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Nearly uniform MgO-supported pentaosmium cluster catalysts
V A Bhirud1, G Panjabi, S N Salvi
1Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616, USA.
Langmuir : the ACS Journal of Surfaces and Colloids
|July 14, 2004
Summary
Osmium carbonyl clusters, specifically [Os5C(CO)14]2-, were synthesized on MgO. These clusters retained their structure after decarbonylation in helium but formed larger metallic clusters in hydrogen, impacting catalytic activity for toluene hydrogenation.
Area of Science:
- * Inorganic Chemistry
- * Materials Science
- * Catalysis
Background:
- * Osmium carbonyl clusters are of interest for catalysis.
- * Synthesis and characterization of supported osmium clusters are crucial for understanding their properties.
Purpose of the Study:
- * To synthesize and characterize the osmium pentanuclear carbide carbonyl cluster [Os5C(CO)14]2- on a magnesium oxide (MgO) surface.
- * To investigate the structural stability and transformations of the supported cluster under decarbonylation conditions (He and H2).
- * To compare the catalytic activity of the intact cluster and its derived forms in toluene hydrogenation.
Main Methods:
- * Synthesis via reductive carbonylation of Os3(CO)12 on MgO at 548 K and 1 bar.
- * Characterization using infrared (IR) spectroscopy, 13C Nuclear Magnetic Resonance (NMR), and extended X-ray absorption fine structure (EXAFS) spectroscopy.
- * Catalytic testing for toluene hydrogenation.
Main Results:
- * Successful synthesis of MgO-supported [Os5C(CO)14]2- in approximately 65% yield, alongside smaller osmium carbonyl clusters.
- * Decarbonylation in He at 573 K preserved the Os5C frame, confirmed by EXAFS (Os-Os coordination number of 3.4).
- * Treatment in H2 at 573 K led to the formation of larger, aggregated metallic osmium clusters.
- * The intact [Os5C(CO)14]2- cluster exhibited significantly lower catalytic activity for toluene hydrogenation compared to the aggregated osmium clusters.
Conclusions:
- * The Os5C frame of the supported cluster is stable to decarbonylation in helium.
- * Hydrogen treatment induces cluster aggregation and formation of metallic osmium.
- * The catalytic performance in toluene hydrogenation is highly dependent on the osmium cluster's structure and metallic character.