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Simultaneous Removal of Soot and NOx from the Exhaust of Diesel Powered Vehicles
EPA Grant Number: R824970C006Subproject: this is subproject number 006 , established and managed by the Center Director under grant R824970
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: EERC - Center for Airborne Organics (MIT)
Center Director: Seinfeld, John
Title: Simultaneous Removal of Soot and NOx from the Exhaust of Diesel Powered Vehicles
Investigators: Shaw, H. , Pfeffer, Robert , Stevens, John G.
Institution: New Jersey Institute of Technology
EPA Project Officer:
Project Period:
Project Amount: Refer to main center abstract for funding details.
RFA: Center on Airborne Organics (1993)
Research Category: Targeted Research
Description:
Objective:The objective of this project is to gain a scientific understanding associated with the catalytic oxidation of soot with the concomitant reduction of NO, to molecular nitrogen. This information is needed to develop equipment for controlling the most problematic pollutants NOx, and soot from stationary and mobile Diesel engines. We have an NSF grant intended to demonstrate the use of a rotating fluidized bed reactor (RFBR) containing an attrition resistant high surface area catalytic powder to promote the reaction of soot with No.. The present project has as a goal the development of one or more catalysts that will enhance the beneficial properties of copper exchanged ZSM-5 zeolite while minimizing the poisoning effect of sulfur compounds and water. Consequently, in addition to catalyst research, we are conducting experimental and theoretical studies on the mechanism and competitive kinetics of soot reactions with the two oxidants, NO and O2. We are working with the hypothesis that the observed soot oxidation/NOx reduction is due to a stable intermediate. This intermediate, possibly CO, is produced in the non-catalytic oxidation of soot and reduces NOx on the catalyst. A mathematical model of the system is being developed to evaluate a method to test the hypothesis. Approach:
The research consists of both experimental and computer modeling. The experimental work is being conducted in packed and fluidized quartz reactors. The quartz reactors are vertical 2.5 cm by 40 cm long and contain a coarse fritted quartz filter to support approximately one cm of catalyst in the center of a three-zone furnace. Both commercial and experimental catalysts (that we synthesized ourselves) are being evaluated. The catalysts are manually mixed with carbon black or Diesel soot and reacted with an analyzed gaseous mixtures containing NO, NO2, O., and the balance is He. The packed reactor is downflow and the fluidized reactor is upflow through the fritted support. The effluent stream from the reactors flow to one of our on line gas chromatographs. We are using thermal conductivity detection (TCD) for N2 and 029 flame ionization detection (FID) for CO, C02 and unburned hydrocarbons. The CO and C02 are catalytically converted to methane in order to take advantage of the greater sensitivity of FID. A chemiluminescent NOx analyzer is being used to measure NO and NO2. In addition to Cu, modified ZSM-5 that was provided to us by Mobil, we are synthesizing Cu impregnated alumina, ceria, titania, vanadia, and zirconia. We believe these acidic supports will enhance Cu activity. Using Cu impregnated alumina, we have seen similar activity, but at 1OO'C higher temperature, to Cu-ZSM-5. We still need to conduct lifetime studies to ascertain that the activity is indeed similar.
The modeling effort consists of studies of a single spherical particle on which carbon (soot) builds up at low temperatures and reacts at elevated temperatures due to the reaction of carbon with the gas phase oxidants. The carbon oxides then react with NO,, on the catalyst surface. This particle is considered independent of neighboring particles and represents a fluidized bed. A set of kinetic rate constants will be obtained from the literature or determined in our laboratory. Soot is expected to catalytically promote its own oxidation. The combination of catalytic oxidation and poisoning on a particle with a moving external surface area has never been modeled and will require a new innovative approach.
Rationale:This project is designed to find ways to overcome some of the shortcomings of current technology consisting of small passage zeolite catalysts that are used to oxidize Diesel soot, or Pt based oxidation of NO to NO2 which is then used to oxidize soot collected on a filter. In the first case, the zeolite acts as a filter for soot capture and plugs when the catalytic surface becomes ineffective due to low temperature operating conditions of the Diesel engine (i.e., city driving). In the second case, much of the N02 is reduced to NO rather than N2, thus emitting excessive quantities of NOx. Our research is directed at obtaining the required mechanistic understanding to develop a catalyst to reduce No. while oxidizing soot. Soot, captured under low power operation, will be oxidized in situ by NO., at higher temperatures to produce non hazardous CO2 and N2. Consequently, this system can be self cleaning, if we can stoichiometrically balance soot and NOx. The use of a RFBR may allow convenient replacement of the filtration solids or catalyst charge over the long life of Diesel engines. Furthermore, the RFBR rate of rotation couples very well to that of the Diesel engine. Thus, at low load the bed will rotate relatively slowly and primarily act as a soot filter, and at high load the bed will rotate rapidly and promote the soot-Nox reaction. The envisioned RFBR has a relatively small footprint and is expected to fit into the tight design of an automobile. Supplemental Keywords:
soot, emission, air, combustion, modeling. , Air, Scientific Discipline, RFA, Atmospheric Sciences, particulate matter, Environmental Chemistry, mobile sources, tropospheric ozone, automotive, automotive exhaust, urban air, sulfur, diesel exhaust, automobiles, diesel, soot , particulates, motor vehicles, atmospheric chemistry, cars, modeling studies, vehicular exhaust, soot, motor vehicle emissions, catalytic oxidation
Main Center Abstract and Reports:
R824970 EERC - Center for Airborne Organics (MIT)
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R824970C001 Chemical Kinetic Modeling of Formation of Products of Incomplete Combustion
from Spark-ignition Engines
R824970C002 Combustion Chamber Deposit Effects on Engine Hydrocarbon Emissions
R824970C003 Atmospheric Transformation of Volatile Organic Compounds: Gas-Phase
Photooxidation and Gas-to-Particle Conversion
R824970C004 Mathematical Models of the Transport and Fate of Airborne Organics
R824970C005 Elementary Reaction Mechanism and Pathways for Atmospheric Reactions
of Aromatics - Benzene and Toluene
R824970C006 Simultaneous Removal of Soot and NOx from the Exhaust of Diesel Powered
Vehicles
R824970C007 Modeling Gas-Phase Chemistry and Heterogeneous Reaction of Polycyclic
Aromatic Compounds
R824970C008 Fundamental Study on High Temperature Chemistry of Oxygenated Hydrocarbons
as Alternate Motor Fuels and Additives
R824970C009 Markers for Emissions from Combustion Sources
R824970C010 Experimental Investigation of the Evolution of the Size and Composition Distribution of Atmospheric Organic Aerosols
R824970C011 Microengineered Mass Spectrometer for in-situ Measurement of Airborne
Contaminants