Methanol to Olefins Reaction over Cavity-type Zeolite:
Cavity Controls the Critical Intermediates and Product Selectivity
Wenna Zhang
Jingrun Chen
Shutao Xu
Yueying Chu
Yingxu Wei
Yuchun Zhi
Jindou Huang
Anmin Zheng
Xinqiang Wu
Xiangju Meng
Fengshou Xiao
Feng Deng
Zhongmin Liu
10.1021/acscatal.8b02164.s001
https://acs.figshare.com/articles/journal_contribution/Methanol_to_Olefins_Reaction_over_Cavity-type_Zeolite_Cavity_Controls_the_Critical_Intermediates_and_Product_Selectivity/7258439
Methanol to olefins
(MTO) reaction over H-RUB-50 zeolite, an eight-membered
ring (8-MR) and cavity-type zeolite, presents higher selectivity for
ethene. The host–guest interaction was dissected and used to
explain the cavity-controlled reaction route and product selectivity.
By the aid of the in situ <sup>13</sup>C MAS NMR spectroscopy, GC-MS, <sup>12</sup>C/<sup>13</sup>C-methanol switch experiments, and theoretical
calculations, the methylbenzenium cations, methylcyclopentenyl cations
(triMB<sup>+</sup>, tetraMB<sup>+</sup>, and triMCP<sup>+</sup>),
and their deprotonated forms with less methyl groups substitution
were captured over LEV zeolite and confirmed as the critical reaction
intermediates. The energetic span model was employed to identify the
preferred reaction mechanism and provide the theoretical evidence
to understand product selectivity. The side-chain methylation mechanism
was theoretically predicated to be the energetically favorable route
for olefins generation with the participation of these active intermediates.
Paring cycle with trimethlycyclopentadienyl cation as the intermediate
makes less contribution to ethene formation due to the relatively
large energy span. Based on the overall evaluation of the catalytic
cycle, the difference of energy span of the whole reaction pathway
for ethene and propene formation can give direct theoretical evidence
for product selectivity. Additional study to the steps for generating
precursors of ethene and propene offers extra support on the understanding
of product selectivity and the dominant generation of ethene. This
study captured the critical intermediates and established a rational
and energetically feasible route of light olefins generation from
MTO reaction over H-RUB-50. More importantly, it is exhibited that
cavity controls the product selectivity via the important steric constraint
for the formation of critical intermediates and the proceeding of
critical reaction steps, based on the understanding of the host–guest
interaction of the cavity-type zeolite catalyzed MTO reaction.
2018-10-16 00:00:00
13 C MAS NMR spectroscopy
side-chain methylation mechanism
ethene
energy span
product selectivity
formation
GC-MS
cavity-type zeolite
intermediate
H-RUB -50 zeolite
light olefins generation
methyl groups substitution
LEV
cation
Product Selectivity Methanol
MTO reaction
cavity-controlled reaction route