Palladium decoration of hybrid carbon nanotubes/charcoal composite and its catalytic behavior in the hydrogenation of trans-cinnamaldehyde

•Palladium decoration of multiwalled carbon nanotube/activated carbon composite.•Pd nanoparticles in a microemulsion adsorb onto the MWCNT/AC composite.•MWCNT/AC composite may have hierarchical Pd adsorption properties dependent on the MWCNT network type grown onto the AC surface.•Pd–MWCNT/AC composite display high catalytic activity for the selective hydrogenation of trans-cinnamaldehyde.•Pd–MWCNT/AC catalyst displayed higher selectivity to hydrocinnamaldehyde formation.

In the present study, we addressed the palladium (Pd) decoration of multiwalled carbon nanotube (CNT)/activated carbon (AC) hybrid composites (MWCNT/AC), and examined the catalytic behavior of the composites in the hydrogenation of trans-cinnamaldehyde. The MWCNT/AC composites were prepared by growing CNT network on the surface of AC granules, using the chemical vapor deposition method. XPS analysis revealed that the MWCNT/AC and COOH–MWCNT/AC composites and isolated AC adsorbed Pd at different oxidation states when dipped into a Pd0 microemulsion: isolated AC and the COOH–MWCNT/AC composite adsorbed Pd nanoparticles at di- and tetravalent states (Pd2+/4+), while the MWCNT/AC composite adsorbed Pd nanoparticles at zero and tetravalent states (Pd0/Pd4+). The MWCNT/AC composite may thereby have hierarchical Pd adsorption properties dependent on the MWCNT network type grown onto the AC surface. Regarding the catalytic performance, the (Pd0/4+)-MWCNT/AC catalyst displayed higher selectivity to hydrocinnamaldehyde formation (95.9%) when compared with the (Pd2+/4+)-AC and (Pd2+/4+)-COOH–MWCNT/AC catalysts (72.1% and 91.4% selectivity, respectively). The catalytic performance of the (Pd0/4+)-MWCNT/AC catalyst with 2.8 wt% of Pd loading was also superior than the catalytic performance of commercial catalysts with 5 and 10 wt% of Pd loading and other Pd/CNTs catalysts reported in the literature.

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