Title

Molecular sieve and ceramic membrane metal oxides: Synthesis, modification, and application

Date of Completion

January 2003

Keywords

Chemistry, Inorganic

Degree

Ph.D.

Abstract

The research has employed novel methods to synthesize and modify molecular sieves such as cryptomelane (OMS-2) manganese oxide and akaganeite iron oxide as well as perovskite ceramic membranes for various applications in catalysis and fuel cell hydrogen purification. Different synthetic routes and methods have been investigated to find better, faster, and cheaper ways to produce metal oxide molecular sieves. Air oxidation is used to prepare layer structure birnessite (OL-1) manganese oxide and calcination is employed to thermally transform layer structure OL-1 to tunnel structure OMS-2. Microwave heating is adopted to study its effect on the formation of akaganeite. Cation and anion dopants in these molecular sieve metal oxides greatly influence their physical and chemical properties. A framework doping method is developed to dope various metal cations into the framework of OMS-2 and an anion exchange method is used to dope different anions into the tunnels of akaganeite. Preparative parameters such as the pH values, the airflow rates, and the types and amounts of dopants are investigated in the syntheses of molecular sieve metal oxides. ^ In the studies of perovskite ceramic membranes, a variety of synthetic methods such as sol-gel and microemulsion have been investigated to form nanosize perovskite powder and to dope different types and amounts of rare earth metal cations into the perovskite. The perovskite powder is then pressed and sintered to form ceramic membranes to study the effects of particle size and doping metals on the protonic and electronic conductivities of perovskite ceramic membranes. ^