Effects of Hydrothermal Aging on CO and NO Oxidation Activity over Monometallic and Bimetallic Pt-Pd Catalysts

Schütz, Jochen; Störmer, Heike; Lott, Patrick; Deutschmann, Olaf

doi:10.3390/catal11030300

Cited by 25 publications

(13 citation statements)

References 66 publications

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“…However, once the catalyst has been aged at elevated temperatures, the Pd oxide seems to have limited opportunities for epitaxy. By making observations on four sets of Pt–Pd catalysts, we feel that our observations are reproducible and consistent with the literature where other research groups also show biphasic particles but do not comment on them …”

Section: Discussionsupporting

confidence: 86%

“…8 This study was performed in situ in TEM with 10 kPa of O 2 at 773 K, conditions very different from those to which DOCs are subjected. Schuẗz et al 35 examined the effects of hydrothermal aging on CO and NO oxidation activity of bimetallic Pt−Pd catalysts. In this investigation, representative powder catalysts were mounted into monoliths and subjected to aging and reactivity tests.…”

Section: Introductionmentioning

confidence: 99%

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Biphasic Janus Particles Explain Self-Healing in Pt–Pd Diesel Oxidation Catalysts

et al. 2023

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The addition of Pd to Pt-based diesel oxidation catalysts is known to enhance performance and restrict the anomalous growth of Pt nanoparticles when subjected to aging at high temperatures in oxidative environments. To gain a mechanistic understanding, we studied the transport of the mobile Pt and Pd species to the vapor phase, since vapor phase transport is the primary route for sintering in these catalysts. The results are surprising: there is a 30-fold drop in the effective vapor pressure of Pt in the Pt−Pd catalysts compared to monometallic Pt. At the same time, there is a significant enhancement in the vapor pressure of Pd, compared to PdO, which otherwise has a negligible vapor pressure at the aging temperature. Such behavior cannot be explained simply by alloying Pt and Pd in the metallic phase, or a core−shell morphology where a PdO shell covers a Pt core. Transmission electron microscopic examination of catalysts aged up to 50 h in air at 800 °C shows that the particles exhibit a biphasic "Janus"-like structure. The metal and oxide phases are conjoined, exposing a metal and an oxide face to the gas phase. The high mobility of the Pt and Pd allows them to be partitioned into the metal and oxide phases, in apparent thermodynamic equilibrium. The PdO helps to trap mobile PtO 2 and as a result contains high concentrations of Pt oxide, consistent with its role in mitigating the transport of Pt to the vapor phase and preventing the growth of anomalously large particles. In turn, Pt allows Pd to remain metallic, allowing the catalyst to retain both metal and oxide functionality for catalysis. The regeneration of deactivated catalysts typically requires an external input, such as a change in the working environment from reducing to oxidizing or vice-versa. Here, we show that the mobile species, which are primary contributors to catalyst sintering are effectively returned to the active site, hence our use of the term "selfhealing". The detailed insights into the inner workings of the Pt−Pd diesel oxidation catalysts can help provide clues to the design of robust and durable heterogeneous catalysts.

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Section: Discussionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Biphasic Janus Particles Explain Self-Healing in Pt–Pd Diesel Oxidation Catalysts

et al. 2023

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“…Catalytic activity measurements of the monolithic samples were conducted in an in-house developed laboratory catalyst testing bench that was already described in a previous publication, optimized for three-way catalysis during the present work. The monolithic catalyst sample was mounted in a cylindrical quartz glass sample holder and placed in a plug-flow quartz glass tubular reactor.…”

Section: Methodsmentioning

confidence: 99%

Detailed Microkinetics for the Oxidation of Exhaust Gas Emissions through Automated Mechanism Generation

et al. 2022

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Emissions from vehicles contain a variety of pollutants that must be either oxidized or reduced efficiently in the catalytic converter. Improvements to the catalyst require knowledge of the microkinetics, but the complexity of the exhaust gas mixture makes it challenging to identify the reaction network. This complexity was tackled by using the “Reaction Mechanism Generator” (RMG) to automatically generate microkinetic models for the oxidation of combustion byproducts from stoichiometric gasoline direct injection engines on Pt(111). The possibilities and the limitations encountered during the generation procedure are discussed in detail. A combination of first-principles-based mechanism construction and top-down parameter refinement allows a description of experimental results obtained by kinetic testing of a Pt/Al2O3 monolith under stoichiometric conditions. The study can serve as a blueprint for the usage of RMG for other challenging heterogeneously catalyzed reactions.

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“…Setup Catalytic activity measurements of the monolithic samples were conducted in an inhouse developed laboratory catalyst testing bench that was already described in a previous publication, 40 optimized for three-way catalysis during the present work. The monolithic catalyst sample was mounted in a cylindrical quartz glass sample holder and placed in a plug-flow quartz glass tubular reactor.…”

Section: Catalyst Testingmentioning

confidence: 99%

Detailed microkinetics for the oxidation of exhaust gas emissions through automated mechanism generation

Kreitz

Lott

Bae

et al. 2022

Preprint

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Emissions from vehicles contain a variety of pollutants that must be either oxidized or reduced efficiently in the catalytic converter. Improvements to the catalyst require knowledge of the microkinetics, but the complexity of the exhaust gas mixture makes it challenging to identify the reaction network. This complexity was tackled by using the "Reaction Mechanism Generator" (RMG) to automatically generate microkinetic models for the oxidation of combustion byproducts from stoichiometric gasoline direct injection engines on Pt(111). The possibilities and the limitations encountered during the generation procedure are discussed in detail. A combination of first-principles-based mechanism construction and top-down parameter refinement allows to describe experimental results obtained by kinetic testing of a Pt/Al2O3 monolith under stoichiometric conditions. The study can serve as a blueprint for the usage of RMG for other challenging heterogeneously catalyzed reactions.

show abstract

Effects of Hydrothermal Aging on CO and NO Oxidation Activity over Monometallic and Bimetallic Pt-Pd Catalysts

Cited by 25 publications

References 66 publications

Biphasic Janus Particles Explain Self-Healing in Pt–Pd Diesel Oxidation Catalysts

Biphasic Janus Particles Explain Self-Healing in Pt–Pd Diesel Oxidation Catalysts

Detailed Microkinetics for the Oxidation of Exhaust Gas Emissions through Automated Mechanism Generation

Detailed microkinetics for the oxidation of exhaust gas emissions through automated mechanism generation

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