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.
see publications and monographies on zeolites