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Gold catalysts supported on TiO2 and TiO2/SiO2 were used in gas-phase propene epoxidation with a hydrogen−oxygen mixture. The catalysts were characterized by ¹⁹⁷Au Mössbauer absorption spectroscopy (MAS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Gold particle sizes of 1 wt % Au catalysts calcined at 673 K ranged from 3 to 6 nm. Two Au contributions were found in Mössbauer spectra and assigned to bulk metallic Au atoms in the core of a gold particle and metallic gold on the outer surface of this particle. By MAS, no evidence for charge transfer from support to Au particle could be found. The Auger parameters confirmed that the surface layer of 3−5 nm gold particles is metallic. Deactivation is not due to a change in the active gold species but is related to the TiO2 support. In the preparation via deposition-precipitation, Au(OH)3 species are converted to metallic gold during calcination. Gold particles do not gradually grow during calcination, possibly due to the simultaneous conversion of Au(OH)3 moieties with dehydroxylation of the TiO2 support. Epoxidation activity increases with the amount of surface metallic gold. No evidence for oxidized gold under reaction conditions was found.

TiCx coatings were chemically vapour deposited in an industrial reactor on Fe-C substrates with carbon contents between 0.06 and 1.20 wt % C. Electron probe microanalyses showed that significant amounts of chromium and iron were present in the coatings and that chromium was also present in the substrate region adjacent to the coatings. By comparing calculated and measured lattice parameters (corrected for the internal stresses present) it became evident that the chromium was in solid solution in TiCx, whereas the iron was not. This was confirmed by micro Auger electron spectroscopy and X-ray diffraction phase analyses. The carbon to metal ratio,x, of the TiCx coatings decreased with increasing distance to the coating/substrate interface. The effect of iron on the X-ray diffraction line broadening and hardness of the coatings was large (in contrast with the effect of chromium) and increased with increasing distance to the coating/substrate interface because of a decreasing iron particle size. The TiCx crystallite size was small and constant throughout the thickness of the coatings. The chromium present in the substrate region adjacent to the TiCx coatings influenced the microstructure of the substrate by formation of iron, chromium-carbides and reduced the growth rate of the coatings.