This document describes the development of a lean NOx trap (LNT) catalyst that does not require precious metals. It proposes using ultrasmall nanoparticles of iron, vanadium, and cerium oxides as the active catalytic components, supported on a porous barium oxide substrate. During lean exhaust conditions, NOx would be oxidized and stored as nitrates in the barium oxide. Under brief rich conditions, the stored NOx would be reduced to N2 via reactions with hydrocarbons facilitated by the redox activity of the iron, vanadium, and cerium oxides. Laboratory testing of prototypes made with this design could evaluate the catalyst's performance versus EPA emissions standards at reducing temperatures compared to conventional precious metal-based

1. Lean NOx Trap
Frederick F. Ratel
F. Ratel from Public Domain 1 February 17, 2015
1.0 The Lean NOx Adsorber /Trap (LNT) Which Does Not Require Precious Metal Catalysts
1.1 The Problem: The Need to Reduce NOx Emissions at a Lower Cost
Engines that operate at lean air-to-fuel ratios (AFR) offer the potential to reduce fuel consumption and
thereby lower greenhouse gas emissions.
1
Oxygen Rich / Lean Burn engines, similar to diesel engines, are
more efficient than traditional gasoline engines, and produce far less carbon monoxide. Yet, under the high
pressure, high temperature conditions found in lean burn and /or diesel engines, more species of nitrogen
oxides (collectively known as NOx) are produced. These oxides of nitrogen are far more harmful to human
health than carbon monoxide or hydrocarbons.
Since the Clean Air Act of 1970, modern air quality standards have become increasingly stringent, and
decades of progress have become apparent (Fig. 1). However, the “Today” photo only shows the results of
the regulations of US EPA 2007 Tier II (“BIN 5”) wherein California permitted a maximum NOx emission of
0.07g/mi
2
Subsequently, more stringent regulations have been passed by California, and then the EPA,
which reduced NOx emissions to 0.02g/mi
3
, equivalent to an EPA SULEV Tier 2 (“BIN 2”). The ultimate goal
is a zero emissions vehicle by 2026. Clearly, legislation is the primary driver for the evolution of engine
technology as well as the development of catalytic exhaust after treatment materials to meet these
requirements. This project will assist my client in developing better, more economical materials, testing them
for the requisite efficiency of 90% at 150°C, and i ntegrating them into a new type of catalytic converter.
With the increased emphasis on fuel economy improvements, considerable engineering effort has been
refocused on Lean Burn (LB) and Direct Injection (DI) engines, similar to the more efficient diesel engines
currently in use. The vehicles which employ this engine technology operate with a non-stoichiometric air to
fuel mix that is typically from 25:1 (at idle) and may be as high as 40:1 in DI engines. The three way catalytic
converter (TWC) developed for gasoline engines removes carbon monoxide and hydrocarbons (CO and HC,
respectively), but has a low removal efficiency for nitrogen oxides (NOx) which are more prevalent in lean
burn technology. More research needs to focus on improving the catalyst contained within the TWC itself in
order to comply with new EPA SULEV Tier II (“BIN 2”) and European Union mandates for NOx emissions.
1
H. Eichlseder, E. Bauman, P. Muller, S. Ruddert, “Gasoline Direct Injection – A Promising Engine Concept for Future
Demands”, SAE Technical Paper 2000-01-0248, 2000
2
T.V. Johnson, Corning Inc.; “Diesel Emission Control in Review”, SAE Technical Paper 2006-01-0030, 2006.
3
“World Wide Emission Standards”; Delphi Passenger Car and Light Duty Truck Emissions Brochure, p. 27, 2011.
Fig.1) Los Angeles in the Early 1970’s as Compared to Los Angeles Today
Photos: Courtesy of Chris Heckle, Corning, Inc., 2012 CAMP Presentation: “Novel Uses for Cellular Ceramics”. Center for
Advanced Materials Processing, CAMP, / Clarkson University;
First Joint Spring Symposium; Fairport, NY. March 5 &6, 2012

2. Lean NOx Trap
Frederick F. Ratel
F. Ratel from Public Domain 2 February 17, 2015
A diesel engine operates by compressing the air until it is hot enough to spontaneously ignite a fine mist of fuel
that is sprayed into the combustion chamber near its point of maximum compression. There is no external
source of ignition. Direct combustion of fuels produces NOx principally from the direct high temperature reaction
of oxygen and nitrogen present in the combustion air. This thermally driven form of nitrogen fixation is
described by the following chemical reaction ½ N2 (g: P = 0.8 atm) + ½ O2 (g; P = 0.2 atm) → NOx (95% NO
and 5% NO2, with a baseline concentration of 667 to 1200 ppm NOx). NOx is toxic because the iron in
hemoglobin preferentially absorbs NOx even in the presence of an excess of oxygen. Additionally, NO has a
toxicity of 25 ppm and NO2 has a toxicity of 5 ppm as compared to carbon monoxide (CO) which has a toxicity
level of 50 ppm. NOx is also an irritant to the skin and bronchial mucosa, is especially harmful to those with
chronic respiratory disease, and contributes to the formation of acid rain as well as smog. Thus, the trade-off for
increased efficiency and fuel economy are more toxic emissions.
Research has focused on the catalytic decomposition of NOx, but to date, a suitable catalyst with significant
activity in real world driving conditions – stop and go urban driving (175C to 250C) alternating with extended
high speed /long distance driving (300C - 450C) – has yet to be achieved. NOx catalysts to date either fail to
exhibit good low temperature activity and /or high temperature durability. Earlier attempts to achieve NOx
control have focused on one of two technologies: 1.) the NH3- SCR NOx Catalyst similar to LANL’s hybrid NOx
HyCat® that extends the automobile’s TWC to accommodate the 9:1 ratio NO to NO2 emitted by lean burn
diesel engines. This catalyst system requires a urea reservoir and metering system to supply ammonia and is
similar to the systems found in stationary applications such as power plants or electric generators. While the
HyCat® system purportedly operates well as low as 113°C, it requires recharging of the urea reservoir and
ceases working when the reductant reservoir runs dry. 2.) The lean NOx trap (LNT) developed by Delphi
combines the 3-way catalyst used with stoichiometric gasoline engines with a porous barium oxide (BaO)
adsorbent to trap NOx as barium nitrate. At temperatures above 250°C, the NOx is oxidized to NO 2 with the aid
of an oxidation catalyst such as platinum, and subsequently reduced to N2 during a brief rich burn purge cycle
when the trap becomes full. The embodiment, as designed by BASF, requires the use of two expensive metals
as co-catalysts: Platinum and Rhodium as the oxidation and reduction catalysts, respectively. Their sequence
of steps is as follows: Lean Burn - 1.) NO + ½ O2
Pt
NO2; 2.) BaCO3 + 2 NO2
Pt
Ba(NO3)2; Rich Burn –
1.) Ba(NO3)2 → BaO + 2 NO2; 2.) 2 NO2 + 2 CO /HC
Pt /Rh
N2 + 2 CO2; 3.) BaO + CO2 → BaCO3 (or CO2 out).
1.2 The Solution:
A hybrid TWC incorporating a lean NOx trap that does not use precious metals is proposed. Rather, this device
will utilize the redox properties of both the iron and vanadium oxide systems, as well as a BaO adsorber trap.
This approach is an extension of core technology technology developed by other OEMs whose profit margins
are being beaten down by the rising cost of precious metals such as Platinum and Palladium. The ultrasmall
size (≈ 4 nm) of nanoparticles renders them with properties not normally seen in their bulk counterparts. For
example, 4 nm magnetite iron oxide is superparamagnetic, while 15 nm magnetite is not. And, 4 nm thick Fe2O3
or α-hematite is an n-type semiconductor, while bulk hematite is just rust. It is then reasonable to believe that
ultrasmall nanocrystalline base metal oxides will possess as high a redox catalytic activity as bulk micron sized
Platinum, Palladium, or Rhodium. In this proposal, the cerium oxide will exist as a solid solution of
nanoparticulate CexZr1-xO2 or zirconia supported cerium to serve as an oxygen storage reservoir in the wash
coat thus assisting the oxidation of NO to NO2 as well as the oxidation of CO to CO2. The oxidized NOx is then
stored in the form of nitrate (NO3
-
)2 in the porous barium-based storage material described previously. Iron and
vanadium oxides are well known redox catalysts - Fe
3+
/Fe
2+
and V
4+
/ V
3+
- upon which the porous barium oxide
will be interspersed as the top coat. During lean burn / low temperature conditions, the abundant oxygen in the
exhaust stream will oxidize HC, H2, and CO into water and carbon dioxide. After the lean burn interval, a brief
rich burn period occurs wherein a stoichiometric mix of air to fuel is combusted, resulting in a comparatively
oxygen deficient atmosphere. Consequently, the HC, H2, and CO are not oxidized. Thus, these components
are free to react with the NO3
-
stored in the porous barium-based catalyst thereby reducing them to N2, water,
and carbon dioxide. During this period, the iron and cerium are also reduced to Fe
2+
and V
3+
, respectively.
While the lean NOx storage reduction technology has been is use for some time, the idea of substituting
ultrasmall nanocrystalline base metal oxides atop a porous zeolite wash coat is novel. Also novel is the premise
that a single phase nanocrystalline iron vanadate with ceria may replace the more expensive platinum as a
reducing agent. The magnetite phase of iron oxide (Fe3O4), with its face centered cubic structure, is the best
polymorph of iron oxide to have its iron substituted with vanadium as its iron exists in two oxidation states Fe
2+

3. Lean NOx Trap
Frederick F. Ratel
F. Ratel from Public Domain 3 February 17, 2015
and Fe
3+
, with the 3+ ionic radii being almost identical with the ionic radii of vanadium 4+. Therefore, during
thermal decomposition of iron and vanadium precursors, it is quite easy for vanadium to substitute for iron in the
crystal lattice of magnetite with minimal crystal distortion. Cerium 4+ has a much larger ionic radii than even
iron 2+, thus the amount of cerium that can be easily incorporated into magnetite will be significantly less and
the substitiution will result in a somewhat distorted, yet single phase crystal of ceria doped iron vanadate.
The specifics of the nitric oxide storage and subsequent reduction cycle are illustrated by the means of the
following mechanism: NO(g)
O2, Fe / V /Ce
NO2(g)
O2, Ba
Ba(NO3)2. And, NOx is not stored in the catalyst without
the presence of an oxygen rich environment. In a rich burn, O2 deficient atmosphere, where HC, H2, and CO
are present in excess, Ba(NO3)2 is reduced to N2 and BaCO3 by the following mechanism: Ba(NO3)2
HC, H2, CO
BaCO3 + NO2; and then,
HC, H2, CO
N2 + CO2 + H2O will be the end product.
2.0 Fabrication Method for LNT Which Does Not Require Precious Metal Catalysts
Materials: The lean NOx catalyst will be constructed similar to an ordinary three-way catalyst. A honeycomb
ceramic substrate will be coated with a concentrated solid solution of iron doped zirconia nanoparticles as a
washcoat so that it has an extremely high and porous surface area. The resulting rough coating will then have a
topcoat of an iron /vanadium oxide containing some ceria upon which the barium oxide will be dispersed on the
surface in close proximity as shown in the second row of images. The first row is the precious metal LNT
schematic.
In previous iterations of the lean NOx storage-reduction system, NOx trapped in the porous Ba-based zeolite
would begin to oxidize at 250°C with the aid of pre cious metals (Top Row). It is envisioned that with the aid of
the 3-4 nm Fe, V, and Ce doped oxide catalysts, the “light-off” temperature will be lowered significantly. The
exact temperature is unknown but will be determined during the course of these studies. When the atmosphere
switches to a reducing mixture such as HC and N2 with H2, N2 should be the only nitrogen species detected by
mass spectroscopy at the outlet of the reactor. The ratios of Fe, V and Ce oxides will be adjusted to achieve the
target operating temperature of ≤150°C with 90% efficiency to meet EPA standards for SULEV Tier 2 (“BIN 2”).
Laboratory Apparatus: The honeycomb substrate will be constructed of a monolith ceramic material having a
small diameter so as to fit into a thermocouple equipped quartz flow tube reactor which can be heated. It is
essential that the ceramic material have the same coefficient of thermal expansion (CTE) as the catalytic
coatings themselves and that the length and channel density promote the most effective interaction of NOx and
catalysts. The catalytic coatings will be applied to the substrate as illustrated below:
Fe, V, CeO
Fe, V, CeO

4. Lean NOx Trap
Frederick F. Ratel
F. Ratel from Public Domain 4 February 17, 2015
The catalyst coated honeycomb will then be placed within the heated quartz tube flow reactor in the orientation
shown below to simulate the conditions of a catalytic converter on a laboratory bench:
The inlet gasses will each have mass flow controllers to individually vary the flow rate or disable it entirely. In
this way, the conditions of lean burn and rich burn may be simulated in the laboratory. (The Helium gas line is
for when purge conditions are needed to cleanse the monolith as well as analysis equipment calibration.)
Additionally, by varying the flow rates of the individual gasses and the temperature within the tube furnace, the
conditions of stop and go city driving and long distance high speed driving may be better simulated in the
laboratory. Of extreme interest in this project is the number of lean burn /rich burn cycles a lean NOx trap can
tolerate without losing efficiency, as well as the overall effectiveness of the catalyst system in achieving the
DOE’s target values of 90% efficiency at 150°C. It is envisioned the vanadium component of the mixed nano-
metal oxide catayst will make the LNT more resistant to sulfur poisoning
Series Arrangement of LNTs:
Another point of interest is that of a series arrangement for 2 LNT bricks. The first upstream LNT(A) would be
combined with a DPF and placed close to the hot engine for the cold conditions encountered just after starting
the motor. The second downstream LNT(B) would act to catch any NOx slip while LNT(A) is being regenerated.
Being further away from the engine’s heat, it will also be more resistant to thermal aging.
With the growing popularity of small vehicle diesel engines for urban driving cycles in personal autos, the LNT
system offers reduced cost and complexity for the driver of a personal vehicle who needs to meet government
mandates at the least possible cost, and who would not be willing to maintain the urea fluid level on an SCR.
Drawing Taken from Defense Technical Information
Center, Report # ESL-TR-89-29; Environics Division
Tyndall AFB, FL. Helipump Corporation, Final
Report, September 1990, M.A. Petrik, Cleveland, OH