Razvoj magnetnih katalizatorjev na osnovi rutenija in njegovih zlitin za magnetno segrevano sintezo in razklop amonijaka

Ponikvar, Žiga

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Title:	Razvoj magnetnih katalizatorjev na osnovi rutenija in njegovih zlitin za magnetno segrevano sintezo in razklop amonijaka
Authors:	ID Ponikvar, Žiga (Author) ID Gyergyek, Sašo (Mentor) More about this mentor... ID Likozar, Blaž (Comentor)
Files:	DOK_Ponikvar_Ziga_2025.pdf (11,28 MB) MD5: 4172C1BDB2D949CBDD13D3704C8DE133
Language:	Slovenian
Work type:	Doctoral dissertation
Typology:	2.08 - Doctoral Dissertation
Organization:	FKKT - Faculty of Chemistry and Chemical Engineering
Abstract:	Doktorsko delo predstavlja raziskave in izsledke na področju magnetno grete katalize za razklop in sintezo amonijaka. Magnetno gretje za namene katalize je relativno nov pristop, ki omogoča izredno hitro gretje katalizatorja brez fizičnega stika med indukcijsko tuljavo in ferimagnetnim ali feromagnetnim materialom v njeni notranjosti, ki se segreje v izmeničnem magnetnem polju (100–300 kHz). Brezkontaktni prenos energije in Joulovo gretje v električnem prevodniku zaradi induciranih vrtinčnih tokov je že uveljavljena tehnologija, trenutno v uporabi za kaljenje, taljenje, lotanje in varjenje kovinskih izdelkov. Zanimiv je tudi način izdelave z interferenčnim prileganjem sestavnih delov, kjer je potrebno segreti eno komponentno, da se razširi, nakar je vanjo mogoče vstaviti drugo. V redkih primerih lahko ta pristop uporabimo za gretje kovinskega medija znotraj reaktorja za katalizo. Za indukcijsko gretje prevodnika potrebujemo večje delce, vsaj nekaj mikronov, kar pa močno presega red velikosti zrn katalizatorja, ki morajo biti zaradi čim večje specifične površine majhna. V delu smo se osredotočili na razvoj nanostrukturnih materialov, ki so zmožni katalize in gretja po drugem mehanizmu sproščanja energije, na račun histereznih izgub v visokofrekvenčnem magnetnem polju, kar smo za namene naših raziskav poimenovali magnetno gretje. Razvili smo več kompozitnih materialov, ki smo jih prilagodili trenutnim potrebam. Zaradi potrebe po dolgoročni stabilnosti katalizatorja v reduktivni atmosferi smo pripravili kompozit, ki sestoji iz magnetne podlage in katalitskih nanodelcev. Podlaga vsebuje feromagnetna jedra zlitine Co in Ni, ki tekom reakcije v reduktivnih pogojih ohranijo feromagnetne lastnosti, s spreminjanjem razmerja med kovinama pa vplivamo na lastnosti histerezne zanke in posledično sposobnosti gretja. Jedra so ukleščena v katalitsko podlago, γ-Al2O3 z veliko specifično površino (200 m2/g), ki preprečuje njihovo rast pri povišanih temperaturah in omogoča prenos toplote s feromagnetnih jeder do nanodelcev Ru, ki se nahajajo na njeni površini. Opisani katalizator vsebuje dve vrsti nanodelcev. Feromagnetna zlitina CoNi omogoča gretje, Ru pa nudi katalitska mesta. Ker v literaturi nismo zasledili materialov, zmožnih hkratnega magnetnega gretja in katalize, smo razvili zlitino Ru in Co, s čemer smo želeli poenostaviti postopek priprave in omogočiti sproščanje toplote neposredno na katalitskem mestu. Bimetalni delci se najahajo na površini nemagnetnega γ-Al2O3, ki pa v tem primeru zgolj služi kot podlaga in ne omogoča gretja. Rutenij je žlahtna kovina, ki katalizira razklop in tvorbo amonijaka, reakcija pa je ravnotežna. Amonijak je molekula z visoko vsebnostjo vodika, ker pa je transport vodika pri povišanem tlaku nevaren, se raziskujejo možnosti kemijske vezave. S katalitskim razklopom amonijaka pri povišani temperaturi lahko po potrebi proizvedemo vodik, sinteza amonijaka pa je eksotermna reakcija. Za testiranje plinske katalize z magnetnim gretjem smo sestavili nov reaktorski sistem. V tuljavo indukcijskega ogrevalnika smo namestili cevko iz kremenovega stekla z magnetnim katalizatorjem, temperaturo pa smo spremljali z nemagnetnim termočlenom. Za preučevanje razklopa amonijaka smo uporabili razredčen amonijak pri sobnem tlaku, razpadne produkte in preostali amonijak pa smo spremljali s plinskim kromatografom in z masnim spektrometrom. Z bimetalnim katalizatorjem RuCo na nemagnetni podlagi smo pri 520 °C dosegli popolno pretvorbo 2,5 vol.% NH3 (40 mL/min). Z rutenijevim katalizatorjem na magnetnem γ-Al2O3 smo ugotovili, da je pri pretoku 30 mL/min 10 vol.% NH3 pretvorba popolna že pri 400 °C. Za sintezo amonijaka smo uporabili vodik in dušik pri 30 bar ter enak rutenijev katalizator, saj je bil cilj pokazati reverzibilnost razvite tehnologije, ki jo usmerjamo z izbiro pogojev. Največji delež NH3 v efluentu in s tem najvišjo proizvodnost smo zaznali pri 550 °C (0,66 %), ki je z nadaljnjim dvigom temperature pričel upadati.
Keywords:	Magnetna kataliza, razklop amonijaka, kompozitni katalizator, rutenij, nanodelci RuCo
Place of publishing:	Maribor
Publisher:	[Ž. Ponikvar]
Year of publishing:	2025
PID:	20.500.12556/DKUM-91907
UDC:	537:620.3(043.3)
COBISS.SI-ID:	230881795
Publication date in DKUM:	28.03.2025
Views:	160
Downloads:	71
Metadata:
Categories:	KTFMB - FKKT
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Licences

License:	CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International

Link:	http://creativecommons.org/licenses/by-nc-nd/4.0/
Description:	The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.
Licensing start date:	26.02.2025

Secondary language

Language:	English
Title:	Development of ruthenium and ruthenium alloy-based catalysts for magnetically heated synthesis and decomposition of ammonia
Abstract:	This thesis work focuses on experimental research in the field of magnetic catalysis for ammonia decomposition and synthesis. Induction heating in catalysis is a rather new approach enabling rapid heating of a catalyst bed eliminating the need for direct contact between an induction coil and the ferromagnetic material within which heats up due to the presence of an alternating magnetic field (100–300 kHz). Within bulk electrical conductors, Joule heating ensues on the account of induced eddy currents which is an already tried and tested approach widely utilized for cooking, quenching, melting and welding. In some instances, induction heating is used for interference assembly of metallic components and in niche cases, heating of metallic susceptor particles within a chemical reactor. For this purpose, particles exceeding several microns are required which strongly surpass the size of conventional catalyst particles that need to be smaller in order to maximize surface area. In our work, we focused on the development of nanostructured materials capable of catalysis and heating in accordance with another mechanism, namely hysteresis losses within a high-frequency magnetic field which we will be referring to as magnetic heating. We developed several composite materials which were tuned to suit the needs at hand. To provide long-term stability while operating in a reductive environment, we prepared a composite comprising magnetic support and surface-bound catalytic nanoparticles. The support contains alloyed ferromagnetic CoNi nanoparticles which retain their magnetic properties during the course of a chemical reaction under reducing conditions. By tuning the composition ratio, hysteresis loop properties are altered which effects the support's heating abilities. CoNi nanoparticles are encapsulated within a high-surface catalyst support (γ-Al2O3) which prevents their coalescence at elevated temperatures while enabling heat transfer to Ru nanoparticles located on the surface. The described catalyst contains two types of nanoparticles. The ferromagnetic CoNi alloy enables heating while Ru serves as the catalyst. Since no materials capable of simultaneous magnetic heating as well as catalysis were to be found in literature, we developed a RuCo alloy which allows for a simplified catalyst preparation procedure while enabling heat generation directly where the reaction takes place. Bimetallic particles are adhered onto the non-magnetic γ-Al2O3 which serves solely as support and is thus not used for heat generation. Ruthenium is a noble metal used to catalyze ammonia decomposition and synthesis (equilibrium reaction). Ammonia is a simple molecule boasting a high hydrogen content and since transportation of pressurized hydrogen poses a significant threat, various options of chemical storage are under research. On-demand hydrogen can be produced at elevated temperatures by catalytic decomposition of ammonia while its synthesis is exothermic. For induction-heated gas-phase catalysis testing, a new reactor was constructed. A quartz tube containing said magnetic catalyst was placed within the induction coil while the temperature changes were tracked using a non-magnetic thermocouple. For ammonia decomposition testing at ambient pressure, a flow of diluted ammonia was directed over the catalyst bed. During decomposition, nitrogen and hydrogen gas are produced which were detected using gas chromatography and mass spectrometry. Using a supported RuCo composite, complete ammonia conversion (2.5 vol.%, 40 mL/min) was achieved at 520 °C. At a 30 mL/min 10 vol.% NH3 flow, complete conversion was achieved at 400 °C. For ammonia synthesis, hydrogen and nitrogen were employed (30 bar) and using the existing Ru-based catalyst, we set to demonstrate the reversiblity of the reaction controlled by varying the conditions. At this pressure, maximum ammonia production was detected at 550 °C (0.66 %) while its content started to decline with higher temperatures.
Keywords:	Magnetic catalysis, ammonia decomposition, composite catalyst, ruthenium, RuCo nanoparticles

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