INFLUENCE OF PLATINUM AND BARIUM PRECURSORS ON THE NSR
BEHAVIOR OF Pt-Ba/Al2O3 MONOLITHS FOR LEAN-BURN ENGINES
B. Pereda-Ayo(*), D. Divakar, R. López-Fonseca and J.R. González-Velasco
Departamento de Ingeniería Química, Facultad de Ciencia y Tecnología,
Universidad del País Vasco/EHU, 48940 Leioa, Bizkaia, Spain
(*)
Tel.: +34 946013486, e-mail: pereda.ayo@gmail.com
Topic: Structured catalysts and reactors for innovative environmental, automotive and energy applications.
The increasing environmental awareness has promoted the popularity of lean burn and diesel engines in
Europe, due to their higher fuel efficiency. These engines use higher A/F ratios, and consequently the excess of
oxygen in the exhaust makes TWCs inefficient for NOx reduction. The most promising technology for
controlling exhaust gases is the so called NOx storage reduction (NSR) [1]. Nitrogen oxides are stored during the
lean period and then reduced to nitrogen during the rich period using a Pt-BaO/Al2O3 catalyst.
In the present work, we have prepared four different
Table 1. Precursors used for catalyst preparation.
NSR monolithic catalysts varying the precursor used for
Catalyst
Pt precursor
Ba precursor
the incorporation of the active phases: hexachloroplatinic
TAPN
HCPA
BaAc
BaN
acid (HCPA) or tetraammineplatinum nitrate (TAPN) for


A
noble metal incorporation, and barium acetate (BaAc) or


barium nitrate (BaN) for incorporation of the NOx storage
B


compound (Table 1). The objective is to determine the
C
influence of the precursors in the physico-chemical


D
characteristics of the monolithic catalysts and their
relation with the NSR behavior.
The monolithic substrate (D=L=2 cm) was cut from a larger cylinder supplied by Corning with a cell density of
400 cells in-2. Several immersions were done in a γ-Al2O3 slurry until 500 mg of alumina were washcoated as
reported elsewhere [2]. Afterwards, the platinum was incorporated by adsorption from solution to obtain ≈1wt.%
Pt as referred to washcoat. The monoliths were maintained in contact with the precursor solution for 24 hours to
reach the adsorption equilibrium. Then, the samples were dried for 24 h, calcined in air at 500 ºC for 4 hours and
reduced in 5% H2/N2 stream for 1 hour. Finally, the barium (15%) was incorporated by dry impregnation.
Physical and chemical properties of the final catalysts were determined by TEM and SEM, H2 chemisorption,
XRD and ICP/MS.
The NOx storage and reduction behavior of the catalyst was evaluated in a flow reactor, with a space velocity
of 32100 h-1. The inlet gas composition of the 150 s-lean period was 380 ppm NO/6% O2/N2. For the 20 s-rich
period the composition was 380 ppm NO/2.3% H2/N2. The outlet gases concentration was continuously
measured by chemiluminiscence, paramagnetic and infrared detectors, for NOx, O2, and NH3 respectively.
As it can be seen in Figure 1 the NOx storage capacity
(NSC) and selectivity to nitrogen (SN2) increased in the
order D<C<B<A, while the reduction conversion (XR)
remained nearly constant at values higher than 95%.
The incorporation of Pt with both precursors resulted
in similar dispersion values, 46% and 51% for TAPN
and HCPA respectively. Therefore, the lower NSC
obtained with HCPA precursor should be related to the
negative effect of the chlorine on the basic properties
required for efficient trapping [3]. Comparing catalysts
prepared with the same Pt precursor (A and B or C and
D), the precursor BaAc gave better catalytic behavior
than barium nitrate.
In conclusion, the catalyst prepared with tetraammine
Figure 1. Storage reduction behavior and selectivity
platinum nitrate and barium acetate achieved the best
for the prepared catalysts.
catalytic behavior, c.a. NSC, 74.3%; XR (reduction
conversion), 98.3; and selectivity to nitrogen, 78%.
References
[1] N. Takahashi, H. Shinjoh, T. Iijima, T.Suzuki, K. Yamazaki, K. Yokota, H. Suzuki, N. Miyoshi, S.I. Matsumoto, T.
Tanizawa, T. Tanaka, S.S. Tateishi, K. Kasahara, Catalysis Today, 27 (1996) 63-69.
[2] B. Pereda-Ayo, J.J. Delgado, R. López-Fonseca, J.J. Calvino, S. Bernal, J.R. González-Velasco, Proceeding of the
AIChE Annual Meeting, Philadelphia, PA, Nov. 2008.
[3] W.S. Epling, L.E. Campbell, A. Yezerets, N.W. Currier, J.E. Parks, Catalysis Reviews, 46 (2004) 163-245.