Gold Yolk-shell Nanoparticles as Model Sinter-stable Materials for Support and Size Effect Studies in CO-oxidation

GALEANO, C.; GUETTEL, R.; ARNAL, P. M.; SCHÜTH, F.

Nürenberg

Congreso; 3rd EuCheMS Chemistry Congress; 2010

Yolk-shell catalysts have recently attracted interest, since they combine high-temperature stability with monodisperse and narrow size distributions, leading to a reduced complexity for kinetic and mechanistic investigations. For CO oxidation Au nanoparticles supported on metal oxides have emerged as one of the best catalysts, however, particularly for this reaction the catalytic activity is strongly influenced by synergistic effects between Au nanoparticle size and the kind of supports used[1]. In order to discriminate the contribution of each factor, it would be desirable to measure the catalytic activity of Au nanoparticles on an inactive support like carbon. For this reason Au, @C was prepared by nanocasting and compared with the standard Au,@ZrO2 material. The preparation principle for the Au, @C material shown in Fig. 1 is based on the standard procedure for Au, @ZrO2[2]. The intermediate Au@SiO2@ZrO2 composite material is used as exotemplate for the nanocasting of the carbon shell[3]. For this purpose a carbon precursor is polymerized in the pore system of the zirconia shell, followed by a carbonization step. Finally, the SiO2 and ZrO2 are removed by NaOH and HF, respectively. Our investigations have shown that Au, @C of 15 nm core size exhibits temperature of half conversion of 315°C in CO oxidation, compared to 140°C for Au, @ZrO2. Deactivation by agglomeration of gold cores up to 315°C was not observed. Additionally, using our ex-post size reduction strategy[4] for both materials the size dependency has been studied. Finally, the doping of the material by the addition of small amounts of titania has also been explored resulting in a significant increase in activity, without additional efforts in preparation.