Title Hidrotermalna sinteza i karakterizacija bakrom dopiranoga cerijeva(IV) oksida Title (english) Hydrothermal synthesis and characterization of copper doped cerium(IV) oxide Author Katarina Mužina Mentor Stanislav Kurajica (mentor)Committee member Hrvoje Ivanković (predsjednik povjerenstva)Committee member Juraj Šipušić (član povjerenstva)Committee member Lidija Ćurković (član povjerenstva)Granter University of Zagreb Defense date and country 2022-07-21, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 66 - Chemical technology. Chemical and related industries 54 - Chemistry. Crystallography. Mineralogy Abstract Cerijev(IV) oksid (CeO2) jedan je od najvažnijih oksida lantanoida te se intenzivno primjenjuje u različitim područjima od poliranja, proizvodnje i skladištenja energije, zaštite okoliša do najistraživanije katalize. Svojstvo CeO2 ključno za primjenu u katalizi je sposobnost parcijalne redukcije Ce4+ u Ce3+ unutar kristalne rešetke bez narušavanja strukture pri čemu nastaju vakancije kisika. Kisikove vakancije mogu se slobodno kretati unutar kristalne rešetke te se na njih mogu lako adsorbirati molekule kisika iz okoline. Smanjenje veličine čestica te dopiranje raznim elementima s nižom valencijom i radijusom dodatno potiče stvaranje vakancija kisika te poboljšava primjenska svojstva cerijevog oksida. Među brojnim metodama sinteze nanomaterijala hidrotermalna metoda ističe se svojom jednostavnošću, ekološkom prihvatljivošću, niskom cijenom te mogućnošću dobivanja produkata visoke čistoće i homogenosti te male veličine čestica. U ovom radu hidrotermalnom metodom pripremljene su nanočestice bakrom dopiranoga cerijeva(IV) oksida (CuxCe1-xO2, x = 0, 0,1, 0,2, 0,3, 0,4 i 0,5), toplinski obrađene i temeljito analizirane različitim metodama karakterizacije nanomaterijala. Katalitička aktivnost pripremljenih nanokatalizatora ispitivana je na procesu oksidacije hlapivih organskih spojeva korištenjem plinovite mješavine benzena, toluena, etilbenzena i o-ksilena (BTEX). Provedena je i kinetička analiza rasta zrna pri izotermnim uvjetima s ciljem utvrđivanja utjecaja dodatka bakra na toplinsku stabilnost cerijeva(IV) oksida. Rendgenskom difrakcijskom analizom (XRD) utvrđeno je da do nominalnog udjela od 40 mol. % Cu ne dolazi do pojave sekundarnih faza. Veličine kristalita uzoraka bez toplinske obrade dosad su nezabilježene za bakrom dopirani cerijev(IV) oksid te iznose ispod 4 nm. Veličine čestica određene transmisijskom elektronskom mikroskopijom (TEM) u suglasju su s vrijednostima dobivenim za veličine kristalita. Masenom spektrometrijom induktivno spregnute plazme (ICP-MS), energijski razlučujućom rendgenskom spektroskopijom (EDS) i rendgenskom fotoelektronskom spektroskopijom (XPS) utvrđeno je da je stvarni udio bakra u uzorcima manji od nominalnog. Međutim, sveukupni rezultati pokazuju kako dodatak bakra ima pozitivan utjecaj na brojna svojstva CeO2, što uključuje smanjenje zabranjene zone, poboljšanje reducibilnosti i toplinske stabilnosti, te povećanje katalitičke aktivnosti. Dobiveni rezultati ukazuju na postojanje snažne interakcije između bakra i CeO2, što bi značilo je došlo do stvaranja čvrste otopine. Među pripremljenim uzorcima posebno se ističe uzorak s nominalnim udjelom bakra od 40 mol. % kao uzorak s najboljom toplinskom stabilnošću u cijelom ispitivanom području (od 300 do 700 °C), najboljom katalitičkom aktivnošću za ispitivane hlapive organske spojeve, te najvećim udjelom vakancija kisika u strukturi.
Abstract (english) Cerium(IV) oxide (CeO2) is one of the most important lanthanide oxides extensively used in various fields such as polishing, energy production and storage, environmental protection and the most researched catalysis. The key property of CeO2 for catalytic application is the ability of a partial reduction of Ce4+ to Ce3+ within the crystal lattice without the collapse of structure. During this process oxygen vacancies are formed, which can move freely within the crystal lattice and adsorb oxygen molecules from the environment. The reduction of particle size and doping with various elements with lower valence and radius further encourage the creation of oxygen vacancies and improve the properties of cerium oxide. Among many nanomaterial's synthesis methods, the hydrothermal method stands out for its simplicity, environmental friendliness, low cost and the ability to obtain products of high purity and homogeneity, as well as small particle size. In this work, nanoparticles of copper doped cerium(IV) oxide (CuxCe1-xO2, x = 0, 0,1, 0,2, 0,3, 0,4 i 0,5) were prepared by hydrothermal method, thermally treated and thoroughly characterized. The catalytic activity of the prepared nanocatalysts was investigated in the oxidation of volatile organic compounds using a gaseous mixture of benzene, toluene, ethylbenzene and o-xylene (BTEX). An isothermal grain growth kinetics analysis was also performed in order to determine the effect of copper addition on the thermal stability of cerium(IV) oxide. X-ray diffraction analysis (XRD) showed that no secondary phases occur up to the nominal share of 40 mol. % Cu. The crystallite sizes of samples without thermal treatment have not been recorded so far for copper doped cerium oxide and are below 4 nm. Particle sizes determined by transmission electron microscopy (TEM) are in agreement with the values obtained for crystallite sizes. Inductively coupled plasma mass spectrometry (ICP-MS), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) showed that the actual copper content in the samples is lower than nominal. However, the overall results show that the addition of copper has a positive effect on a number of CeO2 properties, which includes the reduction of the band gap, improvement of reducibility and thermal stability, and an increase in catalytic activity. The obtained results indicate the existence of a strong interaction between copper and CeO2, which would mean that a solid solution was formed. Among the prepared samples, the sample with the nominal copper share of 40 mol. % stands out as the sample with the best thermal stability in the studied temperature range (from 300 to 700 °C), the best catalytic activity for the tested volatile organic compounds, and the largest share of oxygen vacancies in the structure.
Keywords
bakar
cerijev(IV) oksid
dopiranje
hidrotermalna sinteza
hlapivi organski spojevi
kataliza
rast zrna
Keywords (english)
copper
cerium(IV) oxide
doping
hydrothermal synthesis
volatile organic compounds
catalysis
grain growth
Language croatian URN:NBN urn:nbn:hr:149:162780 Promotion 2022 Project Number: IP-2018-01-2963 Study programme Title: Chemical Engineering and Applied Chemistry - Doctoral course Type of resource Text Extent 114 str. ; 30 cm File origin Born digital Access conditions Open access Terms of use Created on 2022-12-01 09:48:42
