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it Remains a challenge for catalysis experts to completely
characterize a solid catalyst. Due to the complexity
of these catalysts, they do not form a uniform
phase, but display various polymorphic solid phases
at once, which are also not defined at the molecular
level. As a result, many physical and chemical properties
are subject to broad distribution. Good examples
include the particle sizes of the carrier materials,
the size of the metal particles on the carriers, the
acidity or basicity of surface centers, or even the oxidation
conditions of the active transition metal components.
It becomes even more complicated when the conditions
on the edges of the distribution functions influence
the catalytic properties. With their content
being so infinitesimally small, it is difficult or impossible
to use physicochemical methods to identify and
quantify them.
As a catalyst producer, however, Evonik must ensure
the consistent quality and performance of its
products. In addition to the standard methods of physicochemical
characterization, such as determining
particle sizes, elementary analysis, determining pore
Figure 1
Property profile of catalysts: Profiling
illustrates the performance features “activity”
and “selectivity” in various test reactions
100
90
80
70
60
50
40
30
20
10
Catalyst 001 Catalyst 002 Catalyst 003
MtBe cracking [%]
0
Activity
(1)
Selectivity
(1)
Activity
(2)
Selectivity
(2)
Activity
(3)
Selectivity
(3)
Characterization using catalysis
volumes, and pore radius distribution, the company
now has a method of evaluating the catalyst: Profiling.
This tool, developed in-house, reliably indicates
the extent to which changes in the manufacturing
process influence the catalytic properties.
The method is based on testing precious metal
powder catalysts (PMPC) in different catalytic reactions
that represent the key fields of application:
Hydrogenation of CC double and CC triple bonds, of
CO and CN groups, and of aromatic nitro groups. It
also factors the hydrogenation of substrates that
simultaneously display different hydrogenizable
functional groups. The various reactions test the
catalysts’ activity and selectivity—the actual performance
features described in the property profile
of each catalyst (see Fig. 1).
The profiles differ greatly, depending on the composition
of the catalyst— the type of precious metal, the
precious metal loading, and the carrier type— 333
CAtALYsIs
Activity
(4)
Selectivity
(4)
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elements39 Issue 2|2012