The interaction of methane with unsupported and supported molybdenum compounds (Mo, MoO 2 , MoO 3 , Mo 2 C, and MoC (1−x) ) has been investigated at 973 K. ZSM-5 was used as a support. Reaction products were analyzed using gas chromatography. Changes in the composition of catalyst samples were followed by X-ray photoelectron spectroscopy. Molybdenum metal and oxides interacted strongly with methane at 973 K to give H 2 (Mo) and H 2 O and CO 2 (oxides), but only a trace amount of ethane. When these compounds were contacted with ZSM-5, the reaction pathway of methane initially was the same. Afterward, however, a dramatic change occurred in the product distribution: the formation of ethane, ethylene, and benzene came into prominence. This was particularly the case when these compounds were highly dispersed on ZSM-5. The selectivity to benzene was 80-85%. XPS analysis of Mo-containing catalysts demonstrated the formation of Mo carbides during the catalytic reaction. Unsupported Mo carbides behaved like metallic Mo; the dominant process was the decomposition of methane to hydrogen and carbon. The deposition of Mo 2 C on ZSM-5 in a well-dispersed state, however, produced a very active and selective catalyst for the conversion of methane into benzene. The results suggest that Mo 2 C is the active surface species in the Mo-containing catalysts, which converts methane into ethylene, the primary compound for the production of benzene on the zeolite surface.

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.

High-aspect-ratio titanate nanotubes (NT) and nanowires (NW) were produced by the hydrothermal conversion of TiO2 at 400 K. The titanate morphology was studied by high-resolution transmission electron microscopy (HRTEM). The formation of ordered titanate nanoobjects depended on the time of conversion. Shorter synthesis times favored hollow nanotube production while during prolonged treatment the thermodynamically more stable nanowires were formed. Titanate nanotubes and nanowires were decorated by Rh nanoparticles. The structure and stability of titanate nanocomposites were studied by thermal gravimetric (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS), Fourier transformed infrared spectroscopic (FTIR), and Raman spectroscopic methods. The nanowires preserve their structure up to 850 K, while the nanotubes start to recrystallize above 600 K. FTIR measurements showed that the water and hydroxyl content gradually decreased with increasing temperature in both cases. XPS data revealed the existence of high binding energy, highly dispersed Rh species on both supports. A small portion of Rh may participate in an ion exchange process. Support transformation phenomena were observed in Rh containing titanate nanowires and nanotubes. Rh decorated nanowires transform into the β-TiO2 structure, whereas their pristine counterparts' recrystallize into anatase. The formation of anatase was dominant during the thermal annealing process in both acid treated and Rh decorated nanotubes. Transformation to anatase was enhanced in the presence of Rh. The average diameters Rh nanoparticles were 4.9 ± 1.4 and 2.8 ± 0.7 nm in the case of nanowires and nanotubes, respectively.

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