Microwave-enhanced Processing of Transition Metal oxides, Silicates, and Aluminosilicates and Their Catalytic Studies
Date of Completion
This research work delves into various aspects of heterogeneous catalysis, notably, the synthesis and catalytic applications of inorganic catalytic materials using emerging technologies. Selected transition metal oxide and aluminosilicate materials have been synthesized under continuous microwave heating as well as microwave hydrothermal processes and applied to selected catalytic reactions. ^ The first part presents the development of a continuous microwave technique for the synthesis of transition metal oxides. Two classes of manganese oxides have been synthesized through this technique; cryptomelane-type manganese oxide octahedral molecular sieves (K-OMS-2) and gamma manganese oxide. Microwave power, flow rate (thus residence time); temperature, co-solvent volume, and nature of reactor are some of the parameters that have been optimized for this system. Through this system, materials with small particle sizes have been synthesized and tested for catalytic activity. ^ The second and third parts of this thesis present catalyzed oxidation reactions in the liquid phase using K-OMS-2. K-OMS-2 showed high activity for the oxidation of 9H-Fluorene to 9-Fluorenone. This reaction is important since 9-Fluorenone is a compound that is showing promise in its use as a component of organic light emitting diodes, among other uses. The kinetics as well as a proposed mechanism of 9H-Fluorene oxidation has been reported. It has been found that 9H-Fluorene oxidizes through a first order kinetics where the breaking of the C-H bond is the rate determining step. It has also been found that this oxidation reaction is dependent on the nature of the K-OMS-2 used with K-OMS-2 synthesized under acidic buffer conditions giving the best performance. Another important industrial reaction that K-OMS-2 was exposed to was the oxidation of 2,3,6-trimethyl phenol (TMP). TMP oxidizes catalyzed by K-OMS-2 to 2,3,6-trimethyl-4- hydroquinone (TMQ) is a short time period of 30 mins. This reaction requires the presence of tert-butyl hydroperoxide (TBHP) as the oxidant in a 2:1 ratio of TBHP to substrate. ^ K-OMS-2 has also been used in the gas phase oxidation of benzyl alcohol. This had hitherto this not been done and so provides an impetus to use K-OMS-2 for gas phase catalyzed reactions. Benzyl alcohol flow rates, oxidant flow rate, temperature, and catalyst loading are the variables that have been optimized for >90% conversion of benzyl alcohol to benzaldehyde. ^ Lastly, microwave irradiation has been used to synthesize zeolite Y in a short time period of 1 h under hydrothermal conditions. Further, the synthesized zeolite was exchanged for nickel and also impregnated with 10% nickel and reduced in a hydrogen atmosphere for use as a catalyst for steam reforming of glycerol. Steam reforming of glycerol gave good yields of hydrogen gas. ^
Opembe, Naftali Nandera, "Microwave-enhanced Processing of Transition Metal oxides, Silicates, and Aluminosilicates and Their Catalytic Studies" (2012). Doctoral Dissertations. Paper AAI3529370.