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In this study, the role of the noble metals Pt and Rh (0.5 wt.%) for the selective reduction of NO into N 2 is evaluated by the transient TAP technique and in-situ spectroscopy using a commercial stable ceria support (denoted as CZ) and applying isotopically labelled 15 NO and 18 O 2 . The transient operation was mimicked by multi-pulse oxidation (using O 2 or NO) and reduction cycles (using CO, H 2 , C 3 H 6 and C 3 H 8 ), while following quantitatively the catalyst and reactants response. Pt and Rh significantly lowered the temperature of CZ reduction. CO and H 2 only reduce the surface of CZ, while a 2.5 times deeper reduction was achieved by the hydrocarbons C 3 H 6 and C 3 H 8 , removing also lattice oxygen. Pt and Rh also promoted carbon deposition after surface reduction. Rh was a more active promoter than Pt, while propene was more reactive than propane over both metals. During the NO reduction the pre-reduced CZ support became gradually re-oxidised and after filling 70–80% of the oxygen vacancies the NO started to appear in the product mixture. In the presence of carbon deposits the lattice oxygen of the CZ reacted with the carbon keeping the CZ in a reduced state, extending the NO decomposition process as long as the carbon was present. The reduction of NO over pre-reduced noble metal/CZ showed a selective formation N 2 , while N 2 O and NO 2 were never observed. During the NO reduction process some unidentified N-species remained on the catalyst, the amount depending on the type of catalyst, but finally all nitrogen was released as N 2 . The presence of the noble metal led less unidentified N-species on the CZ surface and to a faster N 2 formation rate than that over the bare CZ. [ABSTRACT FROM AUTHOR]

This study reports a method to determine the absolute crystallinity of partly crystalline brookite TiO 2 photocatalysts. A natural, a commercial and various home-prepared brookite powders were characterized by X-ray diffraction analysis, Raman spectroscopy, scanning electron microscopy, UV–vis diffuse reflectance spectroscopy and nitrogen adsorption measurements. The absolute crystallinity was calculated from the ratio between the full width at half maximum intensity of the (121) X-ray diffraction peaks of the brookite samples and the (111) peak of CaF 2 as internal standard. The photocatalytic activity of the powders was tested employing the photodegradation of 4-nitrophenol as well as the selective oxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde ( p -anisaldehyde) under UV irradiation. The results indicated that crystallinity positively influenced the photooxidation of 4-nitrophenol and 4-methoxybenzyl alcohol but reduced the selectivity toward the synthesis of p -anisaldehyde. [ABSTRACT FROM AUTHOR]

CoMo-catalysts modified by boron were studied. Boron was added to alumina support by kneading. Supports and catalysts were characterized by nitrogen adsorption, XPS, IR-spectroscopy of adsorbed CO. Catalysts were tested in hydrotreating of straight-run diesel fuel with 5 vol.% catalytic cracking gasoil (initial S content was 2750 ppm). It is found that boron has no significant influence on textural characteristics of catalysts. However, it increases slab length and visualization degree of active component, while stacking number remains unchanged (preferential formation of monolayers). Difference in morphology is caused by changes of Lewis acidity and generation of Brønsted acid sites. It is found that all catalysts with boron provide production of ultra-low sulfur diesel fuels (less than 10 ppm). The catalyst with a boron content of 2 wt.% combines high activity in HDS and HDN. [ABSTRACT FROM AUTHOR]