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Christine Fountzoula


chfountz@teiath.gr

Journal articles

2008
P G Savva, K Goundani, J Vakros, K Bourikas, C Fountzoula, D Vattis, A Lycourghiotis, C Kordulis (2008)  Benzene hydrogenation over Ni/Al2O3 catalysts prepared by conventional and sol-gel techniques   APPLIED CATALYSIS B-ENVIRONMENTAL 79: 3. 199-207 MAR 1  
Abstract: Nickel supported on alumina catalysts have been prepared using various synthesis methods (dry impregnation, co-precipitation, sol-gel) and evaluated for the hydrogenation of benzene contained in gasoline. The evaluation was carried out in a laboratory scale high pressure fixed bed reactor fed with a stream of surrogated reformate gasoline consisted by a mixture of hexane, benzene and toluene. All catalysts have been characterized by the joint use of various physicochemical characterization methods (XRF, BET, TGA, SEM, XRD, UV-vis DRS and XPS) in order to correlate their catalytic performances to their physicochemical properties. The results obtained revealed that sol-gel procedure, especially when it is followed by supercritical drying (aerogel), produced the most promising catalysts for the aforementioned catalytic process. Sol-gel methodology ensured the best compromise between dispersion of the nickel phase and its interaction with the support surface. Co-precipitated catalysts exhibited important activities but lower than those of the sol-gel catalysts. The catalyst prepared by dry impregnation proved to be the less active. Calcination of the catalysts before their activation by reduction decreased their activities. (C) 2007 Elsevier B.V. All rights reserved.
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2007
K Bourikas, J Vakros, C Fountzoula, C Kordulis, A Lycourghiotis (2007)  Interface science for optimizing the size of oxidic nanoparticles in supported catalysts   CATALYSIS TODAY 128: 3-4. 138-144 OCT 30  
Abstract: In the present work we attempt to optimize the size of the supported "molybdenum oxide"/titania and "cobalt oxide"/gamma-alumina nanoparticles formed after calcination by "selecting", respectively, the proper mode of deposition and the local structure of the deposited species achieved upon the impregnation step of catalyst preparation. Concerning the first system, it was found that the disubstituted Mo inner sphere surface complexes, which are bound on the support surface stronger than the monosubstituded ones, resist more effectively to the sintering taking place during calcination where the above complexes are transfortned progressively into MoO3 supported nanoparticles. This leads to a catalyst with very small MoO3 nanoparticles and thus with very high activity for the selective reduction of NO by NH3. Concerning the "cobalt oxide" /gamma-alumina catalysts, it was found that a relatively large (small) size of the supported nanocrystallites is imposed by the bulk deposition (formation of inner sphere surface complexes). A quite small size of the supported "cobalt oxide" nanocrystallites, not strongly interacted with the support surface, is imposed by the interface precipitation. This is the optimum supported phase for the complete oxidation of benzene. () 2007 Elsevier B.V. All rights reserved.
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2006
L Giakoumelou, C Fountzoula, C Kordulis, S Boghosian (2006)  Molecular structure and catalytic activity of V2O5/TiO2 catalysts for the SCR of NO by NH3 : In situ Raman spectra in the presence of O-2, NH3, NO, H-2, H2O, and SO2   JOURNAL OF CATALYSIS 239: 1. 1-12 APR 1  
Abstract: In situ Raman spectroscopy has been used at temperatures LIP to 400 degrees C under O-2. NH3/N-2, H-2/N-2), NH3/NO/O-2/N-2, O-2/H2O/N-2), and SO2/O-2/N-2 for Studying tile influence of these gases oil the molecular Structure Of V2O5/TiO2 catalysts with V surface density, it, in the range 2.5-18.7 VOx/nm(2). The catalyst activities for the SCR of NO by NH3 have been determined to derive structure-activity relationships in combination with the Raman data. Isolated monovanadates and polyvanadates are formed at various proportions (depending oil the loading) oil the catalyst Surface Under dehydrated conditions. The hand positions and characteristics are discussed in terms of possible configurations for the dispersed VOx, species. The bands observed, the surface composition, and the bond conservation rule allow to propose a small size for the V-O-V chains of polyvanadates (i.e., 2, 3). The reducing action of NH3 is favored in the presence of adjacent V sites; at low loadings. the presence of NH3 has not effect on the structural properties of surface VOx. The reducibility in H-2 follows an oppostite trend and is favored at low n(s), as indicated by both effect oil the structural properties of surface VOx. The reducibility in H-2 follows all opposite trend and is favored at low it, ill Situ Raman and H-2-TPR. The SO,) presence affects only the molecular Structure of catalysts with low n(s). for which a significant part of surface TiO2,) sites are vacant; the effect (judged from the ill Situ Raman data) is merely one of driving the dispersed vanadia species in a state of"virtually" high Surface density by crowding them together, thereby providing more adjacent V sites for activation of NH3 in SCR reaction conditions. The NO TOF Values initially increase with increasing its, suggesting that the number of active sites per V atom increases with increasing its below s or at conditions of "virtually" high n(s) (in the presence of monolayer. The formation of adjacent V-O-Ti sites is favored either at increasing n(s), or at conditions of "virtually" high n(s) (in the presence of SO2). The increase in the number of such centers per V atom correlates with the increase in TOF values with increasing its. (c) 2006 Elsevier Inc. All rights reserved.
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2005
T Ataloglou, C Fountzoula, K Bourikas, J Vakros, A Lycourghiotis, C Kordulis (2005)  Cobalt oxide/gamma-alumina catalysts prepared by equilibrium deposition filtration : The influence of the initial cobalt concentration on the structure of the oxide phase and the activity for complete benzene oxidation   APPLIED CATALYSIS A-GENERAL 288: 1-2. 1-9 JUL 15  
Abstract: In the present work we studied the influence of the initial concentration of the impregnating solution used for mounting Co(II) species on the gamma-alumina surface by equilibrium deposition filtration method (edf) on the physicochemical properties and the catalytic activity of the "cobalt oxide" /gamma-alumina catalysts. The complete oxidation of benzene has been used as a model reaction. Two series of catalysts (edf-X-A and edf-X-B) of varying Co content (X: up to 21 wt.% Co) were prepared using the above-mentioned method and tested at various temperatures in the range 200-300 degrees C using a fixed-bed reactor. In the first series (A) various Co loadings were obtained by varying the initial Co(II) concentration of the impregnating solution. In the second series (B) the corresponding Co loadings were obtained by using the impregnating solution used for the preparation of the catalyst of A series with the maximum Co(II) content and varying the impregnation time. All catalysts were characterized using various techniques, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), X-ray powder analysis (XRD), nitrogen adsorption (BET) and temperature-programmed reduction (TPR). It was found that the initial Co(II) concentration of the impregnating solution used for depositing the corresponding species on the gamma-alumina surface by edf influences the catalytic activity of the "cobalt oxide" /y-alumina catalysts with respect to the complete oxidation of benzene. The increase of the initial Co(II) concentration of the impregnating solution brings about a change in the composition of the deposited phase formed in the impregnation step by decreasing the ratio "Co(II) surface inner-sphere complexes/surface Co(II) precipitates". Upon calcination, the Co(II) surface inner-sphere complexes are transformed to well-dispersed "cobalt oxide" phase strongly interacting with the support surface while the surface Co(II) precipitates are transformed to Co3O4 crystallites loosely interacting with the support surface. The former phase is responsible for the relatively high dispersion of Co observed in the A series of catalysts but it is rather inactive, while the latter exhibits lower dispersion but higher activity. Thus, the edf catalysts prepared using high initial Co(II) concentration exhibited higher catalytic activity than the corresponding ones prepared using low initial Co(II) concentration. (c) 2004 Elsevier B.V. All rights reserved.
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T Ataloglou, J Vakros, K Bourikas, C Fountzoula, C Kordulis, A Lycourghiotis (2005)  Influence of the preparation method on the structure-activity of cobalt oxide catalysts supported on alumina for complete benzene oxidation   APPLIED CATALYSIS B-ENVIRONMENTAL 57: 4. 299-312 MAY 26  
Abstract: In the present work we studied the influence of the methodology used for mounting Co(II) species on the γ-alumina surface on the physicochemical properties and the catalytic activity of the 'cobalt oxide'/γ-alumina catalysts for complete oxidation of benzene. Three series of catalysts of varying Co content (up to 21 wt.% Co) were prepared using three preparation methods: pore volume impregnation (pvi), equilibrium deposition filtration (edf) and pore volume impregnation adding nitrilotri acetic acid (ma) in the impregnation solution. It was found that the catalytic activity for low, medium and high Co content follows, respectively, the orders, nta-pvi &MGT; pvi &MGT; edf, nta-pvi &MGT; edf ≈ pvi and edf > nta-pvi > pvi. The catalysts prepared were characterized using various techniques (BET, UV-vis/DRS, XRD and XPS) at each step of the preparation procedure, namely after the Co(II) mounting on the support surface, after drying as well as after calcination. It was inferred that the most active sites are located on CO3O4-supported crystallites, loosely or moderately interacting with the γ-alumina surface. Two critical parameters, related with the method followed for mounting Co(II) species on the γ-alumina surface, control the characteristics of the supported phase and thus the amount and the size of the above-mentioned CO3O4 crystallites: the ratio 'amount of Co(II) deposited in the impregnation step to that remaining in the liquid phase inside the pores precipitating thus in the drying step' closely related with the ratio 'amount of Co(II) in the deposited phase (isolated Co(II) surface inner sphere complexes and Co(II) surface precipitates)/amount of Co(II) in the precipitated phase formed in the drying step' as well as the composition of the precipitated phase. The application of the pvi technique resulted to low values for the above ratios and thus to the formation of a rather unstable precipitated phase consisted mainly by Co(H2O)(6)(2+) (.) 2NO(3)(-). Upon calcination it is transformed into loosely bounded CO3O4 crystallites of relatively big size. This is related with the low Co dispersion and thus with the low catalytic activity exhibited by these catalysts. The application of edf resulted to high values for the above-mentioned ratios. Therefore, the deposited phase is predominant. Upon calcination it is transformed to well (very well) dispersed cobalt phases strongly (too strongly) bounded with the support surface and thus reducible at high temperatures (non reducible up to 800 ° C). Although these phases are responsible for the high Co dispersion achieved they do not contribute to the catalytic activity unless the deposited phase mainly comprises a Co(II) surface precipitate with relatively large number of layers as it is the case for the sample with the maximum Co content. The application of the nta-pvi technique resulted to very low values for the ratios mentioned above. This is because the [Co(Il)-nta](-) and [Co(Il)-2nta](4-) complexes, in which the Co(H2O)6 2, complex is completely transformed, are not practically adsorbed on the support surface. Therefore, in the nta-pvi catalysts a precipitated phase containing the [Co(II)-nta](- .) NH4+(or H+) and [Co(II)-2nta](4- .) 4NH(4)(+) (or 4H(+)) complex salts predominates. Upon calcination these are transformed into CO3O4 crystallites of small size, which are moderately interacting with the support surface. This is related with the relatively high Co dispersion, mainly that for the catalytically active species, and thus with high catalytic activity. © 2004 Elsevier B.V. All rights reserved.
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2004
K Bourikas, C Fountzoula, C Kordulis (2004)  Monolayer transition metal supported on titania catalysts for the selective catalytic reduction of NO by NH3   APPLIED CATALYSIS B-ENVIRONMENTAL 52: 2. 145-153 SEP 15  
Abstract: Monolayer catalysts were prepared by supporting transition metal ionic (t.m.i.)-oxo species (VOx, CrOx, MoOx and WOx) on the TiO2 (anatase) surface using the equilibrium-deposition-filtration (EDF) technique. The prepared samples were characterized by N-2 adsorption, UV/Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and tested for the selective catalytic reduction of NO by NH3 (NH3-SCR) in the temperature range 250-450 degreesC. Using the EDF method the transition metal ion (V, Cr, Mo or W) loading of the supported Titania catalysts achieved at monolayer coverage follows the order V > Mo > W > Cr. It is mainly determined by the deposition of polymeric t.m.i.-oxo species on the surface of titania in the impregnation step. The activity of the corresponding monolayers follows the order V > Cr > Mo > W. It was also demonstrated that the activity of the above catalysts correlates well with the intensity of a DRS absorption band appearing at ca. 400 nm. The intensity of this absorption band, which is considered as a measure of the extent of interactions exerted between the active phase and the support surface, depends on the kind and the amount of the transition metal. (C) 2004 Elsevier B.V. All rights reserved.
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K Bourikas, C Fountzoula, C Kordulis (2004)  Monolayer binary active phase (Mo-V) and (Cr-V) supported on titania catalysts for the selective catalytic reduction (SCR) of NO by NH3   LANGMUIR 20: 24. 10663-10669 NOV 23  
Abstract: Monolayer catalysts containing binary active phases (VOx-CrOx, VOx-MoOx,) were prepared by simultaneous deposition of the corresponding transition metal-oxo species on the TiO2 (anatase) surface using the equilibrium deposition filtration technique. The prepared samples contained various amounts of each transition metal but almost the same total metal loading. They were characterized by atomic absorption spectroscopy, N-2 adsorption, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and tested for the selective catalytic reduction of NO by NH3 in the temperature range 250-450 degreesC. It was found that the transition-metal ionic species used for the preparation of these catalysts compete for the same surface sites of the TiO2 carrier upon co-deposition. Small amounts of the second phase (Mo- or Cr-oxo phase) are sufficient in order to promote the catalytic activity at relatively high temperatures, in contrast to what happens in the corresponding industrial catalysts prepared by conventional methods. An electronic interaction between V- and Cr-oxo species favored at a V/Cr atomic ratio around 3 is probably responsible for the relatively high catalytic performance of the corresponding TiCrV catalyst. The activity of the studied catalysts is well correlated with the intensity of a DRS absorption band that appeared at ca. 400 nm, which is considered as a measure of the magnitude of interactions exerted between the monolayer transition metal-oxo species and the TiO2 carrier. This correlation is independent of the transition metals combination used and follows the same linear relationship found previously for single-active-phase catalysts.
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2002
C Fountzoula, N Spanos, H K Matralis, C Kordulis (2002)  Molybdenum-titanium oxide catalysts : the influence of the preparation conditions on their activity for the selective catalytic reduction of NO by NH3   APPLIED CATALYSIS B-ENVIRONMENTAL 35: 4. 295-304 JAN 25  
Abstract: MoO3/TiO2 catalysts of varying molybdenum content were prepared at various pHs and concentrations of the impregnating solution using the equilibrium deposition filtration (EDF) method. Moreover, a catalyst corresponding to the EDF one with the maximum Mo loading was prepared using the conventional non-dry impregnation (NDI) method. The above catalysts were characterized using X-ray powder analysis, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy, and tested for the selective catalytic reduction of NO by NH3 in the temperature range 250-450degreesC. It was found that the application of EDF results in an improved MoO3/TiO2 catalyst exhibiting higher activity than the corresponding sample prepared by the conventional NDI method. The catalytic activity correlates well with the concentration of the Mo species strongly interacting with the anatase surface. The concentration of the above species is maximized when the EDF method is employed to prepare the catalysts. This is especially, so when low pH and Mo concentration of impregnating solution are used. (C) 2002 Elsevier Science B.V. All rights reserved.
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I Giakoumelou, C Fountzoula, C Kordulis, S Boghosian (2002)  NO reduction with NH3 over chromia-vanadia catalysts supported on TiO2 : an in situ Raman spectroscopic study   CATALYSIS TODAY 73: 3-4. 255-262 APR 15  
Abstract: In situ Raman spectroscopy was used for studying the ternary 2% CrO3-6% V2O5/TiO2 catalyst, for which a synergistic effect between vanadia and chromia leads to enhanced catalytic performance for the selective catalytic reduction (SCR) of NO with NH3. The structural properties of this catalyst were studied under NH3/NO/O-2/N-2/SO2/H2O atmospheres at temperatures up to 400degreesC and major structural interactions between the surface chromia and vanadia species are observed. The effects of oxygen, ammonia, water vapor and sulfur dioxide presence on the in situ Raman spectra are presented and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
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2001
C Kordulis, A A Lappas, C Fountzoula, K Drakaki, A Lycourghiotis, I A Vasalos (2001)  NiW/gamma-Al2O3 catalysts prepared by modified equilibrium deposition filtration (MEDF) and non-dry impregnation (NDI) - Characterization and catalytic activity evaluation for the production of low sulfur gasoline in a HDS pilot plant   APPLIED CATALYSIS A-GENERAL 209: 1-2. 85-95 FEB 28  
Abstract: The aim of this study was to investigate the desulfurization of fluid catalytic cracking (FCC) gasoline using NiW supported on gamma -Al2O3 catalysts prepared by conventional non-dry impregnation (NDI) method and a new one, the equilibrium deposition filtration, (EDF). The latter has been modified (MEDF) to produce the required catalyst quantity for its evaluation in a hydrodesulfurization (HDS) pilot plant. The modification of the typical EDF method showed that it is possible to apply the principles of this technique for practical catalyst preparations. In the first part of this work, the catalyst preparation methodology and the catalyst characterization results are presented. In the second part, the catalyst evaluation is described, in relation to a commercial catalyst, concerning their HDS, hydrogenation (HYG) and isomerization (ISO) activities. The main conclusion of this study was that the MEDF method is more promising than the conventional NDI method for preparing NiW hydrotreatment catalysts. The catalyst prepared by MEDF exhibited higher HDS activity than that of the NDI one, comparable to that of a commercial CoMo catalyst and the highest HYG and ISO activities. The enhanced catalytic activity of the NiW-MEDF catalyst was attributed to the high dispersity of the supported phases achieved by the corresponding preparation method. (C) 2001 Elsevier Science B.V. All rights reserved.
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1999
C Fountzoula, H K Matralis, C Papadopoulou, G A Voyiatzis, C Kordulis (1999)  Chromia-vanadia catalysts supported on TiO2 : Effect of composition on the physicochemical properties and catalytic performance for the selective catalytic reduction of NO with NH3   JOURNAL OF CATALYSIS 184: 1. 5-18 MAY 15  
Abstract: Chromia-vanadia on titania catalysts containing 8 mol% (Cr + V) were prepared and tested for the selective catalytic reduction (SCR) of NO by NH3, in excess O-2, in the temperature range 250-450 degrees C. The physicochemical properties of the prepared catalysts as well as those of the corresponding single active phase-containing samples were investigated by specific surface area and pore volume measurements, X-ray powder analysis, UV-visible diffuse reflectance spectroscopy, laser-Raman microscopy, X-ray photoelectron spectroscopy, analytical electron microscopy, and temperature-programmed reduction experiments, The best catalytic performance was achieved by the catalyst containing 2 mol% Cr and 6 mol% V (TiCr2V6), while all the binary active phase-containing catalysts proved to be more active than the corresponding single active phase-containing catalysts, at reaction temperatures higher than 350 degrees C, The enhanced catalytic performance of the binary active phase-containing catalysts is attributed to a synergy developed between the two active phases, This synergy is maximized in the TiCr2V6 sample, where a new Raman band, at 971 cm(-1) has also been observed, This peak is attributed to isolated Cr6+ species decorated by well-dispersed V5+ species. Deposition of the chromia phase on the titania surface stabilizes the texture of the final catalysts against changes provoked by deposition of the vanadia phase. (C) 1999 Academic Press.
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1997
C Fountzoula, H K Matralis, C Papadopoulou, G A Voyiatzis, C Kordulis (1997)  The influence of the chromium content on the physicochemical properties and the catalytic behavior of CrOx/TiO2 catalysts for the selective catalytic reduction of nitric oxide by ammonia at relatively high temperatures   JOURNAL OF CATALYSIS 172: 2. 391-405 DEC  
Abstract: Chromia on titania catalysts containing chromium loading ranged from 0 up to 8 mol% Cr have been prepared and calcined at high temperature (500 degrees C). These catalysts have been tested for the selective catalytic reduction of NO by NH3 in excess of O-2 at relatively high reaction temperatures (250-450 degrees C). The physicochemical properties of the prepared samples have been investigated by specific surface area and pore volume measurements, X-ray powder analysis, UV-visible diffuse reflectance spectroscopy, laser-Raman microscopy, X-ray photoelectron spectroscopy, analytical electron microscopy, and temperature programmed reduction experiments. The best catalytic performance has been found for the catalyst containing the lowest amount of active phase (2 mol% Cr). The relatively high catalytic performance of this catalyst has been attributed to the isolated Cr-(vi) surface species strongly interacting with the anatase surface. In fact the physicochemical characterization mentioned above showed that these species are predominant at this low Cr-loading. Increase in the Cr-loading has been found to favor the formation of badly dispersed chromia phases with lower oxidation states. Besides the title reaction, the direct oxidation of NH3 by O-2 and the reaction of NH3 with NO producing N2O take also place at intermediate reaction temperatures (250-350 degrees C). At elevated reaction temperatures (400-450 degrees C) the direct oxidation of NH3 was found to be significant. (C) 1997 Academic Press.
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