<p>Ispitivani su dvostruki slojeviti hidroksidi, LDH i mešoviti oksidi nastali njihovom<br />razgradnjom, sa različitim sadržajem Mg-Al-Fe i proširenom supstitucijom aluminijuma.<br />Koprecipitacione metode male i velike prezasićenosti odabrane su za sintezu LDH opšte<br />formule [Mg1<sub>-x </sub>M(III)<sub>x </sub>(OH)<sub>2</sub>](CO<sub>3</sub>)<sub>x/2</sub> ⋅ mH<sub>2</sub>O, gde M(III) pretstavlja Al i/ili Fe, a x udeo<br />trovalentnih anjona, x = M(III) / [M(II) + M(III)], variran u intervalu 0,15 < x < 0,7.<br />Katalizatori na bazi mešovitih oksida sa gvožđem pogodni za upotrebu u redoks<br />reakcijama, formirani su nakon termičke aktivacije - razlaganja LDH. Izvršena je<br />karakterizacija mešovitih oksida nastalih iz LDH, kao i netretiranih LDH, ispitivanjem<br />kristalne strukture (XRD), termičke stabilnosti (TG-DTA), teksture (adsorpcija N<sub>2</sub>), redoks<br />(H<sub>2</sub> TPR) i kiselo-baznih karakteristika (NH<sub>3</sub> TPD), a utvrđena je i priroda prisutnih vrsta<br />gvožđa (Moessbauer spektroskopija). Pokazano je kako metoda pripreme i obim<br />supstitucije M(III) jona utiču na strukturne, površinske i redoks karakteristike LDH i<br />njihovih mešovitih oksida u korelaciji sa katalitičkim svojstvima u odabranim test<br />reakcijama (razgradnja N<sub>2</sub>O i redukcija sa NH<sub>3</sub>). Utvrđeno je da na katalitičku aktivnost<br />dominantno utiču redoks karakteristike i priroda vrste gvožđa u mešovitom oksidu, ali<br />takođe i strukturne karakteristike polaznog LDH, pri čemu je površinska struktura aktivnih<br />centara intervalentnog Fe<sup>2+</sup>-Fe<sup>3+ </sup>gvožđa ključna za redoks procese ispitivanih reakcija.<br />Kod svih mešovitih oksida dobijenih iz LDH aktivni centri imaju relativno jednake jačine,<br />dok razlike u katalitičkom ponašanju potiču od razlika u dostupnosti aktivnih centara.<br />Najbolje performanse u katalitičkim reakcijama pokazali su uzorci sa najmanjom<br />stabilnošću inicijalnih LDH kod kojih je količina supstituisanih M(III) jona bila blizu<br />granice za inkorporaciju u LDH matricu (x = 0,5), a naročito uzorak sintetisan metodom<br />velike prezasićenosti sa malom količinom dodatne Al(OH)<sub>3</sub> faze.</p> / <p>Layered double hydroxides (LDHs) and derived mixed oxides with different Mg-Al-Fe content and extended aluminum substitution were investigated. High and low supersaturation precipitation methods were used for the synthesis of LDHs with general formula [Mg1<sub>-x</sub> M(III)<sub>x</sub> (OH)<sub>2</sub>](CO<sub>3</sub>)<sub>x/2</sub> ⋅ mH<sub>2</sub>O where M(III) presents Al and/or Fe and x the content of trivalent ions, x = M(III) / [M(II) + M(III)], varied between 0.15 < x < 0.7. Iron-containing mixed oxides, suitable as catalysts for redox reactions, were formed after thermal activation - decomposition of LDH. Both, LDHs and derived mixed oxides were characterized with respect to crystalline structure (XRD), thermal stability (TG-DTA), textural (N<sub>2</sub> adsorption), redox (H<sub>2</sub> TPR) and acid-base properties (NH<sub>3</sub> TPD) as well as the nature of the iron species (Moessbauer spectroscopy). It was demonstrated how preparation method and the extent of M(III) substitution influence the structure, surface and redox properties of LDHs and derived mixed oxides in correlation to catalytic properties in chosen test reactions (N<sub>2</sub>O decomposition and reduction with NH3). The catalytic behavior is mainly determined by the redox properties and the nature of the iron species in mixed oxides, but also by the structural properties of initial LDHs. It was confirmed that surface structure of intervalent Fe<sup>2+</sup>-Fe<sup>3+</sup> iron active sites is crucial for the redox processes in chosen reactions. The strength of active sites is similar for all mixed oxides derived from LDH, but the differences in catalytic behavior arise from the differences in active sites accessibility. The best catalytic results were obtained when the stability of the initial LDH matrix was lowest e.g. when the amount of substituted M(III) was near the limit for the incorporation into LDH matrix (x = 0.5), especially for the sample synthesized with high superasaturation method containing a small amount of additional Al(OH)<sub>3</sub> phase.</p>
| Identifer | oai:union.ndltd.org:uns.ac.rs/oai:CRISUNS:(BISIS)71236 |
| Date | 29 December 2006 |
| Creators | Vulić Tatjana |
| Contributors | Marinković-Nedučin Radmila, Kiš Erne, Nikolić Aleksandar |
| Publisher | Univerzitet u Novom Sadu, Tehnološki fakultet Novi Sad, University of Novi Sad, Faculty of Technology at Novi Sad |
| Source Sets | University of Novi Sad |
| Language | Serbian |
| Detected Language | English |
| Type | PhD thesis |
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