Vol 4 - Characterization I 2004.pdf - Supramolecular - ziolek6661

Preface to the Series

Following Springer’s successful series Catalysis – Science and Technology ,this

series of monographs has been entitled Molecular Sieves – Science and Techno-

logy. It will cover, in a comprehensive manner, all aspects of the science and

application of zeolites and related microporous and mesoporous materials.

After about 50 years of prosperous research, molecular sieves have gained a

firm and important position in modern materials science, and we are witnessing

an ever increasing number of industrial applications. In addition to the more

traditional and still prevailing applications of zeolites as water softeners in

laundry detergents, as adsorbents for drying, purification and separation pur-

poses, and as catalysts in the petroleum refining, petrochemical and chemical

industries, novel uses of molecular sieves are being sought in numerous labo-

ratories.

By the beginning of 1999, the Structure Commission of the International

Zeolite Association had approved approximately 120 different zeolite structures

which, altogether, cover the span of pore diameters from about 0.3 nm to 2 nm.

The dimensions of virtually all molecules (except macromolecules) chemists are

concerned with fall into this same range. It is this coincidence of molecular

dimensions and pore widths which makes zeolites so unique in adsorption and

catalysis and enables molecular sieving and shape-selective catalysis. Bearing in

mind that each zeolite structure can be modified by a plethora of post-synthesis

techniques, an almost infinite variety of molecular sieve materials are nowadays

at the researcher’s and engineer’s disposal. In many instances this will allow the

properties of a zeolite to be tailored to a desired application. Likewise, remark-

able progress has been made in the characterization of molecular sieve mater-

ials by spectroscopic and other physico-chemical techniques, and this is par-

ticularly true for structure determination. During the last decade, we have seen

impressive progress in the application of quantum mechanical ab initio and

other theoretical methods to zeolite science. The results enable us to obtain a

deeper understanding of physical and chemical properties of zeolites and may

render possible reliable predictions of their behavior. All in all, the science and

application of zeolites is a flourishing and exciting field of interdisciplinary

research which has reached a high level of sophistication and a certain degree

of maturity.

The editors believe that, at the turn of the century, the time has come to collect

and present the huge knowledge on zeolite molecular sieves. Molecular Sieves –

Science and Technology is meant as a handbook of zeolites, and the term “zeo-

VIII

Preface to the Series

lites” is to be understood in the broadest sense of the word. While, throughout

the handbook, some emphasis will be placed on the more traditional alumo-

silicate zeolites with eight-, ten- and twelve-membered ring pore openings,

materials with other chemical compositions and narrower and larger pores

(such as sodalite, clathrasils, AlPO 4 –8, VPI-5 or cloverite) will be covered as well.

Also included are microporous forms of silica (e. g., silicalite-1 or -2), alumo-

phosphates, gallophosphates, silicoalumophosphates and titaniumsilicalites

etc. Finally, zeolite-like amorphous mesoporous materials with ordered pore

systems, especially those belonging to the M41S series, will be covered. Among

other topics related to the science and application of molecular sieves, the book

series will put emphasis on such important items as: the preparation of zeolites

by hydrothermal synthesis; zeolite structures and methods for structure deter-

mination; post-synthesis modification by, e. g., ion exchange, dealumination or

chemical vapor deposition; the characterization by all kinds of physico-chemi-

cal and chemical techniques; the acidic and basic properties of molecular sieves;

their hydrophilic or hydrophobic surface properties; theory and modelling;

sorption and diffusion in microporous and mesoporous materials; host/guest

interactions; zeolites as detergent builders; separation and purification proces-

ses using molecular sieve adsorbents; zeolites as catalysts in petroleum refining,

in petrochemical processes and in the manufacture of organic chemicals;

zeolites in environmental protection; novel applications of molecular sieve

materials.

The handbook will appear over several years with a total of ten to fifteen

volumes. Each volume of the series will be devoted to a specific sub-field of the

fundamentals or application of molecular sieve materials and contain five to ten

articles authored by renowned experts upon invitation by the editors. These

articles are meant to present the state of the art from a scientific and, where

applicable, from an industrial point of view, to discuss critical pivotal issues and

to outline future directions of research and development in this sub-field. To this

end, the series is intended as an up-to-date highly sophisticated collection of

information for those who have already been dealing with zeolites in industry or

at academic institutions. Moreover, by emphasizing the description and critical

assessment of experimental techniques which have been used in molecular

sieve science, the series is also meant as a guide for newcomers, enabling them

to collect reliable and relevant experimental data.

The editors would like to take this opportunity to express their sincere grati-

tude to the authors who spent much time and great effort on their chapters. It is

our hope that Molecular Sieves – Science and Technology turns out to be both a

valuable handbook the advanced researcher will regularly consult and a useful

guide for newcomers to the fascinating world of microporous and mesoporous

materials.

Hellmut G. Karge

Jens Weitkamp

Preface to Volume 4

After synthesis and modification of molecular sieves (cf. Volumes 1 and 3,

respectively), the important task arises of appropriately and unambiguously

characterizing the materials thus-obtained. Proper characterization is an indis-

pensable prerequisite for judging the reproducibility of the syntheses and mod-

ifications of the materials as well as their suitability for application in catalytic

and separation processes.

Naturally, a fundamental requirement is the determination of the structure

of the molecular sieves under study (cf. Volume 2) through techniques such as

X-ray diffraction, neutron scattering, electron microscopy and so on. However,

a remarkably broad variety of methods and tools are at our disposal for charac-

terizing the physical and chemical properties of molecular sieves. Volume 4 of

the series “Molecular Sieves – Science and Technology” focuses on the most

widely used spectroscopic techniques. Thereby, the contributions to this volume

not only review important applications of these techniques, but also comprise, to

a greater or lesser extent, the basic principles of the methods, aspects of instru-

mentation, experimental handling, spectra evaluation and simulation, and, final-

ly,employing spectroscopies in situ for the elucidation of processes with molec-

ular sieves, e.g. synthesis, modification, adsorption, diffusion, and catalysis.

Infrared spectroscopy was amongst the first physico-chemical methods

applied in zeolite research. Thus, the first Chapter, “Vibrational Spectroscopy”,

by H.G. Karge and E. Geidel ,covers the application of IR spectroscopy for molec-

ular sieves characterization with and without probe molecules, including also

Raman spectroscopy and inelastic neutron scattering as well as a rather detailed

theoretical treatment of vibrational spectroscopy as far as it is employed in zeo-

lite research.

With the advent of solid-state NMR, another powerful tool for the character-

ization of zeolites and related materials emerged. Similarly and, in many respects,

complementarily to infrared spectroscopy, solid-state NMR spectroscopy

enabled investigations to be carried out of the zeolite framework, extra-frame-

work cations, hydroxyl groups in zeolites, pore structure, and zeolite/adsorbate

systems. The contributions of solid-state NMR to molecular sieves research is

reviewed by M. Hunger and E. Brunner in Chapter 2.

The great potential of electron spin resonance in zeolite science, in particu-

lar in the characterization of zeolitic systems containing transition metal cations,

paramagnetic clusters, or molecules or metal particles, is demonstrated by

B.M. Weckhuysen, R. Heidler and R. Schoonheydt ,who co-authored Chapter 3.

Preface to Vo l ume 4

Chapter 4 by H. Förster is devoted to the potential of and achievements

obtained by electron spectroscopy in the field of molecular sieves. This contri-

bution comprises, in a rather detailed manner, the theoretical fundamentals and

principles, the experimental techniques, as well as a wealth of applications and

results obtained. Results are, e.g., reported on the characterization of zeolites as

hosts, guest species contained in zeolite structures, framework and non-frame-

work cations, and zeolitic acidity.

The usefulness of X-ray absorption spectroscopies in zeolite research, i.e.

extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge

structure (XANES), as well as electron energy loss spectroscopy and resonant

X-ray diffraction is demonstrated by P. B e h r e n s (Chapter 5) and illustrated by

a number of interesting examples, e.g., the EXAFS of manganese-exchanged

A- and Y-type zeolites and guest-containing molecular sieves, or the XANES of

oxidation states of non-framework species.

Photoelectron spectroscopy of zeolites is another very interesting technique

for zeolite characterization. This is shown by W. G r ü n e r t and R. Schlögl in

Chapter 6. The authors carefully describe special aspects of the photoelectron

experiments with zeolites, the information obtainable through the spectra, the

accuracy and interpretation of the data and, finally, provide a number of illus-

trative case studies on, e.g., surface composition, isomorphous substitution,

host/guest systems, etc.

The last contribution (Chapter 7) dealing with the role of Mössbauer spec-

troscopy in the science of molecular sieves was provided by Lovat V.C. Rees, one

of the pioneers in this field. Although Mössbauer spectroscopy is applicable

in zeolite research only to a small extent because of the limited number of suit-

able Mössbauer nuclei, we are indebted to this technique for valuable knowledge

of and a deeper insight into some special groups of zeolites and zeolite/guest

systems. This is particularly true of molecular sieves, which contain the most

important Mössbauer nucleus 57 Fe in their framework and/or extra-framework

guests (cations, adsorbates, encapsulated complexes, and so on).

Of course, there are many other methods of characterizing zeolites and zeo-

lite-containing systems, in particular non-spectroscopic ones such as chemical

analysis, thermal analysis, temperature-programmed desorption of probe mol-

ecules, 129 Xe NMR, etc. These will be dealt with in one of the subsequent volumes

of the series.

November 2003

Hellmut G. Karge

Jens Weitkamp

Vol 4 - Characterization I 2004.pdf

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