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(224f) Enhanced NO, CO and C3H6 Conversions on Precious Group Metal Catalysts: Impact of Oxygen Storage Material and Catalyst Architecture

Authors: 
Zhou, Z., University of Houston
Harold, M., University of Houston
Luss, D., University of Houston

Enhanced NO, CO and C3H6
Conversions on Precious Group Metal Catalysts: Impact of Oxygen Storage
Material and Catalyst Architecture

text-align:center;line-height:normal"> " times new roman>Zhiyu Zhou, Michael P. Harold*, Dan Luss**

normal">Department of
Chemical and Biomolecular Engineering, University of Houston
, Houston, TX 77204

text-align:center">*
mharold@uh.edu, **
dluss@central.uh.edu

 

text-indent:.5in;line-height:150%"> 150%;font-family:" times new roman>Three-way catalysts (TWC)
are used in gasoline vehicles to simultaneously eliminate CO, NOx and
hydrocarbons. Ceria has been widely utilized in TWC as the oxygen storage
material ( " times new roman>OSM) for enhanced oxidation (of CO, H2, HC)
and reduction (of NO and NO2) since its introduction by Ford [1]. Recently researchers [2] reported that spinel-type mixed
metal oxides exhibit excellent oxygen storage capacity (OSC) and can reduce
precious group metal (PGM) loading requirements. We studied in a bench scale
reactor the simultaneous abatement of NO, CO and C3H6
over a series of precious group metal (PGM)-OSM catalysts with
near-stoichiometric feed under steady-state and lean-rich modulation conditions.
The studied OSMs include the model spinel Mn0.5Fe2.5O4
and conventional zirconia stabilized ceria (CZO). The results show that NO, CO,
C3H6 conversions are enhanced by the addition of OSM (either
CZO or spinel). While the single layer design with direct deposited PGM onto
OSM results in the best performance for CZO, the dual-layer design is the best
for spinel. The study provides insight into the
beneficial impact of oxygen storage material and provides guidance for
optimization of TWC catalyst formulation.

text-indent:.5in;line-height:150%"> 150%;font-family:" times new roman>Monolith samples were provided by
CDTi Advanced Materials Inc., including PGM-only and
PGM-OSM catalysts. The studied OSMs include spinel (Mn0.5Fe2.5O4)
and CZO. The PGM-only monolith sample had a single layer formulation with
PGM dispersed on alumina support.   Two different architecture PGM-OSM monolith
samples were used: the first is a single layer with PGM dispersed on OSM; the
second is a dual-layer with a top PGM layer and a bottom OSM layer. For each of
the samples the PGM loading is 30 g/ft3
with a Pt:Pd ratio of 19:1. For PGM-OSM catalysts, the OSM layer had a loading
of 100 g/L with the composition of 22.5 wt% OSM/Al2O3. For
brevity, the PGM-only sample was denoted as “PA”. The PGM-spinel samples with
single or dual layer design were denoted as “PSS” or “PSD” respectively. The
PGM-CZO samples with single or dual layer design were denoted as “PCS” or “PCD”
respectively.

text-indent:.5in;line-height:150%"> 150%;font-family:" times new roman>The steady stoichiometric
feed had a space velocity of 70k hr-1 and a feed composition of 500
ppm NO, 0.17% H2, 0.52% CO, 400 ppm C3H6, 0.5%
O2, 7% CO2, 7% H2O and the balance Ar. For
modulated feeds, the stoichiometric number SN (SN=) was varied with an amplitude of ±0.018 and a cycle timing was 2s
lean/ 2s rich. A FTIR (Thermo Scientific, Nicolet 6700) measured the effluent
concentrations in the bench reactor system.

text-indent:.5in;line-height:150%"> 150%;font-family:" times new roman>Figure 1 shows the cycle-averaged NO
and C3H6 conversion over PGM-only (PA) and PGM-CZO (PCD
and PCS) samples using the stoichiometric steady feed from 200°C to 500°C. The results
obtained with PA are used as a reference for CZO-containing samples. Both PCD
and PCS have a lower NO and C3H6 light-off, confirming
the promotional impact from CZO. In comparison to PA, the promotion from
dual-layer design is rather limited, with a ~ 25 12.0pt;line-height:150%">° 150%;font-family:" times new roman>C lower T50 value (temperature
giving 50% conversion) for both NO and C3H6 conversion. Further,
the single-layer design with direct PGM deposition on CZO results in a dramatic
decrease (~ 100 °C)
for NO and C3H6 light-off temperature. Although not shown
here, the CO conversion is enhanced by addition of CZO and the single layer
design (PCS) provides the largest promotional impacts.

line-height:150%"> " times new roman>

Figure 1. Cycle-averaged NO and C3H6
conversion as a function of feed temperature on CZO contained samples with
PGM-only sample as reference. [Conditions: steady-state feed: 500ppm NO, 0.17%
H2, 0.52% CO, 400 ppm C3H6, 7% CO2,
7% H2O, balance Ar].

 

text-indent:.5in;line-height:150%"> 150%;font-family:" times new roman>Figure 2 shows the cycle-averaged NO
and C3H6 conversion over PGM-only (PA) and PGM-spinel
(PSD and PSS) samples using the stoichiometric steady feed from 200°C to 500°C.
Similarly, the results obtained on PA is used as a reference. The addition of
spinel (PSD and PSS) promotes NO and C3H6 light-off,
suggesting the promotional impact from spinel. In comparison to PA, a ~ 50 ° line-height:150%;font-family:" times new roman>C lower T50
value is achieved for both NO and C3H6 conversion with
the single-layer design (PSS). The promotional impact from spinel is more
exaggerated with the dual-layer design, resulting in a ~ 70 ° line-height:150%;font-family:" times new roman>C lower T50
value for both NO and C3H6 conversion. Although not shown
here, CO conversion is enhanced by addition of spinel and the dual layer design
(PSD) provides the largest promotional impacts.

line-height:150%"> " times new roman>

Figure 2. Cycle-averaged NO and C3H6
conversion as a function of feed temperature on spinel contained samples with
PGM-only sample as reference. [Conditions: steady-state feed: 500ppm NO, 0.17%
H2, 0.52% CO, 400 ppm C3H6, 7% CO2,
7% H2O, balance Ar].

 

text-indent:.5in;line-height:150%"> 150%;font-family:" times new roman>The reactor data will be supplemented
with measurements of the oxygen storage capacity of the materials. The
collective results will be interpreted with a phenomenological mechanism.

150%;text-autospace:none"> font-family:" times new roman>Reference

1.      H.C. Yao, Y.F. Yu Yao, Journal of Catalysis, 86 (1984) 254-265

2.      S. Golden, Z. Nazarpoor, M.
Launois, R-F. Liu, P. Maram, Society of Automotive
Engineering
. SAE 2016-01-0933 (2016)