Title

Part I. Manganese oxide containing layered double hydroxides materials: Synthesis and characterization. Part II. Manganese oxide octahedral molecular sieves (OMS-2): Synthesis, particle size control, characterization, and catalytic applications

Date of Completion

January 2006

Keywords

Chemistry, Inorganic|Engineering, Materials Science

Degree

Ph.D.

Abstract

The work presented here comprises the development of new routes for the preparation of manganese oxide-based materials with controlled properties. The first part of the research consists of the preparation of a new series of layered double hydroxide (LDH) materials containing intercalated manganese oxide species. Characterization of the resulting materials will be sub-divided in two major parts: (1) Composition, structural, and textural properties and (2) Determination of the oxidation state of the manganese species formed. The process of incorporating manganese oxides into the LDH materials takes place by a simple two-step method which involves the ion-exchange of nitrate anions with high valence manganese precursor anions followed by the in-situ reaction between the manganese anions and organic reducing agents. The method developed allows the preparation of a wide range of Mn-intercalated LDHs by simply changing the reducing agent used. ^ In the second part of the research a new "soft" chemistry method to prepare manganese oxide octahedral molecular sieves (OMS-2) materials with controlled crystalline particle sizes will be presented. The synthesis is based on the use of H2O2 to reduce MnO4- under acidic conditions. The particle size is controlled by the concentration of H2O2 in the reaction media. The structural and textural properties of the synthesized OMS-2 are investigated. The catalytic activity and structural properties of these OMS-2 nanomaterials for oxidation catalysis will also be discussed. ^ The work will continue with the investigation on the framework substitution of higher valency transition metal ions (TM = Nb, V) into the OMS-2 materials. The incorporation of TM into the structure of OMS-2 occurs by reacting the manganese and TM source with an oxidant under hydrothermal conditions. The structural properties, oxidation state of manganese, TM loading, and location of the TM in the OMS-2 structure will be investigated. The versatility of OMS-2 to accommodate higher valence TM metals is demonstrated. ^ The last part of the research comprises the study of the electrical resistivity of OMS-2 materials. The effect of the different OMS-2 synthesis method and the framework doping is investigated. A correlation of the resistivities of all the OMS materials prepared in our laboratory and their structures is presented. ^