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Author:Vikla, Anna Kaisa
Title:Catalyst deactívation in aqueous phase reforming induced by a phase change of gamma-Al2O3-catalyst support
Gamma-Al2O3-kantajan faasin muutoksen aikaansaama katalyytin deaktivoituminen vesifaasireformoinnissa
Publication type:Master's thesis
Publication year:2012
Pages:vii + 90 + [6]      Language:   eng
Department/School:Biotekniikan ja kemian tekniikan laitos
Main subject:Teknillinen kemia   (Kem-40)
Supervisor:Lehtonen, Juha
Instructor:Karinen, Reetta ; Vlieger, Dennis de
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  1961   | Archive
Keywords:APR
Pt/gamma-Al2O3
AlOOH
deactivation
sintering
deaktivoituminen
sintrautuminen
Abstract (eng): Aqueous phase reforming (APR) is an efficient way to convert dilute biomass streams to hydrogen.
The process is operated at elevated pressures in order to keep hot water in a liquid phase (e.g.
T=225-450°C, p=2.9-25 MPa).
Heterogeneous catalysts, especially Pt/y-Al2O3, have been reported to be active and selective catalyst for the conversion of biomass based oxygenates to hydrogen with APR.
However, maintaining catalysts stability in hot pressurized water is challenging.
It has been reported by several researchers that the phase of the y-Al2O3 support changes to boehmite (AlOOH) during APR resulting in decrease in the support surface area and changes in acidity.
Furthermore, the active metals on the support surface lose their surface area due to sintering, resulting in changes in the catalyst performance.
However, there are contradictory explanations in the literature about how the phase change alters the catalysts properties and in turn the performance.

In this study the deactivation of Pt/y-Al2O3 catalyst in APR of ethylene glycol (EG) was studied.
Pt/y-Al2O3 and Pt/AlOOH catalysts with similar particle size were prepared.
Their properties, such as surface area, support structure and acidity, and activity in APR of EG were compared.
Based on the results the y-Al2O3-support loses it acidity during APR due to the phase change.
Acidity is required to bind the metals on the surface.
After loss of the acidity, Pt particles are detached from the support surface and they create larger Pt clusters due to coalescence.
This results in catalysts deactivation due to loss of active metal surface area.
Abstract (fin): Vesifaasireformoinnilla (APR) voidaan tehokkaasti tuottaa vetyä laimeista biomassavirroista.
Prosessia operoidaan ylipaineessa, jotta kuuma vesi pysyy nestemäisenä (esim.
T=225-450 °C, p=2,9-25 MPa).
Heterogeenisten katalyyttien, ja etenkin Pt/y-Al2O3, on raportoitu olevan aktiivisia ja selektiivisiä vesifaasireformointikatalyytteja biomassaperäisten oksygenaattien konversiossa vedyksi.
Katalyytin aktiivisuuden ylläpitäminen on kuitenkin haastavaa näissä olosuhteissa.
Useat tutkijat ovat raportoineet, että y-Al2O3 kantajan faasi muuttuu böhmiitiksi (AlOOH) APR:n aikana.
Tästä seuraa, että kantajan pinta-ala pienenee ja happamuus muuttuu.
Kantajan pinnalla olevien aktiivisten metallien pinta-ala myös muuttuu sintrautumisen seurauksena vaikuttaen katalyytin toimintaan.
Kirjallisuudessa on kuitenkin ristiriitaisia johtopäätöksiä siitä miten faasin muutos muuttaa katalyytin toimintaa.

Tässä diplomityössä on tutkittu Pt/y-Al2O3 katalyytin deaktivoitumista etyleeniglykolin (EG) vesifaasireformoinnissa.
Tätä varten valmistettiin Pt/y-Al2O3 ja Pt/AlOOH katalyytit, joilla on sama partikkelikoko.
Näiden katalyyttien ominaisuuksia, kuten pinta-alaa, kantajan rakennetta ja happamuutta, sekä katalyytin aktiivisuutta EG:n APR:ssa vertailtiin keskenään.
Työssä todettiin, että y-Al2O3 kantaja menettää faasinmuutoksen seurauksena happamuutensa.
Happamuus vaikuttaa kantajan kykyyn sitoa metallipartikkelit sen pinnalle.
Kun happamuus menetetään Pt-partikkelit irtoavat pinnalta, leviävät ja törmätessään toisiinsa muodostavat isompia platinaklustereita.
Tämän seurauksen platinan aktiivinen pinta-ala pienenee johtaen katalyytin deaktivoitumiseen.
ED:2012-11-07
INSSI record number: 45404
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