Francisco Ivars-Barceló - Academia.edu (original) (raw)

Papers by Francisco Ivars-Barceló

Research paper thumbnail of Oxidative dehydrogenation of ethane to ethylene and preparation of multimetallic mixed oxide catalyst for such process

Research paper thumbnail of Spectators Control Selectivity in Surface Chemistry: Acrolein Partial Hydrogenation Over Pd

Journal of the American Chemical Society, 2015

We present a mechanistic study on selective hydrogenation of acrolein over model Pd surfaces-both... more We present a mechanistic study on selective hydrogenation of acrolein over model Pd surfaces-both single crystal Pd(111) and Pd nanoparticles supported on a model oxide support. We show for the first time that selective hydrogenation of the C═O bond in acrolein to form an unsaturated alcohol is possible over Pd(111) with nearly 100% selectivity. However, this process requires a very distinct modification of the Pd(111) surface with an overlayer of oxopropyl spectator species that are formed from acrolein during the initial stages of reaction and turn the metal surface selective toward propenol formation. By applying pulsed multimolecular beam experiments and in situ infrared reflection-absorption spectroscopy, we identified the chemical nature of the spectator and the reactive surface intermediate (propenoxy species) and experimentally followed the simultaneous evolution of the reactive intermediate on the surface and formation of the product in the gas phase.

Research paper thumbnail of Selective Oxidation of Propane Over AMoVSbO Catalysts (A = Li, Na, K, Rb or Cs)

Topics in Catalysis, 2008

Alkali metal-containing Mo-V-Sb-O catalysts (AMoVSbO, with A = Li, Na, K, Rb or Cs), prepared hyd... more Alkali metal-containing Mo-V-Sb-O catalysts (AMoVSbO, with A = Li, Na, K, Rb or Cs), prepared hydrothermally and activated at 600°C in N 2 , have been characterized and tested for the selective oxidation of propane. Alkali-doped catalysts resulted to be more selective to acrylic acid and less selective to acetic acid than the corresponding alkali-free Mo-V-Sb-O catalyst. However, the nature of crystalline phases and the catalytic behaviour strongly depend on the alkali metal added. In this way, the catalytic activity decreases as follows: unpromoted [ Li-* Na-* K-[ Rb-[ Cs-containing catalyst. However the selectivity to acrylic acid decreases in the order: K-[ Rb-* Na-[ unpromoted [ Li-[ Cscontaining catalyst. The role of the presence/absence of acid sites and cations on both the nature of crystalline phases and the catalytic performance will be discussed.

Research paper thumbnail of Oxidative dehydrogenation of ethane: A study over the structure and robustness of Ni–W–O catalysts

Fuel Processing Technology

The robustness of one selected Ni–W–O catalyst has been studied in the oxidative dehydrogenation ... more The robustness of one selected Ni–W–O catalyst has been studied in the oxidative dehydrogenation of ethane. This catalyst initially deactivates for the first 10 h online decreasing 15% of its catalytic activity compared to its initial stable catalytic activity. However from 10 to 60 h online the catalytic activity keeps almost stable. On the other hand, it has been shown that the Ni–W–O catalyst cannot tolerate an oxygen-free atmosphere (C2 and He) as nickel oxide is transformed into metallic nickel. Methane and hydrogen as well as abundant coke were formed on the surface of the catalyst in these O-free conditions. However a re-calcination in air leads to the removal of coke, the catalytic performance in the oxidative dehydrogenation of ethane being almost completely restored. Ni–W–O catalysts are active and selective in the oxidative dehydrogenation of ethane. However, their catalytic performance highly depends on the catalyst composition. At the present paper we have prepared Ni–W...

Research paper thumbnail of Selective oxidation of short-chain alkanes over hydrothermally prepared MoVTeNbO catalysts

Topics in Catalysis, 2006

MoVTe-Nb oxide catalysts have been prepared by a hydrothermal method and tested in the selective ... more MoVTe-Nb oxide catalysts have been prepared by a hydrothermal method and tested in the selective oxidation of propane to acrylic acid and in the oxidative dehydrogenation of ethane to ethylene. The influence of the concentration of oxalate anions in the hydrothermal gel has been studied for two series of catalysts, Nb-free and Nb-containing, respectively. Results show that the development of

Research paper thumbnail of Size-Dependent Room Temperature Oxidation of Tin Particles

Particle & Particle Systems Characterization, 2014

ABSTRACT Using transmission electron microscopy, the size-dependent room temperature oxidation of... more ABSTRACT Using transmission electron microscopy, the size-dependent room temperature oxidation of tin nanoparticles is studied. The oxide that forms during room temperature oxidation of Sn particles is amorphous SnO, and it retains this stoichiometry and structure over extended time periods. From the investigation of arrays of Sn nanoparticles with broad size distribution, under identical conditions, the Sn oxide thickness is evaluated as a function of size and oxidation time. The oxide thickness depends strongly on the size of the Sn nanoparticles, which is in excellent agreement with predictions for a Mott–Cabrera model corrected for a non-uniform electric field. The results demonstrate the accelerated oxidation kinetics of nanoscale particles with high curvature, due to the amplified electric field at the interface to a continuously shrinking metal core.

Research paper thumbnail of Oxidative dehydrogenation of ethane over Ni–W–O mixed metal oxide catalysts

Journal of Catalysis, 2011

Nickel tungsten metal oxide catalysts Oxidative dehydrogenation of ethane Ethylene oxidation Cata... more Nickel tungsten metal oxide catalysts Oxidative dehydrogenation of ethane Ethylene oxidation Catalyst characterization XPS TPR XRD Raman FTIR of adsorbed CO Oxygen isotopic exchange a b s t r a c t Ni-W-O mixed oxides were prepared through the evaporation of aqueous solutions of nickel nitrate and ammonium tungstate and calcined in air at 500°C for 2 h. The catalysts were characterized by several techniques (N 2 adsorption, X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy of adsorbed CO, and 18 O/ 16 O isotope exchange) and tested in the oxidative dehydrogenation of ethane. The catalytic activity and catalyst reducibility decrease when the W content increases. Thus, nickel sites seem to be the active centers for ethane activation in these catalysts. However, the selectivity to ethylene strongly changes depending on the Ni/W ratio. In W-rich catalysts, in which NiWO 4 and WO 3 are mainly observed, a strong influence of ethane conversion on the selectivity to ethylene is observed. However, in Ni-rich catalysts, in which NiO crystallites and WO x nanoparticles are mainly observed, ethane conversion hardly influences the selectivity to ethylene. It has been demonstrated that the nature of the Ni sites and the characteristics and number of the acid sites determine the catalytic behavior of these catalysts. The presence of Lewis acid sites with high acid strength in W-rich catalysts facilitates the decomposition of ethylene during ethane oxidation.

Research paper thumbnail of Selective oxidation of propane and ethane on diluted Mo–V–Nb–Te mixed-oxide catalysts

Journal of Catalysis, 2007

Te-free and Te-containing Mo-V-Nb mixed oxide catalysts were diluted with several metal oxides (S... more Te-free and Te-containing Mo-V-Nb mixed oxide catalysts were diluted with several metal oxides (SiO 2 , γ -Al 2 O 3 , α-Al 2 O 3 , Nb 2 O 5 , or ZrO 2 ), characterized, and tested in the oxidation of ethane and propane. Bulk and diluted Mo-V-Nb-Te catalysts exhibited high selectivity to ethylene (up to 96%) at ethane conversions <10%, whereas the corresponding Te-free catalysts exhibited lower selectivity to ethylene. The selectivity to ethylene decreased with the ethane conversion, with this effect depending strongly on the diluter and the catalyst composition. For propane oxidation, the presence of diluter exerted a negative effect on catalytic performance (decreasing the formation of acrylic acid), and α-Al 2 O 3 can be considered only a relatively efficient diluter. The higher or lower interaction between diluter and active-phase precursors, promoting or hindering an unfavorable formation of the active and selective crystalline phase [i.e., Te 2 M 20 O 57 (M = Mo, V, and Nb)], determines the catalytic performance of these materials.

Research paper thumbnail of Selective propane oxidation over MoVSbO catalysts. On the preparation, characterization and catalytic behavior of M1 phase

Journal of Catalysis, 2009

Nb-free (SbO) 2 M 20 O 56 catalysts (M = Mo, V) presenting pure M1 phase have been prepared by a ... more Nb-free (SbO) 2 M 20 O 56 catalysts (M = Mo, V) presenting pure M1 phase have been prepared by a post-synthesis treatment with hydrogen peroxide of a heat-treated MoVSbO mixed metal oxide catalyst previously prepared by hydrothermal method. The characterization of catalysts and their results for propane oxidation suggest that the optimization in the preparation of the M1 phase depends strongly on the washing procedure. The optimal removing of Sb species formed during post-synthesis treatment can explain the improvement in the catalytic activity; while the better selectivity to acrylic acid of the catalysts obtained by post-synthesis treatment can be explained by the elimination of M2 phase and the modification of the M1 phase crystals surface. The importance of M1 phase in the catalytic performance during the selective propane oxidation over Nb-free Mo-V-Sb based catalysts is also discussed. (J.M. López Nieto). (i) (SbO) 2 M 20 O 56 (with M = Mo, V, Nb) as the M1-like phase [26], and (ii) (Sb 2 O)M 6 O 19 (with M = Mo, V, Nb) as the M2-like

Research paper thumbnail of Selective oxidation of n-butane over MoV-containing oxidic bronze catalysts

Journal of Catalysis, 2007

MoV-containing oxidic bronze catalysts were synthesized, characterized, and tested in the selecti... more MoV-containing oxidic bronze catalysts were synthesized, characterized, and tested in the selective oxidation of n-butane. For comparison, an activated V-P-O catalyst was also studied. The catalytic behavior of MoV-containing catalysts was found to be dependent on both the catalyst composition and the nature of crystalline phases. In this way, the M1 phase (i.e., Te 2 M 20 O 57 and (SbO) 2 M 20 O 56 in Te-and Sb-containing catalysts, respectively) is proposed as an active and selective crystalline phase for n-butane oxidation on these catalysts. The selectivity to maleic anhydride/acid obtained on MoV-catalysts follows the order: MoVTeNbO > MoVTeO = MoVSbNbO > MoVSbO > MoVNbO. Although less selective than a vanadium phosphorous catalyst, a higher productivity to MA is obtained over a MoVTeNbO mixed oxide catalyst as a consequence of its remarkably superior catalytic activity. Moreover, the amount of maleic anhydride obtained on oxidic bronze catalysts strongly depends on the composition of the feed. In addition, the nature of active sites, the reaction network for n-butane oxidation, and a comparison of their catalytic performance in the oxidation of C 2 -C 4 alkanes are discussed.

Research paper thumbnail of Understanding effects of activation-treatments in K-free and K-MoVSbO bronze catalysts for propane partial oxidation

Catalysis Today, 2014

The effect of activation treatments of K-free and K-MoVSbO bronzes on either their physico-chemic... more The effect of activation treatments of K-free and K-MoVSbO bronzes on either their physico-chemical characteristics or catalytic properties for propane partial oxidation have been studied. The as-synthesized materials, hydrothermally prepared and presenting (SbO) 2 M 20 O 56 type structure (the so called M1phase), were activated by different heat-treatments, characterized (XRD, SEM-EDS, HRTEM, V K-edge, Sb L 1 -and K-edges XANES, EPR, XPS, NH 3 -TPD) and tested in propane partial oxidation. In general, the selectivity to acrylic acid (the most valuable product) was higher in K-containing MoVSbO catalysts. In addition, different trend in the catalytic behavior was found between K-free and K-containing MoVSbO series, mostly related to different changes in crystalline phases distribution and catalysts surface characteristics (composition and acid properties) induced by the several activation treatments which also modified the average Sb oxidation state.

Research paper thumbnail of Alkali-promoted V2O5 catalysts for the partial oxidation of H2S to sulphur

Catalysis Today, 2012

Vanadium oxide (V2O5 V4O9) Alkali metal (lithium sodium potassium caesium) a b s t r a c t Presen... more Vanadium oxide (V2O5 V4O9) Alkali metal (lithium sodium potassium caesium) a b s t r a c t Present paper describes the influence of the incorporation of alkali metal cations (AM = Li, Na, K, Cs; and an AM/V ratio of 0.04) and Na-content (Na/V ratio of 0.02-0.30) in alkali metal promoted V 2 O 5 catalyst on both the catalyst structure and the catalytic performance in H 2 S partial oxidation reactions. The catalytic activity depends on the alkali metal and the amount of alkali metal added, although Nacontaining catalysts seem to be the more active ones. However, selectivity to sulphur higher than 98% is achieved in the main of catalysts when working at reaction temperature lower than 220 • C. According to the characterization results of used catalysts, V 4 O 9 is selectively formed during the catalytic tests on catalysts presenting V 2 O 5 crystallites. In catalysts with Na/V ratios higher than 0.04, V 4 O 9 and Na 0.33 V 2 O 5 are observed, the presence of Na 0.33 V 2 O 5 increasing when increasing the Na/V ratio. Accordingly, V 4 O 9 and Na 0.33 V 2 O 5 can be proposed as the active and selective crystalline phase in Na-containing catalysts. The role of the presence of V 4+− O-V 5+ pairs in partial oxidation of H 2 S is also discussed.

Research paper thumbnail of Influence of gel composition in the synthesis of MoVTeNb catalysts over their catalytic performance in partial propane and propylene oxidation

Catalysis Today, 2010

ABSTRACT MoVTeNb mixed oxides catalysts have been prepared by a slurry method with different mola... more ABSTRACT MoVTeNb mixed oxides catalysts have been prepared by a slurry method with different molar compositions (Mo/Te ratio from 2 to 6 and Nb/(V + Nb) ratio from 0 to 0.7) in the synthesis gel leading to different crystalline phases distribution and catalytic behaviour in the partial oxidation of both propane and propylene to acrylic acid. Chemical analysis indicates that the composition of samples before and after the heat-treatment changes, especially the Te-content, since a significant amount of Te is lost during the heat-treatment step when the amount of oxalate (from niobium oxalate) increases in the synthesis gel. Thus, the nature of the crystalline phases and the catalytic performance of heat-treated materials will be related to the final chemical composition. On the other hand, only the catalysts presenting Te2M20O57 (M = Mo, V, Nb) crystalline structure, the so-called M1 phase, were active and selective in the partial oxidation of propane to acrylic acid. Moreover, all catalysts were active and relatively selective to the formation of O-containing products, i.e. acrolein and/or acrylic acid, during the partial propylene oxidation although the more active ones were those presenting M1 phase.

Research paper thumbnail of Selective oxidation of propane over alkali-doped Mo–V–Sb–O catalysts

Catalysis Today, 2009

ABSTRACT Alkali metal-doped MoVSbO catalysts have been prepared by impregnation of a MoVSbO-mixed... more ABSTRACT Alkali metal-doped MoVSbO catalysts have been prepared by impregnation of a MoVSbO-mixed oxide (prepared previously by a hydrothermal synthesis) and finally activated at 500 or 600 °C in N2. The catalysts have been characterized and tested for the selective oxidation of propane and propylene. Alkali-doped catalysts improved in general the catalytic performance of MoVSbO, resulting more selective to acrylic acid and less selective to acetic acid than the corresponding alkali-free MoVSbO catalysts. However, the specific behaviour strongly depends on both the alkali metal added and/or the final activation temperature. At isoconversion conditions, catalysts activated at 600 °C present selectivity to acrylic acid higher than that achieved on those activated at 500 °C, both K-doped catalysts presenting the highest yield to acrylic acid. The changes in the number of acid sites as well as the nature of crystalline phases can explain the catalytic behaviour of alkali-doped MoVSbO catalysts.

Research paper thumbnail of Reaction products and pathways in the selective oxidation of C2–C4 alkanes on MoVTeNb mixed oxide catalysts

Research paper thumbnail of Isolation of high quality graphene from Ru by solution phase intercalation

Applied Physics Letters, 2013

ABSTRACT We introduce a method for isolating graphene grown on epitaxial Ru(0001)/α-Al2O3. The st... more ABSTRACT We introduce a method for isolating graphene grown on epitaxial Ru(0001)/α-Al2O3. The strong graphene/Ru(0001) coupling is weakened by electrochemically driven intercalation of hydrogen underpotentially deposited in aqueous KOH solution, which allows the penetration of water molecules at the graphene/Ru(0001) interface. Following these electrochemically driven processes, the graphene can be isolated by electrochemical hydrogen evolution and transferred to arbitrary supports. Raman and transport measurements demonstrate the high quality of the transferred graphene. Our results show that intercalation, typically carried out in vacuum, can be extended to solution environments for graphene processing under ambient conditions.

Research paper thumbnail of Oxidative dehydrogenation of ethane to ethylene and preparation of multimetallic mixed oxide catalyst for such process

Research paper thumbnail of Spectators Control Selectivity in Surface Chemistry: Acrolein Partial Hydrogenation Over Pd

Journal of the American Chemical Society, 2015

We present a mechanistic study on selective hydrogenation of acrolein over model Pd surfaces-both... more We present a mechanistic study on selective hydrogenation of acrolein over model Pd surfaces-both single crystal Pd(111) and Pd nanoparticles supported on a model oxide support. We show for the first time that selective hydrogenation of the C═O bond in acrolein to form an unsaturated alcohol is possible over Pd(111) with nearly 100% selectivity. However, this process requires a very distinct modification of the Pd(111) surface with an overlayer of oxopropyl spectator species that are formed from acrolein during the initial stages of reaction and turn the metal surface selective toward propenol formation. By applying pulsed multimolecular beam experiments and in situ infrared reflection-absorption spectroscopy, we identified the chemical nature of the spectator and the reactive surface intermediate (propenoxy species) and experimentally followed the simultaneous evolution of the reactive intermediate on the surface and formation of the product in the gas phase.

Research paper thumbnail of Selective Oxidation of Propane Over AMoVSbO Catalysts (A = Li, Na, K, Rb or Cs)

Topics in Catalysis, 2008

Alkali metal-containing Mo-V-Sb-O catalysts (AMoVSbO, with A = Li, Na, K, Rb or Cs), prepared hyd... more Alkali metal-containing Mo-V-Sb-O catalysts (AMoVSbO, with A = Li, Na, K, Rb or Cs), prepared hydrothermally and activated at 600°C in N 2 , have been characterized and tested for the selective oxidation of propane. Alkali-doped catalysts resulted to be more selective to acrylic acid and less selective to acetic acid than the corresponding alkali-free Mo-V-Sb-O catalyst. However, the nature of crystalline phases and the catalytic behaviour strongly depend on the alkali metal added. In this way, the catalytic activity decreases as follows: unpromoted [ Li-* Na-* K-[ Rb-[ Cs-containing catalyst. However the selectivity to acrylic acid decreases in the order: K-[ Rb-* Na-[ unpromoted [ Li-[ Cscontaining catalyst. The role of the presence/absence of acid sites and cations on both the nature of crystalline phases and the catalytic performance will be discussed.

Research paper thumbnail of Oxidative dehydrogenation of ethane: A study over the structure and robustness of Ni–W–O catalysts

Fuel Processing Technology

The robustness of one selected Ni–W–O catalyst has been studied in the oxidative dehydrogenation ... more The robustness of one selected Ni–W–O catalyst has been studied in the oxidative dehydrogenation of ethane. This catalyst initially deactivates for the first 10 h online decreasing 15% of its catalytic activity compared to its initial stable catalytic activity. However from 10 to 60 h online the catalytic activity keeps almost stable. On the other hand, it has been shown that the Ni–W–O catalyst cannot tolerate an oxygen-free atmosphere (C2 and He) as nickel oxide is transformed into metallic nickel. Methane and hydrogen as well as abundant coke were formed on the surface of the catalyst in these O-free conditions. However a re-calcination in air leads to the removal of coke, the catalytic performance in the oxidative dehydrogenation of ethane being almost completely restored. Ni–W–O catalysts are active and selective in the oxidative dehydrogenation of ethane. However, their catalytic performance highly depends on the catalyst composition. At the present paper we have prepared Ni–W...

Research paper thumbnail of Selective oxidation of short-chain alkanes over hydrothermally prepared MoVTeNbO catalysts

Topics in Catalysis, 2006

MoVTe-Nb oxide catalysts have been prepared by a hydrothermal method and tested in the selective ... more MoVTe-Nb oxide catalysts have been prepared by a hydrothermal method and tested in the selective oxidation of propane to acrylic acid and in the oxidative dehydrogenation of ethane to ethylene. The influence of the concentration of oxalate anions in the hydrothermal gel has been studied for two series of catalysts, Nb-free and Nb-containing, respectively. Results show that the development of

Research paper thumbnail of Size-Dependent Room Temperature Oxidation of Tin Particles

Particle & Particle Systems Characterization, 2014

ABSTRACT Using transmission electron microscopy, the size-dependent room temperature oxidation of... more ABSTRACT Using transmission electron microscopy, the size-dependent room temperature oxidation of tin nanoparticles is studied. The oxide that forms during room temperature oxidation of Sn particles is amorphous SnO, and it retains this stoichiometry and structure over extended time periods. From the investigation of arrays of Sn nanoparticles with broad size distribution, under identical conditions, the Sn oxide thickness is evaluated as a function of size and oxidation time. The oxide thickness depends strongly on the size of the Sn nanoparticles, which is in excellent agreement with predictions for a Mott–Cabrera model corrected for a non-uniform electric field. The results demonstrate the accelerated oxidation kinetics of nanoscale particles with high curvature, due to the amplified electric field at the interface to a continuously shrinking metal core.

Research paper thumbnail of Oxidative dehydrogenation of ethane over Ni–W–O mixed metal oxide catalysts

Journal of Catalysis, 2011

Nickel tungsten metal oxide catalysts Oxidative dehydrogenation of ethane Ethylene oxidation Cata... more Nickel tungsten metal oxide catalysts Oxidative dehydrogenation of ethane Ethylene oxidation Catalyst characterization XPS TPR XRD Raman FTIR of adsorbed CO Oxygen isotopic exchange a b s t r a c t Ni-W-O mixed oxides were prepared through the evaporation of aqueous solutions of nickel nitrate and ammonium tungstate and calcined in air at 500°C for 2 h. The catalysts were characterized by several techniques (N 2 adsorption, X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy of adsorbed CO, and 18 O/ 16 O isotope exchange) and tested in the oxidative dehydrogenation of ethane. The catalytic activity and catalyst reducibility decrease when the W content increases. Thus, nickel sites seem to be the active centers for ethane activation in these catalysts. However, the selectivity to ethylene strongly changes depending on the Ni/W ratio. In W-rich catalysts, in which NiWO 4 and WO 3 are mainly observed, a strong influence of ethane conversion on the selectivity to ethylene is observed. However, in Ni-rich catalysts, in which NiO crystallites and WO x nanoparticles are mainly observed, ethane conversion hardly influences the selectivity to ethylene. It has been demonstrated that the nature of the Ni sites and the characteristics and number of the acid sites determine the catalytic behavior of these catalysts. The presence of Lewis acid sites with high acid strength in W-rich catalysts facilitates the decomposition of ethylene during ethane oxidation.

Research paper thumbnail of Selective oxidation of propane and ethane on diluted Mo–V–Nb–Te mixed-oxide catalysts

Journal of Catalysis, 2007

Te-free and Te-containing Mo-V-Nb mixed oxide catalysts were diluted with several metal oxides (S... more Te-free and Te-containing Mo-V-Nb mixed oxide catalysts were diluted with several metal oxides (SiO 2 , γ -Al 2 O 3 , α-Al 2 O 3 , Nb 2 O 5 , or ZrO 2 ), characterized, and tested in the oxidation of ethane and propane. Bulk and diluted Mo-V-Nb-Te catalysts exhibited high selectivity to ethylene (up to 96%) at ethane conversions <10%, whereas the corresponding Te-free catalysts exhibited lower selectivity to ethylene. The selectivity to ethylene decreased with the ethane conversion, with this effect depending strongly on the diluter and the catalyst composition. For propane oxidation, the presence of diluter exerted a negative effect on catalytic performance (decreasing the formation of acrylic acid), and α-Al 2 O 3 can be considered only a relatively efficient diluter. The higher or lower interaction between diluter and active-phase precursors, promoting or hindering an unfavorable formation of the active and selective crystalline phase [i.e., Te 2 M 20 O 57 (M = Mo, V, and Nb)], determines the catalytic performance of these materials.

Research paper thumbnail of Selective propane oxidation over MoVSbO catalysts. On the preparation, characterization and catalytic behavior of M1 phase

Journal of Catalysis, 2009

Nb-free (SbO) 2 M 20 O 56 catalysts (M = Mo, V) presenting pure M1 phase have been prepared by a ... more Nb-free (SbO) 2 M 20 O 56 catalysts (M = Mo, V) presenting pure M1 phase have been prepared by a post-synthesis treatment with hydrogen peroxide of a heat-treated MoVSbO mixed metal oxide catalyst previously prepared by hydrothermal method. The characterization of catalysts and their results for propane oxidation suggest that the optimization in the preparation of the M1 phase depends strongly on the washing procedure. The optimal removing of Sb species formed during post-synthesis treatment can explain the improvement in the catalytic activity; while the better selectivity to acrylic acid of the catalysts obtained by post-synthesis treatment can be explained by the elimination of M2 phase and the modification of the M1 phase crystals surface. The importance of M1 phase in the catalytic performance during the selective propane oxidation over Nb-free Mo-V-Sb based catalysts is also discussed. (J.M. López Nieto). (i) (SbO) 2 M 20 O 56 (with M = Mo, V, Nb) as the M1-like phase [26], and (ii) (Sb 2 O)M 6 O 19 (with M = Mo, V, Nb) as the M2-like

Research paper thumbnail of Selective oxidation of n-butane over MoV-containing oxidic bronze catalysts

Journal of Catalysis, 2007

MoV-containing oxidic bronze catalysts were synthesized, characterized, and tested in the selecti... more MoV-containing oxidic bronze catalysts were synthesized, characterized, and tested in the selective oxidation of n-butane. For comparison, an activated V-P-O catalyst was also studied. The catalytic behavior of MoV-containing catalysts was found to be dependent on both the catalyst composition and the nature of crystalline phases. In this way, the M1 phase (i.e., Te 2 M 20 O 57 and (SbO) 2 M 20 O 56 in Te-and Sb-containing catalysts, respectively) is proposed as an active and selective crystalline phase for n-butane oxidation on these catalysts. The selectivity to maleic anhydride/acid obtained on MoV-catalysts follows the order: MoVTeNbO > MoVTeO = MoVSbNbO > MoVSbO > MoVNbO. Although less selective than a vanadium phosphorous catalyst, a higher productivity to MA is obtained over a MoVTeNbO mixed oxide catalyst as a consequence of its remarkably superior catalytic activity. Moreover, the amount of maleic anhydride obtained on oxidic bronze catalysts strongly depends on the composition of the feed. In addition, the nature of active sites, the reaction network for n-butane oxidation, and a comparison of their catalytic performance in the oxidation of C 2 -C 4 alkanes are discussed.

Research paper thumbnail of Understanding effects of activation-treatments in K-free and K-MoVSbO bronze catalysts for propane partial oxidation

Catalysis Today, 2014

The effect of activation treatments of K-free and K-MoVSbO bronzes on either their physico-chemic... more The effect of activation treatments of K-free and K-MoVSbO bronzes on either their physico-chemical characteristics or catalytic properties for propane partial oxidation have been studied. The as-synthesized materials, hydrothermally prepared and presenting (SbO) 2 M 20 O 56 type structure (the so called M1phase), were activated by different heat-treatments, characterized (XRD, SEM-EDS, HRTEM, V K-edge, Sb L 1 -and K-edges XANES, EPR, XPS, NH 3 -TPD) and tested in propane partial oxidation. In general, the selectivity to acrylic acid (the most valuable product) was higher in K-containing MoVSbO catalysts. In addition, different trend in the catalytic behavior was found between K-free and K-containing MoVSbO series, mostly related to different changes in crystalline phases distribution and catalysts surface characteristics (composition and acid properties) induced by the several activation treatments which also modified the average Sb oxidation state.

Research paper thumbnail of Alkali-promoted V2O5 catalysts for the partial oxidation of H2S to sulphur

Catalysis Today, 2012

Vanadium oxide (V2O5 V4O9) Alkali metal (lithium sodium potassium caesium) a b s t r a c t Presen... more Vanadium oxide (V2O5 V4O9) Alkali metal (lithium sodium potassium caesium) a b s t r a c t Present paper describes the influence of the incorporation of alkali metal cations (AM = Li, Na, K, Cs; and an AM/V ratio of 0.04) and Na-content (Na/V ratio of 0.02-0.30) in alkali metal promoted V 2 O 5 catalyst on both the catalyst structure and the catalytic performance in H 2 S partial oxidation reactions. The catalytic activity depends on the alkali metal and the amount of alkali metal added, although Nacontaining catalysts seem to be the more active ones. However, selectivity to sulphur higher than 98% is achieved in the main of catalysts when working at reaction temperature lower than 220 • C. According to the characterization results of used catalysts, V 4 O 9 is selectively formed during the catalytic tests on catalysts presenting V 2 O 5 crystallites. In catalysts with Na/V ratios higher than 0.04, V 4 O 9 and Na 0.33 V 2 O 5 are observed, the presence of Na 0.33 V 2 O 5 increasing when increasing the Na/V ratio. Accordingly, V 4 O 9 and Na 0.33 V 2 O 5 can be proposed as the active and selective crystalline phase in Na-containing catalysts. The role of the presence of V 4+− O-V 5+ pairs in partial oxidation of H 2 S is also discussed.

Research paper thumbnail of Influence of gel composition in the synthesis of MoVTeNb catalysts over their catalytic performance in partial propane and propylene oxidation

Catalysis Today, 2010

ABSTRACT MoVTeNb mixed oxides catalysts have been prepared by a slurry method with different mola... more ABSTRACT MoVTeNb mixed oxides catalysts have been prepared by a slurry method with different molar compositions (Mo/Te ratio from 2 to 6 and Nb/(V + Nb) ratio from 0 to 0.7) in the synthesis gel leading to different crystalline phases distribution and catalytic behaviour in the partial oxidation of both propane and propylene to acrylic acid. Chemical analysis indicates that the composition of samples before and after the heat-treatment changes, especially the Te-content, since a significant amount of Te is lost during the heat-treatment step when the amount of oxalate (from niobium oxalate) increases in the synthesis gel. Thus, the nature of the crystalline phases and the catalytic performance of heat-treated materials will be related to the final chemical composition. On the other hand, only the catalysts presenting Te2M20O57 (M = Mo, V, Nb) crystalline structure, the so-called M1 phase, were active and selective in the partial oxidation of propane to acrylic acid. Moreover, all catalysts were active and relatively selective to the formation of O-containing products, i.e. acrolein and/or acrylic acid, during the partial propylene oxidation although the more active ones were those presenting M1 phase.

Research paper thumbnail of Selective oxidation of propane over alkali-doped Mo–V–Sb–O catalysts

Catalysis Today, 2009

ABSTRACT Alkali metal-doped MoVSbO catalysts have been prepared by impregnation of a MoVSbO-mixed... more ABSTRACT Alkali metal-doped MoVSbO catalysts have been prepared by impregnation of a MoVSbO-mixed oxide (prepared previously by a hydrothermal synthesis) and finally activated at 500 or 600 °C in N2. The catalysts have been characterized and tested for the selective oxidation of propane and propylene. Alkali-doped catalysts improved in general the catalytic performance of MoVSbO, resulting more selective to acrylic acid and less selective to acetic acid than the corresponding alkali-free MoVSbO catalysts. However, the specific behaviour strongly depends on both the alkali metal added and/or the final activation temperature. At isoconversion conditions, catalysts activated at 600 °C present selectivity to acrylic acid higher than that achieved on those activated at 500 °C, both K-doped catalysts presenting the highest yield to acrylic acid. The changes in the number of acid sites as well as the nature of crystalline phases can explain the catalytic behaviour of alkali-doped MoVSbO catalysts.

Research paper thumbnail of Reaction products and pathways in the selective oxidation of C2–C4 alkanes on MoVTeNb mixed oxide catalysts

Research paper thumbnail of Isolation of high quality graphene from Ru by solution phase intercalation

Applied Physics Letters, 2013

ABSTRACT We introduce a method for isolating graphene grown on epitaxial Ru(0001)/α-Al2O3. The st... more ABSTRACT We introduce a method for isolating graphene grown on epitaxial Ru(0001)/α-Al2O3. The strong graphene/Ru(0001) coupling is weakened by electrochemically driven intercalation of hydrogen underpotentially deposited in aqueous KOH solution, which allows the penetration of water molecules at the graphene/Ru(0001) interface. Following these electrochemically driven processes, the graphene can be isolated by electrochemical hydrogen evolution and transferred to arbitrary supports. Raman and transport measurements demonstrate the high quality of the transferred graphene. Our results show that intercalation, typically carried out in vacuum, can be extended to solution environments for graphene processing under ambient conditions.