The trad-off ICE energy efficiency and waste heat recovery for

harmful emission reduction.

Abstract
Lean NOx trap catalysts (LNTs) are investigated to simultaneously reduce NOx and particulate matter
emissions but are limited in start up condition . The kinetics of the NOx storage reduction process in
LNT catalysts were revealed via means of the study of oxygen storage capacity and NOx storage
selectivity adsorbed in the reduction catalysts surface .Compared with monometallic Pt/BaO and
Rh/BaO catalysts, the bimetallic Pt/Rh-BaO-CuCo LNT catalyst exhibits better catalytic performance
under low-temperature lean combustion conditions . Studies have found that the presence of Cu in the
Pt/Rh-BaO-M system can accelerate the release of NOx at lower temperatures, thereby improving the
NOx reduction efficiency. The physicochemical properties of Pt in Pt/Rh-BaO/M-Al2O 3-LNT
catalyst, such as surface area and particle size and other factors were studied to understand the storage
process of nitrogen oxides. The reduction treatment of Pt/Rh-BaO/M-Al2O 3 catalyst at high
temperature promoted the increase in NOx absorption, which was attributed to the interaction between
Pt and BaO phases. The intereaction between the metallic phase and the trap material, were studied
using detailed kinetic models and operating spectral measurements. The relationship between thermal
energy and catalyst efficiency is resolved experimentally and concocted via a close-coupled after
treatment system.

Highlights :
 Effects of operational parameters (e.g. flow, temperature, species concentration) and design
approaches (sizing, layout, insulation, etc) on regulated and unregulated emissions and
emission control system efficiency and performance.
 Thermal energy optimisation by recyclying the waste heat energy emitted from IC .
 Employement of thermochemical energy from waste heat of engine thermal losses to
empower the catalytic potential of the emission-purification converter.
 Emproving the effieciency of ICE, by downsizing the engine innovating a design provided
with : waste heat recovery and thermally boosted catalytic converter.
 The use of both type of energy saving and reutilisation has contributed to a less complex ICE
operation with both aims : energy efficiency and fuel economy.
  Expensive physical testing was the only means to solve practical problems before simulation
or CFD analysis came into the picture. It involved rigorous testing using prototypes with lots
of recalls and failures
Introduction:
Modern catalytic converters contain a cordierite or metallic substrate coated with alumina and oxygen
storage materials to support dispersed platinum group metals. Palladium, platinum, and rhodium are
commonly used, either singly or in combination. Promoters such as ceria, barium, and lanthanides
improve performance. Formulations balance cost, regulatory targets, fuel composition, and exhaust
characteristics. Despite success, catalytic converters limitations remain including thermal degradation
of noble metals and inadequate cold start activity. Advanced synthesis methods may increase stability
and reduce noble metal usage. New catalysts with improved low temperature performance are also
needed. Automotive research should focus on producing internal combustion engines (ICs) that
essentially, improve combustion quality and reduce environmental emissions. It is currently
impossible to eliminate the internal combustion engine's dependence on fossil fuels. However,
improving efficiency can reduce fuel consumption and emissions
Diesel Engine Systems
Diesel after-treatment involves oxidation catalysts (DOC), selective catalytic reduction (SCR),
particulate filters (DPF), and ammonia slip catalysts (ASC). SCR uses ammonia to reduce nitrogen
oxides over catalysts like copper or iron zeolites. DOC units oxidize carbon monoxide, hydrocarbons
and convert nitric oxide to nitrogen dioxide upstream of SCR. DPF remove particulate matter, while
ASC prevent ammonia slippage.
Some of the most recent lean NOx trap (LNT) materials and technologies studied and developed
worldwide include:
1. Perovskite-type catalysts - Researchers at Oak Ridge National Laboratory recently developed
perovskite nanocubes (LaFeO3) for LNTs that show excellent NOx conversion and durability.
2. Platinum-nickel alloys - Scientists at the University of Houston synthesized PtNi nanoparticle
catalysts supported on ceria that demonstrated improved NOx reduction performance
compared to standard Pt-based LNTs.
3. Double-layer LNTs - Engineers at Ford Motor Company patented a double layer NOx
adsorber system in 2021 using both alkaline and acidic materials to optimize NOx trapping.
4. Modified zeolites - Adam Matros at the University of Tulsa works on zeolite-based LNTs like
ion exchanged Cu-SSZ-13 that have optimal pore sizes and active sites for NOx reactions.
5. Sulfur-tolerant materials - Researchers at General Motors recently tested sulfur-tolerant
layered perovskite oxides using Pr, Zr and Cu that showed excellent selectivity and stability
for NOx storage.
In summary, some promising recent directions are perovskite nanocubes, bifunctional alloy catalysts,
zeolite modification, layered oxides and multi-zone LNT architectures enabling sulfur tolerance and
prolonged NOx conversion under lean burn conditions relevant to diesel engines.
xperimental works:
 Synthesis of new materials using techniques like sol-gel, hydrothermal, chemical vapor
deposition etc.
 Characterization of materials using XRD, SEM, TEM, XPS, FT-IR, Raman spectroscopy etc.
 Testing for properties like optical, electrical, thermal, mechanical, morphological, catalytic
etc.
 Device fabrication and measurement of figures of merits
 Setting up bench experiments to collect data on chemical reactions, thermodynamics, fluid
flows
Numerical works:
 Development of computer models and simulations using methods like finite element analysis
 Molecular modeling using quantum chemistry packages to study interactions
 Kinetic modeling of processes using rate equations, Arrhenius relations etc.
 Statistical analysis of data using R, MATLAB etc. Regression, ANOVA testing
 Machine learning on data - classification models, neural networks, cluster analysis
 Simulations using CFD, Monte Carlo, molecular dynamics, density functional theory
 Designing and optimization of systems using genetic algorithms, response surface methods
Additional activities:
 Survey of literature review and prior art search
 Theoretical calculations and derivations
 Engineering drawings and CAD designs
 Writing computer programs and codes

Copper zeolites like Cu/SSZ-13 are widely used for their stability and resistance to hydrocarbons, but
inferior low temperature activity. Iron zeolites are more active at high temperatures with less sulfur
sensitivity, but have similar issues. Vanadium catalysts better resist sulfur but lack stability. Dual
layer ASC placements let excess ammonia react again, improving overall conversion.
Further improvements to diesel systems include enhancing cold start SCR activity through fast SCR
methods or passive NOx adsorbers. Additionally, developing hydrothermally robust zeolites would
benefit the long-term stability of copper catalysts.
Vehicle emissions have tightened substantially and are expected to tighten further. While current
after-treatment systems are capable, better catalytic materials, reactor designs, and control methods
can improve performance and durability. Future systems may also accommodate emerging zero-
carbon fuels and carbon capture strategies in pursuit of net-zero transportation emissions.
SCR activity can be improved at low temperatures either through fast SCR methods or using passive
NOx adsorbers (PNAs).
Fast SCR:
Involves increasing NO oxidation to NO2 before the SCR catalyst using a dedicated diesel oxidation
catalyst (DOC).
Having more NO2 allows the fast SCR reaction which has faster kinetics than standard SCR especially
below 200°C.
Can achieve over 90% NOx conversion at temperatures as low as 150°C.
Needs precise control of NO/NO2 ratio for optimal performance.
Passive NOx Adsorbers:
Use materials like BaO that can adsorb NOx species at low temperatures below 200°C.
NOx released and catalytically reduced by SCR reaction once exhaust temperature rises over 200°C.
Achieved >90% NOx conversion during cold start phase before SCR light-off.
Performance dependent on thermal management to trigger NOx release.
In summary, both fast SCR through NO oxidation and PNAs which temporarily store NOx can
significantly improve low temperature SCR performance during cold start conditions. They offer
complementary approaches to overcoming slow SCR kinetics before light-off.
SCR activity can be improved at low temperatures either through fast SCR methods or using passive
NOx adsorbers (PNAs).

The molar flow rate of an exhaust gas will depend greatly on the size and operating conditions of
the diesel engine that is being emitted and treated. Larger, higher output diesel engines will have
higher exhaust gas flow rates than smaller engines.
Typical major components of diesel exhaust gas include nitrogen (N2), carbon dioxide (CO2),
water vapor (H2O), oxygen (O2), and smaller amounts of pollutants like particulate matter,
carbon monoxide (CO), nitrogen oxides (NOx), etc.
As a very rough estimate, a molar flow rate entering a diesel oxidation catalyst may be in the
range of 10-100 moles/second based on typical diesel exhaust conditions. But this could vary by
an order of magnitude or more depending on the specific engine.
To calculate an actual molar flow rate, details would be needed on the diesel engine performance
specifications, exhaust system dimensions, exhaust gas temperature, composition analysis, and
potentially modeling of the exhaust characteristics under different operating loads.
So in summary, published emissions data, modeling values, and back-of-the-envelope
calculations could provide an order-of-magnitude estimate in the ballpark of 10-100 moles/second
- but the actual rate could vary substantially. Please let me know if any other details are available
to make a more accurate estimate.
The oxide you are referring to that can convert thermal energy to electrical energy for storage and
reuse when thermal energy input is low is a thermoelectric oxide material. Some key points about
Thermoelectric oxides:
They can generate an electrical voltage/current from a thermal gradient across the material, via
the thermoelectric effect. This allows direct conversion of heat to electricity. Thermoelectric
technology is an attractive method for converting ambient heat into electricity for various
applications such as Internet-of-Things devices and wearable electronics [1].Organic
electrochemical devices can also harvest electricity from surrounding ambient heat through
reversible organic electron transfer reactions [2]. Another approach is thermally integrated
pumped-thermal electricity storage (TI-PTES), which stores electricity as thermal exergy at sub-
[3]
ambient temperatures and generates electricity using an organic Rankine cycle . Additionally,
electricity can be generated from the thermal motion of ions across a two-dimensional silicon
surface or using low-dimensional materials like graphite and clay [4] [5]. These methods offer
potential for energy harvesting from ambient heat sources, providing sustainable power for
various applications.
Common thermoelectric oxide materials include calcium cobalt oxide (Ca3Co4O9), strontium
titanate (SrTiO3), and sodium cobalt oxide (NaxCoO2). These can withstand high temperatures.
The electrical power output and efficiency of thermoelectric oxides improves the larger the
temperature difference (ΔT) across the material.
Thermoelectric generators made from these oxide materials can harvest waste heat and convert it
to electricity for storage in batteries/capacitors. The stored electricity can then be used later to
power electronics or reconverted to heat using resistors when the thermal energy input to the
system is low.
Overall, thermoelectric oxides enable thermal energy storage from heat sources that can fluctuate,
charging when hot and discharging when cold to maintain more consistent power.
So in summary, thermoelectric oxide materials like Ca3Co4O9 can convert heat to electricity
which can be stored and reused, providing a thermal energy buffering effect. This allows thermal
energy storage and reuse when input is below average. passive NOx adsorbers (PNAs) do require
thermal energy and heating for regeneration of the adsorbent sites and desorption of the stored
NOx species. Some key points:

PNAs work by adsorbing NOx from cold engine exhaust streams onto materials like alkali metals
or metal oxides. This stores the NOx until higher temperatures are reached.
Most PNA adsorbent materials, especially BaO, require temperatures above 200°C to initiate
NOx release.
This regeneration is driven by endothermic reactions between the stored nitrates/nitrites and
adsorbent to re-form NOx gas.
Strategies like close-coupling the PNA bricks with engine exhaust headers have been used to
ensure sufficient heating.
Some fuel penalty (~1-2%) is incurred since a bit of extra heat and temperature is required
relative to an already-warm exhaust system.
So in summary, the fundamental Chemisorption process for NOx storage on PNAs is exothermic
during adsorption under cold-start conditions. But energy must later be provided to break those
bonds and desorb the NOx once light-off temperatures are attained. This makes thermal
integration critical to implement PNAs for cold-start NOx control while avoiding inadvertently re-
adsorbing the NOx before SCR conversion .Based on some reasonable assumptions and reported
material properties, we can estimate the order-of-magnitude potential:
Assumptions:
Diesel engine output: 100 kW
Exhaust gas flow rate: 1 kg/s
Inlet T: 500°C, Outlet T: 300°C
Published material properties at 900°C:
Ca3Co4O9 ZT ~ 0.8
SrTiO3 ZT ~ 0.35
NaCoO2 ZT ~ 0.7
Where ZT is the thermoelectric figure of merit that governs efficiency.
Using simple heat engine assumptions and average ZT values, the electrical power that could be
extracted is very roughly around ~2-5 kWe. Over 1 hour that would yield 2-5 kWHr.
Now most thermoelectric systems in vehicles target recovering <100W, so 2+ kWe extraction
seems very promising. Though without further system modeling it's hard to provide an exact
number.
Generating a 200°C temperature difference (ΔT) across a thermoelectric oxide to reach 200°C
would be very challenging with only 100 kWh of electricity. We can make a rough feasibility
estimate as follows:
Assumptions:
 Thermoelectric material: NaCoO2
 Dimension: 10 cm x 10 cm plates
 Electricity: 100 kWh
Material properties (at 200°C):
 Thermal conductivity (k) = 4 W/mK
 Seebeck coefficient (S) = 100 μV/K
 Electrical resistivity (ρ) = 0.1 Ωcm
Heat flux capacity: q′′ = S2σΔT/ρk q'' = 1002 x 5.7x105 x ΔT / 0.1 x 4 q'' = 14,250 ΔT (W/m2)
 For 200°C ΔT across a 0.01 m2 area: Heat flux = 1.4 million W For 1 hour (100 kWh) -> 1.4
million Wh.
So the 100 kWh is not sufficient. Requires a bigger ΔT or more electricity to reach 200°C. More
reasonable might be a 50°C rise, which would take ~35 kWh.
In terms of comparison, the energy recaptured can offset some percentage of the 100 kW engine
output to improve fuel efficiency. More analysis is needed but order 10% recovery seems
potentially viable.

To obtain some preliminary modeling results to estimate the thermoelectric power generation
potential, we could follow these steps:

DFT calculations of material properties

Perform density functional theory (DFT) simulations for the 3 oxides to calculate electronic structure
and obtain properties like Seebeck coefficient and electrical conductivity as a function of temperature
Use calculated properties in simple thermoelectric efficiency models
Provides intrinsic material performance estimates
Data-driven modeling of module performance
Gather experimental data from literature on measured ZT, thermal conductivity etc.
Use collected data to empirically fit relationships between efficiency, ΔT etc
Apply relationships to estimate module-level power output
Less rigorous than coupled multiphysics simulations
0-D Thermodynamic system model
Specify engine exhaust conditions like flow rate, inlet/outlet temps
Apply thermoelectric efficiency definitions
Parameterize based on some reference ZT values
Provides system-level estimate of potential power recovery
Of these, Option 3 is the simplest to apply using high-level exhaust specs and reasonable material
assumptions. This can give an order-of-magnitude estimate fairly easily.
Here are the typical steps for performing a DFT calculation to study a catalysis material:
1. Choose the catalyst material you want to study and decide on the chemical reaction it
facilitates. For example, platinum catalyzing the oxygen reduction reaction in fuel cells.
2. Determine the crystal structure and composition of the material. For catalysis usually
surfaces, nanoparticles, or defects in crystals are most relevant rather than bulk materials.
3. Build a model of the system - this includes specifying the unit cell, surfaces, location of
impurities etc. Choose whether to model the full nanoparticle or just a representative surface
slab model.
4. Select a suitable DFT functional and basis set. Test different functionals if accuracy is critical.
Include dispersion corrections if studying organic molecules.
 5. Relax the geometry of the model to find optimized structure. May require creating extra
vacuum space in unit cell.
6. Calculate the electronic structure and properties. Focus on the band structure, density of
states, charge distribution and reaction energies.
7. Model the catalysis mechanism steps and intermediates by geometry optimization along
reaction coordinates. Calculate reaction energy barriers.
8. To model larger nanoparticle sizes or longer timescales use DFT in tandem with other
methods like force fields, tight binding or mesoscale techniques.
9. Analyze the electronic factors, such as d-band centers and charges, governing the catalytic
activity and selectivity. Suggest ways to improve catalyst design.
10. Validate against experimental catalytic performance data. Repeat calculations as needed for
better accuracy.
how density functional theory (DFT) calculations could be performed to investigate the thermoelectric
oxide material Ca3Co4O9:
Computational Details
 Use a DFT software package such as VASP or Quantum ESPRESSO
 Apply generalized gradient approximation (GGA) exchange-correlation functional
 Model the crystal structure of Ca3Co4O9 using available X-ray diffraction data
 Relax atomic positions and lattice parameters to minimize interatomic forces
 Sample the Brillouin zone using a Monkhorst-Pack k-point mesh
Electronic Structure
 Calculate the electronic band structure of Ca3Co4O9
 Determine the band gap (Eg) and density of states near Fermi level
 Analyze orbital contributions from Ca, Co, and O sites
 Evaluate impact of temperature induced electron excitations
Transport Properties
 Boltzmann transport theory to estimate Seebeck coefficient (S)
 Relaxation time approximation for electrical conductivity (σ)
 Lattice dynamics and phonon calculations to obtain thermal conductivity (k)
 Evaluate figure of merit zT = S2σT/k as function of T
The computations provide theoretical insights into electronic, optical, thermal and thermoelectric
processes in Ca3Co4O9. This guides experimental characterization and material optimization
strategies.
Key aspects are choosing the right model system, computational method and analysis of rate-limiting
steps and electronic structure factors.
NOx emissions are widely regulated due to their toxicity and detrimental effects on health and the
environment. An NH3-SCR system with a state-of-the-art catalyst can effectively reduce NOx
generated from a lean burn engine once the exhaust temperature exceeds 200 °C[9–11]. Similarly,
lean NOx traps (LNTs) and three-way catalysts (TWCs) with optimized formulations are highly
effective in reducing NOx[10,12–15]. However, with kinetic limitations at low temperature, neither
system can remediate NOx emissions effectively during cold start. Arguably, LNT and TWC low
temperature activity can be further improved to minimize NOx emitted during cold start, but the
inability of decomposing the currently required aqueous urea solution at low temperature (makes
application of NH3-SCR systems prohibitive.
To address NOx emitted during cold start, a device with the ability to temporarily store NOx and
thermally release NOx has been proposed. A series of patents from the automobile and catalyst
manufacturing industries indicate that this technology has been conceptually established for some
time[17–19], but due to the rapid development of a variety of other deNOx technologies it apparently
did not attract the same attention as it has more recently. Over the last few years there has been
renewed interest in this approach with publications in the open literature by Johnson Matthey Inc.,
specifically referring to nitric oxide adsorbents that can be thermally regenerated as part of a cold-start
concept[19,20]. Since then, different groups of materials have been extensively evaluated for NOx
adsorption and release. To date, this approach has been developed into one of the most promising
technologies for cold start NOx emission control, and the systems are often referred to as passive NOx
adsorbers or PNAs[].
Functionality As a supplemental device for currently existing after treatment systems, PNAs are
designed to reduce NOx emissions during the cold start period[30]. Notably, cold start is a transient
process with a relatively fixed time duration, therefore, the amount of NOx generated within such a
period is finite. And because of this unique behavior, PNAs are able to overcome the catalytic
reduction reaction challenge by simply adsorbing NOx at low temperatures instead of converting them
immediately. The exhaust gas temperature will eventually exceed 200 °C, where NOx reduction
catalysts are efficient, and ideally in the time to reach 200 °C, all the NOx from the engine will adsorb
on the PNA. Furthermore, again ideally, as soon as the exhaust gas temperature reaches 200 °C all the
NOx that adsorbed during cold start would be released, the driving force of desorption will be nothing
but the higher exhaust temperature. However, instead of generating a sharp NOx pulse in the after-
treatment system that might be hard to handle, several factors that will be covered in later sections
could elongate the NOx release process, but desorption temperatures around 200 °C are favored[11].
An immediate release after warm up takes advantage of a downstream highly active NH3-SCR
catalyst, because by the time NOx desorbs from the PNA, the minimum temperature for aqueous urea
decomposition has been reached. However, too high of a NOx desorption temperature could possibly
make the device inefficient since an adsorption-desorption cycle cannot be completed.
PNA efficacy and application should be evaluated based on the following factors: a. Low temperature
NOx storage capacity
b. Rate of adsorption
c. NOx desorption temperature
d. Real exhaust compatibility
e. Degradation resistance