Search

Formation of vanadia species during the calcination of ball milled mixt. of V2O5 with TiO2 was studied by Raman spectroscopy in situ and at ambient conditions. Calcination in air leads to fast (1-3 h) spreading of vanadia over TiO2 followed by a slower process giving a monolayer vanadia. The calcinated catalyst showed higher activity during toluene oxidn. than the uncalcinated one, but the selectivity towards C7-oxygenated products (benzaldehyde and HOBz) remains unchanged. The activity of the catalysts is ascribed to the formation of vanadia species in the monolayer. The details of the parallel-consecutive reaction scheme of toluene oxidn. are presented from steady-state and transient kinetics studies. Different O species seem to participate in the deep and partial oxidn. of toluene. Coke formation was obsd. during the reaction presenting an av. compn. C2nH1.1n. The amt. of coke on the catalyst was not dependent on the calcination step and the V content in the catalyst. Coke formation is responsible for the deactivation of the catalyst. [on SciFinder (R)]

Innovative structured catalysts based on nanoparticles of gold supported on activated carbon fibers (ACF) in the form of woven fabrics are presented for low-temperature CO oxidation. Gold was deposited by adsorption from aqueous solution of ethylenediamine complex [Au(en)2]Cl3 followed by reduction in hydrogen. The catalysts were studied under transient reaction conditions and characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray energy dispersive analysis (EDS). HRTEM-EDS shows that gold is present on the surface of Au/ACF catalyst in the form of metallic particles with sizes of ~2.5–5 and ~30–50 nm. A predeposition of iron oxide on the ACF was beneficial for the Au dispersion and catalytic activity in CO oxidation. Gold particles in the Au/FeOx/ACF samples were not in direct contact with the Fe2O3 phase and their size was smaller than without doping by iron oxide. The mechanism of catalyst formation, its morphology, and the influence of preparative conditions are discussed. The activity of Au/FeOx/ACF was substantially higher as compared to Au/Al2O3 and Au/FeOx/Al2O3 catalysts. A reductive pretreatment with H2 was necessary to activate the catalyst, but the activity decreased rapidly in CO/O2 atmosphere. Addition of hydrogen or water vapors to the reaction mixture increases the catalyst activity.

The catalytic decomposition of ozone (200-1600 ppm) to molecular oxygen was investigated over activated carbons in the form of woven fibre fabrics (ACF) or granules (ACG) at room temperature. The dynamics of carbon activity was characterised by two distinct regions. First the "high activity" towards ozone decomposition was observed, which was mainly due to chemical interaction of ozone with carbon. This interaction resulted in the formation of oxygen containing surface groups on carbon until saturation. Then the conversion was sharply decreased and carbons went to "low activity" region. The ozone decomposition to molecular oxygen takes place in this region following a catalytic route. The carbon activity in dry atmosphere was compared with the activity in the presence of water vapour and NOx Water vapour diminished the catalytic activity, but in the presence of NO, carbons were observed to be more active due to the change in the C-surface functionality. The surface functional groups were modified in two ways: by boiling in diluted HNO3 or by thermal treatment in He at temperatures up to 1273 K. The acid pre-treatment was found to increase the activity of carbons under the quasi steady-state, while the thermal treatment at 1273 K renders catalysts with lower activity. The ozone decomposition toward gasification of carbon producing CO, took place with the selectivity less then 25%. The catalysts were characterised by temperature-programmed decomposition of surface functional groups, X-ray photo-electron and IR-spectroscopy. Mechanistic aspects of the reaction are discussed.