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Author:Melander, Marko
Title:Tiheysfunktionaaliteoreettinen tutkimus hiilimonoksidin dissosiaatiosta Fe78-nanopartikkelin pinnalla
Dissociation of Carbon monoxide on Fe78-nanoparticle: A DFT stydy
Publication type:Master's thesis
Publication year:2011
Pages:vi + 103 s. + liitt. 6      Language:   fin
Department/School:Kemian laitos
Main subject:Fysikaalinen kemia   (Kem-31)
Supervisor:Laasonen, Kari
Instructor:
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  1902   | Archive
Keywords:iron nanoparticle
CO dissociation
rautananopartikkeli
CO:n dissosiaatio
Abstract (eng): Nanoparticles are known to possess, e.g., catalytic, magnetic, geometric, and electric properties that deviate from both molecular and bulk phase properties.
These phenomena are not very well understood, since experimental work is often difficult to conduct.
Thus, computational methods are viable for the study of these phenomena on atomistic scale.

In this work the capability of Fe78 nanoparticle to catalyse the dissociation of carbon monoxide was studied using GPAW -software based on density functional theory with grid-based plane augmented wave approach.
Magnetic and geometric properties as well as adsorption of carbon monoxide, carbon and oxygen on this particle were also studied.

Fe78 has a diameter of 1,2 nm, iron-iron bond lengths varying between 2,21 and 2,54 Å and the magnetic moment is 2,78 µB /atom.
For bulk iron the corresponding values are 2,78 Å and 2,2 µB /atom, respectively.
Carbon monoxide adsorbs tightly to top-and hollow-sites.
Carbon is adsorbed to highly-coordinated hollow-sites and carbon is buried deep into the surface.
Oxygen favours less coordinated hollow sites.
Carbon monoxide dissociation reactions with the lowest activation energies were found to start from top-sites and the lowest barrier for CO dissociation was 1,12 eV.
This value is lower than on smooth surfaces but higher than on kinked or stepped surfaces.
It seems that catalytic properties of the nanoparticle are more dependent on the very dense surface structure than on the favourable electronic properties of the particle.
Abstract (fin): Nanopartikkeleilla on havaittu olevan muun muassa katalyyttisia, rakenteellisia, magneettisia ja elektronisia ominaisuuksia, jotka poikkeavat sekä molekyylien että bulkkifaasien ominaisuuksista ja joita ei ymmärretä.
Nanopartikkelien kokeellinen tutkimus on usein vaikeaa, mutta laskennalliset menetelmät mahdollistavat partikkelien tutkimisen ja ymmärtämisen atomitasolla.

Tässä työssä tutkittiin Fe78-nanopartikkelin kykyä katalysoida hiilimonoksidin hajoamista käyttämällä tiheysfunktionaaliteoriaan perustuvaa GPAW -ohjelmaa.
Katalyyttisen aktiivisuuden lisäksi tarkasteltiin partikkelin geometrisia ja magneettisia ominaisuuksia sekä hiilimonoksidin, hiilen ja hapen adsorptiota kaikille mahdollisille adsorptiopaikoille.

Fe78:n halkaisija on n. 1,2 nm, rauta-rauta -sidospituudet ovat 2,21 - 2,54 Å ja magneettinen momentti 2,78 µB /atomi.
Bulkkiraudan sidospituus on 2,87 Å ja magneettinen momentti 2,2 µB /atomi.
Hiilimonoksidi sitoutuu vahvimmin kuoppa- ja siltapaikoille.
Hiili adsorboituu tiukimmin vahvasti koordinoituihin kuoppapaikkoihin ja painuu syvälle rauta-atomien keskelle.
Happi suosii heikoimmin koordinoituja kuoppapaikkoja.
Hiilimonoksidi dissosioituu helpoiten huippupaikoilta alkavissa reaktioissa ja pienin havaittu aktivoitumisenergia on 1,12 eV, mikä on suurempi kuin askelmaisilla mutta pienempi kuin tasaisilla pinnoilla.
Nanopartikkeleilla sidosten lyhentymisestä johtuva pinnan hyvin tiivis rakenne näyttäisi laskevan aktiivisuutta enemmän kuin elektroniset tekijät nostavat.
ED:2012-05-21
INSSI record number: 44595
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