Alena Vondrová

The effect of AI, Fe, and in substitution in the MFI silicate structure on the aromatic hydrocarbon transformation: SiOHM site strength

The conversion of toluene in toluene disproportionation and its alkylation with ethylene over metallosilicates (AI, Fe, In) of the MFI structure has been found to be proportional to the concentration of the individual framework bridging SiOHM groups, and when related to one SiOHM site, it increases in the sequence of the isomorphous substitution of Si for In < Fe <AI. This clearly reflects the increasing acid strength of the SiOHM group from In, Fe, to AI. As the alkylation of toluene with isopropanol is controlled by the desorption/transport rate of the bulky propyltoluenes from the molecular sieve channels, no correlation between the molecular sieve acidity and conversion- selectivity for this reaction has been found. All metallosilicates (AI, Fe, In) exhibit para-shape selectivity; however, no definite conclusion on the effect of the acidity on the para-shape selectivity can be drawn. Although the AI-silicates contain SiOHM sites with the highest acid strength, the deactivation of Fe and In-silicates by coking is greater compared to AI analogs, likely due to the higher relative amount of extraframework metal species.

Differences in the structure of copper active sites for decomposition and selective reduction of nitric oxide with hydrocarbons and ammonia

Abstract Cu ion co-ordination-location in zeolites of MFI, erionite, mordenite matrices has been determined and the activity of the individual Cu sites compared for NO decomposition and its selective reduction by hydrocarbons or ammonia. It appears that Cu ions in the vicinity of one framework Al (site II), able to form stable Cu + -dinitrosyl complexes, and abundant in MFI structure, are responsible for high activity in NO decomposition. The Cu ions neighbouring two framework Al atoms (site I), and forming mostly mononitrosyl complexes, which dominate in erionite structure, provide a high activity in selective reduction of NO.

10-O-04 - Site selective adsorption and catalytic properties of iron in FER and BEA zeolites

Publisher Summary This chapter discusses the site-selective adsorption and the catalytic properties of iron in ferrierite (FER) and beta (BEA) zeolites. Fourier transform infrared spectroscopy (FTIR) spectroscopy, interaction with oxygen, nitric oxide (NO), nitrous oxide (N 2 O), catalytic oxidation of NO to NO 2 , and reduction of mononitrogen oxide (NO x ) with propane have been used to characterize iron (Fe) cations in FER and BEA zeolites. Three cationic positions for Fe ions in the dehydrated samples of Fe-FER and one in Fe-BEA have been identified. A complex nature of the reversible interaction of the Fe (II) cations in FER and BEA with O 2 , NO, and N 2 O has also been described. The experimental study is complemented with a simple theoretical investigation of Fe (II) and Fe (III) coordination over the most populated 13 site.

On the necessity of a basic revision of the redox properties of H-zeolites

Negligible activity in NO-NO 2 equilibration and SCR of NOx by propane, as well as benzene hydroxylation and N 2 O decomposition reactions was obtained over laboratory synthesized H-MFI, H-FER and H-BEA zeolites containing Fe with concentration below 50 ppm. On the other hand significant activity was found over H-zeolite samples of the same structural type and similar Si/Al values, but with the content of iron impurities of several hundreds of ppm. The consequence of this evidenced role of such low levels of iron content, i.e. at the level usually present in the commercial samples mostly used for the catalytic studies, and not considered in the analysis of the redox function of these systems, is discussed.

Targeted preparation of Fe-zeolites with iron prevailing in extraframework cationic positions

The process for preparation of iron-zeolite catalysts is disclosed, providing for targeted preparation of materials with iron prevailing in extraframework cationic positions and efficient control of the amount of iron in the final catalyst. The procedure uses impregnation with FeCl3 solution in aeetylacetone, providing for decrease of the rate of FeCl3 hydrolysis by zeolite hydroxyls. Evidence for the state of the iron as a single cation in the prepared material is provided by a cluster of methods, including Mossbauer, EPR, and FTIR spectroscopies. Thus prepared Fe-FER, Fe-BEA and Fe-MFI proved their high activity and selectivity for NO oxidation, SCR of NOx by paraffins, and N2O decomposition.