Bimetallic Catalyst Particle Nanostructure. Evolution from Molecular Cluster Precursors
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- 作者：Michael S. Nashner ; David M. Somerville ; Philip D. Lane ; David L. Adler ; John R. Shapley ; and Ralph G. Nuzzo
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：December 25, 1996
- 年：1996
- 卷：118
- 期：51
- 页码：12964 - 12974
- 全文大小：499K
- 年卷期：v.118,no.51(December 25, 1996)
- ISSN：1520-5126
文摘
A set of supported bimetallic catalysts, designated[Re7Ir-N], [Re7Ir-P],[Re5IrRe2-N], and[Re5IrRe2-P], has been prepared from two structural isomers (1 and2) of the cluster compound[Z]2[Re7IrC(CO)23](Z+ =NEt4+,N(PPh3)2+) by deposition ontohigh surface area alumina (
1% Re) and activation in H2at 773 K. Thespecific activities of the catalysts for ethane hydrogenolysis at 500 Kvary significantly (3-63 mmol of CH4/mol ofRe7Ir per s) and depend on both the metal frameworkstructure and the counterion present in the precursor.Interpretation of EXAFS data (from both Re and IrL3-edges) has enabled the development of specific modelsforthe catalyst particle nanostructures that correlate with the catalyticactivities. The more active catalysts([Re7Ir-N]and [Re5IrRe2-N]) are modeled by ahemisphere of close-packed (hcp) metal atoms (average diameter 1 nm)withIr at the core. On the other hand, the less active catalysts([Re7Ir-P] and[Re5IrRe2-P]) are better describedastwo-dimensional layer structures. A combination of techniques,TPDE, IR, XANES, and EXAFS, applied undertemperature-programmed conditions, has demonstrated that evolution ofthe final catalyst particle nanostructure dependson significant initial fragmentation of the cluster framework followedby preferential nucleation at iridium centers.
1% Re) and activation in H2at 773 K. Thespecific activities of the catalysts for ethane hydrogenolysis at 500 Kvary significantly (3-63 mmol of CH4/mol ofRe7Ir per s) and depend on both the metal frameworkstructure and the counterion present in the precursor.Interpretation of EXAFS data (from both Re and IrL3-edges) has enabled the development of specific modelsforthe catalyst particle nanostructures that correlate with the catalyticactivities. The more active catalysts([Re7Ir-N]and [Re5IrRe2-N]) are modeled by ahemisphere of close-packed (hcp) metal atoms (average diameter 1 nm)withIr at the core. On the other hand, the less active catalysts([Re7Ir-P] and[Re5IrRe2-P]) are better describedastwo-dimensional layer structures. A combination of techniques,TPDE, IR, XANES, and EXAFS, applied undertemperature-programmed conditions, has demonstrated that evolution ofthe final catalyst particle nanostructure dependson significant initial fragmentation of the cluster framework followedby preferential nucleation at iridium centers.