(304e) 3D Activity Map for Predicting the Performance of Commercial Pd-Based TWCs As a Function of the Catalyst Mileage and Pd Loading

3D activity map for predicting the performance of commercial Pd-based
TWCs

 as a function of the
catalyst mileage and Pd loading

Sung Bong Kang, In-Sik Nam^*, Byong K. Cho,

Chang Hwan Kim^**, Se H. Oh^**

Department
of Chemical Engineering/School of Environmental Science and Engineering,

Pohang
University of Science and Technology (POSTECH), san 31 Hyoja, Pohang, 790-784, Korea

^**
General Motors R&D and Planning Center, 30500 Mound Road, Warren, MI,
48090-9055, USA

^*Corresponding author; Tel: +82-54-279-2264, Fax: +82-54-279-8299,
E-mail: isnam@postech.ac.kr

              The
two key parameters determining the TWC activity under real driving conditions
are the catalyst mileage (i.e., time-on-stream)
and its noble metal content.  An effective way for the optimum design
of a commercial TWC converter is to develop the catalyst activity function that can be used to predict
the TWC performance as a function of both the catalyst mileage and the noble
metal loading.¹ Though the concept of the activity function of a catalyst is soundly based
on the theory of catalytic kinetics, it has rarely been applied in practice due
probably to the difficulty involved in obtaining catalyst samples – required in
developing such a function – covering a wide range of the catalyst mileages and
their noble metal loadings.²

With the
alteration of the Pd metallic surface area (MSA) of the commercial Pd TWCs, a
deactivation function has been developed recently to predict the change of the
catalytic performance as a function of the field-aged catalyst mileage ranging from
4k (stabilized) to 98k miles.³ In addition, an activity function has also
been developed to describe the effect of the Pd loading on the TWC performance
of the commercial 4k Pd-based catalyst, using a series of catalyst samples with
the Pd loadings from 20 to 240 g/ft³.⁴

              In
the present study, a comprehensive activity function in the form of a 3-dimensional
surface has been derived in terms of both the Pd loading and mileage of the catalyst,
which can be used to predict the performance of a commercial Pd-based TWC over
a wide range of the Pd loading from 20 to 240 g/ft³ and the mileage
from 4k to 100k miles.  The
derivation has been carried out in two steps.  In the first step, we have demonstrated
that the catalytic activity as a function of the catalyst mileage can be well
correlated by a 2^nd order deactivation kinetics, regardless of the
Pd loading of the catalyst.  In the
second step, a 3D activity surface (a)
has been obtained as a function of both the Pd loading (L) and mileage (M) as
depicted in Figure 1 by integrating the second order deactivation kinetics
model with a _ref (L) as
the boundary condition, where a
_ref (L) is the activity function of the reference catalyst (i.e., Pd-based
TWC at 4k miles) as a function of Pd loading as reported previously.⁴

The
overall reaction kinetic model was obtained by combining the 3D activity map
and the detailed TWC reaction kinetics over the reference catalyst (i.e., 4k
Pd240), and it has proven to be capable of predicting the Pd-based TWC
performance with respect to both the Pd loading and mileage.  It is remarkable that the newly
developed 3D activity map reasonably captures the highly nonlinear catalytic
activity as a function of the Pd loading at any levels of the catalyst mileages
as shown in experimental data (closed symbol) in Figure 1.  The capability of the activity map has
been further validated by the reasonable accuracy of its prediction of the
performance of another series of commercial and Lab-prepared Pd-based TWCs with
respect to the catalyst Pd loading and mileage.  Thus, the 3D activity map has so far
been quite useful and reliable in describing the performance variation of any
Pd-based TWCs as a function of the two key parameters in the design of a modern
TWC catalytic converter.

Figure 1. The 3D activity
map for the commercial Pd-based TWC as a function of both the Pd loading and
mileage.

References

1. J.A. Moulijn, A.E. Van
Diepen, F. Kepteijn, Appl. Catal. A.:Gen., 212 (2001) 3.

2. W. Boll, S. Tischer, O.
Deutschmann, Ind. Eng. Chem. Res., 49 (2010) 10303.

3. S.B. Kang, H.J. Kwon, I.-S.
Nam, Y.I. Song, S.H. Oh, Ind. Eng. Chem. Res., 50 (2011) 5499.

4. S.B. Kang, S.J. Han,
S.B. Nam, I.-S. Nam, B.K. Cho. C.H. Kim, S.H. Oh, Chem. Eng. J., 207-208 (2012)
117.