Correlation of light-off activity for full size and cored catalyst samples
Blades, L., Douglas, R., McCullough, G., & Woods, A. (2016). Correlation of light-off activity for full size and
cored catalyst samples.
International Journal of Powertrains
,
5
(2), 148-166.
https://doi.org/10.1504/IJPT.2016.076567
Published in:
International Journal of Powertrains
Document Version:
Early version, also known as pre-print
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Download date:09. Aug. 2022
Int. J. Powertrains, Vol. X, No. Y, xxxx 1
Copyright © 20XX Inderscience Enterprises Ltd.
Correlation of light-off activity for full size and cored
catalyst samples
Luke Blades*, Roy Douglas and
Geoffrey McCullough
School of Mechanical and Aerospace Engineering,
Queen’s University Belfast, UK
Email: lblades01@qub.ac.uk
Email: r.douglas@qub.ac.uk
Email: g.mccullough@qub.ac.uk
*Corresponding author
Andrew Woods
Catagen Limited,
5 Elmbank Channel, Commercial Park, Queen’s Road,
Titanic Quarter, Belfast, BT3 9DT, UK
Email: andrew@catagen.co.uk
Abstract: This study identifies, and analyses, the correlation that exists in the
CO light-off performance of full size canned catalytic converters and cored
samples taken from the front and rear sections of the same catalyst brick.
Testing was conducted under laboratory conditions, with full size samples
tested using the Catagen Labcat, and testing of cored samples conducted using
the Horiba SIGU 2000. From experimental tests alone, there was no clear
correlation between the CO light-off activities of full size and cored catalyst
samples. However, by performing simulations using the QUB global catalyst
model, which accounts for the variation of precious metal dispersion and
differences in the heat transfer characteristics of the test rigs, correlation was
shown to be good.
Keywords: catalyst ageing; catalyst correlation; catalyst light-off; catalyst
modelling; catalyst performance.
Reference to this paper should be made as follows: Blades, L., Douglas, R.,
McCullough, G. and Woods, A. (xxxx) ‘Correlation of light-off activity for full
size and cored catalyst samples’, Int. J. Powertrains, Vol. X, No. Y,
pp.xxx–xxx.
Biographical notes: Luke Blades is a Post-Doctoral Researcher, working in
the Clean Energies Research Cluster at Queen’s University Belfast. He
graduated with a MEng in Aerospace Engineering from Queen’s University
Belfast in 2010. He continued his studies at the same institution, earning a PhD
in Mechanical Engineering for his work in the area of three-way catalyst ageing
in 2015. During this work, he investigated the change in catalyst activity
due to static and dynamic ageing, and used mathematical catalyst modelling to
identify correlation between full size bricks and cored catalyst samples. His
other research areas of interest include waste heat recovery.
2 L. Blades et al.
Roy Douglas is a Professor of IC Engines Technology and Director of Clean
Energy Research in Mechanical Engineering at Queen’s University, Belfast.
He has over 35 years experience in the areas of engine research and
development, systems modelling and automotive after-treatment. For the past
ten years, his research has concentrated on automotive drive cycles and systems
energy management, with particular emphasis on bus applications such as
hybrid electric vehicles and thermal management of heavy duty powertrains.
He is a senior member of the School of Mechanical and Aerospace Engineering
and a member of the management board.
Geoffrey McCullough is a Senior Lecturer at Queen’s University Belfast.
He completed his PhD degree in 1997 on the subject of reaction kinetics
within automotive catalysts. The main focus of his research is the reduction
of emissions from automotive engines, which includes theoretical model
development combined with experimental validation. He has published
65 papers in peer-reviewed journals and international conferences on this
subject. He is an academic partner of the Centre for the Theory and Application
of Catalysis (CenTACat) and teaches the internal combustion engines courses
on both the Bachelors and Masters degree programs.
Andrew Woods is the CEO and co-founder of Catagen. He received both his
Masters and PhD in Mechanical Engineering from Queen’s University Belfast.
His PhD degree (ageing and characterisation of automotive catalysts)
culminated in the co-development of the original prototype that evolved
into Catagen’s product range. He holds two patents as co-inventor, one of
which protects the innovation in the Catagen products. He, co-author on a
number of papers, continues research within the Catagen organisation,
making regular discoveries related to after treatment system development.
He is extensively travelled and has participated in entrepreneurship training
programs, the most notable of which was in Stanford University.
This paper is a revised and expanded version of a paper entitled ‘Correlation of
light-off activity for full size and cored catalyst samples’ presented at the 1st
Biannual International Conference on Powertrain Modelling and Control,
Testing, Mapping and Calibration, University of Bradford, Yorkshire, UK,
4–6 September 2012.
1 Introduction
Regulations concerning automotive exhaust emissions are becoming more and more
stringent, requiring the development of more efficient and durable catalytic control
systems. The three-way catalytic converter is the most common method of reducing
harmful exhaust gas emissions, by performing the simultaneous oxidation of carbon
monoxide (CO) and hydrocarbons (HC), and reduction of oxides of nitrogen (NO
x
). A
three-way catalyst has a honey-comb like, monolithic structure, and is usually made from
a synthetic cordierite ceramic material. The monolith has uniformly sized, parallel
channels, onto which the washcoat is bonded. Alumina, Al
2
O
3
, is the most commonly
used washcoat as it has a very complex pore structure, providing a large surface area onto
which the catalytic material is finely dispersed. The catalytic material is usually platinum
(Pt), palladium (Pd) or rhodium (Rh), and these precious metals may be used individually
or in combination. Commercially used three-way catalysts are often a bimetallic
Correlation of light-off activity for full size and cored catalyst samples 3
combination of precious metals, such as Pt/Rh or Pd/Rh, as rhodium is known to be an
efficient catalyst for NO
x
reduction, whereas platinum and palladium are effective
catalysts for the oxidation of carbon monoxide and hydrocarbons (Aitani and Siddiqui,
1995; Gandhi et al., 2003).
Thermal ageing is one of the primary causes of catalyst deactivation, and has become
an increasingly important factor due to the converter being installed close to the engine
for more efficient hydrocarbon conversion. Exothermic reactions can cause temperatures
within the catalyst reaching higher than 1,000°C, causing thermal deactivation such as
sintering of the precious metal particles. At high temperatures, the precious metal
particles agglomerate, decreasing the surface area of catalyst available to reactant gases
and therefore reducing the catalyst activity (Harris, 1995; Heck et al., 2002; Martin et al.,
2003; Martinez-Arias et al., 2002; Meyer Fernandes et al., 2010; Polvinen et al., 2004;
Tanabe et al., 2008; Winkler et al., 2010; Yang et al., 2008; Zanon Zotin et al., 2005).
Sintering of the washcoat can also occur, with a decrease in surface area and a loss of
internal pore structure. The washcoat undergoes irreversible phase changes, with the
alumina washcoat transforming from the gamma phase, γ-Al
2
O
3
, through delta, δ-Al
2
O
3
and theta, θ-Al
2
O
3
, to the stable alpha alumina, α-Al
2
O
3
, with loss of surface area and
hence loss of catalyst activity (Heck et al., 2002; Martinez-Arias et al., 2002;
Meyer Fernandes et al., 2010; More et al., 1997; Zanon Zotin et al., 2005). Catalyst
deactivation can also be caused by catalyst poisoning, which can occur by two
mechanisms. Selective poisoning is the mechanism by which an undesirable contaminant
reacts directly with the precious metal or washcoat, and non-selective poisoning, by
masking or fouling, occurs when a heavy contaminant is deposited onto the catalytic
surface. Poisoning results in a reduced number of active sites available to the reactant
gases and therefore causes reduced catalyst activity (Heck et al., 2002; Zanon Zotin et al.,
2005). Another form of catalyst deactivation is mechanical deactivation, were the
decrease in catalytic activity is caused by loss of catalyst material due to fractures in the
ceramic monolith (Zanon Zotin et al., 2005).
A study of the literature has shown that much research has been conducted, which
involves the laboratory analysis of engine aged catalyst samples. Catalyst light-off is
regularly used to indicate the activity level of an automotive catalyst and is defined as the
temperature of 50% conversion, of CO, HC or NO
x
. Smelder et al. (1991) carried out
activity tests, in a synthetic exhaust flow reactor system, on catalyst samples taken from
various locations of full size field aged catalysts. Light-off tests showed how deactivation
by thermal effects followed a radial profile, with major deactivation occurring at the
centre of a cylindrical catalyst brick and decreasing outwards towards the edges. Martin
et al. (2003) analysed catalyst samples taken from an automobile aged catalyst in order to
measure the axial deterioration. This study concluded that poisoning had a low influence
on ageing and that deactivation is mainly produced by thermal mechanisms. A similar
study was carried out by Lopez Granados et al. (2006), which analysed samples taken
from different axial coordinates of three-way catalyst monoliths aged under real life
traffic conditions. This research showed that the front and rear catalyst samples were
aged to a similar deactivated state. Loss of specific surface due to sintering of washcoat
components was found to be present throughout the catalyst. Research conducted by
Zanon Zotin et al. (2005) showed that the deactivation of catalyst samples, aged on an
engine bench, was not due to one factor, but a combination of thermal, chemical and
mechanical deactivation. A study by Meyer Fernandes et al. (2008) showed that thermal
4 L. Blades et al.
effects were the major contributor to catalyst deactivation. CO light-off tests conducted
on samples aged on a chassis dynamometer showed that the loss of activity was
consistent with the decrease in BET surface area. Lassi (2003) showed that for ageing on
an engine test bench, thermal deactivation mechanisms were important. These included
sintering of the precious metal active sites, loss of washcoat surface area and phase
transitions. Moldovan et al. (2003) showed that, after automobile ageing, the loss of
precious metal particles, and therefore a reduction in dispersion, was much greater at the
front face of a three-way catalyst than in any other region of the brick. A study by
Harkönen et al. (1994) showed that for engine and on-road ageing, the highest
deactivation occurred at the front zone of a catalyst. Engine ageing followed by
laboratory analysis has also been conducted by Usmen et al. (1992), Zhang et al. (1997),
Hughes (2005), Kallinen et al. (2005), He et al. (2003) and Hietikko et al. (2004).
In the literature, there are many examples of work which conducts laboratory analysis
of catalyst cores or cuttings. However, there are no published results of laboratory
analysis on full size commercial catalysts. This study analyses the effect that engine
ageing has on a full size catalyst brick, and then compares the results with cored size
samples taken from these bricks. No studies have been published that attempt to correlate
the activity of full size and cored catalyst samples. The successful correlation of full size
and cored samples is the main aim of this paper. It is important to understand if
correlation does exist, as studies such as that conducted by Dubien et al. (1998), have
used light-off results from cored samples to develop reaction kinetics for catalyst models.
In the study carried out by Dubien, the kinetics developed from laboratory tests did not
correlate well with engine kinetics.
2 Experimental
Four commercial three-way catalysts were used throughout this study. The cylindrical
ceramic cordierite monoliths had a volume of 1 litre (103 mm diameter, 130 mm length)
and a cell density of 400 channels per square inch. The alumina washcoat was loaded
with a combination of Pd and Rh precious metals. Each of the catalysts were obtained
after engine ageing had been conducted for 100 hours, however, further details of the
engine ageing procedure are unknown as the ageing was performed by an outside
company. The full size catalysts used throughout this study are referred to as
Catalysts 1, 2, 3 and 4. CO light-off activity tests were conducted for each of the full size
catalysts using the Catagen Labcat, and for a range of cores taken from these bricks using
the Horiba SIGU 2000, in order to analyse the effects that engine ageing had on the
catalyst activity and to identify if correlation exists between the testing methods.
The Labcat is a highly innovative dynamic, catalytic ageing and evaluation system,
which artificially creates exhaust gas composition and temperature using computer
controlled synthetic gases (Catagen Ltd., 2013). The simulated exhaust gas passes
through an infrared tube furnace, which heats the gas to a predefined temperature and
then through the catalyst brick. Each of the four canned catalyst samples were mounted in
the interchangeable sample manifold, with thermocouples located both upstream and
downstream of the catalyst brick, as well as two thermocouples probing into the centre of
the catalyst bed at 1/3 and 2/3 the height of the brick, as shown in Figure 2. Inlet gas
concentrations were measured using the Horiba MEXA-584L portable automotive