Journal
ACS CATALYSIS
Volume 11, Issue 21, Pages 13575-13590Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.1c03912
Keywords
molybdenum oxide; silica; olefin metathesis; initiation mechanism; active site; reduction; cluster model; DFT
Categories
Funding
- National Science Centre, Poland [2015/19/B/ST4/01836]
- PLGrid Infrastructure
Ask authors/readers for more resources
This study investigates the initiation mechanisms for alkene metathesis on the MoOx/SiO2 catalyst using comprehensive density functional theory studies, revealing the key role of surface silanol groups in reduction processes and alkene activation. The proposed silanol-assisted mechanisms are predicted to be more kinetically and thermodynamically accessible, providing advantages over commonly assumed mechanisms and suggesting a preferential activation pathway by propene for the Mo(IV) species.
A MoOx/SiO2 system is an effective catalyst for alkene metathesis; however, the mechanism of the transformation of the surface metal oxide species into active alkylidene sites is not well recognized. In this work, comprehensive density functional theory studies of the initiation mechanisms for alkene metathesis on the MoOx/SiO2 catalyst have been performed. It is shown that surface silanol groups interacting with Mo species and constituting Brionsted acid sites can play a key role in reduction of the dioxo Mo(VI) species to the mono-oxo Mo(IV) species by alkene, through Mo(VI) alkoxy species, and in subsequent formation of the Mo(VI) alkylidene species. An alternative activation pathway avoiding the reduction step is also possible. The proposed mechanisms of silanol-assisted reduction/initiation with propene are predicted to be more kinetically and thermodynamically accessible than the often assumed pseudo-Wittig mechanism. The silanol-assisted activation of the mono-oxo Mo(IV) species by propene is kinetically preferred over non-silanol-assisted initiation mechanisms, that is, 1,2-hydrogen shift mechanism, ally! mechanism, and oxidative coupling mechanism involving molybdacyclopentane species. The reactivity of the Mo sites is significantly affected by their geometry and the local structure of silica. Our results suggest that only a small fraction of the Mo oxide species with a suitable geometry and neighborhood can be effectively activated by alkenes.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available