Banca de QUALIFICAÇÃO: JILDIMARA DE JESUS SANTANA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : JILDIMARA DE JESUS SANTANA
DATE: 21/12/2021
LOCAL: Ambiente virtual / Plataforma Google Meet às 9h
TITLE:

Bimetallic hierarchical nanocatalysts (Fe/Co) for the hydrogenation reactions of CO and CO₂

KEY WORDS:

MOFs; catalysis; hydrogen production; CO₂ hydrogenation; Fischer-Tropsch

PAGES: 97
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUMMARY:

Metal-Organic Frameworks (MOFs) compose a class of hybrid materials constituted by metals or metallic clusters coordinated by polyfunctional organic ligands. These materials have crystalline structures with pores or channels that give them high specific surface area, making them of great interest for applications in catalysis, adsorption, separation, and gas storage. M-BTC type MOFs (M = Fe, Co) were synthesized via solvothermal method using trimesic acid (H₃BTC) as the organic ligand and later used as precursors to obtain metallic nanocatalysts dispersed in carbonaceous support via pyrolysis. In the second stage of the thesis work, these catalysts will be tested for the CO₂ hydrogenation reaction via Fischer-Tropsch Synthesis (FTS). In this first moment, both the MOFs and the pyrolysis products were tested in a model reaction, hydrogen production via dehydrogenation of sodium borohydride. X-ray diffraction analysis confirmed the crystallization of metal-organic structures for all compositions produced. The experimental diffractograms showed a single set of peaks in good agreement with the simulated pattern of MOF MIL-100(Fe). The pyrolyzed materials were also characterized by X-ray diffraction, confirming the formation of the respective metallic oxides, in addition to the probable presence of amorphous carbonaceous matter. SEM images revealed the formation of soft agglomerates composed of particles of submicrometric or manometric size in the MOFs containing cobalt, but hard agglomerates of micrometer size in the sample containing only iron. The pyrolyzed samples, in turn, showed very similar morphological characteristics without clear evidence of compositional influence. Texture analyzes 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 323.9 and 570.5 m²/g, respectively. Surprisingly, this behavior was not observed in the pyrolysis products, where there was a significant increase in the surface area following the increase in iron content of the samples, reaching approximately 120 m²/g for the P-FB sample. Additionally, the samples were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Energy-Dispersive X-ray Fluorescence Spectrometry (EDXRF) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The samples obtained were tested as heterogeneous catalysts for the NaBH₄ dehydrogenation reaction, having shown high activity, with hydrogen yields above 90% at temperatures below 50 ^oC. These results suggest the feasibility of using both MOFs and pyrolysis products in hydrogen recovery systems chemically stored in borohydrides.

Furthermore, the samples tested in this reaction started to show magnetic behavior, which suggests the reduction of cationic to metallic species. Thus, the results of the NaBH₄ dehydrogenation tests can also be used to develop a study on the reducibility of the tested samples. Thus, the materials developed in this work have desired characteristics and properties for heterogeneous catalysts and can be used in hydrogen production via dehydrogenation reactions, as confirmed by the tests carried out, but also appear as possible alternatives for CO₂ hydrogenation reactions.

BANKING MEMBERS:
Externo ao Programa - 2823856 - LUCIANO COSTA ALMEIDA
Externo à Instituição - LEONIS LOURENÇO DA LUZ - UFPE
Externo à Instituição - RODRIGO DA SILVA VIANA - UFPE