The effect of catalysts in plasma oxidation of nitrogen oxides
Date
2019-07-04
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Abstract
Õhureostus on tihedalt asustatud piirkondades kasvav probleem ja seda põhjustav oluline saasteainete klass on lämmastikoksiidid – NO ja NO2. Nende gaaside üks tähtsamaid allikaid on kütuste põlemisprotsessid ja atmosfääri sattudes võivad nad tekitada happevihmasid ning avaldada otsest kahjulikku mõju inimeste tervisele. Seetõttu on vajalik nende ühendite eemaldamine gaasivoogudest enne atmosfääri jõudmist.
Üks võimalus selleks on eemaldamine plasma abil, mis väldib mõningaid laiemalt kasutusel olevate meetodite puudusi. Plasmaga eemaldamise efektiivsust saab omakorda parandada katalüsaatorite abil ning sellele aspektile on pühendatud käesolev doktoritöö. Uuringute käigus leiti, et kogu gaasivoo otse läbi plasmareaktori juhtimise asemel on kasulikum plasma rakendamine osooni tekitamiseks ja sellega saastunud gaasivoo töötlemine. Uuritud katalüsaatoritest andis parima tulemuse raudoksiid Fe2O3, mis ühelt poolt suurendas protsessi efektiivsust kuni kolm korda ja teiselt poolt lagundas ülejäävat osooni, vältides selle õhku paiskamist. Katalüsaatori toime seisnes selle pinnal täiendavate ühendite ja reaktsioonikanalite tekkimises, mis parandasid kogu protsessi efektiivsust.
Air pollution is a growing problem in densely populated areas and an important class of compounds that contribute to the pollution is nitrogen oxides – NO and NO2. A major source of these gases is fuel combustion and upon reaching the atmosphere they can be the precursors of acid rains and have direct adverse health effects. Because of this it is important to remove nitrogen oxides from exhaust gases before they enter the atmosphere. A possibility for that is removal by plasma, which avoids some drawbacks of more widely used methods. Removal by plasma can in turn be improved by catalysts and this aspect is dealt with in the current thesis. It was found that plasma is best used only for the production of ozone, instead of directing the whole polluted gas stream through the plasma reactor. Of the catalysts that were investigated, iron oxide (Fe2O3) lead to the best results, increasing the efficiency of the process up to three times and at the same time decomposing excessive ozone, which prevented its emission into the atmosphere. The effect of the catalysts was caused by additional compounds and reaction pathways on their surfaces, which improved the efficiency of the whole process.
Air pollution is a growing problem in densely populated areas and an important class of compounds that contribute to the pollution is nitrogen oxides – NO and NO2. A major source of these gases is fuel combustion and upon reaching the atmosphere they can be the precursors of acid rains and have direct adverse health effects. Because of this it is important to remove nitrogen oxides from exhaust gases before they enter the atmosphere. A possibility for that is removal by plasma, which avoids some drawbacks of more widely used methods. Removal by plasma can in turn be improved by catalysts and this aspect is dealt with in the current thesis. It was found that plasma is best used only for the production of ozone, instead of directing the whole polluted gas stream through the plasma reactor. Of the catalysts that were investigated, iron oxide (Fe2O3) lead to the best results, increasing the efficiency of the process up to three times and at the same time decomposing excessive ozone, which prevented its emission into the atmosphere. The effect of the catalysts was caused by additional compounds and reaction pathways on their surfaces, which improved the efficiency of the whole process.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
lämmastikuoksiidid, metalloksiidid, katalüüs, katalüütiline oksüdeerimine, osoneerimine, plasmafüüsika