Dramatic synergy in CoPt nanocatalysts stabilized by "click" dendrimers for evolution of hydrogen from hydrolysis of ammonia borane
Hydrolysis of ammonia borane (AB) is a very convenient source of H 2 , but this reaction needs catalytic activation to become practical under ambient conditions. Here this reaction is catalyzed by bimetallic late transition-metal nanoparticles (NPs) that are stabilized and activated by "click&q...
| Autores: | , , , , , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2019 |
| País: | Argentina |
| Institución: | Consejo Nacional de Investigaciones Científicas y Técnicas |
| Repositorio: | CONICET Digital (CONICET) |
| Idioma: | inglés |
| OAI Identifier: | oai:ri.conicet.gov.ar:11336/125351 |
| Acceso en línea: | http://hdl.handle.net/11336/125351 |
| Access Level: | acceso abierto |
| Palabra clave: | AMMONIA BORANE COBALT DENDRIMER HYDROLYSIS NANOCATALYST SYNERGY https://purl.org/becyt/ford/2.10 https://purl.org/becyt/ford/2 |
| Sumario: | Hydrolysis of ammonia borane (AB) is a very convenient source of H 2 , but this reaction needs catalytic activation to become practical under ambient conditions. Here this reaction is catalyzed by bimetallic late transition-metal nanoparticles (NPs) that are stabilized and activated by "click" dendrimers. Dendrimers 1 and 2 contain 27 or 81 triethylene glycol terminal groups and 9 or 27 1,2,3-triazole ligands, respectively, located on the dendritic tethers. A remarkable synergy between Pt and Co in the Pt-Co/"click" dendrimer nanocatalysts is revealed. These Pt-Co/"click" dendrimer catalysts are much more efficient for hydrolysis of AB than either "click" dendrimer-stabilized Co or Pt analogues alone. The best catalyst, Pt 1 Co 1 1, stabilized by the nonatriazole "click" dendrimer 1 achieves a turnover frequency number (TOF) of 303 mol H 2 mol cat -1 min -1 (606 mol H 2 mol Pt -1 min -1 ) at 20 ± 1 °C. The AB hydrolysis reaction catalyzed by Pt 1 Co 1 1 is boosted by NaOH, the TOF value reaching 476.2 mol H 2 mol cat -1 min -1 (952.4 mol H2 mol Pt -1 min -1 ), one of the very best results ever obtained for this reaction. The presence of ≥25% Pt in the CoPt nanoalloy provides a reaction rate higher than that obtained with the pure PtNP catalyst alone. The kinetics involves in particular a kinetic isotope effect k D k H of 2.46 obtained for the hydrolysis reaction with D 2 O, suggesting that an O-H bond of water is cleaved in the rate-determining step. Tandem reactions were carried out for the hydrogenation of styrene with hydrogen generated from the hydrolysis of AB. Performing this tandem reaction with D 2 O shows deuteration of the ethylbenzene products, confirming O-D bond cleavage and H/D scrambling on the bimetallic NP surface. Finally, a full reaction mechanism is proposed. This dramatic synergy type should also prove to be useful in a number of other catalytic systems. |
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