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Fastställande av PGM-tillgänglighet för dieseloxidationskatalysator med hjälp av kemisorption
KTH, School of Chemical Science and Engineering (CHE).
2015 (Swedish)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Determination of PGM Availability on DOC Using CO Chemisorption (English)
Abstract [en]

The Diesel Oxidation Catalyst (DOC) is subjected to harsh conditions, causing its performance to

diminish over time as the result of different aging mechanisms, which either decreases or lowers the

accessibility to the catalyst’s active sites. Previous work using chemisorption to quantify aging progression

has resulted in a reproducibility of 17%. In this study it has been attempted to lower this, while

also performing performance evaluations to see if correlations exist between dispersion and Light-Off

Temperature (LOT).

Two catalysts have been investigated, LLC (Low Loading Catalyst) and HLC (High Loading Catalyst).

These were hydrothermally aged at 600 C, 700 C and 800 C. In addition to these, two HLC engine cell

samples were also investigated.

To ensure sample homogeneity, different sample preparation methods were investigated. Catalyst samples

were crushed, or had their washcoat layer removed, or were milled and then sieved. A total of 5 runs were

done using fresh catalysts of LLC and HLC to calculate the standard deviation. Evaluation of performance

was done on all samples using Synthetic Catalyst Activity Testing (SCAT).

It was deemed that the only viable sample preparation method was to mill and sieve as other methods

would be hard to reproduce. The results showed that the reproducibility for LLC was %STD = 4% and

for HLC %STD = 2%. For LLC, a correlation between catalytic activity and dispersion was found. The

activity dropped with respect to the dispersion in a close to linear fashion without a large effect on BET

surface area. For HLC the dispersion decreased largely upon hydrothermal aging, however no correlation

was found with the activity; only when aged at 800 C a significant change in LOT was noted. The BET

surface area measurements were inconsistent. Lower dispersion sometimes resulted in higher surface area.

Engine cell samples exhibited notable decrease in dispersion, but not in surface area, and did not correlate

to the hydrothermally aged catalysts, which might be due to other effects inhibiting CO chemisorption

during measurements.

Abstract [sv]

Dieseloxidationskatalysatorn (DOC) utsätts för tuffa förhållanden, vilket medför att dess prestanda

minskar med tiden på grund av olika åldringsmekanismer, vilka antingen minskar dess aktiva säten eller

minskar tillgängligheten till dessa. Tidigare studier då kemisorption använts för att kvantifiera vilken

utsträckning katalysatorn har blivit deaktiverad har resulterat i en reproducerbarhet på 17%. Denna

studie har syftat till att minska detta, men även till att utföra prestandamätningar för att se om det

existerar korrelationer mellan dispersion och tändtemperatur (LOT).

Två katalysatorer undersöktes, LLC (lågladdad katalysator) och HLC (högladdad katalysator), både

som färska, men även som hydrotermiskt åldrade i 600 C, 700 C and 800 C. Dessutom undersöktes två

motorcellsprover av HLC.

För att säkerställa provhomogenitet undersöktes olika provprepareringsmetoder. Katalysatorprover

krossades, eller fick washcoat avlägsnat eller maldes samt siktades. Totalt fem körningar gjordes på färska

katalysatorer (LLC och HLC). Prestandamätningar gjordes på samtliga prov i Synthetic Catalyst Activity

Testing (SCAT).

Det bedömdes att den enda gångbara provprepareringsmetoden var att mala samt sikta katalysatorn

då de andra metoderna skulle bli svåra att upprepa på ett reproducerbart sätt. Resultaten visade att

reproducerbarheten för LLC var %STD = 4% och för HLC %STD = 2%. LLC visade på korrelation

mellan katalytisk aktivitet och dispersion. Aktiviteten minskade linjärt utan större förluster i BETytarea.

För HLC minskade dispersionen i hög grad med ökad åldringstemperatur, däremot kunde ingen

korrelation med katalytisk aktivitet påvisas; enbart då katalysatorn åldrades vid 800 C ändrades LOT

signifikant. Förändringarna i BET-ytarean var inte beroende av åldringstemperatur då lägre dispersion

ibland resulterade i högre ytarea. För motorcellsproverna uppmättes en märkbart låg dispersion, medan

ytarean var relativt oförändrad. Dessa resultat kunde inte korreleras till de hydrotermiskt åldrade proverna,

vilket kan bero på att andra effekter inhiberat CO kemisorptionen.

Place, publisher, year, edition, pages
2015. , 46 p.
Keyword [en]
chemisorption, dispersion, bimetallic, PGM, DOC, performance correlation, method development
National Category
Other Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-174135OAI: oai:DiVA.org:kth-174135DiVA: diva2:858086
Available from: 2015-10-01 Created: 2015-10-01 Last updated: 2015-10-01Bibliographically approved

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