Deactivation modes of DOCs
Transcript of Deactivation modes of DOCs
Rama Krishna Dadi
Krishna Gunugunuri, Hongmei An, Anand Srinivasan, Rohil
Daya, Yuhui Zha, Saurabh Joshi, Michael Cunningham, Krishna
Kamasamudram
Deactivation modes of DOCs
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Introduction
▪ Precious metals like Pt and Pd are typically used in DOCs due to their superioroxidation capability
▪ Thermal aging and chemical aging of DOCs can result in their loss of oxidationperformance due to change in particle size and morphology of PGM particles
▪ Chemical aging of DOC is caused by inorganic elements present in diesel fuel andengine oil
▪ The deactivation due to S is recoverable with a thermal regeneration of DOC. Pdeactivation is irreversible under typical thermal regeneration events done indiesel after treatment system
▪ The objective of this work is to give general perspective on physical processesleading to different deactivation modes of DOCs
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Outline of aging models
▪ Sintering type of models for PGM can be used to capture impact of HTA onoxidation performance
▪ Heat transfer model involving reaction heat source can capture solid temperatureexotherm inside DOC
▪ SOx poisoning models including SOx storage, SO2 oxidation and the impact onoxidation performance model can be used to capture impact of S on DOCperformance
▪ PGM oxidation rate is dependent on particle size, presence of S, and Pt: Pd ratio▪ P poisoning can be captured by two different sub-models. One for P accumulation
with engine operation, other for impact of P loading on oxidation performance
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Hydrothermal Aging
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HTA impact on Oxidation Performance
1. Applied Catalysis B: Environmental 283 (2021) 119655
𝑑Ψ
𝑑𝑡= −𝑘𝑑 Ψ−Ψ∞
𝑛; Ψ∞ = 𝐴∞ exp −𝐸∞
𝑅𝑔𝑇𝑎𝑔𝑒
▪ Limiting process for Aging changes withextreme HTA
▪ Aging model with two sets of parameterswere developed: one for mild aging and theother extreme aging [1]
NO=200ppm
O2 =10%
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HTA impact on PGM oxidation
▪ PGM Oxidation → Time on stream deactivation▪ Higher Pd → Lower PGM oxidation rate▪ Larger PGM particles→ Lower PGM oxidation rate [1]
1. Applied Catalysis B: Environmental 283 (2021) 119655
NO=1000ppm+O2=10%
NO=1000ppm+O2=10%
Higher Pd contentHigher Pt content
550°C-4h 550°C-4h700°C-50h
NO=1000ppm; O2 =10%
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DOC solid temperature exotherm
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▪ In cylinder HC dosing to generate exotherm▪ Multiple thermocouples instrumented▪ Key heat transfer phenomena to be modeled
• Exotherm generation by HC oxidation• Radial heat loss• Axial heat convection
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DOC Bed temperature exothermicity
▪ Model predicted solid temperature histogram is more appropriate to understandthe extent of thermal aging of PGM based catalysts
▪ Thermal gradients become particularly important for zone coated formulations
Data Model
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Chemical Aging (S, P)
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TPO on sulfated DOC
▪ TPO on catalyst saturated with S▪ Bimodal profile: Surface sulfates and bulk sulfates▪ Pt role: Migration of sulfur to support, oxidation of low oxidation states of S [2]
2. Applied Catalysis B: Environmental 181 (2016) 587–598
Data Model
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Impact of SOx on oxidation performance
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3. Catalysis Science & Technology, 5(3), pp.1731-1740
▪ Oxidation performance gets inhibited by S▪ Performance recovery dependent on DeSOx temperature and time▪ Facile PGM particles → More prone to S poisoning [3]▪ Model: S impact on oxidation
I. Surface S coverage (Slide. 10)II. Performance as a function of coverage
NO=1000ppm; O2 =10%
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Impact of S on PGM oxidation
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Temperature = 250°C
4. Catalysis Today 258 (2015) 169–174
▪ S on catalyst protects PGM from getting oxidized [4]▪ Sulfated catalyst with reductants in the feed → Significantly suppressed PGM oxidation
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Real World Aged DOCs – NO oxidation
▪ Impact of P on Oxidation – Reactor and Elemental characterization of RWA DOCs▪ Oxidation performance before and after acid washing▪ Acid washing → Removes irreversible chemical contaminants▪ ICP analysis before and after acid washing▪ Activity recovered showed good trend with irreversible P but not S
NO=1000ppm; O2 =10%
5. SAE 2005-01-1758
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HC Oxidation
▪ Same experimental tests as NO oxidation▪ Aging model framework is same as NO oxidation
▪ Aging parameters can be different
P removed (g/l)
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Conclusions
▪ Real world aged DOCs can be represented by hydro-thermal aging, regardless ofactual dominant mode of deactivation
▪ Irreversible S present on catalyst suppresses deactivation due to PGM oxidesformation
▪ Deactivation of catalysts showed clear trend with P loading on catalyst surface
▪ Mimicking real world P loading of catalyst is important to simulate field deactivationdue to P
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Acknowledgements (Advanced Chemical
System Integration team at Cummins)
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Q+A
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