Intermetallic compounds consist of elements positioned to the left of the Zintl line [1]. Despite forming one of the most extensive families of inorganic materials [2], they gained the attention of the scientific community mainly for their distinctive crystal structures and physical properties. As a result, their chemical behavior has often received limited attention. The development of advanced DFT-based bonding analysis techniques and the successful testing of certain intermetallics as heterogeneous catalysts [3], opened new avenues for exploring their chemistry. In recent years, we have focused on testing RENi5 intermetallics (RE: La, Ce) in CO2 valorization processes, with particular attention to the Sabatier reaction within the 523–773 K temperature range [4]. The Ce-containing sample exhibited the best performance, achieving a 49% CH4 yield at 723 K after reduction at 873 K for 4 hours. XRPD and FE-SEM analyses revealed that both LaNi5 and CeNi5 completely decompose into metallic Ni nanoparticles and La2O3 and CeO2, a process initiated during the pre-reduction treatment under H2 flow. As the decomposition of intermetallic compounds plays a crucial role in the formation of the active material, gaining insight into the surface phenomena that drive this process is essential. To this aim, quantum chemical density functional theory (DFT) calculations were performed on different surface cuts and terminations, revealing the (001) to be the most stable, as experimentally confirmed by X-ray diffraction on LaNi5 crystals, grown following the reactive metal-flux technique. The interaction of H2 over selected sites of different terminations reveals different adsorption behaviour, with a remarkable tendency of the molecules to dissociate confirmed by high adsorption energies (Eads < -1 eV). The Electron Localizability Indicator (ELI-D) mapping of the surface revealed that the dissociation of H2 molecules into hydrides is favoured in correspondence of crystal regions comprising dangling bonds. These results provide the basis for the fine-tuning of machine-learned interatomic potentials for molecular dynamic simulations and for exploring the surface interactions of other molecules, such as CO, CO2, H2O and CH4, involved in the studied processes. [1] F. R.Wagner, Y. Grin, Chemical Bonding Analysis in Position Space in Comprehensive Inorganic Chemistry III, 3rd ed.; Elsevier, 2023; 222– 237. [2] R. Nesper, Angew. Chemie, 1991, 30, 7, 789. [3] M. Armbrüster, Science and Technology of Advanced Materials, 2020, 21, 1, 303. [4] R. Freccero, E. Spennati, G. Garbarino, P. Riani, Applied Catalysis B: Environmental, 2024, 343, 123532.
The surface chemistry of RENi5 (RE: La, Ce) intermetallics: stability and H2 adsorption
Riccardo Freccero;Giorgio Palla;Elena Spennati;Gabriella Garbarino;Paola Riani
2026-01-01
Abstract
Intermetallic compounds consist of elements positioned to the left of the Zintl line [1]. Despite forming one of the most extensive families of inorganic materials [2], they gained the attention of the scientific community mainly for their distinctive crystal structures and physical properties. As a result, their chemical behavior has often received limited attention. The development of advanced DFT-based bonding analysis techniques and the successful testing of certain intermetallics as heterogeneous catalysts [3], opened new avenues for exploring their chemistry. In recent years, we have focused on testing RENi5 intermetallics (RE: La, Ce) in CO2 valorization processes, with particular attention to the Sabatier reaction within the 523–773 K temperature range [4]. The Ce-containing sample exhibited the best performance, achieving a 49% CH4 yield at 723 K after reduction at 873 K for 4 hours. XRPD and FE-SEM analyses revealed that both LaNi5 and CeNi5 completely decompose into metallic Ni nanoparticles and La2O3 and CeO2, a process initiated during the pre-reduction treatment under H2 flow. As the decomposition of intermetallic compounds plays a crucial role in the formation of the active material, gaining insight into the surface phenomena that drive this process is essential. To this aim, quantum chemical density functional theory (DFT) calculations were performed on different surface cuts and terminations, revealing the (001) to be the most stable, as experimentally confirmed by X-ray diffraction on LaNi5 crystals, grown following the reactive metal-flux technique. The interaction of H2 over selected sites of different terminations reveals different adsorption behaviour, with a remarkable tendency of the molecules to dissociate confirmed by high adsorption energies (Eads < -1 eV). The Electron Localizability Indicator (ELI-D) mapping of the surface revealed that the dissociation of H2 molecules into hydrides is favoured in correspondence of crystal regions comprising dangling bonds. These results provide the basis for the fine-tuning of machine-learned interatomic potentials for molecular dynamic simulations and for exploring the surface interactions of other molecules, such as CO, CO2, H2O and CH4, involved in the studied processes. [1] F. R.Wagner, Y. Grin, Chemical Bonding Analysis in Position Space in Comprehensive Inorganic Chemistry III, 3rd ed.; Elsevier, 2023; 222– 237. [2] R. Nesper, Angew. Chemie, 1991, 30, 7, 789. [3] M. Armbrüster, Science and Technology of Advanced Materials, 2020, 21, 1, 303. [4] R. Freccero, E. Spennati, G. Garbarino, P. Riani, Applied Catalysis B: Environmental, 2024, 343, 123532.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
