Catalysis : an Integrated Approach to Homogeneous ...

Chapter 9
Preparation of supported
catalysts
9.1 INTRODUCTION
The preparation of supported catalysts is, as the saying goes, still much more
an art than a science. Usually, after the catalyst for a particular purpose has been
identified, its manufacture is optimized through varying experimentally easily
accessible parameters (pH, T, loading of the active phase, additives) in a pre-
viously established basic recipe. It is not that the fundamental chemistry involved
is not known, but the best catalyst-preparation recipes are generally so compli-
cated, chemically speaking, that no precise description of the reactions taking
place during the manufacturing process can be given. Nevertheless, the scientific
basis of catalyst preparation has received quite a lot of attention in recent years,
and in a few cases a rather detailed understanding of the various steps in the
preparation procedure has been achieved. Since the aim of the present work is to
emphasize molecular aspects wherever possible, it is these cases that will receive
most attention, more than perhaps would be warranted on the basis of their
(industrial) importance.
It is worth mentioning again that supported catalysts are often applied, be-
cause they combine a relatively high dispersion (amount of active surface) with
a high degree of thermostability of the catalytic component, cf. Fig. 9.1. The
support, which is itself usually not catalytically active (but it may be), is a
thermostable, highly porous material onto which the active component is ap-
plied. Frequently used support materials are y-Al203, SiO, active C, and, to a
lesser extent, Ti02. Supported catalysts can be prepared basically in two ways: (i)
selective removal of a component from a non-porous phase containing (a precur-
sor of) the active component(s) and the support, e.g. a coprecipitate; and (ii)
separate application of (a precursor of) the catalytically active material(s) onto a
pre-existing support, e.g. by impregnation or precipitation. Which one will be
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