Banca de DEFESA: MOISÉS DA COSTA BORGES SOARES

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : MOISÉS DA COSTA BORGES SOARES
DATA : 26/07/2019
HORA: 08:00
LOCAL: Auditório do CCET
TÍTULO:

OXIDATIVE DEHYDROGENATION OF ETHYLBENZENE TO STYRENE IN PRESENCE OF CO2 OVER CoFe₂O₄-MCM-41 CATALYST: preferential adsorption on the O^2-Fe³⁺O^2- sites located at octahedral positions

PALAVRAS-CHAVES:

oxidative dehydrogenation, ethylbenzene, cobalt ferrite, CO₂ role, catalytic mechanism

PÁGINAS: 130
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Físico-Química
ESPECIALIDADE: Cinética Química e Catálise
RESUMO:

The present study describes the catalytic performance of cobalt ferrite supported on MCM-41 for the oxidative dehydrogenation of ethylbenzene and evaluates the role of CO ₂ on the surface of the catalyst during the reaction using experimental data and density functional theory (DFT) calculations. A mechanism has been described indicating the role of the O^-2-Fe³⁺-O^2- and O^-2-Co²⁺-O^2- acid-base sites present in the tetrahedral and octahedral positions of the cobalt ferrite structure. The solids were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), Mössbauer spectroscopy (MS), X-ray photoelectron spectroscopy (XPS), vibration-sample magnetometry (VSM), temperature-programmed reduction (H₂-TPR), chemical adsorption of NO and pyridine followed by infrared (FTIR) analysis, temperature-programmed desorption of CO₂ (TPD-CO₂), N₂ physisorption and transmission electron microscopy (TEM). The results of XRD, RS, MS and VSM, before and after catalytic tests, confirmed the formation of partially inverted cobalt ferrite and showed the role of CO₂ in the reactivation of the acid-base sites during the catalytic cycle, observing that the ferrite phase of cobalt was maintained when the reaction was carried out in the presence of CO₂ and reduced in the tests without CO₂. N₂ isotherms, low angle XRDs and TEM images showed the formation of MCM-41 support. The catalytic tests showed that CO2 is essential to obtain good conversion values of ethylbenzene and that cobalt ferrite is more active and stable than the traditional hematite catalyst. Thermogravimetric analyzes showed that CO₂ favors the oxidation of deposited carbon during the reaction. The results of TPD-CO₂ and FTIR-CO₂ indicated the presence of weak basic sites and the preferential adsorption of CO₂ as carbonate and bicarbonate bridges. The computational results confirmed the preferential form of CO₂ adsorption as bicarbonate. The proposed catalytic cycle, through a theoretical approach (DFT), shows that the adsorption of CO₂ and ethylbenzene occurs preferentially at the octahedral sites O^-2-Fe³⁺-O^2- - compared to the O^-2-Co²⁺-O^2- sites, due to to a higher acidity of the iron sites compared to cobalt on the surface of the spinel, evidencing the role of CO₂ in regenerating lattice oxygen and the iron phase of the spinel. By approaching the surfaces of complementary electrostatic potential, the adsorption of ethylbenzene occurs preferentially at the outermost FeO_X (x> 4) sites (Lewis acid) and the dehydrogenation reaction occurs predominantly in the oxygens bound to iron (Lewis base).

MEMBROS DA BANCA:
Externo à Instituição - MARCO ANDRE FRAGA - INT
Externo à Instituição - MARIO ROBERTO MENEGHETTI - UFAL
Interno - 1859346 - MIGUEL ANGELO FONSECA DE SOUZA
Presidente - 2087667 - TIAGO PINHEIRO BRAGA
Interno - 1149328 - VALTER JOSE FERNANDES JUNIOR