Kvantnokemijsko modeliranje fotokatalitične pretvorbe ogljikovega dioksida v spojine z višjo dodano vrednostjo : doctoral dissertation

Kovačič, Žan

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Title:	Kvantnokemijsko modeliranje fotokatalitične pretvorbe ogljikovega dioksida v spojine z višjo dodano vrednostjo : doctoral dissertation
Authors:	ID Kovačič, Žan (Author) ID Huš, Matej (Mentor) More about this mentor... ID Likozar, Blaž (Comentor)
Files:	DOK_Kovacic_Zan_2024.pdf (8,06 MB) MD5: D5BCADFC63DC8D715FE8857FE1BBCA03
Language:	Slovenian
Work type:	Doctoral dissertation
Typology:	2.08 - Doctoral Dissertation
Organization:	FKKT - Faculty of Chemistry and Chemical Engineering
Abstract:	Zajem in pretvorba CO2 sta v zadnjih desetletjih požela veliko pozornost tako industrije kot znanstvene skupnosti, predvsem zaradi prispevka CO2 k globalnemu segrevanju Obstaja že ogromno študij fotokatalitične redukcije CO2, večina katerih je podprta z eksperimentalnimi tehnikami, medtem ko so teoretične metode pogosto prezrte. Teoretične metode se večinoma uporabljajo le kot dodatna razlaga eksperimentalnih podatkov, redko so teoretične študije glavni predmet raziskave. Zaradi naglega razvoja računalniške moči v zadnjih desetletjih in postavitve več modernih, zmogljivih računalniških centrov se povečuje tudi interes za teoretične metode. Razvoj teoretičnih orodij, kot je na primer teorija gostotnega funkcionala (DFT), dodatno pospešuje in izboljšuje teoretične izračune, ki nam lahko služijo za analizo reakcijskih mehanizmov, lastnosti materialov in napoved izboljšav na ogromno področjih, predvsem pri razvoju novih katalizatorjev. Namen doktorske naloge je bila karakterizacija TiO2 za fotoredukcijo CO2 s teoretičnimi metodami in primerjava različnih pristopov za pravilen opis različnih lastnosti katalizatorja. Rezultati kažejo, da je izbira funkcionalov in popravkov odvisna od fenomenov, ki jih želimo obravnavati. Analiza adsorpcije in aktivacije CO2 na več nemodificiranih in modificiranih površinah anataza in rutila je pokazala, da je aktivacija CO2 pomemben, a kompleksen proces, saj je aktivacija CO2 predpogoj za fotoredukcijo. Aktivacija se odraža kot prenos elektronov s površine na molekulo CO2, medtem ko se to geometrijsko izrazi kot deformacija molekule ob adsropciji (zmanjša se kot v molekuli). Sledila je preučitev reakcijskega mehanizma fotoredukcije CO2 na čisti in z bakrom dopirani površini anataza (101) in rutila (110) ter na s Pd dopirani površini anataza. Izkazalo se je, da reakcija v osnovnem stanju zaradi visokih aktivacijskih energij praktično ne poteka na nobeni od preučevanih površin, kar je bilo podkrepljeno z mikrokinetičnim modelom. V sistem smo nato uvedli fotovzbujen elektron, ki smo ga iz najvišje zasedene molekulske orbitale (HOMO) prestavili v najnižjo nezasedeno molekulsko orbitalo (LUMO), medtem ko je elektronska vrzel ostala v valenčnem pasu (VB), kar smo dosegli z uporabo metode ∆SCF. Rezultati so pokazali, da se aktivacijske energije v nekaterih primerih znatno znižajo. Mikrokinetični model je napovedal, da v primeru dopiranja anataza (101) s Cu lahko pričakujemo H2 kot produkt, medtem ko je v primeru dopiranja rutila (110) s Cu glavni produkt CO. Slednje kaže ujemanje z obstoječo literaturo. Preizkusili smo tudi računsko intenzivnejšo metodo, in sicer časovno odvisen DFT (TDDFT). Zaradi računske in pomnilniške zahtevnosti je metoda primerna le za manjše sisteme. Na površino anataza (101) smo dodali atome Pd in izvedli izračune za določitev reakcijskega mehanizma. Rezultati so pokazali, da se aktivacijske energije znižajo, vendar ne dovolj, da bi bil katalizator primeren za fotoredukcijo CO2. Na istem sistemu smo izvedli ∆SCF, ki je pokazal, da se izračunane vrednosti aktivacijske barier med pristopoma razlikujejo za približno 10 %, kar upravičuje uporabo ∆SCF na večjih sistemih, kjer TDDFT ni izvedljiv. Doktorska disertacija prikazuje možnost uporabe najnovejših metod za teoretično modeliranje vzbujenih stanj na primeru fotoredukcije CO2 in je glede na trenuten pregled literature prva izmed takšnih raziskav, predvsem zaradi kompleksnosti metodologije in računske zahtevnosti.
Keywords:	Mikrokinetika, CO2, vzbujena stanja, TDDFT, ∆SCF, fotokataliza
Place of publishing:	Maribor
Place of performance:	Maribor
Publisher:	[Ž. Kovačič]
Year of publishing:	2024
Number of pages:	XII, 121 str.
PID:	20.500.12556/DKUM-88162
UDC:	543.272.62:544.526.5(043.3)
COBISS.SI-ID:	221345795
Publication date in DKUM:	07.01.2025
Views:	275
Downloads:	112
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Categories:	KTFMB - FKKT
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Licences

License:	CC BY 4.0, Creative Commons Attribution 4.0 International

Link:	http://creativecommons.org/licenses/by/4.0/
Description:	This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.
Licensing start date:	06.05.2024

Secondary language

Language:	English
Title:	Quantumchemical modeling of photocatalysed conversion of carbon dioxide into value added compounds
Abstract:	Capture and conversion of CO2 has garnered significant attention from both industry and the scientific community in recent decades, primarily due to CO2 contribution to global warming. Numerous studies on the photocatalytic reduction of CO2 have been conducted, with the majority supported by experimental techniques, while theoretical methods are often overlooked. Theoretical approaches are mostly used as supplementary explanations for experimental data, with theoretical studies rarely being the main focus of research. However, with the rapid development of computational power and the establishment of modern, powerful computing centers, there is a growing interest in theoretical methods. The development of theoretical tools, such as density functional theory (DFT), further accelerates and improves theoretical calculations, which can serve us in analyzing reaction mechanisms, material properties, and predicting improvements in various areas, particularly in the development of new catalysts.One of the goals of the doctoral thesis was to characterize TiO2 for CO2 photoreduction using theoretical methods and to compare different approaches to accurately describe various catalyst properties. The results indicate that the choice of functionals and corrections depends on the desired calculated characteristics. The analysis of CO2 adsorption and activation on several unmodified and modified surfaces of anatase and rutile showed that CO2 activation is a crucial but complex process, as CO2 activation facilitates photocatalytic reduction. Activation is reflected as the transfer of electrons from the surface to the CO2 molecule, while geometrically expressed as the deformation of the molecule upon adsorption (the angle in the molecule decreases). Subsequently, the reaction mechanism of CO2 photoreduction on the clean and copper-doped surface of anatase (101) and rutile (110), as well as on the palladium-doped surface of anatase, was examined. It was found that the reaction hardly proceeds in the ground state due to high activation energies on any of the investigated surfaces, which was supported by a microkinetic model. We then introduced a photo-excited electron into the system, which we moved from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), while the electron hole remained in the valence band (VB), achieved using the ΔSCF method. The results showed that activation energies significantly decreased in some cases. A microkinetic model predicted that in the case of doping anatase (101) with Cu, we can expect H2 as the main product, while in the case of doping rutile (110) with Cu, the main product is CO. This is consistent with existing literature. We also tested a computationally more intensive method, namely time-dependent DFT (TDDFT). Due to computational and memory demands, this method is suitable only for smaller systems. We added Pd atoms to the surface of anatase (101) and performed calculations to determine the reaction mechanism. The results showed that activation energies decreased, but not enough to make the catalyst suitable for CO2 photoreduction. On the same system, we performed ΔSCF calculations, which showed that the calculated values of activation barriers between the approaches differed by approximately 10%, justifying the use of ΔSCF on larger systems where TDDFT is not feasible. The doctoral dissertation demonstrates the possibility of using the latest methods for theoretical modeling of excited states in the case of CO2 photoreduction and is, according to the current literature review, the first of such studies, primarily due to the complexity of the methodology and computational requirements.
Keywords:	Microkinetics, CO2, excited states, TDDFT, ∆SCF, photocatalysis

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