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Volumn 20, Issue 7, 2008, Pages 2592-2601

Transition-metal nanocluster stabilization versus agglomeration fundamental studies: Measurement of the two types of rate constants for agglomeration plus their activation parameters under catalytic conditions

Author keywords

[No Author keywords available]

Indexed keywords

AUTOCATALYTIC AGGLOMERATION; BIMOLECULAR AGGLOMERATION;

EID: 42449110364     PISSN: 08974756     EISSN: None     Source Type: Journal    
DOI: 10.1021/cm062001h     Document Type: Article
Times cited : (33)

References (72)
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    • 4 (and, indeed, are experimentally apparent in the present work, such as the lack of a critical coagulation concentration for the polyxoanion-stabilized Ir(0) nanoclusters used in the present work). However, for the sake of simplicity, herein, we have chosen to distinguish the terms nanocluster from colloid or nanocolloid only where we felt it was important.
    • 4 (and, indeed, are experimentally apparent in the present work, such as the lack of a critical coagulation concentration for the polyxoanion-stabilized Ir(0) nanoclusters used in the present work). However, for the sake of simplicity, herein, we have chosen to distinguish the terms "nanocluster" from "colloid" or "nanocolloid" only where we felt it was important.
  • 42
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    • In the solid-state, one useful practical definition of stability is the ability of a given stabilizer to prevent nanocluster agglomeration when the chosen nanoclusters are taken to dryness and then redissolved. Can they be fully redissolved without agglomeration as assayed by TEM (as well as by ≥ 1 other, independent method) and without bulk metal formation as judged by the eye, This definition, albeit qualitative, has proven to be one of the most stringent tests within the five-criteria method of ranking catalytically active nanoclusters.12
    • 12
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    • Pyridine as a classic agglomerant of (classical) colloids: (a) Weitz, D. A.; Huang, J. S.; Lin, M. Y.; Sung, J. Phys. Rev. Lett. 1985, 54, 1416.
    • Pyridine as a classic agglomerant of (classical) colloids: (a) Weitz, D. A.; Huang, J. S.; Lin, M. Y.; Sung, J. Phys. Rev. Lett. 1985, 54, 1416.
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    • 4 kinetic run.
    • 4 kinetic run.
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    • (a) Piatt, J. R. Science 1964, 146, 347.
    • (1964) Science , vol.146 , pp. 347
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    • ∼900 nanoclusters.
    • ∼900 nanoclusters.
  • 61
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    • The reader may wonder if the change in solvent from that employed in many of our earlier studies, acetone, to propylene carbonate, can contribute to a change in mechanism. The data in Table S1 of the Supporting Information demonstrate that the answer is no, at least in the present case and under the specific conditions used in the present studies.
    • The reader may wonder if the change in solvent from that employed in many of our earlier studies, acetone, to propylene carbonate, can contribute to a change in mechanism. The data in Table S1 of the Supporting Information demonstrate that the answer is no, at least in the present case and under the specific conditions used in the present studies.
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    • η‡, see (a) Barthel, J.; Neueder, R.; Roch, H. J. Chem. Eng. Data 2000, 45, 1007.
    • η‡, see (a) Barthel, J.; Neueder, R.; Roch, H. J. Chem. Eng. Data 2000, 45, 1007.
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    • 3‡; = 6.2(3) kcal/mol is, therefore, larger than just the barrier to diffusion in propylene carbonate, so that other factors besides diffusion must be introducing a barrier into the B + B - C agglomeration process.
    • 3‡; = 6.2(3) kcal/mol is, therefore, larger than just the barrier to diffusion in propylene carbonate, so that other factors besides diffusion must be introducing a barrier into the B + B - C agglomeration process.
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    • Intriguing mechanistic questions are opened up by these findings. One is whether an associative mechanism occurs via bridging ligands that might, conceivably, bind the two metal particles, thereby giving the surface ligands more time to move, leaving larger bare-metal spots that are presumably key to the metal-metal bond formation process that leads to larger metal aggregates. Alternatively, another interesting question is if there are sufficient bare-metal spots on the surface of the nanocluster to support a direct, associative agglomeration, or is a mere single, bare-metal atom sufficient to initiate agglomeration? A third important question is how much the olefin (i.e, the cyclohexene used in the reporter reaction) is influencing the observed activation parameters, something that should be addressable by examining other olefins or, better, repeats of the present studies by other methods without and then with cyclohexene, H2, and then both cyclohexene and H 2pr
    • 2present.
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    • W. E. Buhro and R. G. Finke research groups. Collaborative studies in progress
    • W. E. Buhro and R. G. Finke research groups. Collaborative studies in progress.
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    • (b) http://uwmml.pharmacy.wisc.edu.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.