Comparative Behaviour of Standard Pt/Rh and of Newly Developed Pd-only and Pd/Rh Three-Way Catalysts under Dynamic Operation of Hybrid Vehicles

Tagliaferri, S.; Köppel, René A.; Baiker, A.

doi:10.1016/s0167-2991(98)80864-1

Cited by 11 publications

(6 citation statements)

References 10 publications

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“…Nonetheless, both Rh and Pt form irreversible oxides under net oxidizing conditions, whereas Pd shows more oxygen tolerance. This reason promotes shifting of TWCs from Rh-/Pt-based to Pd-based catalysts . Therefore, the kinetics of the most representative reactions involved on TWCs, such as the NO + H 2 and NO + H 2 + O 2 reactions on Pd-based materials, have been the subject of a wide number of publications from surface science approaches, performed under ultrahigh vacuum (UHV), − to more realistic conditions at atmospheric pressures. − …”

Section: Introductionmentioning

confidence: 99%

Sustainable and Near Ambient DeNO_x Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces

2014

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Catalytic conversion of NO in the presence of H 2 and O 2 has been studied on Pd(111) surfaces, by using a molecular beam instrument with mass spectrometry detection, as a function of temperature and reactants composition. N 2 and H 2 O are the major products observed, along with NH 3 and N 2 O minor products under all conditions studied. Particular attention has been paid to the influence of O 2 addition toward NO dissociation. Although O 2rich compositions were found to inhibit the deNO x activity of the Pd catalyst, some enhancement in NO reduction to N 2 was also observed up to a certain O 2 content. The reason for this behavior was determined to be the effective consumption of the H 2 in the mixture by the added O 2 and O atoms from NO dissociation. NO was proven to compete favorably against O 2 for the consumption of H 2 , especially ≤550 K, to produce N 2 and H 2 O. Compared with other elementary reaction steps, a slow decay observed with the 2H + O → H 2 O step under SS beam oscillation conditions demonstrates its contribution to the rate-limiting nature of the overall reaction. Pd(111) surfaces modified with O atoms in the subsurface (Md-Pd( 111)) induces steady-state NO reduction at near-ambient temperatures (325 K) and opens up a possibility to achieve room temperature emission control. A 50% increase in the reaction rates was observed at the reaction maximum on Md-Pd(111), as compared with virgin surfaces. Oxygen adsorption is severely limited below 400 K, and effective NO + H 2 reaction occurs on Md-Pd(111) surfaces. Valence band photoemission with a UV light source (He I) under different oxygen pressures with APPES clearly identified the characteristics of the Md-Pd(111) surfaces and PdO. The electron-deficient or cationic nature of Md-Pd(111) surfaces enhances the NO dissociation and inhibits oxygen chemisorption ≤400 K under lean-burn conditions.

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Section: Introductionmentioning

confidence: 99%

Sustainable and Near Ambient DeNO_x Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces

2014

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“…Further, NO x reduction performance at low temperatures and resistance to oxidation of the metal particles at high temperatures has led to an increased interest in Pd . Recent reports on Pd−CeO 2 and Pd−Rh−CeO 2 show similar or even superior catalytic performance over the conventional Rh−Pt−CeO 2 . Other than the above, a few new technologies were introduced in the past decade such as NO x storage and zeolite based catalysts in order to tackle NO x abatement. − Nonetheless, stability problems associated with NO x storage and the inability of zeolites to cause NO reduction in the presence of water vapor are problems faced in real applications.…”

Section: Introductionmentioning

confidence: 99%

A Molecular Beam Study of the NO + CO Reaction on Pd(111) Surfaces

et al. 2005

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Nitric oxide (NO) reduction with carbon monoxide (CO) on the Pd(111) surface was studied under isothermal conditions by molecular beam techniques as a function of temperature, NO:CO beam composition, and beam flux. Systematic experiments were performed under transient and steady state conditions. Displacement of adsorbed CO by NO in the transient state of the reaction was observed at temperatures between 375 and 475 K for all the NO:CO compositions studied. NO accumulation occurs on Pd(111) surface under steady state conditions, below 475 K, due to stronger chemisorption of NO. The steady state reaction rates attain a maximum at about 475 K, nearly independent of beam composition. N2 was found to be the major product of the reduction, along with a minor production of N2O. The production of N2 and N2O indicates molecular and dissociative adsorption of NO on Pd(111) at temperatures up to 525 K. Postreaction TPD measurements were performed in order to determine the nitrogen coverage under steady-state conditions. Finally, the results are discussed with respect to the rate-controlling character of the different elementary steps of the reaction system.

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“…Although Rh is very active for NO reduction under fuel-rich conditions, this is not the case under net oxidizing conditions, since the excess oxygen inhibits the NO reduction activity of Rh by oxidizing it. Pd has also been added to catalytic converters as one of the active metals for NO reduction for the past few years; however, the mechanistic details of Pd are not fully understood yet. There were few new technologies , introduced in the past decade, like NO x storage or zeolite based catalysts, which provided different insights into the NO reduction.…”

Section: Introductionmentioning

confidence: 99%

Isothermal Kinetic Study of Nitric Oxide Adsorption and Decomposition on Pd(111) Surfaces: Molecular Beam Experiments

et al. 2005

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The kinetics of NO adsorption and dissociation on Pd(111) surfaces and the NO sticking coefficient (s(NO)) were probed by isothermal kinetic measurements between 300 and 525 K using a molecular beam instrument. NO dissociation and N2 productions were observed in the transient state from 425 K and above on Pd(111) surfaces with selective nitrogen production. Maximum nitrogen production was observed between 475 and 500 K. It was found that, at low temperatures, between 300 and 350 K, molecular adsorption occurs with a constant initial s(NO) of 0.5 until the Pd(111) surface is covered to about 70-80% by NO. Then s(NO) rapidly decreases with further increasing NO coverage, indicating typical precursor kinetics. The dynamic adsorption - desorption equilibrium on Pd(111) was probed in modulated beam experiments below 500 K. CO titration experiments after NO dosing indicate the diffusion of oxygen into the subsurface regions and beginning surface oxidation at > or = 475 K. Finally, we discuss the results with respect to the rate-limiting character of the different elementary steps of the reaction system.

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Comparative Behaviour of Standard Pt/Rh and of Newly Developed Pd-only and Pd/Rh Three-Way Catalysts under Dynamic Operation of Hybrid Vehicles

Cited by 11 publications

References 10 publications

Sustainable and Near Ambient DeNO_x Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces

Sustainable and Near Ambient DeNO_x Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces

A Molecular Beam Study of the NO + CO Reaction on Pd(111) Surfaces

Isothermal Kinetic Study of Nitric Oxide Adsorption and Decomposition on Pd(111) Surfaces: Molecular Beam Experiments

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Comparative Behaviour of Standard Pt/Rh and of Newly Developed Pd-only and Pd/Rh Three-Way Catalysts under Dynamic Operation of Hybrid Vehicles

Cited by 11 publications

References 10 publications

Sustainable and Near Ambient DeNOx Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces

Sustainable and Near Ambient DeNOx Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces

A Molecular Beam Study of the NO + CO Reaction on Pd(111) Surfaces

Isothermal Kinetic Study of Nitric Oxide Adsorption and Decomposition on Pd(111) Surfaces: Molecular Beam Experiments

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Sustainable and Near Ambient DeNO_x Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces

Sustainable and Near Ambient DeNO_x Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces