Thermo-responsive polymer grafted carbon nanotubes as the catalyst support for selective hydrogenation of cinnamaldehyde: Effects of surface chemistry on catalytic performance

A wettability-controllable surface on carbon nanotubes (CNTs) was successfully constructed through directly grafting poly( N -isopropylacrylamide) (PNIPAM) from CNT surface (i.e. CNT-PNIPAM) via a facile method. The hybrid was employed as the support to prepare Pd catalyst (i.e. Pd/CNT-PNIPAM) for selective hydrogenation of cinnamaldehyde (CAL). The effects of thermoresponsive surface chemistry on catalytic performance were studied. Results showed that CNT-PNIPAM had the lower critical solution temperature (LCST) at about 37 °C. The hydrophilic surface of CNT-PNIPAM at 25 °C (< LCST) improved the dispersion of Pd nanoparticles on it in catalyst preparation. As-prepared Pd/CNT-PNIPAM then automatically switched its hydrophilic surface to the hydrophobic one at 80 °C (>LCST), which exhibited the good adsorption properties for reactants in the reaction. The high Pd dispersion on Pd/CNT-PNIPAM as well as its good adsorption properties for CAL jointly resulted in an enhanced catalytic activity, meanwhile maintaining the selectivity to cinnamyl alcohol (COL) unchanged in comparison to CNT supported Pd catalyst (Pd/CNT).