magistrsko delo
Matevž Roškarič (Author), Sebastijan Kovačič (Mentor), Albin Pintar (Co-mentor)

Abstract

Namen magistrskega dela je bil raziskati vpliv morfologije cerijevega dioksida (CeO2) in nanosa Pd (Pd) na aktivnost Pd/CeO2 katalizatorja. Za ta namen smo sintetizirali vzorce CeO2 z različnimi oblikami delcev (cevke, kocke, poliedra, dvojni različni nanodelci) in z različnimi nanosi Pd (0.5, 2 in 5 ut. %). Katalizatorje smo analizirali z različnimi tehnikami, kot so XRD, SEM z EDX, BET, piridin-TPD, CHNS in TGA. Aktivnost katalizatorjev smo testirali v cevnem reaktorskem sistemu, sklopljenim z plinskim kromatografom. Ugotovili smo, da so izbrane sintezne poti ustrezne, saj smo pripravili katalizatorje z dobro definiranimi strukturami, kar smo potrdili z vrstično elektronsko mikroskopijo. Opazili smo, da pride do interakcije med Pd in nosilcem na osnovi CeO2, saj so se spremenile fizikalno-kemijske lastnosti Pd/CeO2 napram samemu CeO2. S pomočjo testov smo ugotovili, da ima morfologija nosilca velik vpliv na aktivnost končnega katalizatorja. Prav tako ima stopnja poogljičenja vpliv na aktivnost katalizatorja, katera pa je odvisna od morfologije katalizatorja. Kot najbolj aktiven katalizator se je izkazal katalizator 5Pd/CeO2-P (katalizator na osnovi CeO2 z morfologijo poliedra s 5 % nanosom Pd), kateri izkazuje izkoristek za tvorbo MeOH (STY) 0,090 g/(gkat h) pri temperaturi 260 °C ter tlaku 50 bar in selektivnost za MeOH 24,9 % ter 1 ut. % adsorbiranega ogljika na površini katalizatorja po reakciji. Če preračunamo STY na gram Pd, ugotovimo, da je najbolj aktiven katalizator prav tako 5Pd/CeO2-P s STY=2,373 g/(gPd h). Ugotovili smo, da ima prisotnost Pd vpliv na aktivnost Pd/CeO2 katalizatorja, ki se veča z večanjem količine Pd do 2 % nanosa, nato se vpliv količine Pd na aktivnost Pd/CeO2 zmanjša pri nanosih večjih od 2 %, najverjetneje kot posledica aglomeracije Pd-skupkov. Rezultati stabilnostnih testov kažejo, da se aktivnost katalizatorja po 50 urah zmanjša za 37 % in da po 40 urah kaže težnjo po ohranjanju konstante vrednosti za daljše časovno obdobje, iz česar lahko sklepamo na potencialno dolgoročno uporabo le-tega.

Keywords

Hidrogenacija ogljikovega dioksida;heterogena kataliza;morfologija;sinteza MeOH;magistrske naloge;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher: [M. Roškarič]
UDC: 66.094.25(043.2)
COBISS: 31843075 Link will open in a new window
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Other data

Secondary language: English
Secondary title: Catalytic hydrogenation of carbon dioxide to methanol in the presence of noble metal based catalysts
Secondary abstract: The purpose of this master thesis was to investigate the effect of ceria dioxide (CeO2) morphology and palladium (Pd) loading on the catalytic activity of Pd/CeO2 catalysts. For this purpose, we synthesized CeO2 of different shapes (rods, cubes, polyedra, two different nanoparticles) containing different loadings of Pd (0,5, 2 and 5 wt. %). As-synthesised catalysts have been analyzed by various instrumental techniques, such as XRD, SEM with EDX, BET, pyridine-TPD, CHNS and TGA. The activity tests were carried out in a fixed-bed reactor system coupled to a gas chromatograph for online analysis. SEM images have shown a well-defined structure of CeO2 particles, on the basis of which we can conclude that the chosen synthesis methods were adequate. We have also measured changes in the physical-chemical properties of the Pd-containing catalyst samples and found an interaction of Pd with CeO2. From the activity tests, we further found that the morphology of CeO2 has a strong effect on the activity of the investigated catalysts. The morphology also affects the degree of coking, which reduces the catalytic activity as a function of time on stream. We found that the most active catalyst is 5Pd/CeO2-P (a CeO2 catalyst with morphology of polyethra with a 5 % loading of Pd), which gave the methanol yield (STY) of 0,090 g/(gcath) at a temperature of 260 °C and pressure of 50 bar, and has a methanol selectivity of 24,9 % with only 1 wt. % of coking. If we calculate the STY per mass of Pd, we can find that the most active catalyst is again 5Pd/CeO2-P with the STY of 2,373 g/(gPdh). We further found that the percentage of Pd loading affects the catalyst activity, which increases with increasing loading up to 2 % of Pd and the effect then decreases at loadings above 2 %, most probably due to the agglomeration of Pd ensembles. A catalyst stability test was further conducted, revealing a 37 % loss of activity over the period of 50 hours of time on stream with a trend for a constant STY after 40 hours, which indicates the possibility of long-term catalyst use.
Secondary keywords: Hydrogenation of carbon dioxide;Pd/CeO2;heterogeneous catalysis;morphology;methanol synthesis;
Type (COBISS): Master's thesis/paper
Thesis comment: Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages: XIV, 87 str.
ID: 11936063