Site-Specific Anchoring and Spectral Signatures of Single Atoms, Pairs and Chains for Cs supported on γ-Al2O3 from Atomic-Scale Imaging and 133Cs NMR
- 1Department of Chemistry and Applied Biosciences
- 2Zürich
Abstract
γ-Al2O3 is one of the most widely used supports in heterogeneous catalysis. While the surface of the support provides the anchoring sites for active sites or active phases, e.g. nanoparticles, important for the reactivity and the stability of catalysts, the surface organisation of γ-Al2O3 remains elusive owing to its complexity and heterogeneity. The surface is proposed to host specific anchoring sites depending on the exposed crystalline facets as well as the specific edges between (110) and (100) facets, which are home to distinctive Al coordination environments. Additionally, while alkali metals are essential promoters in heterogeneous catalysis, the way they bind to oxide supports and organise at their surfaces remains poorly understood. In particular, Cs/γ-Al2O3 systems are of practical importance in CO2 conversion processes, where the loading and dispersion of Cs strongly influence activity, yet the nature of the surface Cs species and how their spatial arrangement governs this promoting effect remain poorly understood. Thus, these two interconnected challenges give the opportunity to use specifically designed system to be addressed together. Here, we generate atomically dispersed Cs sites on the surface of well-defined γ-Al2O3 supports with specific crystalline facet organization, according to tailored nanocrystal morphologies. Taking advantage of the high-contrast of Cs (Z=55), we quantify its spatial distribution and specific location by atomic-resolution HAADF-STEM imaging over hundreds of atoms on various support morphologies. Furthermore, we use 133Cs ssNMR and DFT calculations to elucidate the Cs speciation associated with specific anchoring sites. Our work reveals the formation of Cs chains along the (110)/(100) edges of needle-shaped crystals, whereas rhomboids, terminated exclusively by (111) facets, show no such feature. 133Cs NMR and DFT rationalize this behaviour, identifying Cs pairs as the stable configuration at (110)/(100) edges. These results established the specificity of edge anchoring sites, together with bringing details on how Cs binds to surface of relevant oxide support, opening doors to a better understanding of its promotional effect in various catalytic processes, where the spatial distribution of alkali metals is thought to be a crucial factor.
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BibTeX
@misc{sidhoum2026sitespecific,
title = {{Site-Specific Anchoring and Spectral Signatures of Single Atoms, Pairs and Chains for Cs supported on γ-Al2O3 from Atomic-Scale Imaging and 133Cs NMR}},
author = {Charles Sidhoum and Weicheng Cao and Jung-Hua Lin and Nico Richter and Christophe Copéret},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009512/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009512/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Site-Specific Anchoring and Spectral Signatures of Single Atoms, Pairs and Chains for Cs supported on γ-Al2O3 from Atomic-Scale Imaging and 133Cs NMR
AU - Charles Sidhoum
AU - Weicheng Cao
AU - Jung-Hua Lin
AU - Nico Richter
AU - Christophe Copéret
PY - 2026
DA - 2026/09/28
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009512/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009512/v1
AB - γ-Al2O3 is one of the most widely used supports in heterogeneous catalysis. While the surface of the support provides the anchoring sites for active sites or active phases, e.g. nanoparticles, important for the reactivity and the stability of catalysts, the surface organisation of γ-Al2O3 remains elusive owing to its complexity and heterogeneity. The surface is proposed to host specific anchoring sites depending on the exposed crystalline facets as well as the specific edges between (110) and (100) facets, which are home to distinctive Al coordination environments. Additionally, while alkali metals are essential promoters in heterogeneous catalysis, the way they bind to oxide supports and organise at their surfaces remains poorly understood. In particular, Cs/γ-Al2O3 systems are of practical importance in CO2 conversion processes, where the loading and dispersion of Cs strongly influence activity, yet the nature of the surface Cs species and how their spatial arrangement governs this promoting effect remain poorly understood. Thus, these two interconnected challenges give the opportunity to use specifically designed system to be addressed together. Here, we generate atomically dispersed Cs sites on the surface of well-defined γ-Al2O3 supports with specific crystalline facet organization, according to tailored nanocrystal morphologies. Taking advantage of the high-contrast of Cs (Z=55), we quantify its spatial distribution and specific location by atomic-resolution HAADF-STEM imaging over hundreds of atoms on various support morphologies. Furthermore, we use 133Cs ssNMR and DFT calculations to elucidate the Cs speciation associated with specific anchoring sites. Our work reveals the formation of Cs chains along the (110)/(100) edges of needle-shaped crystals, whereas rhomboids, terminated exclusively by (111) facets, show no such feature. 133Cs NMR and DFT rationalize this behaviour, identifying Cs pairs as the stable configuration at (110)/(100) edges. These results established the specificity of edge anchoring sites, together with bringing details on how Cs binds to surface of relevant oxide support, opening doors to a better understanding of its promotional effect in various catalytic processes, where the spatial distribution of alkali metals is thought to be a crucial factor.
ER -