Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Development and Assessment of Regeneration Methods for Commercial Automotive Three-Way Catalysts
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Car exhaust catalysts were introduced in the early 1980’s, to limit the release of pollutants such as hydrocarbons, carbon monoxide and nitrogen oxides. These catalysts contain noble metals such as palladium (Pd), platinum (Pt) and rhodium (Rh) and are able to simultaneously abate all three of the above-mentioned pollutants, hence the name three-way catalyst (TWC). The exposure to high temperatures (800-1000 °C) during operation and the presence of additives in gasoline and lubricants will, after a certain time, lower the activity of the TWC. High temperatures reduce the active area by causing the noble metals to agglomerate and sinter, whereas the additives alter the activity either by fouling the pores of the support material or by interacting with the metals.

The main objective of this work was to develop a method which allows for the removal of contaminants (additives) from the washcoat and enables the redispersion of the active sites (noble metals), in an effort to recover lost catalyst activity. For this purpose, regeneration experiments were carried out on a wide spectrum of different commercial car exhaust catalysts.

The influence of a thermal treatment in a controlled gas atmosphere, such as oxygen or hydrogen, and a redispersing agent, e.g. chlorine, on the activity of TWC was investigated by means of laboratory-scale activity measurements. Several complementary characterization methods such as SEM/TEM, XRD, BET, LA, XPS and TPR were employed to verify the effects of the regeneration treatments on the catalyst morphology (Papers I, II). The results show that partial regeneration of catalyst activity and noble metal dispersion was achieved after thermal treatment in an oxygen-chlorine rich atmosphere at temperatures below 500 °C. A wet-chemical regeneration treatment with dilute oxalic and citric acid solutions is evaluated in Paper III. These acidic solutions are able to dissolve and remove contaminants from the washcoat, thus partly restoring the catalyst activity.

An investigation of the effects of an oxy-chlorine thermal treatment for regeneration of a ‘full-scale’ commercial automotive three-way catalyst was carried out (Paper IV). Improved catalyst activity for a high mileage catalyst could be observed, with emissions lowered by approximately 30 to 40 vol.% over the EC2000 driving cycle.

The properties of fresh, aged and regenerated catalysts were then studied by means of labscale experiments, on a local as well as a global level using a mathematical model (Paper V). The model allows for comparison of the intrinsic properties of the active surface by deriving and tuning parameters of a fresh catalyst and verifying the activity of a regenerated or aged catalyst.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006.
Series
Trita-KET, ISSN 1104-3466 ; 227
Keyword [en]
automotive catalyst, TWC, aging, sintering, Pd/Rh, Pt/Rh, regeneration, oxy-chlorination, dispersion, acid-leaching, mathematical modeling, reaction kinetics
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3931ISBN: 91-7178-343-1 (print)OAI: oai:DiVA.org:kth-3931DiVA: diva2:10070
Public defence
2006-05-12, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100812Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2010-08-12Bibliographically approved
List of papers
1. Thermal gas treatment to regenerate spent automotive three-way exhaust gas catalysts (TWC)
Open this publication in new window or tab >>Thermal gas treatment to regenerate spent automotive three-way exhaust gas catalysts (TWC)
2004 (English)In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 54, 193-200 p.Article in journal (Refereed) Published
Abstract [en]

The effect of regeneration on the metal dispersion and catalyst activity of commercial automotive three-way catalysts (TWC) in oxygen, hydrogen and oxy-chlorine at elevated temperatures has been investigated. In addition, characterisation of the catalysts has been performed using XRD, TEM, TPR, CO chemisorption and BET surface area measurements. Activity tests on monolith fragments were conducted in a micro-reactor supplied with real exhaust gases. An increase in activity was observed with oxygen treatment on catalysts showing heavy sintering as well as a high noble metal loading. Hydrogen proved to be an ineffective treatment procedure, whereas the addition of chlorine to the oxygen stream resulted in an activity increase even on catalysts less sintered and with lower noble metal contents. A comparison of the XRD and BET profiles showed no or small changes in the washcoat structure compared to fresh catalysts after successful regeneration. The TEM, TPR and CO chemisorption measurements suggest a decrease in the size of the largest noble metal agglomerates on the catalyst surface, as well as some Pd and RhO restructuring. The oxy-chlorine regeneration procedure is shown to be the most efficient, both regarding the catalyst activity and the metal dispersion. An increase in the amount of noble metal particles with a size of 20-70 nm, coupled with a decrease in size of larger clusters up to 100 nm in size, was observed for this treatment.

Keyword
Automotive catalyst; Dispersion; Oxy-chlorine; Regeneration; Thermal gas treatment; TWC
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5633 (URN)10.1016/j.apcatb.2004.09.001 (DOI)000224948100007 ()2-s2.0-6044269328 (Scopus ID)
Note
QC 20100812 QC 20110928Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2011-09-28Bibliographically approved
2. An investigation of a new regeneration method of commercial aged three-way catalysts
Open this publication in new window or tab >>An investigation of a new regeneration method of commercial aged three-way catalysts
Show others...
2006 (English)In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 65, 93-100 p.Article in journal (Refereed) Published
Abstract [en]

The ability to modify aged three-way catalysts (TWC) by regaining part of the fresh catalyst surface structure has been verified by both bulk and surface-sensitive characterisation techniques. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM/EDX) techniques were applied to fully evaluate the efficiency of a regeneration procedure of commercial three-way catalysts targeting the washcoat surface. The regeneration comprised combined thermal and liquid chlorine treatments. Structural changes of the washcoat were further investigated with nitrogen adsorption-desorption (BET) and Laser Ablation methods. The investigation showed that the regeneration treatments resulted in an enrichment of the washcoat surface with palladium, thereby increasing the number of catalytically active surface sites. Furthermore, the observed removal of phosphorous and sulphur contaminants resulted in an increase of the relative amount of small pores between 1 and 10 nm and washcoat surface area. An increased catalytic activity regarding CO, NOx, and HC emissions was observed after regeneration. providing proof of the proposed concept.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5634 (URN)10.1016/j.apcatb.2005.12.013 (DOI)000237834800012 ()2-s2.0-33646170972 (Scopus ID)
Note
QC 20100812Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2011-11-08Bibliographically approved
3. Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and Citric Acid Washing
Open this publication in new window or tab >>Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and Citric Acid Washing
2006 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 40, 2030-2036 p.Article in journal (Refereed) Published
Abstract [en]

The efficiency of dilute oxalic and citric acid solutions on improving the oxygen storage capacity (OSC) and catalytic activity of a severely aged (83 000 km) commercial three-way catalyst (TWC) has been investigated. Washing procedures applied after optimization of experimental parameters, namely, temperature, flow-rate, and concentration of acid solution, led to significant improvements of OSC and catalytic activity (based on dynamometer test measurements) of the aged TWC. The latter was made possible due to the removal of significant amounts of various contaminants accumulated on the catalyst surface (e.g., P, S, Pb, Ca, Zn, Si, Fe, Cu, and Ni) during driving conditions, as revealed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and X-ray Photoelectron Spectroscopy (XPS) analyses. For the first time, it is demonstrated that dilute oxalic acid solution significantly improves the catalytic activity of an aged commercial TWC toward CO, CxHy, and NOx conversions under real exhaust gas conditions (dynamometer tests) by two to eight times in the 250-450 degrees C range and the OSC quantity by up to 50%. Oxalic acid appears to be more efficient than citric acid in removing specifically P- and S-containing compounds from the catalyst surface, whereas citric acid in removing Pb- and Zn-containing compounds, thus uncovering surface active catalytic sites.

Keyword
oxygen storage, release properties, calcination temperature, exhaust catalysts, chemical-analysis, metal-oxides, supported rh, deactivation, phosphorus, oxidation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5635 (URN)10.1021/es052310t (DOI)000236213900046 ()2-s2.0-33645220203 (Scopus ID)
Note
QC 20100812Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2011-11-08Bibliographically approved
4. Regeneration of spent commercial automotive three-way exhaust gas catalysts (TWC)
Open this publication in new window or tab >>Regeneration of spent commercial automotive three-way exhaust gas catalysts (TWC)
(English)Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5636 (URN)
Note
QC 20100812Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2010-08-12Bibliographically approved
5. Mathematical Analysis of Thermally Oxy-Chlorine Regenerated Three-Way Catalysts
Open this publication in new window or tab >>Mathematical Analysis of Thermally Oxy-Chlorine Regenerated Three-Way Catalysts
(English)In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405Article in journal (Refereed) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5637 (URN)
Note
QC 20100812Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2010-08-12Bibliographically approved

Open Access in DiVA

fulltext(2400 kB)2942 downloads
File information
File name FULLTEXT01.pdfFile size 2400 kBChecksum MD5
feaf35ebe956b494385e38998c4a93b9bc3094a7b7b836ef4d2cf796c115584b869de94c
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Birgersson, Henrik
By organisation
Chemical Engineering and Technology
Chemical Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 2942 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 953 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf