Characterization of zirconia-based gasification gas clean-up catalysts

Tiia Viinikainen

Characterization of zirconia-based gasification gas clean-up catalysts

Julkaisun otsikon käännös: Zirkonia-pohjaisten kaasutuskaasun puhdistuskatalyyttien karakterisointi

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Katalyyttien karakterisointi on laajeneva katalyysin osa-alue, ja uusia tekniikoita otetaan käyttöön yhä enemmän muilta tieteen aloilta. Karakterisoinnin tulisi vastata ainakin seuraaviin kysymyksiin: 1) mitkä katalyytin ominaisuudet korreloivat sen aktiivisuuden kanssa, 2) mitkä ovat keskeisiä välituotteita ja miten ne adsorboituvat katalyytin pinnalle, 3) millaisia pintapaikkoja välituotteille tarvitaan ja 4) mikä on tutkitun reaktion mekanismi. Tässä työssä tutkittiin zirkonia-pohjaisia (ZrO2) katalyyttejä. Zirkonian katalyyttiset sovellukset usein hyödyntävät sen happamia ja emäksisiä pintaominaisuuksia, vaikka niiden vahvuus on suhteellisen heikko. Zirkonian katalyyttisiä ominaisuuksia ja lämpöstabiilisuutta voidaan edelleen parantaa seostamalla siihen lisäaineita. Zirkonian on raportoitu sietävän rikkipitoisia yhdisteitä ja olevan kestävämpi vettä kohtaan kuin esim. alumiinioksidi. Nämä ainutlaatuiset ominaisuudet ovat johtaneet zirkonia-katalyyttien tutkimukseen myös kaasutuskaasun puhdistuksessa. Biomassan kaasutus on potentiaalinen ja ympäristöystävällinen tapa tuottaa energiaa, biopolttoaineita ja kemikaaleja. Kaasutus on prosessi, jossa biomassa muunnetaan kaasumaiseksi tuotteeksi. Kaasutuskaasun pääkomponentit ovat hiilimonoksidi, vety ja hiilidioksidi. Kaasu sisältää myös epäpuhtauksia, kuten ammoniakkia ja tervaa, joten kaasu on puhdistettava ennen käyttöä. Zirkonia-katalyyttien on havaittu selektiivisesti hapettavan tervamolekyylejä kaasutuskaasun puhdistuksessa 600-900 °C:ssa, kun kaasuun on lisätty pieni määrä happea. Tässä työssä tutkittavat katalyytit olivat ZrO2, Y2O3-ZrO2 ja SiO2-ZrO2. Katalyyttien kaasutuskaasun puhdistusaktiivisuusjärjestys oli ZrO2 > Y2O3-ZrO2 > SiO2-ZrO2. Katalyytin happamuus osoittautui epäsuotuisaksi kaasutuskaasun puhdistuskatalyytin ominaisuudeksi, kun taas emäksisyys näyttäisi olevan hyödyllinen. Mittauksissa havaittiin neljä erilaista tolueenista peräisin olevaa pintayhdistettä: molekulaarisesti adsorboitu tolueeni, bentsoaatti, hiilipitoinen kerrostuma ja bentsyyli, joista jälkimmäinen osoittautui olevan keskeinen välituote tolueenin hapetusreaktiossa. Tolueeni hapettui täysin yli 550 °C:n lämpötilassa kaikilla katalyyteillä muodostaen hiilidioksidia, vettä, hiilimonoksidia ja vetyä. Kaasutuskaasun pääkomponenteista vesi vähensi kaikkien katalyyttien tolueenin hapetusaktiivisuutta; eniten SiO2-ZrO2:lla ja vähiten puhtaalla zirkonialla. Katalyyttien kykyä suojella arvokkaita kaasutuskaasun komponentteja hapettaessaan tolueenia kuvattiin preferentiaaliseksi hapetukseksi. Puhdas zirkonia-katalyytti suosi tolueenin hapetusta ja suojeli hiilimonoksidia ja vetyä parhaiten tutkituista katalyyteistä korkeammissa lämpötiloissa. Puhtaan zirkonian tervan hapetusaktiivisuutta voidaan kuitenkin edelleen parantaa ja kaasutusprosessia optimoida, jotta se olisi kilpailukykyisempi fossiilisiin polttoaineisiin perustuviin sovelluksiin verrattuna.

Julkaisun otsikon käännös	Zirkonia-pohjaisten kaasutuskaasun puhdistuskatalyyttien karakterisointi
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Seppälä, Jukka, Vastuuprofessori Kanervo, Jaana, Ohjaaja Lehtonen, Juha, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-7322-4
Sähköinen ISBN	978-952-60-7321-7
Tila	Julkaistu - 2017
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

Zirkonia
katalyyttien karakterisointi
kaasutuskaasun puhdistus

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-7321-7Lisenssi: Määrittelemätön

Biotalousinfrastruktuuri
Seppälä, J. (Manager)
Kemian tekniikan korkeakoulu
Laitteistot/tilat: Facility

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@phdthesis{da13c063e3604433a12dd7b8c06aa12a,

title = "Characterization of zirconia-based gasification gas clean-up catalysts",

abstract = "Characterization of catalysts is an expanding field of catalysis and new techniques are adapted more and more from other disciplines of science. Catalyst characterization should answer at least to the following questions: 1) which properties of the catalyst correlate well with its activity, 2) what are the key intermediates and how they are adsorbed on the catalyst, 3) what kind of surface sites are involved, and 4) which is the mechanism for the studied reaction. In this thesis, zirconia-based catalysts were studied. Catalytic applications of zirconia often takes advantage of its acidic and basic surface properties although their strength is relatively weak. The catalytic properties and thermal stability of zirconia can be further enhanced by the addition of dopants. ZrO2 has been reported to be sulfur and water tolerant. These unique characteristics have led to study zirconia-based catalysts in gasification gas cleaning applications. Gasification of biomass is one potential and environmental benign way to produce energy, liquid biofuels and chemicals. Gasification is a thermo-chemical process where biomass is converted to gaseous products. The main components of gasification gas are carbon monoxide, hydrogen and carbon dioxide. Gas also contains impurities, such as ammonia and tar, and the gas has to be cleaned before use. Zirconia-based catalysts have shown to selectively oxidize tar molecules during hot gas cleaning at 600-900 °C when a small amount of oxygen is added into the gas. The catalysts selected for this thesis were ZrO2, Y2O3-doped ZrO2 and SiO2-doped ZrO2. The activity of the catalysts in gasification gas cleaning decreased in the order of ZrO2 > Y2O3-ZrO2 > SiO2-ZrO2. Relating the acidity and basicity of the catalysts to their activity suggested that acidity is not a desirable characteristic for gasification gas clean-up catalysts whereas basicity seems to be useful. Four types of toluene-derived surface species were discovered: molecularly adsorbed toluene, surface benzoate species, carbonaceous deposits and benzyl species, the latter being the key intermediate in toluene oxidation. Over all the catalysts, toluene was completely converted at temperatures above 550 °C to carbon dioxide, water, carbon monoxide and hydrogen. Of the main gasification gas components, water was shown to inhibit toluene oxidation activity over all these catalysts; the most over SiO2-ZrO2 and the least over pure ZrO2. The preferentiality, i.e. ability of the catalysts to protect the valuable gas components while oxidizing toluene, was addressed. The highest preferentiality of toluene over both CO and H2 was observed over pure ZrO2 at higher temperatures. Thus, pure ZrO2 was proven to manifest exceptional performance in preferential toluene oxidation. However, the tar oxidation activity of pure ZrO2 could be further improved and the gasification process could be further optimized in order to compete with fossil fuel based applications.",

keywords = "Zirconia, characterization of catalysts, gasification gas cleaning, Zirkonia, katalyyttien karakterisointi, kaasutuskaasun puhdistus, Zirconia, characterization of catalysts, gasification gas cleaning",

author = "Tiia Viinikainen",

year = "2017",

language = "English",

isbn = "978-952-60-7322-4",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "39",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Characterization of zirconia-based gasification gas clean-up catalysts

AU - Viinikainen, Tiia

PY - 2017

Y1 - 2017

N2 - Characterization of catalysts is an expanding field of catalysis and new techniques are adapted more and more from other disciplines of science. Catalyst characterization should answer at least to the following questions: 1) which properties of the catalyst correlate well with its activity, 2) what are the key intermediates and how they are adsorbed on the catalyst, 3) what kind of surface sites are involved, and 4) which is the mechanism for the studied reaction. In this thesis, zirconia-based catalysts were studied. Catalytic applications of zirconia often takes advantage of its acidic and basic surface properties although their strength is relatively weak. The catalytic properties and thermal stability of zirconia can be further enhanced by the addition of dopants. ZrO2 has been reported to be sulfur and water tolerant. These unique characteristics have led to study zirconia-based catalysts in gasification gas cleaning applications. Gasification of biomass is one potential and environmental benign way to produce energy, liquid biofuels and chemicals. Gasification is a thermo-chemical process where biomass is converted to gaseous products. The main components of gasification gas are carbon monoxide, hydrogen and carbon dioxide. Gas also contains impurities, such as ammonia and tar, and the gas has to be cleaned before use. Zirconia-based catalysts have shown to selectively oxidize tar molecules during hot gas cleaning at 600-900 °C when a small amount of oxygen is added into the gas. The catalysts selected for this thesis were ZrO2, Y2O3-doped ZrO2 and SiO2-doped ZrO2. The activity of the catalysts in gasification gas cleaning decreased in the order of ZrO2 > Y2O3-ZrO2 > SiO2-ZrO2. Relating the acidity and basicity of the catalysts to their activity suggested that acidity is not a desirable characteristic for gasification gas clean-up catalysts whereas basicity seems to be useful. Four types of toluene-derived surface species were discovered: molecularly adsorbed toluene, surface benzoate species, carbonaceous deposits and benzyl species, the latter being the key intermediate in toluene oxidation. Over all the catalysts, toluene was completely converted at temperatures above 550 °C to carbon dioxide, water, carbon monoxide and hydrogen. Of the main gasification gas components, water was shown to inhibit toluene oxidation activity over all these catalysts; the most over SiO2-ZrO2 and the least over pure ZrO2. The preferentiality, i.e. ability of the catalysts to protect the valuable gas components while oxidizing toluene, was addressed. The highest preferentiality of toluene over both CO and H2 was observed over pure ZrO2 at higher temperatures. Thus, pure ZrO2 was proven to manifest exceptional performance in preferential toluene oxidation. However, the tar oxidation activity of pure ZrO2 could be further improved and the gasification process could be further optimized in order to compete with fossil fuel based applications.

AB - Characterization of catalysts is an expanding field of catalysis and new techniques are adapted more and more from other disciplines of science. Catalyst characterization should answer at least to the following questions: 1) which properties of the catalyst correlate well with its activity, 2) what are the key intermediates and how they are adsorbed on the catalyst, 3) what kind of surface sites are involved, and 4) which is the mechanism for the studied reaction. In this thesis, zirconia-based catalysts were studied. Catalytic applications of zirconia often takes advantage of its acidic and basic surface properties although their strength is relatively weak. The catalytic properties and thermal stability of zirconia can be further enhanced by the addition of dopants. ZrO2 has been reported to be sulfur and water tolerant. These unique characteristics have led to study zirconia-based catalysts in gasification gas cleaning applications. Gasification of biomass is one potential and environmental benign way to produce energy, liquid biofuels and chemicals. Gasification is a thermo-chemical process where biomass is converted to gaseous products. The main components of gasification gas are carbon monoxide, hydrogen and carbon dioxide. Gas also contains impurities, such as ammonia and tar, and the gas has to be cleaned before use. Zirconia-based catalysts have shown to selectively oxidize tar molecules during hot gas cleaning at 600-900 °C when a small amount of oxygen is added into the gas. The catalysts selected for this thesis were ZrO2, Y2O3-doped ZrO2 and SiO2-doped ZrO2. The activity of the catalysts in gasification gas cleaning decreased in the order of ZrO2 > Y2O3-ZrO2 > SiO2-ZrO2. Relating the acidity and basicity of the catalysts to their activity suggested that acidity is not a desirable characteristic for gasification gas clean-up catalysts whereas basicity seems to be useful. Four types of toluene-derived surface species were discovered: molecularly adsorbed toluene, surface benzoate species, carbonaceous deposits and benzyl species, the latter being the key intermediate in toluene oxidation. Over all the catalysts, toluene was completely converted at temperatures above 550 °C to carbon dioxide, water, carbon monoxide and hydrogen. Of the main gasification gas components, water was shown to inhibit toluene oxidation activity over all these catalysts; the most over SiO2-ZrO2 and the least over pure ZrO2. The preferentiality, i.e. ability of the catalysts to protect the valuable gas components while oxidizing toluene, was addressed. The highest preferentiality of toluene over both CO and H2 was observed over pure ZrO2 at higher temperatures. Thus, pure ZrO2 was proven to manifest exceptional performance in preferential toluene oxidation. However, the tar oxidation activity of pure ZrO2 could be further improved and the gasification process could be further optimized in order to compete with fossil fuel based applications.

KW - Zirconia

KW - characterization of catalysts

KW - gasification gas cleaning

KW - Zirkonia

KW - katalyyttien karakterisointi

KW - kaasutuskaasun puhdistus

KW - Zirconia

KW - characterization of catalysts

KW - gasification gas cleaning

M3 - Doctoral Thesis

SN - 978-952-60-7322-4

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Characterization of zirconia-based gasification gas clean-up catalysts

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

Sormenjälki

Laitteet

Biotalousinfrastruktuuri

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