Abstract
After an extensive introductory chapter (Chapter I), in which the background and
the aim of the research is dealt with, the hydrothermal synthesis and the
characterization of Na-beidellite is discussed in Chapter II and III. The conditions
of temperature, water pressure, and sodium activity under which Na-beidellite can
be synthesized in the chemical system
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Na20-AI203-Si02-H20 are investigated in
Chapter IV. The stability field is limited at low temperatures by the formation of
kaolinite and at high temperatures by that of paragonite and quartz. In Chapter V
solid-state magic-angle spinning 23Na NMR combined with XRD and TGA is used
to study the interlayer collapse and the migration of sodium present at the
interlayer during dehydration of synthetic Na-beidellite. It is shown that the Na+
surrounded by two water molecules is relocated in the hexagonal cavities of the
tetrahedral sheet.
The low-temperature synthesis of ammonium-saponites is considered in Chapter
VI, while solid-state 27AI NMR combined with 29Si I\lMR provides evidence for the
presence of AI at the octahedral and the interlayer sites as dealt with in Chapter
VII. In Chapter VIII a model is developed for the crystallization of saponite based
on the hydrothermal synthesis of ammonium-saponite at increasing periods of
aging time. Chapter IX discusses the synthesis of Mg-saponites using gels
containing different competing cations.
Since the preparation of AI pillaring agents is highly important in the preparation
of pillared clays, much work has been devoted to the study of the forced
hydrolysis of AI3+. Chapter X to XV are dealing with NMR studies of the aqueous
chemistry of AI3+. Chapter X to XIII concentrate on the formation, thermal stability,
and aging of monomeric, oligomeric, and tridecameric A13+ species during forced
hydrolysis. In Chapter XIII direct evidence based on NMR line broadening data for
the existence of the [AI(OH)2] + species is provided. The aging of the tridecameric
AI complex in partly hydrolyzed AI-sec-butoxide solutions and the reaction to
fibrous boehmite are considered in Chapter XIV. Chapter XV and XVI deal with the
characterization, thermal stability, and NMR properties of basic AI sulfate resulting from addition of sodium sulfate solution to partly hydrolyzed AI solutions
containing the tridecameric AI species, such as described in Chapter X to XIII.
Pillaring and thermal treatment of synthetic beidellite and natural montmorillonite
is described in Chapter XVII and the catalytic conversion of thiophene over pillared
clays into which nickel has been applied in Chapter XVIII. Finally in Chapter XIX
some concluding remarks concerning the results obtained in this study and the
implications for the applications of (synthetic) clay minerals in catalytic reactions are made
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