Theophilos Ioannides | Foundation for Research and Technology - Hellas (original) (raw)

Papers by Theophilos Ioannides

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).

Applied Catalysis B: Environmental, 2011

Ce-Fe mixed oxides were prepared by urea gelation coprecipitation method and used as supports of ... more Ce-Fe mixed oxides were prepared by urea gelation coprecipitation method and used as supports of gold catalysts. The impact of the support composition on the catalytic performance for the preferential CO oxidation (PROX) was studied by varying the Ce/(Ce + Fe) ratio. A deep characterization study by different tools such as XRD, HRTEM, TPR and FTIR spectroscopy was undertaken in order to correlate the structural characteristics of the catalysts and the gold oxidation state and dispersion with the catalytic properties. The results revealed that the variation of the support composition led to significant differences in the gold particles size (in the range 1-25 nm), which affected strongly the CO oxidation activity of Au/CeO 2 -Fe 2 O 3 catalysts under PROX conditions. The following activity order was observed: Au/CeO 2 ≈ Au/Ce50Fe50 > Au/Ce75Fe25 > Au/Ce25Fe75 > Au/Fe 2 O 3 . The support with composition 50 wt.% CeO 2 -50 wt.% Fe 2 O 3 appeared beneficial not only for nucleation and growth of highly dispersed gold particles (1-1.8 nm), but also for activation of oxygen and its mobility. Moreover, the presence of Fe 2 O 3 in the supports composition improved the resistance towards deactivation by CO 2 . The CeO 2 -Fe 2 O 3 supports comprised different amount of two phases: cubic CeO 2 -like solid solution and hematite. The analysis of the characterization data suggested that the solid solution formation probably proceeded via a dopant interstitial compensation mechanism.

Applied Catalysis B-environmental, 2009

Applied Catalysis B-environmental, 2008

Applied Catalysis B-environmental, 2007

ABSTRACT Steam reforming of methanol was carried out over a series of doped CuO–CeO2 catalysts pr... more ABSTRACT Steam reforming of methanol was carried out over a series of doped CuO–CeO2 catalysts prepared via the urea–nitrate combustion method. XRD analysis showed that at least part of the dopant cations enter the ceria lattice. The addition of various metal oxide dopants in the catalyst composition affected in a different way the catalytic performance towards H2 production. Small amounts of oxides of Sm and Zn improved the performance of CuO–CeO2, while further addition of these oxides caused a decrease in catalyst activity. XPS analysis of Zn- and Sm-doped catalysts showed that increase of dopant loading leads to surface segregation of the dopant and decrease of copper oxide dispersion. The addition of oxides of La, Zr, Mg, Gd, Y or Ca lowered or had no effect on catalytic activity, but led to less CO in the reaction products. Noble-metal modified catalysts had slightly higher activity, but the CO selectivity was also significantly higher.

Applied Catalysis A-general, 2003

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Applied Catalysis B-environmental, 2006

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Catalysis Communications, 2007

This paper presents a study on the role of additives (samaria, lanthana, zirconia, and zinc oxide... more This paper presents a study on the role of additives (samaria, lanthana, zirconia, and zinc oxide) to ceria as a support of copper catalysts for low-temperature WGSR. A single-step urea-combustion procedure was used for preparation of highly active catalysts. The results revealed the beneficial role of Sm 2 O 3 and ZnO doping in increasing BET surface area and total pore volume of the catalysts and decreasing the degree of crystallinity of ceria. TPR profiles evidenced enhanced reducibility of modified catalysts. The WGS activity of these catalysts correlates well with BET, XRD, and TPR data. By comparing the catalysts with a commercial CuO-ZnO-Al 2 O 3 sample we point out the feasibility of using CuO/doped-ceria catalysts for low-temperature WGSR.

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.

Catalysis Communications, 2004

Hydrogen production by (combined) steam reforming of methanol (CSRM) was investigated over CuO-Ce... more Hydrogen production by (combined) steam reforming of methanol (CSRM) was investigated over CuO-CeO 2 catalysts prepared via the urea-combustion method. The characteristics of the resulting oxides were strongly influenced by the autoignition time during synthesis and the sample prepared with near stoichiometric quantity of urea had less favorable catalytic properties. Catalysts prepared from urea-rich or lean mixtures were more active and selective and an optimum behavior was obtained with 75% excess of urea and Cu/(Cu + Ce) ratio equal to 0.15. The higher methanol conversion in the CSRM process may be attributed to more efficient heat transfer in the bed due to combustion of part of methanol.

Catalysis Communications, 2005

The steam reforming of methanol was studied over a series of copper-manganese spinel oxide cataly... more The steam reforming of methanol was studied over a series of copper-manganese spinel oxide catalysts prepared with the ureanitrate combustion method. All catalysts showed high activity towards H 2 production with high selectivity. Synthesis parameters affected catalyst properties and, among the catalysts tested, the one prepared with 75% excess of urea and an atomic ratio Cu/ (Cu + Mn) = 0.30 showed the highest activity. The results show that formation of the spinel Cu x Mn 3 À x O 4 phase in the oxidized catalysts is responsible for the high activity. Cu-Mn catalysts were found to be superior to CuO-CeO 2 catalysts prepared with the same technique.

Chemical Engineering Journal, 2006

In this paper we compare the catalytic performance of ceria-supported gold and copper oxide catal... more In this paper we compare the catalytic performance of ceria-supported gold and copper oxide catalysts for the preferential CO oxidation (PROX) in the presence of excess hydrogen. The catalytic properties are strongly affected by the synthesis procedure, i.e. deposition-precipitation (DP) and modified deposition-precipitation (MDP), mainly in the case of gold. The DP method leads to the preparation of more active PROX catalysts than the MDP one. Highly dispersed and more easily reducible gold or copper oxide species are formed on the catalyst surface and enhance the catalytic activity. Au/ceria catalysts are significantly more active, while CuO/ceria ones are remarkably more selective. The presence of CO 2 and H 2 O causes a significant decrease in the catalytic activity, especially in the case of the gold catalyst. However, this deactivation is fully reversible. Both catalysts exhibit a perfectly constant behaviour with the reaction time.

Applied Catalysis B-environmental, 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.

Applied Catalysis B-environmental, 2005

The catalytic behavior of Pt and Rh catalysts during the gas-phase oxidation of H2–CO mixtures wa... more The catalytic behavior of Pt and Rh catalysts during the gas-phase oxidation of H2–CO mixtures was studied with commercial Pt/C, Pt–Ru/C and Pt–Sn/C electrocatalysts, as well as laboratory prepared catalysts of Pt and Rh supported on various carriers (γ-Al2O3, TiO2, TiO2(WO3), SiO2, WO3, MoO3 and carbon). The goal of this study was to assess the CO-tolerance of the catalysts, i.e.

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, 2008

Effect of addition of vanadium oxide (vanadia) to Rh/SiO 2 in hydroformylation of ethylene and CO... more Effect of addition of vanadium oxide (vanadia) to Rh/SiO 2 in hydroformylation of ethylene and CO hydrogenation was investigated. In the hydroformylation of ethylene, the addition of vanadia enhanced hydroformylation activity and selectivity; especially the selectivity for 1-propanol formation was drastically promoted. The promoting effect was observed more significantly on the catalyst calcined at higher temperature such as 973 K. It is found that the effect is related to the formation of the RhVO 4 phase, and it is suggested that the active site consists of Rh metal and partially reduced VO x , which is formed by the reduction of RhVO 4 . This can make the interaction between Rh and VO x more intimate. This catalyst was also effective for the alcohol formation in CO hydrogenation. Based on the catalyst characterization by means of the adsorption measurements of H 2 and CO, H 2 -D 2 exchange rate under the presence of CO, temperature-programmed desorption (TPD) of CO, temperature-programmed reduction (TPR) with H 2 and temperature-programmed surface reaction (TPSR) of adsorbed CO with H 2 , it is suggested that the sites for H 2 activation, which cannot be inhibited by the presence of CO, play an important role in the promotion of alcohol formation in hydroformylation and CO hydrogenation.

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).

Applied Catalysis B-environmental, 2005

The present paper deals with the study concerning the CO removal from reforming H 2 -rich gas str... more The present paper deals with the study concerning the CO removal from reforming H 2 -rich gas stream through WGS reaction over Rh-based catalysts supported on CeO 2 carriers. CeO 2 was prepared by two different methods: solution combustion synthesis (SCS) and hard template (HT); incipient wetness impregnation method was used to deposit the active metal on the carriers. The screening at powder level in a fixed bed micro-reactor highlighted that feeding 5% CO and 20% H 2 O (N 2 balance) with the HT-prepared catalyst, CO conversion started at slightly lower temperature, but CH 4 outlet concentrations were higher than those of the SCS-prepared one. With a simulated reformate mixture (5% CO + 20% H 2 O + 11% CO 2 + 40% H 2 , N 2 balance), the equilibrium WGS curve was exceeded for both catalysts (for the HT-prepared catalyst, CO conversion started at lower temperature and reached 100%), due to the parasite methanation reactions of both CO and CO 2 , favoured by the presence of a large hydrogen concentration in the reactor. A very high CH 4 outlet concentration (max 18.6%) was measured for the HT-prepared catalyst. Then, tests at different weight space velocities WSV were carried out: with the SCS-prepared catalyst the best performance was obtained by lowering WSV.

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 B-environmental, 2006

ABSTRACT

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).

Applied Catalysis B: Environmental, 2011

Ce-Fe mixed oxides were prepared by urea gelation coprecipitation method and used as supports of ... more Ce-Fe mixed oxides were prepared by urea gelation coprecipitation method and used as supports of gold catalysts. The impact of the support composition on the catalytic performance for the preferential CO oxidation (PROX) was studied by varying the Ce/(Ce + Fe) ratio. A deep characterization study by different tools such as XRD, HRTEM, TPR and FTIR spectroscopy was undertaken in order to correlate the structural characteristics of the catalysts and the gold oxidation state and dispersion with the catalytic properties. The results revealed that the variation of the support composition led to significant differences in the gold particles size (in the range 1-25 nm), which affected strongly the CO oxidation activity of Au/CeO 2 -Fe 2 O 3 catalysts under PROX conditions. The following activity order was observed: Au/CeO 2 ≈ Au/Ce50Fe50 > Au/Ce75Fe25 > Au/Ce25Fe75 > Au/Fe 2 O 3 . The support with composition 50 wt.% CeO 2 -50 wt.% Fe 2 O 3 appeared beneficial not only for nucleation and growth of highly dispersed gold particles (1-1.8 nm), but also for activation of oxygen and its mobility. Moreover, the presence of Fe 2 O 3 in the supports composition improved the resistance towards deactivation by CO 2 . The CeO 2 -Fe 2 O 3 supports comprised different amount of two phases: cubic CeO 2 -like solid solution and hematite. The analysis of the characterization data suggested that the solid solution formation probably proceeded via a dopant interstitial compensation mechanism.

Applied Catalysis B-environmental, 2009

Applied Catalysis B-environmental, 2008

Applied Catalysis B-environmental, 2007

ABSTRACT Steam reforming of methanol was carried out over a series of doped CuO–CeO2 catalysts pr... more ABSTRACT Steam reforming of methanol was carried out over a series of doped CuO–CeO2 catalysts prepared via the urea–nitrate combustion method. XRD analysis showed that at least part of the dopant cations enter the ceria lattice. The addition of various metal oxide dopants in the catalyst composition affected in a different way the catalytic performance towards H2 production. Small amounts of oxides of Sm and Zn improved the performance of CuO–CeO2, while further addition of these oxides caused a decrease in catalyst activity. XPS analysis of Zn- and Sm-doped catalysts showed that increase of dopant loading leads to surface segregation of the dopant and decrease of copper oxide dispersion. The addition of oxides of La, Zr, Mg, Gd, Y or Ca lowered or had no effect on catalytic activity, but led to less CO in the reaction products. Noble-metal modified catalysts had slightly higher activity, but the CO selectivity was also significantly higher.

Applied Catalysis A-general, 2003

ABSTRACT

Applied Catalysis B-environmental, 2006

ABSTRACT

Catalysis Communications, 2007

This paper presents a study on the role of additives (samaria, lanthana, zirconia, and zinc oxide... more This paper presents a study on the role of additives (samaria, lanthana, zirconia, and zinc oxide) to ceria as a support of copper catalysts for low-temperature WGSR. A single-step urea-combustion procedure was used for preparation of highly active catalysts. The results revealed the beneficial role of Sm 2 O 3 and ZnO doping in increasing BET surface area and total pore volume of the catalysts and decreasing the degree of crystallinity of ceria. TPR profiles evidenced enhanced reducibility of modified catalysts. The WGS activity of these catalysts correlates well with BET, XRD, and TPR data. By comparing the catalysts with a commercial CuO-ZnO-Al 2 O 3 sample we point out the feasibility of using CuO/doped-ceria catalysts for low-temperature WGSR.

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.

Catalysis Communications, 2004

Hydrogen production by (combined) steam reforming of methanol (CSRM) was investigated over CuO-Ce... more Hydrogen production by (combined) steam reforming of methanol (CSRM) was investigated over CuO-CeO 2 catalysts prepared via the urea-combustion method. The characteristics of the resulting oxides were strongly influenced by the autoignition time during synthesis and the sample prepared with near stoichiometric quantity of urea had less favorable catalytic properties. Catalysts prepared from urea-rich or lean mixtures were more active and selective and an optimum behavior was obtained with 75% excess of urea and Cu/(Cu + Ce) ratio equal to 0.15. The higher methanol conversion in the CSRM process may be attributed to more efficient heat transfer in the bed due to combustion of part of methanol.

Catalysis Communications, 2005

The steam reforming of methanol was studied over a series of copper-manganese spinel oxide cataly... more The steam reforming of methanol was studied over a series of copper-manganese spinel oxide catalysts prepared with the ureanitrate combustion method. All catalysts showed high activity towards H 2 production with high selectivity. Synthesis parameters affected catalyst properties and, among the catalysts tested, the one prepared with 75% excess of urea and an atomic ratio Cu/ (Cu + Mn) = 0.30 showed the highest activity. The results show that formation of the spinel Cu x Mn 3 À x O 4 phase in the oxidized catalysts is responsible for the high activity. Cu-Mn catalysts were found to be superior to CuO-CeO 2 catalysts prepared with the same technique.

Chemical Engineering Journal, 2006

In this paper we compare the catalytic performance of ceria-supported gold and copper oxide catal... more In this paper we compare the catalytic performance of ceria-supported gold and copper oxide catalysts for the preferential CO oxidation (PROX) in the presence of excess hydrogen. The catalytic properties are strongly affected by the synthesis procedure, i.e. deposition-precipitation (DP) and modified deposition-precipitation (MDP), mainly in the case of gold. The DP method leads to the preparation of more active PROX catalysts than the MDP one. Highly dispersed and more easily reducible gold or copper oxide species are formed on the catalyst surface and enhance the catalytic activity. Au/ceria catalysts are significantly more active, while CuO/ceria ones are remarkably more selective. The presence of CO 2 and H 2 O causes a significant decrease in the catalytic activity, especially in the case of the gold catalyst. However, this deactivation is fully reversible. Both catalysts exhibit a perfectly constant behaviour with the reaction time.

Applied Catalysis B-environmental, 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.

Applied Catalysis B-environmental, 2005

The catalytic behavior of Pt and Rh catalysts during the gas-phase oxidation of H2–CO mixtures wa... more The catalytic behavior of Pt and Rh catalysts during the gas-phase oxidation of H2–CO mixtures was studied with commercial Pt/C, Pt–Ru/C and Pt–Sn/C electrocatalysts, as well as laboratory prepared catalysts of Pt and Rh supported on various carriers (γ-Al2O3, TiO2, TiO2(WO3), SiO2, WO3, MoO3 and carbon). The goal of this study was to assess the CO-tolerance of the catalysts, i.e.

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, 2008

Effect of addition of vanadium oxide (vanadia) to Rh/SiO 2 in hydroformylation of ethylene and CO... more Effect of addition of vanadium oxide (vanadia) to Rh/SiO 2 in hydroformylation of ethylene and CO hydrogenation was investigated. In the hydroformylation of ethylene, the addition of vanadia enhanced hydroformylation activity and selectivity; especially the selectivity for 1-propanol formation was drastically promoted. The promoting effect was observed more significantly on the catalyst calcined at higher temperature such as 973 K. It is found that the effect is related to the formation of the RhVO 4 phase, and it is suggested that the active site consists of Rh metal and partially reduced VO x , which is formed by the reduction of RhVO 4 . This can make the interaction between Rh and VO x more intimate. This catalyst was also effective for the alcohol formation in CO hydrogenation. Based on the catalyst characterization by means of the adsorption measurements of H 2 and CO, H 2 -D 2 exchange rate under the presence of CO, temperature-programmed desorption (TPD) of CO, temperature-programmed reduction (TPR) with H 2 and temperature-programmed surface reaction (TPSR) of adsorbed CO with H 2 , it is suggested that the sites for H 2 activation, which cannot be inhibited by the presence of CO, play an important role in the promotion of alcohol formation in hydroformylation and CO hydrogenation.

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).

Applied Catalysis B-environmental, 2005

The present paper deals with the study concerning the CO removal from reforming H 2 -rich gas str... more The present paper deals with the study concerning the CO removal from reforming H 2 -rich gas stream through WGS reaction over Rh-based catalysts supported on CeO 2 carriers. CeO 2 was prepared by two different methods: solution combustion synthesis (SCS) and hard template (HT); incipient wetness impregnation method was used to deposit the active metal on the carriers. The screening at powder level in a fixed bed micro-reactor highlighted that feeding 5% CO and 20% H 2 O (N 2 balance) with the HT-prepared catalyst, CO conversion started at slightly lower temperature, but CH 4 outlet concentrations were higher than those of the SCS-prepared one. With a simulated reformate mixture (5% CO + 20% H 2 O + 11% CO 2 + 40% H 2 , N 2 balance), the equilibrium WGS curve was exceeded for both catalysts (for the HT-prepared catalyst, CO conversion started at lower temperature and reached 100%), due to the parasite methanation reactions of both CO and CO 2 , favoured by the presence of a large hydrogen concentration in the reactor. A very high CH 4 outlet concentration (max 18.6%) was measured for the HT-prepared catalyst. Then, tests at different weight space velocities WSV were carried out: with the SCS-prepared catalyst the best performance was obtained by lowering WSV.

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 B-environmental, 2006

ABSTRACT