George Avgouropoulos - Academia.edu (original) (raw)

Papers by George Avgouropoulos

Applied Catalysis B: Environmental, 2006

The reduction of NO by CO + H 2 in the presence of excess O 2 has been studied on dispersed, low ... more The reduction of NO by CO + H 2 in the presence of excess O 2 has been studied on dispersed, low loading 0.5 wt.% Pd-based catalysts. Two different methods of promotion were imposed separately and together, in order to investigate the feasibility of their synergy to enhance de-NO x efficiency of the catalytic system. Therefore, the Pd-catalysed NO + CO + H 2 + O 2 reaction was gradually studied over: (i) Pd/Al 2 O 3 -(TiO 2 ) catalysts (support-mediated promotion by modifying the Al 2 O 3 support with TiO 2 ), (ii) K-dosed Pd(K)/Al 2 O 3 catalysts (surface-induced promotion by modifying the Pd surface with the addition of K), and (iii) doubly-promoted Pd(K)/Al 2 O 3 -(TiO 2 ) catalysts. Both (i) and (ii) methods of promotion were found to significantly promote the system, when acting individually. However, the de-NO x efficiency and N 2 -selectivity of the doubly-promoted Pd(K)/Al 2 O 3 -(TiO 2 ) catalysts were found to be better than both of the other two cases, indicating a synergy during the simultaneous imposition of the two methods of promotion. The resulted benefits with the optimal doubly-promoted catalyst were very high, 8585%, NO x conversion in a very wide temperature range (100-400 8C), accompanied by very good N 2 -selectivities of 8585%, i.e., 15-30 additional percentage units in comparison to the selectivity of the original un-promoted Pd/Al 2 O 3 catalyst. #

Catalysis Today, 2002

Three different catalysts, namely Pt/γ-Al2O3, Au/α-Fe2O3 and CuO–CeO2 were prepared (by wet impre... more Three different catalysts, namely Pt/γ-Al2O3, Au/α-Fe2O3 and CuO–CeO2 were prepared (by wet impregnation, coprecipitation and a sol–gel method, respectively) and their catalytic performance for the selective oxidation of carbon monoxide in the presence of excess hydrogen was evaluated and compared. The effects of the presence of CO2 and H2O in the reactant feed on the activity and selectivity of these catalysts, as well as their stability under realistic reaction conditions were also investigated.Regardless of whether CO2 or both CO2 and H2O are present in the reactant feed, the Au/α-Fe2O3 catalyst is superior to the other two for the selective CO oxidation at relatively low reaction temperatures (<80–120°C, depending on contact time and feed composition employed), while at higher reaction temperatures, best results are obtained with the CuO–CeO2 catalyst, which proved to be more active and remarkably more selective than the Pt/γ-Al2O3 catalyst. The Au/α-Fe2O3 catalyst was the most sensitive, while the Pt/γ-Al2O3 the most resistant towards deactivation caused by the presence of CO2 and H2O in the feed. Finally, while the Au/α-Fe2O3 catalyst lost a considerable portion of its activity during the first 80h under reaction conditions, the CuO–CeO2 and Pt/γ-Al2O3 catalysts exhibited a stable catalytic performance, at least during the time period tested in this work (7–8 days).

Catalysis Letters, 2001

A series of mixed oxide CuO–CeO2 catalysts were prepared by coprecipitation and tested for the se... more A series of mixed oxide CuO–CeO2 catalysts were prepared by coprecipitation and tested for the selective oxidation of carbon monoxide in the presence of excess hydrogen. These catalysts were found to be very active and exceptionally selective for this reaction and exhibited a good resistance towards CO2 and H2O. The catalytic performance of these non-noble metal containing catalysts is compared with that of other selective CO oxidation catalysts reported in literature.

Applied Catalysis A: General, 2015

Formic acid (FA) represents a convenient H 2 -source/storage material. Herein, we introduce two h... more Formic acid (FA) represents a convenient H 2 -source/storage material. Herein, we introduce two highly efficient heterogeneous catalysts for H 2 -generation from FA, Fe II /RPPh 2 @SiO 2 and Fe II /polyRPhphos@SiO 2 , prepared by covalently immobilizing Fe II -phosphine-complexes on SiO 2 particles. EPR shows that in both the homogeneous and the heterogenized system the Fe atom has similar ligand-field parameters, which indicate a moderately-tight coordination of the Fe atom (D = 0.455 cm −1 ) that allows rapid substrate accessibility. Heterogenization of the-commonly used -Fe II /P(CH 2 CH 2 PPh 2 ) 3 system, increased its TOF by 170% vs. the homogeneous catalyst. Remarkably, Fe II /RPPh 2 @SiO 2 is able to generate up to 14 lt of H 2 within 6 h while homogeneous Fe II /RPPh 2 was totally inactive. Both heterogeneous catalysts are able to produce H 2 from FA at near-ambient temperatures (55-90 • C) with no co-catalyst added, with high selectivity and activity, and show excellent stability and reusability.

Catalysis Communications, 2009

Methanol decomposition reaction was studied over combustion-synthesized noble metal (Pt, Pd, Rh)/... more Methanol decomposition reaction was studied over combustion-synthesized noble metal (Pt, Pd, Rh)/ ceria catalysts using the steady-state isotopic transient kinetic analysis (SSITKA) method. The 13 C-containing reactants and products were monitored following a 12 CH 3 OH/Ar/He ? 13 CH 3 OH/He switch. Average life-time and concentration of adsorbed intermediate species which lead to CO, and overall reaction rate at 220°C, were determined. Significant amounts of active intermediate species were formed on the ceria support or/and metal-ceria interface. A clear concave shape of the curve of the semilogarithmic plot of the molar fraction of CO versus time was indicative of a parallel mechanism followed for its formation.

RSC Catalysis Series, 2013

Appl Catal B Environ, 2005

In this work we report on the influence of the preparation method on the physicochemical and cata... more In this work we report on the influence of the preparation method on the physicochemical and catalytic properties of CuO–CeO2 catalysts for the selective CO oxidation in simulated reformate gas. Four CuO–CeO2 samples were prepared using the co-precipitation, the citrate-hydrothermal, the urea-nitrates combustion, and the impregnation methods, and characterized by N2 adsorption–desorption, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by H2 (TPR-H2).The combustion-prepared sample exhibited the best catalytic performance, closely followed by that prepared with the citrate-hydrothermal method. The co-precipitated sample was less active followed by the impregnated one. The activity of all samples decreases in the presence of CO2 and, to a higher degree, in the simultaneous presence of both CO2 and H2O in the feed. The resistance to this deactivation was higher in the case of the sample prepared by the urea-nitrates combustion method, which remained the most active and selective, closely followed by the specimen prepared by the citrate-hydrothermal method. The superior catalytic performance of the samples prepared by the urea-nitrates combustion and the citrate-hydrothermal methods is attributed to the existence of well dispersed, strongly interacting with the ceria surface, copper oxide species.

Applied Catalysis B Environmental, May 1, 2006

ABSTRACT

Bulgarian Chemical Communications, 2008

Applied Catalysis B Environmental, Jul 1, 2006

ABSTRACT The combustion method was employed for the in situ synthesis of nanocrystalline Cu-Ce-O ... more ABSTRACT The combustion method was employed for the in situ synthesis of nanocrystalline Cu-Ce-O and Cu-Mn-O catalyst layers on Al metal foam, without the need of binder or additional calcination steps. Copper-manganese spinel oxides have been proposed as a catalytic system for hydrogen production via methanol steam reforming, while CuO-CeO2 catalysts have been successfully examined for CO removal from reformed fuels via selective oxidation. In this work, the performance of these catalysts supported on Al metal foam has been investigated in the reactions of methanol reforming and selective CO oxidation. The Cu-Ce-O foam catalyst exhibited similar catalytic performance to the one of the powder catalyst in the selective oxidation of CO. The performance of the Cu-Mn-O foam catalyst in the steam reforming of methanol was inferior to the one of the powder catalyst at intermediate conversion levels, but almost complete conversion of methanol was obtained at the same temperature with both foam and powder catalysts.

Journal of Power Sources, 2015

Abstracts: * Avgouropoulos_Methanol Reforming over Pt-TiO2-CeO2 nanostructures.pdf (13.3KB) - Upl... more Abstracts: * Avgouropoulos_Methanol Reforming over Pt-TiO2-CeO2 nanostructures.pdf (13.3KB) - Uploading Abstracts

Studies in Surface Science and Catalysis, 2001

ABSTRACT This chapter examines surface acidity and catalytic activity of cobalt (Co) and magnesiu... more ABSTRACT This chapter examines surface acidity and catalytic activity of cobalt (Co) and magnesium (Mg) incorporated and impregnated in AlPO4-34 with ammonia adsorption, temperature-programmed desorption (TPD) and with the reaction of carbon monoxide (CO) oxidation. Incorporation of Co in the framework of A1PO4-34 leads to the enhancement of surface acidity and to the formation of strong acid sites while in MnAPO-34 this effect is less pronounced. Samples with extraframework Co and Mg possess weak acid centres. CoAPO-34 is one to two orders of magnitude more active than Co/A1PO4-34 while Me/A1PO4-34 and MnAPO-34 are almost inactive in the reaction of CO oxidation.

Journal of Molecular Catalysis A: Chemical, 2008

ABSTRACT

Journal of Catalysis, 2004

The characterization of manganese-lanthanum oxides modified with silver has been performed in ord... more The characterization of manganese-lanthanum oxides modified with silver has been performed in order to identify factors responsible for the variation of their activity in the oxidation of methane. A significant increase in the activity per unit surface area in silver-containing catalysts occurred above 800 K, where a new source of surface oxygen appeared. It is probably oxygen released from filled oxygen vacancies, more weakly bound in the oxides structure in comparison with lattice oxide ions, more mobile, and therefore easily accessible to methane oxidation. Such oxygen is probably neighboring with silver ions. The remaining part of the catalyst may constitute a reservoir of oxygen ions with which the vacancies are filled and which is supplemented with the gaseous oxygen. A consequence of filling up oxygen vacancies is the appearance of a larger number of manganese ions in the unstable oxidation state Mn 4+ . The rate of methane oxidation is a function of the Mn 4+ /Mn 3+ surface ratio which is a parameter characterizing the intrinsic properties of the manganese-lanthanum oxides, influencing their activity.  2004 Elsevier Inc. All rights reserved.

Journal of Catalysis, 2007

Cu-Mn spinel oxide catalysts were synthesized by the combustion method, and their behavior in the... more Cu-Mn spinel oxide catalysts were synthesized by the combustion method, and their behavior in the combined steam reforming of methanol was examined. It was found that despite their low surface areas, these catalysts had comparable activity to that of a commercial Cu-Zn-Al catalyst for the production of H 2 via (combined) steam reforming of methanol. The fresh Cu-Mn catalysts were composed of the spinel phase Cu 1.5 Mn 1.5 O 4 , as well as Mn 2 O 3 and CuO, depending on the Cu/Mn ratio, and were reduced to Cu 0 and MnO under reaction conditions. XPS analysis revealed the presence of two different oxidation states in both copper (Cu 2+ and Cu + ) and manganese (Mn 4+ and Mn 3+ ) in fresh catalysts and decomposition of the spinel in used catalysts. The optimal catalyst was prepared with a Cu/(Cu + Mn) ratio of 0.30. At a higher copper content (x = 0.40, 0.50), the excess copper was not incorporated into the spinel but instead was present as a separate CuO phase. A transient reduction/oxidation behavior was noted in the course of successive TPR/TPO cycles, as the efficiency of spinel reformation during oxidation of the reduced catalyst gradually diminished. The amount of CO produced from reforming was well below water-gas shift equilibrium, indicating that CO 2 was the primary product, whereas CO was produced by the reverse water-gas shift reaction. TPO measurements after methanol-reforming runs indicated only minimal carbon deposition.

International Journal of Hydrogen Energy, 2014

Keywords: Methanol reformer Hydrogen Copper catalyst High temperature PEM fuel cell Internal refo... more Keywords: Methanol reformer Hydrogen Copper catalyst High temperature PEM fuel cell Internal reforming a b s t r a c t

International Journal of Hydrogen Energy, 2012

ABSTRACT

Applied Catalysis B: Environmental, 2006

The reduction of NO by CO + H 2 in the presence of excess O 2 has been studied on dispersed, low ... more The reduction of NO by CO + H 2 in the presence of excess O 2 has been studied on dispersed, low loading 0.5 wt.% Pd-based catalysts. Two different methods of promotion were imposed separately and together, in order to investigate the feasibility of their synergy to enhance de-NO x efficiency of the catalytic system. Therefore, the Pd-catalysed NO + CO + H 2 + O 2 reaction was gradually studied over: (i) Pd/Al 2 O 3 -(TiO 2 ) catalysts (support-mediated promotion by modifying the Al 2 O 3 support with TiO 2 ), (ii) K-dosed Pd(K)/Al 2 O 3 catalysts (surface-induced promotion by modifying the Pd surface with the addition of K), and (iii) doubly-promoted Pd(K)/Al 2 O 3 -(TiO 2 ) catalysts. Both (i) and (ii) methods of promotion were found to significantly promote the system, when acting individually. However, the de-NO x efficiency and N 2 -selectivity of the doubly-promoted Pd(K)/Al 2 O 3 -(TiO 2 ) catalysts were found to be better than both of the other two cases, indicating a synergy during the simultaneous imposition of the two methods of promotion. The resulted benefits with the optimal doubly-promoted catalyst were very high, 8585%, NO x conversion in a very wide temperature range (100-400 8C), accompanied by very good N 2 -selectivities of 8585%, i.e., 15-30 additional percentage units in comparison to the selectivity of the original un-promoted Pd/Al 2 O 3 catalyst. #

Catalysis Today, 2002

Three different catalysts, namely Pt/γ-Al2O3, Au/α-Fe2O3 and CuO–CeO2 were prepared (by wet impre... more Three different catalysts, namely Pt/γ-Al2O3, Au/α-Fe2O3 and CuO–CeO2 were prepared (by wet impregnation, coprecipitation and a sol–gel method, respectively) and their catalytic performance for the selective oxidation of carbon monoxide in the presence of excess hydrogen was evaluated and compared. The effects of the presence of CO2 and H2O in the reactant feed on the activity and selectivity of these catalysts, as well as their stability under realistic reaction conditions were also investigated.Regardless of whether CO2 or both CO2 and H2O are present in the reactant feed, the Au/α-Fe2O3 catalyst is superior to the other two for the selective CO oxidation at relatively low reaction temperatures (<80–120°C, depending on contact time and feed composition employed), while at higher reaction temperatures, best results are obtained with the CuO–CeO2 catalyst, which proved to be more active and remarkably more selective than the Pt/γ-Al2O3 catalyst. The Au/α-Fe2O3 catalyst was the most sensitive, while the Pt/γ-Al2O3 the most resistant towards deactivation caused by the presence of CO2 and H2O in the feed. Finally, while the Au/α-Fe2O3 catalyst lost a considerable portion of its activity during the first 80h under reaction conditions, the CuO–CeO2 and Pt/γ-Al2O3 catalysts exhibited a stable catalytic performance, at least during the time period tested in this work (7–8 days).

Catalysis Letters, 2001

A series of mixed oxide CuO–CeO2 catalysts were prepared by coprecipitation and tested for the se... more A series of mixed oxide CuO–CeO2 catalysts were prepared by coprecipitation and tested for the selective oxidation of carbon monoxide in the presence of excess hydrogen. These catalysts were found to be very active and exceptionally selective for this reaction and exhibited a good resistance towards CO2 and H2O. The catalytic performance of these non-noble metal containing catalysts is compared with that of other selective CO oxidation catalysts reported in literature.

Applied Catalysis A: General, 2015

Formic acid (FA) represents a convenient H 2 -source/storage material. Herein, we introduce two h... more Formic acid (FA) represents a convenient H 2 -source/storage material. Herein, we introduce two highly efficient heterogeneous catalysts for H 2 -generation from FA, Fe II /RPPh 2 @SiO 2 and Fe II /polyRPhphos@SiO 2 , prepared by covalently immobilizing Fe II -phosphine-complexes on SiO 2 particles. EPR shows that in both the homogeneous and the heterogenized system the Fe atom has similar ligand-field parameters, which indicate a moderately-tight coordination of the Fe atom (D = 0.455 cm −1 ) that allows rapid substrate accessibility. Heterogenization of the-commonly used -Fe II /P(CH 2 CH 2 PPh 2 ) 3 system, increased its TOF by 170% vs. the homogeneous catalyst. Remarkably, Fe II /RPPh 2 @SiO 2 is able to generate up to 14 lt of H 2 within 6 h while homogeneous Fe II /RPPh 2 was totally inactive. Both heterogeneous catalysts are able to produce H 2 from FA at near-ambient temperatures (55-90 • C) with no co-catalyst added, with high selectivity and activity, and show excellent stability and reusability.

Catalysis Communications, 2009

Methanol decomposition reaction was studied over combustion-synthesized noble metal (Pt, Pd, Rh)/... more Methanol decomposition reaction was studied over combustion-synthesized noble metal (Pt, Pd, Rh)/ ceria catalysts using the steady-state isotopic transient kinetic analysis (SSITKA) method. The 13 C-containing reactants and products were monitored following a 12 CH 3 OH/Ar/He ? 13 CH 3 OH/He switch. Average life-time and concentration of adsorbed intermediate species which lead to CO, and overall reaction rate at 220°C, were determined. Significant amounts of active intermediate species were formed on the ceria support or/and metal-ceria interface. A clear concave shape of the curve of the semilogarithmic plot of the molar fraction of CO versus time was indicative of a parallel mechanism followed for its formation.

RSC Catalysis Series, 2013

Appl Catal B Environ, 2005

In this work we report on the influence of the preparation method on the physicochemical and cata... more In this work we report on the influence of the preparation method on the physicochemical and catalytic properties of CuO–CeO2 catalysts for the selective CO oxidation in simulated reformate gas. Four CuO–CeO2 samples were prepared using the co-precipitation, the citrate-hydrothermal, the urea-nitrates combustion, and the impregnation methods, and characterized by N2 adsorption–desorption, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by H2 (TPR-H2).The combustion-prepared sample exhibited the best catalytic performance, closely followed by that prepared with the citrate-hydrothermal method. The co-precipitated sample was less active followed by the impregnated one. The activity of all samples decreases in the presence of CO2 and, to a higher degree, in the simultaneous presence of both CO2 and H2O in the feed. The resistance to this deactivation was higher in the case of the sample prepared by the urea-nitrates combustion method, which remained the most active and selective, closely followed by the specimen prepared by the citrate-hydrothermal method. The superior catalytic performance of the samples prepared by the urea-nitrates combustion and the citrate-hydrothermal methods is attributed to the existence of well dispersed, strongly interacting with the ceria surface, copper oxide species.

Applied Catalysis B Environmental, May 1, 2006

ABSTRACT

Bulgarian Chemical Communications, 2008

Applied Catalysis B Environmental, Jul 1, 2006

ABSTRACT The combustion method was employed for the in situ synthesis of nanocrystalline Cu-Ce-O ... more ABSTRACT The combustion method was employed for the in situ synthesis of nanocrystalline Cu-Ce-O and Cu-Mn-O catalyst layers on Al metal foam, without the need of binder or additional calcination steps. Copper-manganese spinel oxides have been proposed as a catalytic system for hydrogen production via methanol steam reforming, while CuO-CeO2 catalysts have been successfully examined for CO removal from reformed fuels via selective oxidation. In this work, the performance of these catalysts supported on Al metal foam has been investigated in the reactions of methanol reforming and selective CO oxidation. The Cu-Ce-O foam catalyst exhibited similar catalytic performance to the one of the powder catalyst in the selective oxidation of CO. The performance of the Cu-Mn-O foam catalyst in the steam reforming of methanol was inferior to the one of the powder catalyst at intermediate conversion levels, but almost complete conversion of methanol was obtained at the same temperature with both foam and powder catalysts.

Journal of Power Sources, 2015

Abstracts: * Avgouropoulos_Methanol Reforming over Pt-TiO2-CeO2 nanostructures.pdf (13.3KB) - Upl... more Abstracts: * Avgouropoulos_Methanol Reforming over Pt-TiO2-CeO2 nanostructures.pdf (13.3KB) - Uploading Abstracts

Studies in Surface Science and Catalysis, 2001

ABSTRACT This chapter examines surface acidity and catalytic activity of cobalt (Co) and magnesiu... more ABSTRACT This chapter examines surface acidity and catalytic activity of cobalt (Co) and magnesium (Mg) incorporated and impregnated in AlPO4-34 with ammonia adsorption, temperature-programmed desorption (TPD) and with the reaction of carbon monoxide (CO) oxidation. Incorporation of Co in the framework of A1PO4-34 leads to the enhancement of surface acidity and to the formation of strong acid sites while in MnAPO-34 this effect is less pronounced. Samples with extraframework Co and Mg possess weak acid centres. CoAPO-34 is one to two orders of magnitude more active than Co/A1PO4-34 while Me/A1PO4-34 and MnAPO-34 are almost inactive in the reaction of CO oxidation.

Journal of Molecular Catalysis A: Chemical, 2008

ABSTRACT

Journal of Catalysis, 2004

The characterization of manganese-lanthanum oxides modified with silver has been performed in ord... more The characterization of manganese-lanthanum oxides modified with silver has been performed in order to identify factors responsible for the variation of their activity in the oxidation of methane. A significant increase in the activity per unit surface area in silver-containing catalysts occurred above 800 K, where a new source of surface oxygen appeared. It is probably oxygen released from filled oxygen vacancies, more weakly bound in the oxides structure in comparison with lattice oxide ions, more mobile, and therefore easily accessible to methane oxidation. Such oxygen is probably neighboring with silver ions. The remaining part of the catalyst may constitute a reservoir of oxygen ions with which the vacancies are filled and which is supplemented with the gaseous oxygen. A consequence of filling up oxygen vacancies is the appearance of a larger number of manganese ions in the unstable oxidation state Mn 4+ . The rate of methane oxidation is a function of the Mn 4+ /Mn 3+ surface ratio which is a parameter characterizing the intrinsic properties of the manganese-lanthanum oxides, influencing their activity.  2004 Elsevier Inc. All rights reserved.

Journal of Catalysis, 2007

Cu-Mn spinel oxide catalysts were synthesized by the combustion method, and their behavior in the... more Cu-Mn spinel oxide catalysts were synthesized by the combustion method, and their behavior in the combined steam reforming of methanol was examined. It was found that despite their low surface areas, these catalysts had comparable activity to that of a commercial Cu-Zn-Al catalyst for the production of H 2 via (combined) steam reforming of methanol. The fresh Cu-Mn catalysts were composed of the spinel phase Cu 1.5 Mn 1.5 O 4 , as well as Mn 2 O 3 and CuO, depending on the Cu/Mn ratio, and were reduced to Cu 0 and MnO under reaction conditions. XPS analysis revealed the presence of two different oxidation states in both copper (Cu 2+ and Cu + ) and manganese (Mn 4+ and Mn 3+ ) in fresh catalysts and decomposition of the spinel in used catalysts. The optimal catalyst was prepared with a Cu/(Cu + Mn) ratio of 0.30. At a higher copper content (x = 0.40, 0.50), the excess copper was not incorporated into the spinel but instead was present as a separate CuO phase. A transient reduction/oxidation behavior was noted in the course of successive TPR/TPO cycles, as the efficiency of spinel reformation during oxidation of the reduced catalyst gradually diminished. The amount of CO produced from reforming was well below water-gas shift equilibrium, indicating that CO 2 was the primary product, whereas CO was produced by the reverse water-gas shift reaction. TPO measurements after methanol-reforming runs indicated only minimal carbon deposition.

International Journal of Hydrogen Energy, 2014

Keywords: Methanol reformer Hydrogen Copper catalyst High temperature PEM fuel cell Internal refo... more Keywords: Methanol reformer Hydrogen Copper catalyst High temperature PEM fuel cell Internal reforming a b s t r a c t

International Journal of Hydrogen Energy, 2012

ABSTRACT