Stereoselective Hydrogenation of Dibenzo-18-crown-6 Catalyzed by Carbon Nanotube–Supported Rhodium Nanoparticles

Abstract

Multiwalled carbon nanotube–supported Rh nanoparticles prepared by a simple sonochemical method are highly active for catalytic hydrogenation of dibenzo-18-crown-6 to dicyclohexyl-18-crown-6. The catalytic hydrogenation reaction shows a selectivity favoring the cis-syn-cis isomer over cis-anti-cis isomer of the product by a factor of ≥6. Conventional Rh catalysts supported by activated wood carbon, SiO₂, or Al₂O₃ can only convert dibenzo-18-crown-6 to dicyclohexyl-18-crown-6 with an cis-syn-cis/cis-anti-cis ratio of <1.7. The Rh nanoparticle catalyst can be reused at least six times without losing its catalytic activity.

Keywords:

• Carbon nanotube
• rhodium nanoparticles
• sonochemical method
• stereoselective hydrogenation

ACKNOWLEDGMENTS

We thank Thomas J. Williams and J. Franklin Bailey for assistance with XRD, TEM, and SEM/EDX analysis of our samples. Hsing-Jung Chen was supported by a scholarship from the National Chung-Hsing University, Taiwan, for her study in the USA.

Notes

Note. Metal/DB18C6 = 0.16 (mol ratio), 10 atm H₂, 323 K, reaction time 60 min.

^a Metal loading (wt%).

^b Ratio of the isomers: cis-syn-cis/cis-anti-cis.

^c Metal/DB18C6 = 0.18 (mol ratio).

^a Reaction conditions: metal/DB18C6 = 0.16 (mol ratio), 10 atm H₂, 323 K, reaction time 60 min.