Untersuchungen zur katalytischen Oxidation von submikronen Kohlenstoffpartikeln aus motorischen Abgasen

The combustion of fossil fuel (e.g. coal, oil, wood) produces gaseous pollutants (e.g. nitrogen oxide, carbon monoxide and hydrocarbons) and a multitude of submicron carbon particles and particles on the micrometer scale (soot) simultaneously. In general, the number of nanoparticles per cubic metre exhaust predominate the number of particles in the micrometer range clearly. For example, modern diesel engines emit a few 10 000 soot particles per cm3 exhaust of size above several 100 nm compared to up to 107 carbon particles in the range between 10 and 200 nm. One promising approach to eliminate the soot particles in the submicron range from engine exhaust is the usage of a catalytic coated electrically heatable SiC-filter following the so- called Jülicher concept. This work is the first step in the development of such an filter. Several catalysts were investigated. They were chosen because of their anticipated applicability. A laboratory reactor was therefore developed with an externally heated reactor tube and a model soot generator. The model soot was produced with an spark discharge generator in a nitrogen carrier gas stream. After adding an oxidation media (oxygen or nitrogendioxide), the aerosol was fed into the reactor, which contains the catalyst coated onto alumina oxide spheres with 1.5 to 1.7 mm in diameter. The oxidation product was recorded in dependence of the granular bed temperature. Furthermore the particle phase was mainly measured before and behind the reactor with a Scanning Mobility Particle Sizer (SMPS) and a Photoelectric Aerosol Sensor (PAS). The contact between soot particles and the catalyst was investigated with the before mentioned equipment taking a theoretical determination of the particle deposition on the catalyst bed based on the Happel-Model into account. The theoretical model includes the deposition mechanisms: particle diffusion, interception, impaction, gravitational settling and thermophoresis together with the mechanisms of tempering and thermal coagulation (agglomeration), which both affect the morphology of the particles. A good agreement between calculation and measurement was achieved with deviations of +/- 20% at the most. Investigations of the catalytic particle oxidation with oxygen pointed out that precious metal as well as non-precious metal catalysts show a significant activity below 200°C. A two-step oxidation process was observed during oxidation of the model soot and could be described with a double Arrhenius equation. The variation of the dwell time in the reactor mainly affected only the soot particle deposition in the granular bed and in conclusion the amount of particle mass accumulated under the chosen experimental conditions. An oxygen content of more than 10 vol.-% had no influence of the oxidation of the deposited particles, whereas a dependence on oxygen concentrations up to 20 vol.-% was observed concerning the transmitted particle phase above 625°C . Compared with oxygen, the usage of nitrogendioxid as oxidation medium lowers the onset of the particle oxidation down to about 100°C approximately. Furthermore a higher turnover was measured in the lower temperature region. Final tests with dry diesel soot and oxygen were performed to compare the diesel soot oxidation with the results obtained with the model soot. A two-step oxidation process with oxygen as oxidation medium was observed as well. The oxidation onset temperature increases by 75°C at the most, when using the diesel soot in stead of the model soot.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2002

Author dc:creator

• Hünnekes, Edgar Viktor

Contributors dc:contributor

• Modigell, Michael

• info:eu-repo/classification/ddc/620
• Ingenieurwissenschaften
• Katalyse
• Kohlenstoffpartikel
• Motorische Abgase

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-119215%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:57147