Oxidative dehydrogenation and ammoxidation of C2 a C3 hydrocarbons over Co-zeolites

Práce se zabývá aktivitou a katalytickými vlastnostmi zeolitů typu MOR. FER, MFI, BEA s iontově vyměněným kobaltem v amoxidaci a oxidativní dehydrogenaci lehkých uhlovodíků.Dokončená práce s úspěšnou obhajobo

Selektivní oxidace parafinů na metallo-zeolitech

Selekticní oxidace propanu a etanu byly studovány na zeolitech modifikovaných kovy (Co, Cu, Fe) v přítomnosti molekulárního kyslíku, oxidu dusného a amoniaku. Z experimentálních technik byly použity FTIR a UV-Vis v ex-situ a in-situ uspořádání, XRD, teplotně programované redukce. Byl zjištěn vliv struktury, jednotlivých částic a velký vliv přítomnosti amoniaku. Oxid dusný zvyšuje aktivitu katalyzátorů v oxidativní dehydrogenaci.Katedra fyzikální chemieDokončená práce s úspěšnou obhajobo

On the effect of cobalt loading on catalytic activity of Co-BEA zeolites in ethane oxidative dehydrogenation and ammoxidation

Metal ion species introduced into zeolite seem to be attractive redox catalysts. There is a great effort to convert light paraffins into more valuable chemicals. Zeolites of BEA type modified by cobalt exhibited the highest activity and selectivity in ammoxidation and oxidative dehydrogenation of ethane in comparison with other high-silica zeolite matrices modified by cobalt. In this paper a set of sample with different cobalt loading has been prepared and their catalytic activity was compared. It was found that the catalytic activity was increased with the increasing cobalt concentration up to molar ratio Co/Al 0.5 in oxidative dehydrogenation. At higher level of ion exchange there was observed a dramatic decrease in activity, , which can be ascribed to formation of oxide clusters of cobalt. Cobalt oxides cause the non-seslctive oxidation of ethane to carbon oxides. On the contrary, in ammoxidation of ethane the catalysts exhibited the activity independent of cobalt content up to Co/Al molar ratio 0.4, which is much higher than activity in oxidative dehydrogenation. This enhanced activity is explained by formation of ammonia adsorption complexes or presence of reactive surface oxygen rising from decomposition of nitrous oxide produced by oxidation of ammonia. At high cobalt loading the activity has the similar history as in oxidative dehydrogenation of ethane. Besides bare cobalt ions and cobalt oxide clusters, the oxygen bridged cobalt dimers are formed in the Co-BEA zeolites with cobalt loading close to theoretical exchange level. These complexes exhibit specific reactivity, which differs from both highly dispersed cobalt oxide and atomically dispersed CO2+ ions in the cationic site of BEA framework

Oxidative dehydrogenation activity of high-silica Co-zeolitesinfluecence of presence of ammonia

The aim of this study is to bring a view on possibility to use high-silica zeolites modified with ion-exchanged Co 2+ ions in oxidative dehydrogenation and ammoxidation of propane. The MFI zeolites chosen are known to possess catalytic activity in ammoxidation of ethane. A set of samples with different content of ionexchanged cobalt, different Si/Al rations and type of co-cations was prepared. The courses of reaction of propane with oxygen or oxygen and ammonia were measured in dependence on temperature. Co-MFI zeolites exhibited catalytic activity in oxidative dehydrogenation of propane to propene and ammoxidation of propane led to formation of acetonitrile. The formation of acetonitrile is explained by destruction of acrylonitrile formed

Determination of extraframework metal content in zeolitic catalysts by means of WD XRF spectrometry

XRF spectroscopy is not widely used for zeolites, but its known advantages are indispensable, i.e. small consumption of the sample (5 mg), analysis of the sample without dissolution, quickly and easy pre-treatment and low-cost analysis. Therefore, development of methodology for determination of metal (Cu, Co, Ga, V) content in zeolites using wavelength dispersive X-ray fluorescence analysis is described in this paper. XRF spectrometer was calibrated for each metal using model pellets containing oxide and boric acid. Response of detector on the amount of metal can be reliably fitted by a linear model. Copper (resp. cobalt) zeolites showed good agreement in metal content determination by XRF and standard validated analysis (AAS and ICP-OES after zeolite dissolution)