Iron oxide layers of 5-10 nm thickness were deposited by pulsed laser techniques (PLD) onto either Au films or nano-sized Au particles supported by SiO2/Si(1 0 0). Samples were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS) before and after measurements of the CO oxidation activity. Comparison was made with reference samples either free of iron oxide and/or free of Au particles/films. The initial activity of iron oxide/Au nano-particles/SiO2/Si(1 0 0) turned out to be the highest followed by the sample containing a sandwiched Au film. While some reaction-induced changes in the chemical composition of the iron oxide overlayer ("FeO x", which can be regarded as a mixture of Fe2O 3, FeO and FeOOH according to the XPS analysis of the Fe 2p and O 1s core levels) were seen, no Au segregation at the surface was detected by TOF SIMS. The XPS Au 4f spectra indicated, however, that Au atoms might be injected and trapped in this layer. The catalytic activity of the FeOx/Au/ SiO2/Si(1 0 0) samples must be attributed to active sites located on the iron oxide overlayer promoted by gold underneath. Since Au nano-particles and Au films caused promotion we infer that an electronic effect is in operation due to the occurrence of an FeOx/Au interface in both cases. Since the promotion is stronger for Au nano-particles the hypothesis of a particle size dependent electronic effect may be advanced. For thicker FeOx of about 40-80 nm no promotion by Au was found.
- CO oxidation
- Iron oxide
ASJC Scopus subject areas
- Process Chemistry and Technology