Control of the Morphology of AuPd Nanoparticles Supported on TiO2 by Adjusting Synthesis Parameters Ângela A. Teixeira Neto, Jéssyca Nobre Pereira, Érico Teixeira Neto Brazilian Nanotechnology National Laboratory, Campinas, São Paulo, Brazil. Nanostructured bimetallic heterogeneous catalysts have lately been explored as an alternative to monometallic catalysts, since the combination of two different metals may offer unique catalytic properties, which can be adjusted according to the preparation method [1]. In particular, the AuPd system is known to improve activity and selectivity of alcohol oxidation reactions, probably due to synergetic electronic interactions between Au and Pd atoms in the individual nanoparticles [2]. In this work, TiO2 supported AuPd nanoparticles (molar fraction 1:1, 1% wt. total metal content) were prepared by means of a simple impregnation method. Different drying temperatures were applied: 40, 80 and 120 oC. After the drying process, the samples were subjected to thermal treatments, either at oxidant or at reducing conditions. X-ray photoelectron spectroscopy (XPS) results show that the surface metal concentration increases as the drying temperature increases which indicates a decrease in particle size. Reducing processes at different temperatures and/or times lead to materials with diverse surface compositions. The samples were also characterized by scanning electron microscopy (SEM, Fig. 1), which reveals that the preparation method (drying and thermal treatment) greatly influences the morphology of the nanoparticles. As an example, oxidized samples (Fig. 1a) generally present particles with asymmetric shapes, while reduced samples (Fig. 1b) present round particles. Oxidized and reduced samples produced from different drying temperatures were used as catalysts in the ascorbic acid oxidation reaction (Fig. 2). It can be observed that reduced samples are more active in this reaction as compared to oxidized samples. In addition, higher drying temperatures produce more active catalysts, because it allows the formation of smaller particles. It has been shown that size and morphology of AuPd nanoparticles can be controlled by modifications in the preparation method, using a simple synthesis procedure. As a consequence, the obtained catalysts present different catalytic activities on the oxidation of ascorbic acid reaction. The authors are thankful to CNPq for AATN and JNP scholarships, to FAPESP (2013/11298-0) for funding and to LME/LNNano/CNPEM for the use of SEM and TEM facilities. References: [1] Facile fabrication of Ag-Pd bimetallic nanoparticles in ultrathin TiO(2)-gel films: nanoparticle morphology and catalytic activity; He J., Ichinose I., Kunitake T., Nakao A., Shiraishi Y., Toshima N., J. Am. Chem. Soc. 125, 11034-40 (2003) doi:10.1021/ja035970b. [2] Alcohol oxidations in aqueous solutions using Au, Pd, and bimetallic AuPd nanoparticle catalysts; Hou W., Dehm N., Scott R., J. Catal. 253, 22-27 (2008) doi:10.1016/j.jcat.2007.10.025 (a) (b) Figure 1. SEM images of (a) oxidized and (b) reduced AuPd nanoparticles supported on TiO2; the samples were dried at 40oC. 0.00 -0.05 -0.10 -0.15 ln(At/A0) -0.20 pure TiO2 -0.25 o dried 40 C ox. o dried 40 C red. o dried 80 C ox. o dried 80 C red. o dried 120 C ox. o dried 120 C red. -0.30 -0.35 -0.40 -0.45 -0.50 0 50 100 150 200 250 300 time / s Figure 2. Ascorbic acid oxidation at 25 oC for AuPd-TiO2 samples dried at different temperatures and subjected to oxidative and reductive conditions.