Edyta Tabor

TNU‐9 Zeolite: Aluminum Distribution and Extra‐Framework Sites of Divalent Cations

The TNU-9 zeolite (TUN framework) is one of the most complex zeolites known. It represents a highly promising matrix for both acid and redox catalytic reactions. We present here a newly developed approach involving the use of 29 Si and 27 Al (3Q) MAS NMR spectroscopy, CoII as probes monitored by UV/Vis and FTIR spectroscopy, and extensive periodic DFT calculations, including molecular dynamics, to investigating the aluminum distribution in the TUN framework and the location of aluminum pairs and divalent cations in extra-framework cationic positions. Our study reveals that 40 and 60 % of aluminum atoms in the TNU-9 zeolite are isolated single aluminum atoms and aluminum pairs, respectively. The aluminum pairs are present in two types of six-membered rings forming the corresponding α and β (15 and 85 %, respectively, of aluminum pairs) sites of bare divalent cations. The α site is located on the TUN straight channel wall and it connects two channel intersections. The suggested near-planar β site is present at the channel intersection.

FeOx/Al2O3 catalysts for high-temperature decomposition of N2O under conditions of NH3 oxidation in nitric acid production

The catalytic activity of a series of FeOx/Al2O3 prepared under various conditions was evaluated for high temperature decomposition of N2O (HT-deN2O) in a complex gas mixture produced by oxidation of ammonia. Thus the relevant step in the industrial nitric acid production process was simulated. The catalyst stability during long-term exposure (12 days) to reaction conditions relevant to HT-deN2O was studied. Both fresh and aged FeOx/Al2O3 exhibited more than 90% conversion of N2O in the 750–900 °C temperature range. Structural analysis showed that the prepared FeOx/Al2O3 catalysts contained various proportions of δ, θ and α alumina phases and up to four individual iron species. In the δ and θ Al2O3 phases, well stabilized Fe(III) in Td or Oh coordination was identified as the active species in HT-deN2O.