CO preferential oxidation in microchannels over dendrimer-encapsulated Au supported on TiO2

N. DIVINS; J. LLORCA; C. MORENO; E. LÓPEZ; D. VEGA; A. RODRIGUEZ

Pallanza

Otro; EFCATS Summer School 2012; 2012

When gold nanoparticles of about 2-5 nm are deposited on metal oxides, such as TiO2, they exhibit exceptionally high activity to preferentially oxidize CO (CO-PrOx) in H2-rich environments. In this work, we have used pre-formed Au nanoparticles encapsulated in a Si-rich dendrimer shell which controls the interparticle distance, thus preventing their aggregation. These Au nanoparticles are stable at elevated temperature, as deduced from AFM, XPS and SEM studies. As a final point, the nanoparticles have been supported over TiO2-tailored microchannels of a silicon micromonolith to test them under CO-PrOx reaction conditions. Silicon micromonoliths (7 mm in diameter, 0.2 mm height) with >106 straight and parallel circular channels of 3.3 micrometers in diameter were first coated with a SiO2 layer and then with a thin uniform layer of TiO2. Finally, the pre-formed Au nanoparticles were anchored onto the TiO2 layer. The catalyst and the functionalized micromonolith were characterized with SEM and TEM, focused ion beam, XPS and XRD. Additionally, a detailed thermal stability study of the encapsulated Au nanoparticles over Si was carried out. The Au nanoparticles were annealed for 30 minutes at 353, 723, 823, 973 and 1173 K. After each calcination step, AFM and SEM images were acquired as well as XP spectra. At 1173 K, the dendrimer shells were almost removed but the Au nanoparticles maintained their size (95% ranged 1-3 nm and the remaining reached 4-30 nm).