Natural clinoptilolite exchanged with iron: characterization and catalytic activity in nitrogen monoxide reduction

Abstract

The aim of this work was to characterize the natural clinoptilolite from Tasajeras deposit, Cuba, modified by hydrothermal ion-exchange with solutions of iron (II) sulfate and iron (III) nitrate in acid medium. Besides this, its catalytic activity to reduce nitrogen monoxide with carbon monoxide/propene in the presence of oxygen was evaluated. The characterization was performed by Mössbauer and UV-Vis diffuse reflectance spectroscopies and adsorption measurements. The obtained results lead to conclude that in exchanged samples, incorporated divalent and trivalent irons are found in octahedral coordination. Both irons should be mainly in cationic extra-framework positions inside clinoptilolite channels as charge compensating cations, and also as iron oxy-hydroxides resulting from limited hydrolysis of these cations. The iron (III) exchanged samples has a larger amount of iron oxy-hydroxides agglomerates. The iron (II) exchanged samples have additionally iron (II) sulfate adsorbed. The catalytic activity in the nitrogen monoxide reduction is higher in the exchanged zeolites than starting. Among all samples, those exchanged of iron (II) has the higher catalytic activity. This lead to outline that, main catalytically active centers are associated with divalent iron.

Keywords

• zeolita natural
• clinoptilolita
• reducción química
• monóxido de nitrógeno
• hierro.