Abstract: By combining multinuclear 1H, 29Si, 27Al and 51V solid-state NMR experimental measurements with reactivity and selectivity data, as well as first-principles calculations, for ternary bi-layered supported VOx/Al2O3/SiO2 catalysts, the structure of the dehydrated surface vanadia species was determined for each combination of supported VOx and AlOx active components. The specific structure of the surface vanadia sites in the ternary bi-layered supported VOx/Al2O3/SiO2 catalyst system have been investigated for the first time. The following vanadia sites are proposed based on the current findings: At low vanadia content, surface VO(OH)(OSi)2 sites form on the alumina-free surface of the SiO2 support in the bi-layered supported VOx/Al2O3/SiO2 catalyst system. In addition, two types of VO(OSi)3 surface species are likely present in this system. On small alumina clusters, weakly bonded surface VO(OH)(OAl)2 sites also form, along with the sites containing mixed Si/Al pods VO(OH)(OAl)(OSi). As the size of alumina clusters increases, strongly bonded VO(OAl)3 centers form, alongside the surface sites containing mixed pods VO(OAl)2(OSi) and VO(OAl)(OSi)2. The content of these sites increases with the loading of vanadia. Comparing supported VOx/SiO2, VOx/Al2O3, and bi-layered VOx/Al2O3/SiO2 catalyst systems revealed differences in catalytic activity due to the presence of new sites with different pods, with OH groups as well as the influence of Al-O-Si bonds on the electronic structure of surface vanadia sites on the alumina clusters. During the formation of dimethyl ether (DME), the turnover frequency (TOFDME) of the catalysts decreases with increasing domain size of the alumina clusters on SiO2. Addition of surface VOx sites, however, slightly decreases the TOFDME with the higher vanadia content weakening the activity of the alumina clusters. When surface VOx exists predominantly as V/Al1 and V/Al2, TOFredox depend on the vanadia content with lower vanadia content resulting in higher the TOFredox values. The 51V NMR spectra show that this decrease in redox TOF value correlates with the appearance of vanadia sites associated with silica pods. The activity of the catalysts was tested in methanol conversion reactions.

Cite: Lapina O.B. , Khabibulin D.F. , Shubin A.A. , Papulovskiy E. , Terskikh V.V. , Wachs I.E.
Structure and Reactivity of Surface Vanadia Sites in bi-Layered Supported VOx/AlOx/SiO2 Catalysts via Solid-State NMR, First-Principles Calculations, and Catalytic Studies
Catalysis Today. 2024. V.441. 114880 :1-14. DOI: 10.1016/j.cattod.2024.114880 WOS Scopus РИНЦ AN OpenAlex

Dates:

Submitted:	Mar 26, 2024
Accepted:	Jun 5, 2024
Published online:	Jun 6, 2024
Published print:	Nov 1, 2024

Identifiers:

Web of science:	WOS:001253234100001
Scopus:	2-s2.0-85195482912
Elibrary:	68553696
Chemical Abstracts:	2024:1382135
OpenAlex:	W4399381709

Citing:

DB	Citing
OpenAlex	2
Scopus	3
Web of science	2
Elibrary	1

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