No abstract

Parallel and fishbone carbon nanofibres have an interesting and varied surface. Although HRTEM (see image) shows some detail, the characterisation provided by infrared spectroscopy reveals a wealth of defect‐rich structures.

The immobilisation of the rhodium/anthranilic acid complex onto fishbone carbon nanofibres (CNFs) was executed by means of the following steps: 1) surface oxidation of the fibres, 2) conversion of the oxygen-containing surface groups into acid chloride groups, 3) attachment of anthranilic acid and 4) complexation of rhodium by the attached anthranilic acid. The immobilisation process was followed and the resulting surface species were characterised by IR, X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS), and by molecular modelling. Anthranilic acid bonds to the CNFs by an amide linkage to the carboxyl groups that are present after surface oxidation of the fibres. The immobilised anthranilic acid coordinates to rhodium through the nitrogen atom and the carboxyl group. The assynthesised Rh III complex itself is not active in the liquid-phase hydrogenation of cyclohexene. Reduction with sodium borohydride yields small particles (d 1.5 ± 2 nm) of rhodium metal that are highly active. The results indicate that different activation procedures for the immobilised Rh/anthranilic acid system should be applied, such as reduction with a milder reducing agent or direct complexation of the rhodium in the Rh I state.

A number of different impregnation and ion-exchange procedures have been employed to synthesize very small rhodium metal particles on HNO 3 /H 2 SO 4 -oxidized fishbone carbon nanofibres. The surface-oxidation of the nanofibres with HNO 3 /H 2 SO 4 is a prerequisite for a good interaction between aqueous catalyst precursor solutions and the fibres. Depending upon the preparation technique applied and using 1 wt% rhodium metal loadings average particle sizes ranging from 1.1 to 2.1 nm were detected with XAFS spectroscopy. The rhodium metal particles are so small that metalsupport interactions on carbon nanofibres can be investigated with XAFS spectroscopy. All catalysts are highly active in the liquidphase hydrogenation of cyclohexene. No significant effect of particle size on the catalytic activity is observed, suggesting that other factors, such as clustering of the support particles in the liquid phase, are much more important. c 2002 Elsevier Science (USA)

A number of different impregnation and ion-exchange procedures have been employed to synthesize very small rhodium metal particles on HNO 3 /H 2 SO 4 -oxidized fishbone carbon nanofibres. The surface-oxidation of the nanofibres with HNO 3 /H 2 SO 4 is a prerequisite for a good interaction between aqueous catalyst precursor solutions and the fibres. Depending upon the preparation technique applied and using 1 wt% rhodium metal loadings average particle sizes ranging from 1.1 to 2.1 nm were detected with XAFS spectroscopy. The rhodium metal particles are so small that metalsupport interactions on carbon nanofibres can be investigated with XAFS spectroscopy. All catalysts are highly active in the liquidphase hydrogenation of cyclohexene. No significant effect of particle size on the catalytic activity is observed, suggesting that other factors, such as clustering of the support particles in the liquid phase, are much more important. c 2002 Elsevier Science (USA)