Liquid-Phase Hydrogenation of Unsaturated Aldehydes: Enhancing Selectivity of Multiwalled Carbon Nanotube-Supported Catalysts by Thermal Activation

• Published in: ChemCatChem 2010-02, Vol.2 (2), p.190-197
• Main Authors: Machado, Bruno F., Gomes, Helder T., Serp, Philippe, Kalck, Philippe, Faria, Joaquim L.
• Format: Article
• Language: English
• Subjects: aldehydes; hydrogenation; nanotubes; supported catalysts; surface chemistry
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.200900230

Platinum and iridium organometallic precursors are used to prepare nanosized, thermally stable multiwalled carbon nanotube‐supported catalysts. The materials are characterized by N2 adsorption at 77 K, temperature‐programmed desorption coupled with mass spectrometry, H2 chemisorption, transmission electron microscopy and thermogravimetric analysis; they are tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol under mild conditions (363 K and 1 MPa). A thermal activation at 973 K is found to have a very positive effect over both activity and selectivity, leading to selectivities of approximately 70 %, at 50 % conversion, regardless of the active metal phase (Pt or Ir). Since no noticeable differences in the metal particle sizes are detected, the results are interpreted in light of an enhanced metal/support interaction. This effect, induced by the removal of oxygenated surface groups, is thought to change the adsorption mechanism of the cinnamaldehyde molecule. Surface‐enhanced selectivity: Highly selective hydrogenation of cinnamaldehyde to cinnamyl alcohol, catalyzed by Pt and Ir supported on multiwalled carbon nanotubes, is achieved after a high temperature thermal treatment of the catalyst. Surface chemistry of the support, rather than the metal particle size, is the key factor.