A correlation of the reaction rate over Fe-Beta catalysts with a concentration of specific isolated Fe 3? sites represented by an ESR signal at g & 4.3 and by UV adsorption bands with k max \ 300 nm was observed. Blocking zeolite cationic positions with Ca 2? and investigation of ''Fe-free'' Beta-zeolites confirmed the idea of isolated Fe complexes in cationic positions being active sites for NH 3 -deNO x .
catalysts (1 wt% Pt, 10 wt%BaO) were sulfated under conditions simulating a real NSR catalyst operation. Comparative TPR and XPS studies of sulfur removal from Pt/Al 2 O 3 and Pt/BaO/Al 2 O 3 catalysts indicate that the sulfur removal from Al 2 O 3 surface precedes reductive decomposition of BaSO 4 (250-400°C). Barium sulfate decomposition started with further increase in desulfation temperature at the point of surface atomic ratio Ba:S = 1 ($450 o ). Simultaneously, an intensive formation of sulfide species on the catalyst surface was observed. Thermodynamic analysis of the desulfation process allows us to hypothesize that barium sulfide formation may hinder sulfur removal under reducing conditions.
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