Page 196 - Principles of Catalyst Development

CATALYST DEACTIVATIOl\r

How They Fail

8.1. PRELIMINARY REMARKS

Ideally catalysts should last forever. In reality, they die with use, victims
of many diseases that rob them of their ability to function. Some go quickly
in a matter of minutes, others last for up to ten years, but ultimately they
all succumb. Catalyst and process designers together can do much to prolong
lifetime, but as one illness is cured the victim falls prey to another. In this
chapter we examine the cause and effect of deactivation, with emphasis on
catalyst modifications that prove effective in combating it. Only those
features that are important in commercial processing are considered, and
numerous review articles should be consulted for additional background.

8.2. EFFECTS OF DEACTIVATION

Deactivation is loss of activity. The rate per unit volume of reactor is
given by

(8.1)

where Nt is the turnover number, A Avogadro's number, C, the surface
concentration of sites, Sg the surface area per gram, and dB the packing
density. We shall identify later the factors that influence each of these
parameters. Usually Nt is invariant and deactivation decn~ases one or more
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