Nanostructured Cerium Oxide “Ecocatalysts”

MRS Bulletin ◽  
2001 ◽  
Vol 26 (11) ◽  
pp. 885-889 ◽  
Author(s):  
Maria Flytzani-Stephanopoulos
Keyword(s):  
Cerium Oxide ◽  
Catalytic Converter ◽  
Oxygen Storage Capacity ◽  
Industrial Applications ◽  
Oxygen Storage ◽  
Metal Catalyst ◽  
Fuel Ratio ◽  
Zirconium Oxides ◽  
Recent Compilation ◽  
Three Way Catalyst

Catalysts based on cerium oxide are now used as effective oxidation systems in numerous environmental applications. Cerium oxide was introduced into the catalysis field relatively recently, in 1976, and not as a catalyst initially. Rather, it was chosen as the key oxygen-storage component of the three-way catalyst (TWC) used in automotive exhausts. Accordingly, ceria is used to extend the air/fuel ratio window in the exhaust gas, releasing or accepting oxygen, respectively, under fuel-rich or fuellean conditions, so that the noble metal catalyst operates at the desirable stoichiometric air/fuel ratio, at which it effectively converts all three gaseous pollutants—CO, hydrocarbons, and NO—to innocuous products. A solid solution of cerium and zirconium oxides is used in today's catalytic converters because of its higher oxygen-storage capacity (OSC) compared with pure ceria. In the years that followed the introduction of ceria into the catalytic converter, many additional merits of cerium oxide were realized, first as an active catalytic component of the TWC and subsequently as a catalyst and sorbent in various industrial applications. A review article by Trovarelli on ceria-based catalysts is a good recent compilation.

Overview: Modification of Cerium Oxide in Three-Way Catalysts

2014 ◽  
Vol 575 ◽  
pp. 97-102 ◽  
Author(s):  
M. Nazri Abu Shah ◽  
S. Hanim Md Nor ◽  
Kamariah Noor Ismail ◽  
Abdul Hadi
Keyword(s):  
Thermal Stability ◽  
Rare Earth ◽  
Metal Oxides ◽  
Cerium Oxide ◽  
Storage Capacity ◽  
Rare Earth Metals ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
Alkaline Metals ◽  
Three Way Catalyst

An overview of modification of cerium oxide, CeO2which is employed in the three-way catalyst (TWCs) is presented in this article. The modifications of cerium oxide, CeO2incorporated with the metal oxides for the improvement of thermal stability, microstructure and oxygen storage capacity (OSC) are discussed. In view of that, the types of metal oxide are grouped into transition metals, rare earth metals, and alkaline metals and the effect of each group into cerium oxide, CeO2are elaborated.

A low-dimensional model for describing the oxygen storage capacity and transient behavior of a three-way catalytic converter

2012 ◽  
Vol 73 ◽  
pp. 373-387 ◽  
Author(s):  
Pankaj Kumar ◽  
Imad Makki ◽  
James Kerns ◽  
Karolos Grigoriadis ◽  
Matthew Franchek ◽  
...  
Keyword(s):  
Storage Capacity ◽  
Catalytic Converter ◽  
Transient Behavior ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
Dimensional Model ◽  
Low Dimensional

scholarly journals Modeling of Three-Way Catalyst Dynamics for a Compressed Natural Gas Engine during Lean–Rich Transitions

2019 ◽  
Vol 9 (21) ◽  
pp. 4610 ◽  
Author(s):  
Dario Di Maio ◽  
Carlo Beatrice ◽  
Valentina Fraioli ◽  
Pierpaolo Napolitano ◽  
Stefano Golini ◽  
...  
Keyword(s):  
Steady State ◽  
Natural Gas ◽  
Catalytic Converter ◽  
Operating Conditions ◽  
Oxygen Storage ◽  
Continuous Control ◽  
Engine Exhaust ◽  
Compressed Natural Gas ◽  
The Impact ◽  
Three Way Catalyst

The main objective of the present research activity was to investigate the effect of very fast composition transitions of the engine exhaust typical in real-world driving operating conditions, as fuel cutoff phases or engine misfire, on the aftertreatment devices, which are generally very sensitive to these changes. This phenomenon is particularly evident when dealing with engines powered by natural gas, which requires the use of a three-way catalyst (TWC). Indeed, some deviations from the stoichiometric lambda value can interfere with the catalytic converter efficiency. In this work, a numerical “quasi-steady” model was developed to simulate the chemical and transport phenomena of a specific TWC for a compressed natural gas (CNG) heavy-duty engine. A dedicated experimental campaign was performed in order to evaluate the catalyst response to a defined λ variation pattern of the engine exhaust stream, thus providing the data necessary for the numerical model validation. Tests were carried out to reproduce oxygen storage phenomena that make catalyst behavior different from the classic steady-state operating conditions. A surface reaction kinetic mechanism concerning CH4, CO, H2, oxidation and NO reduction has been appropriately calibrated at different λ values with a step-by-step procedure, both in steady-state conditions of the engine work plan and during transient conditions, through cyclical and consecutive transitions of variable frequency between rich and lean phases. The activity also includes a proper calibration of the reactions involving cerium inside the catalyst in order to reproduce oxygen storage and release dynamics. Sensitivity analysis and continuous control of the reaction rate allowed evaluating the impact of each of them on the exhaust composition in several operating conditions. The proposed model predicts tailpipe conversion/formation of the main chemical species, starting from experimental engine-out data, and provides a useful tool to evaluate the catalyst’s performance.

A Study on Oxygen Storage Capacity of Zirconium-Cerium-Oxide Nanoparticles

2013 ◽  
Vol 685 ◽  
pp. 123-127 ◽  
Author(s):  
Ajin C. Sajeevan ◽  
V. Sajith
Keyword(s):  
Cerium Oxide ◽  
Storage Capacity ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
Precipitation Method ◽  
Xrd Pattern ◽  
Harmful Emissions ◽  
Uv Visible ◽  
Co Precipitation

One of the methods for the reduction of harmful emissions from diesel engines such as hydrocarbon, soot and NOx is the use of fuel born catalyst Cerium oxide. The oxygen storage capacity of Cerium oxide can be improved by coating it with metal such as Zirconium. Zr – Ce-O nanoparticles were synthesized by Co-precipitation method in the present work. Dynamic Light scattering, XRD pattern and UV-Visible spectroscopy were used for characterization of the prepared samples. Thermo gravimetric studies were conducted to investigate the thermal decomposition of Zr-Ce-O nanoparticles. The oxygen storage capacity of Zr-Ce-O nanoparticles was analyzed using TPR analysis.

Model Predictive Air-Fuel Ratio Control for an Integrated Gasoline Engine and Three-Way Catalytic Converter System

2018 ◽  
Author(s):  
Kuo Yang ◽  
Pingen Chen
Keyword(s):  
Gasoline Engine ◽  
Combustion Engine ◽  
Catalytic Converter ◽  
Fuel Efficiency ◽  
Integrated System ◽  
Oxygen Storage ◽  
System Control ◽  
Fuel Ratio ◽  
Conversion Efficiencies ◽  
Control Methodology

With increasingly demanding regulations on engine emission and fuel efficiency, the optimization of the internal combustion engine and the after-treatment integrated system has become a critical research focus. To address such an issue, this paper aims to achieve a better trade-off between the fuel consumption of a spark-ignited (SI) engine and emission conversion efficiencies of a Three-Way Catalytic converter (TWC) system. A Model Predictive Control (MPC)-based integrated engine and TWC control methodology is presented, which is able to optimize Air/Fuel Ratio (AFR) to maintain oxygen storage of TWC at a desired level and thus meet the tailpipe NOx, CO and HC emission requirements. The effectiveness of the presented control methodology is validated in simulation. Compared with the existing dithering-based AFR control, the proposed MPC-based AFR control can improve CO emission conversion efficiencies by 8.42% and 4.85% in simplified US06 and UDDS driving cycles, respectively. At the same time, Nitrogen Oxides (NOx) conversion efficiency maintains above the required limit of 95% and the fuel efficiency remains at the same level as the existing control methodology in production as well. Such an integrated engine-aftertreatment system control can be instrumental in improving engine efficiency and emission reduction performance.

Towards ECU-Executable Control-Oriented Models of a Three-Way Catalytic Converter

2015 ◽  
Author(s):  
Mario Santillo ◽  
Steve Magner ◽  
Mike Uhrich ◽  
Mrdjan Jankovic
Keyword(s):  
Catalytic Converter ◽  
Control Unit ◽  
Oxygen Storage ◽  
Exhaust Gas ◽  
Sensor Model ◽  
Vehicle Engine ◽  
Robust Model ◽  
Combined Models ◽  
Automated Optimization ◽  
Three Way Catalyst

The nonlinear dynamics of an automotive three-way catalyst (TWC) present a challenge to developing simple control-oriented models that are both useful for control and/or diagnostics and real-time executable within a vehicle engine-control unit (ECU). As such, we begin by developing a first-principles control-oriented TWC model and then proceed to apply simplifications. The TWC models are spatially discretized along the catalyst length to better understand and exploit the oxygen-storage dynamics. The TWC models also include the oxidation reaction of ceria by H2O, which is considered important since it represents the production of H2 within the catalyst. We present automated optimization routines to calibrate the TWC model along with a heated exhaust-gas oxygen (HEGO) sensor model using measured vehicle and emissions data. Finally, we demonstrate the combined models’ ability to accurately reproduce the measured HEGO voltage using engine feedgas constituent inputs, which is necessary for designing a robust model-based feedback controller.

Lean HCCI/Rich SACI Gasoline Combustion Cycling and Three-Way Catalyst for Fuel Efficiency and NOx Reduction

2014 ◽  
Author(s):  
Yi Chen ◽  
Vojtěch Šíma ◽  
Weiyang Lin ◽  
Jeff Sterniak ◽  
Stanislav V. Bohac
Keyword(s):  
Fuel Efficiency ◽  
Nox Reduction ◽  
Oxygen Storage Capacity ◽  
Oxygen Depletion ◽  
Oxygen Storage ◽  
Excess Oxygen ◽  
Nox Emissions ◽  
Compression Ignition ◽  
Brake Mean Effective Pressure ◽  
Three Way Catalyst

Multi-mode combustion (MMC) concepts using homogeneous charge compression ignition (HCCI) gasoline combustion at low loads and spark assisted compression ignition (SACI) gasoline combustion at medium loads have the potential for improved fuel efficiency relative to spark ignition (SI) gasoline combustion. Two MMC concepts are compared in this paper with respect to fuel efficiency and tailpipe NOx emissions. The first concept uses stoichiometric HCCI and SACI to allow standard three-way catalyst (TWC) operation. The second concept also uses HCCI and SACI, but cycles between lean and rich combustion and uses a TWC with increased oxygen storage capacity (OSC) for potentially even greater fuel efficiency improvement. This paper performs a preliminary comparison of the two MMC concepts by analyzing two scenarios: 1) cycling between stoichiometric HCCI at 2 bar BMEP (brake mean effective pressure) and stoichiometric SACI at 3 bar BMEP, and 2) cycling between lean HCCI at 2 bar BMEP and rich SACI at 3 bar BMEP. The effects of excess oxygen ratio during HCCI operation and the frequency of oxygen depletion events on TWC performance and fuel efficiency are investigated. Results show that MMC lean/rich cycling can achieve better fuel efficiency than stoichiometric HCCI/SACI cycling. NOx emissions are moderately higher, but may still be low enough to meet current and future emission regulations.

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