Banca de DEFESA: JILDIMARA DE JESUS SANTANA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : JILDIMARA DE JESUS SANTANA
DATE: 12/07/2024
TIME: 09:00
LOCAL: Google Meet
TITLE:

Hierarchical Bimetallic Nanocatalysts (Fe/Co) for CO and CO2 Hydrogenation Reactions.

KEY WORDS:

MOFs; catalysis; hydrogen production; CO hydrogenation; Fischer-Tropsch.

PAGES: 179
BIG AREA: Outra
AREA: Multidisciplinar
SUMMARY:

Metal-Organic Frameworks (MOFs) form a class of materials composed of metals or metal clusters
coordinated by polyfunctional organic ligands. These materials exhibit crystalline structures with pores or
channels, which confer a high specific surface area, making them highly interesting for catalysis,
adsorption, separation, and gas storage applications. MOFs, specifically M-BTC (M = Fe, Co), were
synthesized via a solvothermal method using trimesic acid (H3BTC) as the precursor for the organic
ligand and subsequently used as precursors to obtain metallic nanocatalysts dispersed on a carbonaceous
support via pyrolysis. These catalysts were evaluated in the hydrogenation of CO by Fischer-Tropsch
synthesis (FTS). Furthermore, the MOFs and the pyrolysis products were tested in a model reaction:
hydrogen production by dehydrogenation of sodium borohydride.
X-ray diffraction data analysis confirmed the crystallization of metal-organic structures for all
compositions produced. The experimental diffractograms showed a single set of peaks that agree with the
simulated MOF MIL-100(Fe) pattern. The pyrolyzed materials were also characterized by X-ray
diffraction, confirming the formation of the respective metal oxides and the probable presence of
amorphous carbonaceous matter. Scanning electron microscopy (SEM) images revealed the formation of
soft agglomerates composed of submicrometric or nanometric-sized particles in the MOFs containing
cobalt and hard micrometric-sized agglomerates in the sample containing only iron. The pyrolyzed
samples, in turn, exhibited very similar morphological characteristics with no clear evidence of
composition influence.
Textural analyses performed by N2 physisorption confirmed a low surface area for the monometallic
samples, approximately 5 m2

/g. On the other hand, the bimetallic samples F4C6B and F6C4B presented

surface area values of 323 and 570 m2

/g, respectively. Surprisingly, this behavior was not observed in the
pyrolysis products, where there was a significant increase in surface area following the increase in iron
content, reaching approximately 120 m2

/g for the P-FB sample. Additionally, the produced materials were
characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA),
Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF), and Inductively Coupled Plasma Optical
Emission Spectroscopy (ICP-OES).
The obtained samples were tested as heterogeneous catalysts for the dehydrogenation of NaBH4, showing
high activity, with hydrogen yields above 90% at temperatures below 50°C. These results suggest the
viability of using MOFs and pyrolysis products in systems to recover chemically stored hydrogen in
borohydrides. Furthermore, the samples tested in this reaction exhibited magnetic behavior, suggesting
the reduction of cationic species to metallic species. Thus, the results of the NaBH4 dehydrogenation tests
can also be leveraged in developing a study on the reducibility of the tested samples. The materials
developed in this work exhibit desired characteristics and properties for heterogeneous catalysts and can
be used for hydrogen production via dehydrogenation reactions.
For Fischer-Tropsch synthesis (FTS), which involves the hydrogenation of CO to hydrocarbons and CO
as a pathway to convert anthropogenic CO2 combined with the reformed water-gas shift reaction (CO2 +
H2 ⇌ CO + H2O) to meet economic and performance objectives—high selectivity for C5+ and high CO
conversion—stable, highly active, and dispersed cheap metallic catalysts are required. Here, we used
monometallic and bimetallic MIL-100 MOFs to create a stable catalyst; the bimetallic Fe-Co catalyst
converted 67% of CO with 30% selectivity for C5+ and 18% selectivity for C2-C5 at 300°C. The
monometallic catalyst converted more CO at the same temperature (87%), but the selectivity for C5+ was
less than 10%. The surface area of the bimetallic catalyst was over 650 m2

/g, while it was only 20 m2
/g
for the monometallic catalyst. The significant difference in surface area is partially explained by the pore
volume, which was 62 mL/g for the bimetallic versus 11 mL/g for the monometallic catalyst. The tests
conducted confirm that the MOFs tested are potential catalyst alternatives for CO hydrogenation
reactions.

COMMITTEE MEMBERS:
Presidente - 1754300 - BRAULIO SILVA BARROS
Externo ao Programa - 1810494 - KLEBER GONCALVES BEZERRA ALVES - nullExterno à Instituição - LEONIS LOURENÇO DA LUZ
Externa ao Programa - 1283408 - MARIANA PAOLA CABRERA - nullInterno - 1354207 - SEVERINO ALVES JUNIOR