Banca de QUALIFICAÇÃO: MOISÉS DA COSTA BORGES SOARES

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : MOISÉS DA COSTA BORGES SOARES
DATA : 29/03/2019
HORA: 08:00
LOCAL: auditório do Química III
TÍTULO:

Oxidative dehydrogenation of ethylbenzene to styrene over CoFe₂O₄-MCM-41 catalyst: Preferential adsorption on the ^-O²-Fe³⁺-O^2- sites located at the octahedral positions

PALAVRAS-CHAVES:

Catalyst, Ferrite, ethylbenzene, MCM-41

PÁGINAS: 100
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Físico-Química
ESPECIALIDADE: Cinética Química e Catálise
RESUMO:

It was synthesized a cobalt ferrite based catalyst supported on MCM-41 in order to evaluate its catalytic activity in the oxidative dehydrogenation of ethylbenzene to styrene compared to traditional catalysts containing hematite and understand the role of the ^-2O-Fe³⁺-O^2- and ^-2O-Co²⁺-O^2- sites present in the tetrahedral and octahedral positions of cobalt ferrite structure. Solids were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), Mössbauer spectroscopy (MS),  X-ray photoelectron spectroscopy (XPS), vibrating-sample magnetometer (VSM), temperature-programmed reduction (H₂-TPR),  chemical adsorption of NO and pyridine followed by infrared analysis, temperature programmed desorption of CO₂ (TPD), N₂ physisorption and transmission electronic microscopy (TEM). The catalytic tests were performed in a fixed bed reactor using a saturator containing ethylbenzene. The XRD, RS, MS and VSM results confirmed the formation of cobalt ferrite in bulk material and solid surface, which was classified as partially inverted ferrite. The low-angle XRD, N2 isotherms and TEM images show the formation of a mesoporous material with high surface area and the porous structure of MCM-41 support was slightly altered after the impregnation process. The catalytic tests confirmed that the cobalt ferrite is more active and stable than the traditional hematite catalyst due to its high structural stability. The catalytic cycle for the ethylbenzene dehydrogenation occurs preferentially in the ²O-Fe³⁺-O^2-  sites compared to ^-2O-Co²⁺-O^2- and mostly in octahedral sites compared to tetrahedral.  The mechanism proposal was supported by a theoretical computational evaluation using the periodic DFT approach, which revealed the higher acidity of iron sites compared to cobalt ones on the surfaces of the partially inverted spinel. Through the complementary electrostatic potential surfaces approach, the adsorption of ethylbenzene take place preferentially in the outermost FeO_X (x > 4) sites (Lewis acid) and the dehydrogenation reaction occurs predominantly in the oxygen bound to iron (Lewis base).

MEMBROS DA BANCA:
Interno - 1859346 - MIGUEL ANGELO FONSECA DE SOUZA
Interna - 1308577 - SIBELE BERENICE CASTELLA PERGHER
Externa ao Programa - 1675199 - SUZANA NOBREGA DE MEDEIROS
Presidente - 2087667 - TIAGO PINHEIRO BRAGA
Interno - 1149328 - VALTER JOSE FERNANDES JUNIOR