ethene through a transition state containing planar CH3 species, which was best stabilized at the intersection of the 10-membered ring channels of MFI. A cyclopropane reaction intermediate was found in all cases; its decomposition necessitated a transition state containing a primary carbocation, which was best stabilized within the 8-membered ring side pockets of MOR. The activation energies corresponding to each transition state geometry depend upon different aspects of the local pore topology, implying that confinement effects can not be simply correlated to pore size.
Methylation of ethene by surface methoxides: A periodic PBE+D study across zeolites
Cococcioni M.
2012-01-01
Abstract
The role of zeolite topology in the stepwise methylation of ethene by surface methoxides was investigated. Density functional theory was employed in the determination of reaction mechanisms and energy barriers. Elementary steps were studied across multiple frameworks (i.e., BEA, CHA, FER, MFI, and MOR) constituting a wide variety of confinement environments. Surface methoxides were found to react with ethene through a transition state containing planar CH3 species, which was best stabilized at the intersection of the 10-membered ring channels of MFI. A cyclopropane reaction intermediate was found in all cases; its decomposition necessitated a transition state containing a primary carbocation, which was best stabilized within the 8-membered ring side pockets of MOR. The activation energies corresponding to each transition state geometry depend upon different aspects of the local pore topology, implying that confinement effects can not be simply correlated to pore size.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
