I. Effects of microwave heating in syntheses of OMS-1 and OMS-2 manganese oxides. II. Coating of sheet and structured materials via microwave heating. III. Microwave-assisted desulfurization of NSR (NOx storage reduction) catalyst

Date of Completion

January 2006

Keywords

Chemistry, Inorganic

Degree

Ph.D.

Abstract

Application of microwave heating in chemical processes has attracted considerable attention in recent years. There are many advantages of using microwave instead of conventional heating based on literature reports. Interaction of a material with microwave radiation causes so-called volumetric heating and therefore homogeneous nucleation, shorter induction times, and enhancement of reaction rates can be achieved. This automatically leads to energy savings. ^ This work presents a study of microwave heating effects on properties of OMS-type manganese oxides in comparison with the conventionally prepared materials. Manganese oxides have a high value of dielectric constant (10,000) that is an important factor determining interaction with microwave radiation. Microwave application during the syntheses of OMS-1 and OMS-2 type manganese oxides resulted in different chemical, physical, and catalytic properties of these materials when compared to the conventionally prepared ones. ^ In addition, application of a high frequency microwave radiation (5.5 GHz) in the synthesis of OMS-2 manganese oxide produced a catalyst with a better activity for the oxidation of 2-thiophenemethanol as compared to the low frequency OMS-2 (2.45 GHz). ^ The second part of this work comprises effects of microwave radiation in producing inorganic coatings in comparison with the conventional methods. Due to the specific mechanism of microwave interaction with matter, uniform coatings of inorganic oxides like alumina, ceria, zirconia, and silica were produced on three-dimensional fibrous substrates. Substantially uniform coatings along the fibers within the substrates were obtained. Removal of a liquid media during the coating process with the conventional heating resulted in the non-uniform coatings. ^ A new approach for regeneration of NOx Storage Reduction (NSR) catalyst via microwave heating was also investigated. Desulfurization of the poisoned NSR catalyst was achieved at temperatures as low as 200 °C in a microwave field and in reducing atmospheres. Presence of water in the system lowered the sulfur desorption temperature to 150 °C. Normally, temperatures above 600 °C are required to promote sulfur desorption using conventional heating in reducing atmospheres. The application of microwave radiation presents a promising method to achieve regeneration of the NSR catalyst. ^

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