Silica-supported Au nanoparticles decorated by TiO2: formation, morphology, and CO oxidation activity.

Au-TiO(2) interface on silica support was aimed to be produced in a controlled way by use of Au hydrosol. In method A, the Au colloids were modified by hydrolysis of the water-soluble Ti(IV) bis(ammoniumlactato)dihydroxide (TALH) precursor and then adsorbed on Aerosil SiO(2) surface. In method B, Au sol was first deposited onto the SiO(2) surface and then TALH was adsorbed on it. Regular and high-resolution transmission electron microscopy (TEM and HRTEM) and energy dispersive spectrometry (EDS) analysis allowed us to conclude that, in method A, gold particles were able to retain the precursor of TiO(2) at 1.5 wt % TiO(2) loading, but at 4 wt % TiO(2) content the promoter oxide appeared over the silica surface as well. With method B, titania was detected on silica at each TiO(2) concentration. In Au-TiO(2)/SiO(2) samples, the stability of Au particles against sintering was much higher than in Au/TiO(2). The formation of an active Au-TiO(2) perimeter was proven by the greatly increased CO oxidation activity compared to that of the reference Au/SiO(2).

Gold nanoparticles deposited on SiO2/Si100: correlation between size, electron structure, and activity in CO oxidation.

Nanosize gold particles were prepared by Ar(+) ion implantation of 10-nm thick gold film deposited onto a SiO(2)/Si(100) wafer possessing no catalytic activity in the CO oxidation. Along with size reduction the valence band of the gold particles and the actual size were determined by ultraviolet- and X-ray photoelectron spectroscopy (UPS, XPS) and by transmission electron microscopy (TEM) as well as atomic force microscopy (AFM), respectively. The catalytic activity was determined in the CO oxidation. Energy distribution of the photoelectrons excited from 5d valence band of gold was strongly affected by Ar(+) implantation. This variation was interpreted by the redistribution of the valence band density of states (DOS). The intrinsic catalytic activity of the gold particles increased with decreasing size. When an Au/FeO(x) interface was created by FeO(x) deposition on large gold nanoparticles, a significant increase in the rate of the CO oxidation was observed. These data can be regarded as an experimental verification of the correlation between the catalytic activity and valence band density of states of gold.