General information and importance of research subject (excerpt text from the full proposal)
The group of zeolites is one of the most important classes of materials, used as catalysts and ion exchangers in various fields, such as oil refinery and detergent industry. The world-wide production is about one million metric tons per year just for the detergent manufacturers. In addition to the established utilizations of zeolites, there is an urgent demand for new materials with optimized and predetermined properties. Modifications of existing materials with natural or synthetic origin at the atomic and molecular level will have an influence on the mechanical, chemical, and physical properties of the material.
Zeolites, in its strict sense, are aluminosilicates with a microporous framework allowing ion exchange and diffusion processes of molecules or gases through one-, two-, and three-dimensional channel systems. The channel dimension can vary in the range of a few nanometers determining the shape of molecules which can enter the pore system. Therefore, zeolites can be used as molecular sieves with shape selective properties.
We propose to study here various types of natural and synthetic zeolites in order to understand the flexibility of their frameworks at ambient conditions and under elevated temperatures. Details are given below.
Aims and expected goals
The aim of this project is to understand the flexibility of zeolite frameworks as a function of cation and sorbate content under ambient and high-temperature conditions. Some zeolites like natural natrolite are very flexible and collapsible, others like the synthetic zeolite A are very rigid and stable upon cation exchange and dehydration. It is proposed to study a series of zeolites with different properties to get detailed information on the zeolite stability ranges and exchange behavior. Especially, the influence of the water content in the zeolite pores will be studied in this context as well. A special goal will be in the preparation of hydrogen zeolites via ammonium exchange and deammoniation procedures to make catalysts for potential applications. The ammonium form can be transformed to a hydrogen form by calcinations at temperatures typically at 300 to 600°C. Charge balance is achieved by the remaining hydrogen ions which serve at acid sites for the catalytical reactions. Finally, new materials with interesting properties might emerge in this project, which cannot be predicted yet.
Wang, Li, 2016. Crystal-chemical studies of cation-exchanged zeolite A. PhD Thesis, Fachbereich Geowissenschaften, Universität Bremen, Bremen urn:nbn:de:gbv:46-00105484-15, 97 pp. SUUB Bremen.