Synthesis of Platinum Nanoparticles Supported on Poly(acrylic acid) Grafted MWNTs and Their Hydrogenation of Citral

Crystalline Pt nanoparticles were electrolessly deposited on poly(acrylic acid) (PAA) grafted multiwalled carbon nanotubes (MWNTs). The density and uniformity of Pt nanoparticles on MWNTs were found dependent on the PAA grafting density, while their morphologies were tailored by the addition of NO 3 − and Cu 2+ ions. The catalytic activity and selectivity of hydrogenation of α,β-unsaturated aldehyde, citral, on Pt/MWNTs nanocomposites with different morphologies was studied. The irregularly shaped polycrystalline Pt nanoparticles showed the highest conversion of citral, 92.2%, in comparison to 24.7% from Pt/active carbon, 45.0%, and 40.4% from polyhedrons and polypods Pt single crystals on MWNTs, respectively. The unusually high conversion on Pt/MWNTs suggests a synergistic effect between the PAA grafted MWNTs and the Pt nanoparticles. In the study of the selectivity of hydrogenation, tetra- and octahedron Pt nanoparticles showed the highest ratio of geraniol/nerol, 5.2, ∼3 times higher than that of Pt/active carbon, whereas those of irregularly shaped polycrystalline and tetra- and octapods of single crystalline Pt on the MWNTs are 1.9 and 2.2, respectively. Electron diffraction patterns revealed that in the case of tetra- and octahedral Pt particles on the MWNT surface only the {111} facet was exposed, which might induce steric hindrance for the cis-isomers but not for the trans-isomers, whereas the {111} facets were deformed in tetrapods and octapods.