SCHEDULED MAINTENANCE
Reversible transformation of sub-nanometer Ga-based clusters to isolated [4]Ga(4Si) sites creates active centers for propane dehydrogenation†
a
Alexander I.
Serykh,
b
Agnieszka
Kierzkowska,
a
Paula M.
Abdala,
a
Christophe
Copéret,
d
Pierre
Florian,
*e
Alexey
Fedorov
*a
and
Christoph R.
Müller
*a
Abstract
Ga-based propane dehydrogenation (PDH) catalysts are explored in industry as an alternative to PtSn and CrOx-based catalysts. Yet, at present, there is only limited understanding of the structural dynamics of surface sites in Ga-based PDH catalysts. Here, we employ atomic layer deposition (ALD) to engineer a sub-monolayer of Ga species on dehydroxylated silica, which serves as a model PDH catalyst. While the ALD-grown shell contains, after calcination at 500 °C, tetra- and pentacoordinate Ga3+ sites with both Si and Ga atoms in the second coordination sphere (i.e., [4]Ga(Si/Ga) and [5]Ga(Si/Ga) sites), its exposure to ambient air leads to sub-nanometer GaxOy(OH)z clusters with [4]Ga(Ga) and [6]Ga(Ga) sites, due to the hydrolysis of the Ga–O–Si linkages by the moisture of ambient air. When calcining the material at 650 °C, the [4]Ga(Ga) and [6]Ga(Ga) sites evolve leading to a silica surface dominated by isolated tetracoordinate [4]Ga(4Si) sites, that is, [(![[triple bond, length as m-dash]](https://www.rsc.org/images/entities/char_e002.gif)
SiO)3Ga(XOSi)] sites, where X is H or Si. Exposure of the dehydroxylated material with [4]Ga(4Si) sites to ambient air reforms the sub-nanometer GaxOy(OH)z clusters, indicating the reversibility of the Ga dispersion and agglomeration as a function of the extent of silica (de)hydroxylation. The presence of [4]Ga(4Si) sites coincides with a high performance in PDH, achieving an initial turnover frequency of ca. 12 h−1 and propene selectivity of ca. 85%, while deactivating by only 34% over 20 h of time on stream. Overall, our results highlight the dynamic nature of the dispersion and agglomeration of Ga3+ sites during the dehydroxylation (by calcination) and rehydration (ambient air exposure).
![Graphical abstract: Reversible transformation of sub-nanometer Ga-based clusters to isolated [4]Ga(4Si) sites creates active centers for propane dehydrogenation](/en/Image/Get?imageInfo.ImageType=GA&imageInfo.ImageIdentifier.ManuscriptID=D3CY01446K&imageInfo.ImageIdentifier.Year=2024)
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