PhD Thesis Defence Presentations - Andriopoulou Chrysanhti
The industrial significance of the oxo-rhenate catalysts has triggered basic research and studies on the nature and functionality of the active sites of such catalysts, and particularly the dispersed surface oxo-rhenate species present. The importance of these catalysts lies in their extensive use in olefin metathesis reactions as well as in hydrodesulfurization, hydrogenation and selective hydrogenation reactions, selective reduction of NOX and partial oxidation of methanol. To this end, the supported oxo-rhenate catalysts have been studied with a variety of techniques. Raman Spectroscopy is very well suited for studying supported metal oxides and consequently supported rhenium oxide. The molecular nature of this characterization and its ability to discriminate between different molecular configurations that can simultaneously exist in the catalytic system make Raman spectroscopy a very powerful characterization tool.
In the present study we study the molecular structure of rhenium oxide catalysts supported on TiO2 (P25) with in situ molecular vibrational Spectroscopy (Raman and IR). The (ReOx)n/TiO2 (P25) catalysts with surface densities from 0.16 to 2.5 Re/nm2 were prepared by the wet impregnation method and the Equilibrium Deposition Filtration (EDF) method. Oxorhenate catalysts supported on two more oxiic carriers (monoclinic ZrO2, γ-Al2O3) with surface densities up to monolayer coverage were also prepared and studied. The use of Raman Spectroscopy under controlled conditions (in situ) allowed the investigation of structural features and changes occurring under oxidative dehydrated conditions at various temperatures. Combinations of i) Raman with IR Spectroscopy and ii) Raman Spectroscopy with 18O/16O isotope substitution experiments provided useful and complementary information for establishing the molecular characteristics of the oxo-rhenate sites. The spectra obtained are adequate to determine the heterogeneity of the deposited rhenium phase and to discuss the vibrational properties and configurations of the various deposited sites (ReOx) as well as their dependence on temperature, loading and support. The results of isotopic substitution shed further light on the termination configurations of the oxo-RevII species.
The temperature-dependent evolution of the configurations and molecular structures of (WOx)n and (MoOx)n species supported on TiO2(P25) prepared by the equilibrium deposition filtration (EDF) method, was also studied with a view to shed light on the mechanisms of the thermal dispersion and temperature evolution of the dispersed sites following the stage of filtration and during the stages of drying and calcination. The main aim had been an attempt to illustrate that the EDF method is able (at least in a certain range of submonolayer loadings) to result in designed site speciations and that particular snapshots of the structural/configurational temperature evolution can be captured by in situ Raman Spectroscopy. The question of the possible temperature-dependence of the structure / configuration of the amorphous dispersed phase on supported transition metal oxides systems has been of great concern to the scientific community, and the prevailing view argues that catalyst heating above the Tamman Temperature (TTAM) which is the half of the melting temperature of the metal oxide activates a surface thermal dispersion and spillover, whereas after the final calcination the "thermodynamically stable form" of the dispersed oxometallic phase will prevail on the surface of the carrier. In the present study, evidence is presented based on in situ Raman Spectroscopy, that controverts the above prevailing view, and it proves that the molecular structure of the dispersed oxometallic phases ((ΜοVIΟx)n, (WVIΟx)n and (ReVΙIΟx)n is subject to reversible temperature-dependent equilibria between mono- oxo and poly-oxo (most likely di-oxo) configurations.
The last part of this thesis pertains to a case study of reference compounds on the coordination chemistry of ReVII in an environment of O ligands and the vibrational properties of Re(=O)x termination configurations. The dissolution reaction of the low melting and volatile (m.p. 297oC, b.p 360oC) Re2O7 in molten K2S2O7 and K2S2O7-K2SO4 in the full composition range is studied by Raman spectroscopy under static equilibrium in oxidative atmosphere at temperatures of 260–470°C. The reaction of Re2O7 with K2S2O7 in the molten phase results in formation of two isomeric ReVII-oxosulafto complexes at a 1:1 stoichiometry. At low contents of Re2O7 and temperatures around 300OC, the majority species is the mononuclear ReO3SO4-(l) complex, in which ReVII takes on a tri-oxo termination conﬁguration with 5-fold coordination. At increasing contents of Re2O7 and higher temperature the ReO3SO4-(l) complex interconverts to its isomeric dinuclear (ReO2)2O2(SO4)22− molten complex where ReVII takes on a dioxo termination conﬁguration with 6-fold coordination and a double oxygen bridge connecting the two Re atoms. The 2ReO3SO4‑(l)«(ReO2)2O2(SO4)22-(l) interconversion is reversible and full reinstatement of the individual spectral features for each complex takes place with appropriate control of the temperature. The ReO3SO4‑ and (ReO2)2O2(SO4)22- molten complexes are useful reference compounds for discerning the termination conﬁguration of dispersed (ReOx)n sites in supported catalysts. The molten (ReO2)2O2(SO4)22- complex reacts with K2SO4 giving rise to formation of S2O72− and ReO4-.
Speakers Short CV (Σύντομο Βιογραφικό Ομιλητή)
Master of Science in Catalysis, Pollution Control and Clean Energy Production. -12/2013-02/2015
Department of Chemistry, University of Patras.
Thesis Topic: “Preparation of cobalt catalysts supported on alumina for transforming sunflower oil to green diesel.”
BSc in Chemistry -09/2009-12/2013
Department of Chemistry, University of Patras.
Degree : 7,76/10
Bachelor Thesis: “Preparation of nickel catalysts for the conversion of sunflower oil to green diesel”
Publications in international journals
- Di-oxo and tri-oxo Re(VII)-oxosulfato complexes in the Re2O7-K2S2O7 molten system. Molecular structure, vibrational properties and temperaturedependent interconversion C. Andriopoulou, I.Anastasiou, S. Boghosian Vibrational Spectroscopy 100 (2019) 14–21
- Ceria Nanoparticles Shape Effects on the structural defects and surface chemistry: Implications in CO oxidation by CuO/CeO2 catalysts
- M. Lykaki, E. Pachatouridou, S. A.C. Carabineiro, E. Iliopoulou, C.Andriopoulou, N. Kallithrakas-Kontos, S. Boghosian, M. Konsolakis Applied Catalysis B: Environmental 2018, 230, 18-28
- Heterogeneity of Depositesd Phases in Supported Transition Metal Oxide Catalysts: Reversible Temperature Dependent Evolution of Molecular Structures and Configurations C. Andriopoulou and S. Boghosian, Phys. Chem. Chem. Phys, 2018, 20, 1742-1751
- Structural and Redox Properties of Ce1-XZrxO2-d and Ce0.8Zr0.15RE0.05O2-d (RE: La, Nd, Pr, Y) Solids Studied by High Temperature in situ Raman Spectroscopy C. Andriopoulou, A. Tribalis, K. C. Petallidou, A. Sgoura, A. M. Efstathiou and S.Boghosian J. Phys. Chem. C, 2017, 121, 7931-7943
- Green diesel production over nickel-alumina co-precipitated catalysts M.Gousi, C. Andriopoulou, K. Bourikas, S. Ladas, M. Sotiriou, C.Kordulis, A.Lycourghiotis Applied Catalysis A: General, 2017,536, 45-56