Molecular modeling of supported precious metal catalyst for the reduction of automobile exhaust : a quantum chemical molecular dynamics study
Notice bibliographique
Résumé
Catalysis is enabling technology to promote sustainability, environmental consciousness, energy conservation, health and quality of life.Catalytic purification has proven to be an efficient way to reduce emissions from exhaust gases and the idea of the three-way catalyst (TWC) is to remove CO and NOx and to oxidize unburnt hydrocarbons.The goal of this research is to investigate insight of the most relevant mechanisms of supported noble meta l catalyst for the reduction of automobile exhaust, which will accelerate the speed of the development of highperformance catalysts by the physicochemical study.In this study I have applied ultra accelerated quantum chemical molecular dynamics (UA-QCMD) to investigate the reaction mechanism that occurs in TWC.As we know hydrogen spillover play a vital role in emerging technologies for the reduction of NO x in automobile exhausts.Besides this CO oxidation NO reduction reaction on small size Pd clusters supported on MgO(100) also has a wide range of application such as reduction of NO x .Considering the application of above two reactions, the present research investigate the reduction of NO x by two UA-QCMD simulations such as by (i) spillover hydrogen and (ii) CO oxidation NO reduction reaction on different supported precious metal catalysts.Supported noble metal catalysts such as Pt/γ-Al 2 O 3 , Pt/CeO 2 show special peculiarities on hydrogen adsorption, the extent of which is increased by hydrogen spillover.The direct observation of dissociative adsorption of hydrogen and diffusion of hydrogen on Pt/γ-Al 2 O 3 and Pt/CeO 2 catalyst surface were successfully investigated by UA-QCMD method.Here I have successfully investigated the mechanism of hydrogen spillover reaction and unveiled the factors that involved in this chemical transformation by UA-QCMD method.Hydrogen spillovers in gas phase were simulated at the first time on Pt/γ-Al 2 O 3 and Pt/CeO 2 catalyst surface.Moreover, this study indicates that the CeO 2 support has strong interaction with Pt catalyst, which may cause an increase in metal support interaction, Pt activity and enhancement of the metal catalyst dispersions.However, Pt/γ-Al 2 O 3 catalyst, compared with Pt/CeO 2 , provides a clear manifestation of the role of the metal-support interaction in modifying the catalytic behavior of the metal.As we know hydrogen spillover reaction consists of several elementary steps o f reactions such as dissociation, adsorption, diffusion and desorption.Among these steps frequent dissociative adsorption of hydrogen on the metal surface is important for hydrogen spillover.But the dissociation of hydrogen depends on coverage of the surface.Since no studies to date have been able to study the spillover step in isolation, all the studies interpret experimental data for a combination of sequential steps.Here influences of surface hydrogen vacancy for the dissociative adsorption of hydrogen on different metal surfaces were investigated.MD simulation together with electronic structure calculation shows that di-vacancy is sufficient for the dissociative adsorption of hydrogen on Pd (100) surface; in contrast at least tri-vacancy is required for Pd (111) surface.It was found that fully hydrogen covered step sites can dissociate hydrogen moderately and that a monovacancy site is suitable for significant dissociation of hydrogen.However, in terrace sites of the Pd (332) surface, it was observed that hydrogen dissociation takes place only at the Pd sites where the metal atom is not bound to any preadsorbed H atom.CO oxidation and NO reduction reaction on supported precious metal catalyst were investigated by quantum chemical molecular dynamics method.Here catalyst aids the reaction of the CO with the remaining oxygen in the exhaust gas.Here the pathways and energetic of the involved elementary reactions under different catalytic conditions were investigated.
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Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,001 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,001 | 0,001 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,003 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».