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The effect of the nature of the support and the promotion achieved by a Rh additive on Co-based catalysts in the ethanol steam reforming reaction were studied. The catalysts with 2% Co loading were characterized by temperatureprogrammed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). In situ diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS) identified the surface intermediates formed during the reaction, whereas gas phase products were detected by gas chromatography (GC). Upon heating in hydrogen to 773 K, cobalt could not be reduced to Co 0 on alumina, but on silica the reduction was almost complete. On ceria, half of the Co could be reduced to the metallic state. By the presence of a small amount (0.1%) of Rh promoter, the reduction of both cobalt and ceria was greatly enhanced. For Co on the acidic Al 2 O 3 support, the dehydration mechanism was dominant, although on the basic CeO 2 support, a significant amount of hydrogen was also formed. Addition of a small amount of Rh as promoter to the Co/CeO 2 catalyst resulted in a significant further increase in the hydrogen selectivity.

The photocatalytic transformation of the methane-carbon dioxide system was investigated by in-situ methods in the present study. Titanate nanotube (TNT) supported gold and rhodium catalysts were used in the catalytic tests. Our main goal was the analysis of the role of the catalysts in the different parts of the reaction mechanism. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and diffuse reflectance UV-vis spectroscopy (DR-UV-vis). Photocatalytic tests were performed in a continuous flow quartz reactor equipped with mass spectrometer detector and mercury-arc UV source. Diffuse reflectance infrared spectroscopy (DRIFTS) was used to analyze the surface of the catalyst during photoreaction. Post-catalytic tests were also carried out on the catalysts including XPS, temperature programmed reduction (TPR) and Raman spectroscopy methods in order to follow the changes of the materials. Titanate nanotube can stabilize even the smallest, molecular-like Au clusters which showed the highest activity in the reactions. Approximately 3% methane conversion was reached in the best cases while the carbon dioxide conversion was not traceable. It was revealed that water has a very important role in the oxidation reaction. The main discovered reaction routes are methane dehydrogenation and oxidation, the methyl coupling and the forming of structured carbon deposits on the catalyst surface. The source of the surplus CO can be mostly the reduction of carbon dioxide. During the reduction process photoelectrons and hydrogen ions brings about the CO 2 reduction via CO 2 • − radical anion.

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a b s t r a c tAu and Rh clusters, as well as Au-Rh bimetallic nanoparticles were prepared on titanate nanowires, nanotubes and on TiO 2 (1 1 0). They were characterized by X-ray photoelectron spectroscopy (XPS), low energy ion scattering spectroscopy (LEIS) and Fourier transform infrared spectroscopy (FTIR). By performing careful LEIS experiments, it was found that for appropriate Au and Rh coverage, a thin Au layer almost completely covers the Rh nanoparticles, a Rh core-Au shell structure was detected. The formation of this structure was not affected by alkali (K) adatoms. LEIS and FTIR measurements disclosed that adsorbed CO at 300 K causes the segregation of Rh atoms to the surface of metal clusters in order to bind to CO. Upon CO adsorption on Rh/titanate nanostructures the IR stretching frequencies characteristic of the twin form were dominant, whereas bimetallic nanosystems featured a pronounced linear stretching vibration as well. In spite of this structure adsorbed CO is detectable during the ethanol adsorption on gold-rhodium bimetallic cluster and the ethanol decomposition rate is twice higher than on Au/TiO 2 .