N-doped ordered mesoporous carbon supported PdCo nanoparticles for the catalytic oxidation of benzyl alcohol

Abstract

A highly ordered nitrogen doped mesoporous carbon was prepared by passing acetonitrile as carbon and nitrogen source over a mesoporous SBA-15 silica template at 900 °C by using a CVD bubbling method. The silica template was removed by etching with HF, followed by filtration, washing and functionalization with HNO3 to give N-CMK-3 (N = 11.3 wt%). This material exhibited good mesostructural ordering (XRD analysis), a high surface area (885 m2/g) and a large pore volume (1.70 cm3/g). Addition of a monodispersed colloidal solution of PdCo (d = 3.3 nm), Pd (4.2 nm) or Co (10.5 nm) nanoparticles to N-CMK-3 as support gave highly uniform and well dispersed nano-sized Pd, PdCo and Co nanoparticle supported catalysts. The synthesized catalysts were activated with H2 (5%)/Ar at 400 °C to remove capping agents. These activated PdCo, Pd and Co/N-CMK-3 catalysts were tested for benzyl alcohol oxidation under solvent free conditions using oxygen as an oxidant at different temperatures (110–140 °C) and times (1–8 h) and compared with an equivalent carbon (Vulcan XC-72) supported catalyst. In the aerobic oxidation of alcohols, the PdCo/N-CMK-3 showed similar activity to the Pd/N-CMK-3 catalyst but only using 50% of the amount of Pd in a PdCo catalyst. An important role of Co is to reduce the bulk Pd content of the catalyst. This can be explained by a core-shell structure for the PdCo catalyst. The catalytic oxidation of a range of benzyl alcohols (no solvent, O2 as oxidant, 130 °C) in the presence of PdCo/N-CMK-3 typically gave aldehydes with conversions in the range 87–99% (selectivity 99%) after 5 h. The catalyst also retained its selectivity and activity after four recycles.