The Influence of Pd Nanoparticle Size On Pd/ Tio₂ Catalysts for Cinnamaldehyde Hydrogenation Reaction

Palladium nanoparticles (PdNP) supported onto the anatase phase of TiO₂ were successfully synthesised using a colloidal method. This synthesis method involved the reduction of K₂PdCl₄ solution by NaBH₄ at different temperatures (1, 25, 50, 75 degree Celsius) and stabilised with PVA ligand. Transmission electron microscope (TEM) was used to determine the particle size of PdNP on the TiO₂. Colloidal synthesis at 1 degree Celsius and 25 degree Celsius produced PdNP with less than a 3 nm diameter, whereas when the synthesis temperatures were higher than 25 degree Celsius, PdNP were produced with a size larger than 4 nm. The catalytic activity of Pd/ TiO₂ was significantly improved when palladium (Pd) was produced at 1 degree Celsius with high selectivity towards the hydrogenation of cinnamaldehyde to hydrocinnamaldehyde. The conversion and selectivity trends from the cinnamaldehyde hydrogenation reaction demonstrated the influence of Pd nanoparticle size to provide active sites for the reduction of C=C and C=O bonds. Pd with a diameter of 2.58 nm favoured hydrogenation of C=C bond to produce high selectivity towards hydrocinnamaldehyde, meanwhile a large Pd diameter > 4 nm allowed simultaneaous reduction of C=C and C=O bonds to give comparable selectivity between hydrocinnamaldehyde and hydrocinnamylalcohol. (author)