Synergistic effect of potassium hydroxide and steam co-treatment on the functionalization of carbon nanotubes applied as basic support in the Pd-catalyzed liquid-phase oxidation of ethanol

Surface functionalization of carbon nanotubes (CNTs) was achieved by a thermal treatment in the presence of pre-adsorbed potassium hydroxide and steam at 350-550 °C. The generated oxygen-containing functional groups were more basic and thermally stable compared with conventional acid-generated groups. The influence of the KOH-steam co-treatment conditions on the functionalization of CNTs was systematically investigated. Residual K species were found to intercalate in the inner graphene layers of the CNTs providing additional Brønsted basicity. Owing to the favorable basic properties and high thermal stability of the generated functional groups, Pd nanoparticles supported on the co-treated CNTs were found to be strongly anchored leading to a high degree of Pd dispersion and a high resistance to sintering. The Pd nanoparticles on the co-treated CNT support produced at 450 °C and 550 °C showed the highest activity and yields of acetic acid in the aerobic oxidation of aqueous ethanol reaching almost full conversion after 5 h in the absence of additional base. In addition, the KOH-steam co-treatment was found to enhance the recyclability of the Pd/CNT catalysts.

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