Jürgen Arras

Binary Au/MWCNT and Ternary Au/ZnO/MWCNT Nanocomposites: Synthesis, Characterisation and Catalytic Performance

Gold nanoparticles of 10-24 and 5-8 nm in size were obtained by chemical citrate reduction and UV photoreduction, respectively, on acid-treated multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNT composites. The shape and size of the deposited Au nanoparticles were found to be dependent upon the synthetic method used. Single-crystalline, hexagonal gold particles were produced in the case of UV photoreduction on ZnO/MWCNT, whereas spherical Au particles were deposited on MWCNT when the chemical citrate reduction method was used. In the UV photoreduction route, n-doped ZnO serves as the e(-) donor, whereas the solvent is the hole trap. All materials were fully characterised by UV/Vis spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and BET surface analysis. The catalytic activity of the composites was studied for the selective hydrogenation of alpha,beta-unsaturated carbonyl compound 3,7-dimethyl-2,6-octadienal (citral). The Au/ZnO/MWCNT composite favours the formation of unsaturated alcohols (selectivity=50% at a citral conversion of 20%) due to the presence of single-crystalline, hexagonal gold particles, whereas saturated aldehyde formation is favoured in the case of the Au/MWCNT nanocomposite that contains spherical gold particles.

Highly Dispersed Gold Particles on Polyaniline – A New Nanocatalyst for Selective Hydrogenation

A new nanocatalyst which comprises gold particles (average size = (2.5±1.3) nm) supported on intrinsically conductive polyaniline (PANI) was prepared via a sol-method. This Au/PANI catalyst was used for the first time in hydrogenation of the α,β-unsaturated aldehyde citral exhibiting high activity (93% conversion) and selectivity (76%) towards the products of C=O group hydrogenation, geraniol and nerol, whereas the selectivity towards the product of the hydrogenation of the conjugated C=C bond (citronellal) is rather low (23%).