Chemisorption of Rh4(CO)12 on to a highly divided silica (Aerosil "0" from Degussa), Leads to the transformation: 3 Rh4(CO)12 → 2 Rh6(CO)16 + 4 CO. Such an easy rearrangement of the cluster cage implies mobility of zerovalent rhodium carbonyl fragments on the surface. Carbon monoxide is a very efficient inhibitor of this reaction, and Rh4(CO)12 is stable as such on silica under a CO atmosphere. Both Rh4(CO)12 and Rh6(CO)16 are easily decomposed to small metal particles of higher nuclearity under a water atmosphere and to rhodium(I) dicarbonyl species under oxygen. From the RhI(CO)2 species it is possible to regenate first Rh4(CO)12 and then Rh6(CO)16 by treatment with CO (Pco ≥ 200 mm Hg) and H2O (PH2O ≥ 18 mm Hg). The reduction of RhI(CO)2 surface species by water requires a nucleophilic attack to produce an hypothetical [Rh(CO)n]m species which can polymerize to small Rh4 or Rh6 clusters in the presence of CO but which in the absence of CO lead to metal particles of higher nuclearity. Similar results are obtained on alumina.
ASJC Scopus subject areas
- Chemical Engineering (miscellaneous)
- Inorganic Chemistry
- Organic Chemistry
- Physical and Theoretical Chemistry
- Materials Science (miscellaneous)
- Materials Chemistry