Lucie Smoláková

Quantitative LIBS analysis of vanadium in samples of hexagonal mesoporous silica catalysts.

The method for the analysis of vanadium in hexagonal mesoporous silica (V-HMS) catalysts using Laser Induced Breakdown Spectrometry (LIBS) was suggested. Commercially available LIBS spectrometer was calibrated with the aid of authentic V-HMS samples previously analyzed by ICP OES after microwave digestion. Deposition of the sample on the surface of adhesive tape was adopted as a sample preparation method. Strong matrix effect connected with the catalyst preparation technique (1st vanadium added in the process of HMS synthesis, 2nd already synthesised silica matrix was impregnated by vanadium) was observed. The concentration range of V in the set of nine calibration standards was 1.3-4.5% (w/w). Limit of detection was 0.13% (w/w) and it was calculated as a triple standard deviation from five replicated determinations of vanadium in the real sample with a very low vanadium concentration. Comparable results of LIBS and ED XRF were obtained if the same set of standards was used for calibration of both methods and vanadium was measured in the same type of real samples. LIBS calibration constructed using V-HMS-impregnated samples failed for measuring of V-HMS-synthesized samples. LIBS measurements seem to be strongly influenced with different chemical forms of vanadium in impregnated and synthesised samples. The combination of LIBS and ED XRF is able to provide new information about measured samples (in our case for example about procedure of catalyst preparation).

Dehydrogenation of ethane over vanadium, cobalt and nickel based catalysts

Abstract The contribution deals with the catalytic performance of vanadium-, cobalt- and nickel-based catalysts in oxidative dehydrogenation of ethane. Vanadium, cobalt and nickel species were loaded to microporous (MFI) and mesoporous (HMS) materials, and supported on inorganic support (alumina). The activity of catalysts was compared at 600 °C (9 % ethane and 2.5 % oxygen in helium, and W/F 0.12 g.s.cm −3 ). The most effective catalytic system was Ni−Al 2 O 3 , which also was tested at varied oxygen concentration, reaction temperature, and W/F. The most favorable set up corresponded to 46 % in the ethane conversion, 30 % in the ethene yield 30 %, and 0.91 g(C 2 =).g cat −1 .h −1 in the ethene productivity for Ni−Al 2 O 3 . The activity of Ni−Al 2 O 3 was stable for 6 hours in time-on-stream.

Precursors of active Ni species in Ni/Al2O3 catalysts for oxidative dehydrogenation of ethane

Ni/Al2O3 catalysts for oxidative dehydrogenation (ODH) of ethane were prepared by impregnation of Al2O3 with nickel acetate or nickel nitrate, and by mechanical mixing of NiO and Al2O3. The Ni-based catalysts were characterized by N2 adsorption-desorption, X-ray diffraction, diffuse reflectance UV-visible diffuse reflectance spectroscopy, and temperature-programmed reduction of hydrogen. The results showed that formation of crystalline NiO particles with a size of < 8 nm and/or non-stoichiometric NiO species in the Ni/Al2O3 catalysts led to more active species in ODH of ethane under the investigated reaction conditions. In contrast, tetrahedral Ni species present in the catalysts led to higher selectivity for ethene. Formation of large crystalline NiO particles (22–32 nm) over Ni/Al2O3 catalysts decreased the selectivity for ethene.

Aspects of stability of K/Al2O3 catalysts for the transesterification of rapeseed oil in batch and fixed-bed reactors

Abstract Catalytically active, stable, and mechanically durable solid K/Al 2 O 3 catalysts for the transesterification of rapeseed oil with methanol was studied. In a batch reactor, high catalytic activity was accompanied by leaching of K species, caused by glycerol, and mechanical destruction of the solid catalyst as a result of contact with the stirrer. In a fixed-bed reactor, some leaching of K species into the liquid phases was also observed, but approached 0 during 30 h of time-on-stream; the activity of the K/Al 2 O 3 catalyst (∼83% ester yield) was stable for 100 h of time-on-stream and no mechanical destruction of the catalyst was observed. The populations of K 2 O and K-O-Al species for fresh and used K/Al 2 O 3 catalysts were compared using Fourier transform infrared spectroscopy. It was found that some K 2 O species leached into the liquid phases at the beginning of the reaction.