A Four-Step Mechanism for the Formation of Supported-Nanoparticle Heterogenous Catalysts in Contact with Solution: The Conversion of Ir(1,5-COD)Cl/gamma-Al2O3 to Ir(0)(similar to 170)/gamma-Al2O3

作者：Kent Patrick D; Mondloch Joseph E; Finke Richard G^*

来源：Journal of the American Chemical Society, 2014, 136(5): 1930-1941.

DOI：10.1021/ja410194r

Product stoichiometry, particle-size defocusing, and kinetic evidence are reported consistent with and supportive of a four-step mechanism of supported transition-metal nanoparticle formation in contact with solution: slow continuous nucleation, A -> B (rate constant k(1)), autocatalytic surface growth, A + B -> 2B (rate constant k(2)), bimolecular agglomeration, B + B -> C (rate constant k(3)), and secondary autocatalytic surface growth, A + C -> 1.5C (rate constant k(4)), where A is nominally the Ir(1,5-COD)Cl/gamma-Al2O3 precursor, B the growing Ir(0) particles, and C the larger, catalytically active nanoparticles. The significance of this work is at least 4-fold: first, this is the first documentation of a four-step mechanism for supported-nanoparticle formation in contact with solution. Second, the proposed four-step mechanism, which was obtained following the disproof of 18 alternative mechanisms, is a new four-step mechanism in which the new fourth step is A + C -> 1.5C in the presence of the solid, gamma-Al2O3 support. Third, the four-step mechanism provides rare, precise chemical and kinetic precedent for metal particle nucleation, growth, and now agglomeration (B + B -> C) and secondary surface autocatalytic growth (A + C -> 1.5C) involved in supported-nanoparticle heterogeneous catalyst formation in contact with solution. Fourth, one now has firm, disproof-based chemical-mechanism precedent for two Specific, balanced pseudoelementary kinetic steps and their precise chemical descriptors of bimolecular particle agglomeration, B + B -> C, and autocatalytic agglomeration, B + C -> 1.5C, involved in, for example, nanoparticle catalyst sintering.

• 出版日期2014-2-5