Alejandro López Ortiz | Centro de Investigación en Materiales Avanzados, S.C. (original) (raw)

Papers by Alejandro López Ortiz

Journal of New Materials for Electrochemical Systems, 2013

Thermodynamic analysis of the steam reforming of biofuel model compounds using CaO, and Na2ZrO3, ... more Thermodynamic analysis of the steam reforming of biofuel model compounds using CaO, and Na2ZrO3, as CO2 absorbents was performed to determine favorable operating conditions to produce a high hydrogen ratio (HR, molsH2 produced/molsHC fed) and concentration (%H2) gas product. Biofuel compounds (HC’s) used were: 2,4-dimethylphenol (DMP), furfural (FUR) and vanillin (VAI). Equilibrium product compositions were studied at 300-850°C, steam to hydrocarbon molar ratio (S/HC) and CO2 absorbent at 1 atm. S/HC varied from stoichiometric; 15:1 (DMP), 13:1 (VAI) and 8:1 (FUR) to twice and trice their stoichiometric values, respectively. At stoichiometric S/HC ratios results indicate significant carbon formation with conventional reforming at T < 600°C, with no carbon formation using absorbents with any of the HC’s. The use of a CO2 absorbent resulted in an increase in HR and H2 purity of about 3 and 30% higher, respectively. The order from high to low HR was: VA>DMP>FUR.

REVIEWS ON ADVANCED MATERIALS SCIENCE

In the present work, manganese cobaltite (MnCo2O4) spinel (MCO) was synthetized by Pechini and hy... more In the present work, manganese cobaltite (MnCo2O4) spinel (MCO) was synthetized by Pechini and hydrothermal method, characterized and photocatalytically evaluated toward H2 production through water splitting under visible-light irradiation. Characterization consisted in Thermogravimetry analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scattering transmission electronic microscopy, BET surface area, UV-Vis spectroscopy, cyclic voltammetry, Hall effect, and photoluminescence. The MCO were evaluated as photocatalyst using an artificial visible light lamp and monitored by gas chromatography. XRD analysis found a pure spinel phase MCO. The surface area was ∼5 m2·g−1 for the MCO synthetized by Pechini and increased to 155 m2·g−1 with the hydrothermal method with acetates as precursors. The Pechini MCO showed higher carrier mobility but the fastest recombination. Photocatalytic evaluation of the MCOs showed that the highest photocatalytic activity generated was 12...

Catalysts, 2020

In the present work, zinc titanates (ZTO) as photocatalysts were synthesized, characterized, and ... more In the present work, zinc titanates (ZTO) as photocatalysts were synthesized, characterized, and evaluated aiming to study their photocatalytic properties for hydrogen production under visible-light irradiation and employing MeOH (methanol) and TEOA (Triethanolamine) as sacrificial agents. ZTO were synthesized by modified Pechini method. Characterization of materials consisted in TGA, XRD, TEM, EELS, BET, and UV–Vis. Surface interaction studies consisted of FT-IR spectroscopy and determination of MeOH and TEOA adsorption–desorption capacities on the ZTO by TGA. Zinc titanates were evaluated as photocatalyst for H2 production using an artificial visible light and monitored by GC. TGA results led to establish calcination temperatures of 550 °C (Zn2Ti3O8) and 700 °C (ZnTiO3) to reach their crystalline phases. XRD analysis of sample cds-ZTO found cubic Zn2Ti3O8 and traces of the ZnO crystalline phase, while p-ZTO exhibited a mixture of cubic and hexagonal ZnTiO3 crystalline phases. Surf...

International Journal of Hydrogen Energy, 2015

Journal of Nanomaterials, 2015

Currently, the need for more efficient materials that work in the visible light spectrum for hydr... more Currently, the need for more efficient materials that work in the visible light spectrum for hydrogen production has been increasing. Under this criterion, ferrites are ideal because their energetic properties are favorable to photocatalysis as they have a low band gap (1.5 to 3 ev). In this particular research, ferrite is presented as a hydrogen producer. Cobalt ferrites were synthesized by chemical coprecipitation (CP) and ball milling (BM) for comparison of their performance. The characterization of the materials was carried out with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area, UV-VIS spectroscopy, and water adsorption/desorption tests. Evaluation of the photocatalytic activity under visible light was followed by gas chromatography. The results showed that cobalt ferrite by ball milling had a higher photocatalytic activity; this is attributed to the vacancies generated during the milling process at which th...

International Journal of Hydrogen Energy, 2014

International Journal of Hydrogen Energy, 2010

... Veterinaria s/n, Circuito Universitario, Durango 34120, Mexico. b Departamento de Química de ... more ... Veterinaria s/n, Circuito Universitario, Durango 34120, Mexico. b Departamento de Química de Materiales, Centro de Investigación en Materiales Avanzados, SC Miguel de Cervantes 120, Chihuahua, Chih. 31109, Mexico. Received 31 March 2009; accepted 7 July 2009. ...

International Journal of Hydrogen Energy, 2013

International Journal of Chemical Reactor Engineering, 2007

A set of TiO2 samples with different anatase/rutile ratios was prepared by calcinations at differ... more A set of TiO2 samples with different anatase/rutile ratios was prepared by calcinations at different temperatures from commercial photocatalyst Degussa P25. The effects of the two crystalline phases of titanium (IV) oxide on the photocatalytic activity in gaseous phase through oxidation of light hydrocarbons were studied. Crystalline phase transformation from anatase to rutile occurred at 700°C for P25. Results indicate that samples with higher anatase/rutile ratios presented higher intrinsic activities for the photodegradation of a propane/isobutane/butane (40/35/25 %V) mixture. However, the activity did not totally disappear after complete crystalline transformation from anatase to rutile, indicating that the pure rutile phase also presents photoactivity. During the photocatalytic reaction of TiO2 samples, a linear dependence was found between the inverse of the intrinsic reaction rate constant (k intrinsic) and the water adsorption capacity in the surface (WAPS) of the synthesize...

International Journal of Chemical Reactor Engineering, 2007

A redox reaction scheme consisting of two steps as an alternate to the partial oxidation of metha... more A redox reaction scheme consisting of two steps as an alternate to the partial oxidation of methane (POX) for synthesis gas production is proposed. With the use of a thermodynamic analysis the CoWO4 spinel was introduced as a new oxygen carrier material, capable to be reduced with methane (15% CH4/Ar) and reoxidized with steam (30% H2O/Ar) to produce syngas and hydrogen in each redox step, respectively. H2 production is feasible during the regeneration of CoWO4 by oxidation of reduced species (Co and W) with steam. CoWO4 synthesis was performed using the solid state reaction. Characterization included: XRD, SEM and particle size determination. Redox-cycle performance was followed by TGA. Thermal stability of CoWO4 was tested by exposing the material to ten consecutive reduction/oxidation (H2/Ar, H2O/Ar) cycles at 850°C and after. Results indicate that CoWO4 showed no significant loss of activity. This stable behavior is associated to its crystalline structure, which allows the fixat...

International Journal of Chemical Reactor Engineering, 2008

Nanostructured manganese oxides were synthesized towards the catalytic decomposition of hydrogen ... more Nanostructured manganese oxides were synthesized towards the catalytic decomposition of hydrogen peroxide. The effect of the type of precipitant (Na2CO3 and NH4OH) over the particle size and crystallographic phase was determined. Also, the influence of particle size and crystal phase over the catalytic activity was established. Characterization of the obtained nanoparticles was performed through XRD analysis, BET surface area and TEM microscopy. Catalytic activity was followed through gasometry of the oxygen evolution [H2O2(l) ? H2O(l) + O2 (g)] at 25°C. Na2CO3 (Mn-1) and NH4OH (Mn-2) precipitants produced nanoparticles with average sizes of 5-10 nm and 20 nm, respectively. This result was attributed to higher pH stability of precipitant Na2CO3 during the synthesis process. XRD results revealed the presence of ß-MnO2, Mn5O8 and Mn3O4 crystal phase mixture for Mn-1 and Mn5O8 for Mn-2 catalyst. Catalytic activity resulted in intrinsic rate constants (kint = min-1m-2) of 5.2 and 2.3 fo...

Chemical Engineering Communications, 2000

ABSTRACT Noncatalytic gas-solid reactions should exhibit strong temperature dependence when the r... more ABSTRACT Noncatalytic gas-solid reactions should exhibit strong temperature dependence when the rate is controlled by surface kinetics. However, there are a number of examples in the literature where apparent activation energies less than 10 kcal/mol have been reported as being representative of intrinsic kinetics. This conclusion is often based on electrobalance data in which large gas Row rates were used to eliminate mass transfer resistance and the fact that fractional conversion-time results are consistent with the surface kinetics control version of a gas-solid reaction model.

International Journal of Chemical Reactor Engineering, 2005

Novel proposed processes for H2 production and energy generation such as partial oxidation of hyd... more Novel proposed processes for H2 production and energy generation such as partial oxidation of hydrocarbons (POX-MeO) and chemical looping process (CLP), respectively require the use of solid oxides as oxygen carriers. In POX-MeO the required oxygen for the partial oxidation of methane is provided by a transition metal oxide (MeO). First, H2 is produced through CH4+MeO = CO+H2+Me. Secondly, Me is re-oxidized through Me+O2 = MeO to regenerate the oxygen carrier. In the CL process, CH4 is being completely oxidized through CH2 + MeO = CO2 + H2O + Me producing heat and CO2 ready for sequestration. Finally, Me is re-oxidized using air to regenerate the Me back to MeO. In both processes the regenerated MeO is sent back to the initial step to result in a cyclic operation. Continuous exposure of MeO to Redox cycles frequently produces sinterization and MeO stabilization is needed to avoid loss of activity. The objective of this study is to investigate the stabilization effect of TiO2 in Co3O...

Spain Arbitration Review Revista Del Club Espanol Del Arbitraje, 2010

International Journal of Chemical Reactor Engineering, 2000

∗Centro de Investigacion en Materiales Avanzados SC, miguel.escobedo@ujed.mx †Centro de Investiga... more ∗Centro de Investigacion en Materiales Avanzados SC, miguel.escobedo@ujed.mx †Centro de Investigacion en Materiales Avanzados SC, manuel.delgado@cimav.edu.mx ‡Centro de Investigación en Materiales Avanzados SC, virginia.collins@cimav.edu.mx ∗∗Centro de ...

Journal of New Materials for Electrochemical Systems, 2013

Thermodynamic analysis of the steam reforming of biofuel model compounds using CaO, and Na2ZrO3, ... more Thermodynamic analysis of the steam reforming of biofuel model compounds using CaO, and Na2ZrO3, as CO2 absorbents was performed to determine favorable operating conditions to produce a high hydrogen ratio (HR, molsH2 produced/molsHC fed) and concentration (%H2) gas product. Biofuel compounds (HC’s) used were: 2,4-dimethylphenol (DMP), furfural (FUR) and vanillin (VAI). Equilibrium product compositions were studied at 300-850°C, steam to hydrocarbon molar ratio (S/HC) and CO2 absorbent at 1 atm. S/HC varied from stoichiometric; 15:1 (DMP), 13:1 (VAI) and 8:1 (FUR) to twice and trice their stoichiometric values, respectively. At stoichiometric S/HC ratios results indicate significant carbon formation with conventional reforming at T < 600°C, with no carbon formation using absorbents with any of the HC’s. The use of a CO2 absorbent resulted in an increase in HR and H2 purity of about 3 and 30% higher, respectively. The order from high to low HR was: VA>DMP>FUR.

REVIEWS ON ADVANCED MATERIALS SCIENCE

In the present work, manganese cobaltite (MnCo2O4) spinel (MCO) was synthetized by Pechini and hy... more In the present work, manganese cobaltite (MnCo2O4) spinel (MCO) was synthetized by Pechini and hydrothermal method, characterized and photocatalytically evaluated toward H2 production through water splitting under visible-light irradiation. Characterization consisted in Thermogravimetry analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scattering transmission electronic microscopy, BET surface area, UV-Vis spectroscopy, cyclic voltammetry, Hall effect, and photoluminescence. The MCO were evaluated as photocatalyst using an artificial visible light lamp and monitored by gas chromatography. XRD analysis found a pure spinel phase MCO. The surface area was ∼5 m2·g−1 for the MCO synthetized by Pechini and increased to 155 m2·g−1 with the hydrothermal method with acetates as precursors. The Pechini MCO showed higher carrier mobility but the fastest recombination. Photocatalytic evaluation of the MCOs showed that the highest photocatalytic activity generated was 12...

Catalysts, 2020

In the present work, zinc titanates (ZTO) as photocatalysts were synthesized, characterized, and ... more In the present work, zinc titanates (ZTO) as photocatalysts were synthesized, characterized, and evaluated aiming to study their photocatalytic properties for hydrogen production under visible-light irradiation and employing MeOH (methanol) and TEOA (Triethanolamine) as sacrificial agents. ZTO were synthesized by modified Pechini method. Characterization of materials consisted in TGA, XRD, TEM, EELS, BET, and UV–Vis. Surface interaction studies consisted of FT-IR spectroscopy and determination of MeOH and TEOA adsorption–desorption capacities on the ZTO by TGA. Zinc titanates were evaluated as photocatalyst for H2 production using an artificial visible light and monitored by GC. TGA results led to establish calcination temperatures of 550 °C (Zn2Ti3O8) and 700 °C (ZnTiO3) to reach their crystalline phases. XRD analysis of sample cds-ZTO found cubic Zn2Ti3O8 and traces of the ZnO crystalline phase, while p-ZTO exhibited a mixture of cubic and hexagonal ZnTiO3 crystalline phases. Surf...

International Journal of Hydrogen Energy, 2015

Journal of Nanomaterials, 2015

Currently, the need for more efficient materials that work in the visible light spectrum for hydr... more Currently, the need for more efficient materials that work in the visible light spectrum for hydrogen production has been increasing. Under this criterion, ferrites are ideal because their energetic properties are favorable to photocatalysis as they have a low band gap (1.5 to 3 ev). In this particular research, ferrite is presented as a hydrogen producer. Cobalt ferrites were synthesized by chemical coprecipitation (CP) and ball milling (BM) for comparison of their performance. The characterization of the materials was carried out with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area, UV-VIS spectroscopy, and water adsorption/desorption tests. Evaluation of the photocatalytic activity under visible light was followed by gas chromatography. The results showed that cobalt ferrite by ball milling had a higher photocatalytic activity; this is attributed to the vacancies generated during the milling process at which th...

International Journal of Hydrogen Energy, 2014

International Journal of Hydrogen Energy, 2010

... Veterinaria s/n, Circuito Universitario, Durango 34120, Mexico. b Departamento de Química de ... more ... Veterinaria s/n, Circuito Universitario, Durango 34120, Mexico. b Departamento de Química de Materiales, Centro de Investigación en Materiales Avanzados, SC Miguel de Cervantes 120, Chihuahua, Chih. 31109, Mexico. Received 31 March 2009; accepted 7 July 2009. ...

International Journal of Hydrogen Energy, 2013

International Journal of Chemical Reactor Engineering, 2007

A set of TiO2 samples with different anatase/rutile ratios was prepared by calcinations at differ... more A set of TiO2 samples with different anatase/rutile ratios was prepared by calcinations at different temperatures from commercial photocatalyst Degussa P25. The effects of the two crystalline phases of titanium (IV) oxide on the photocatalytic activity in gaseous phase through oxidation of light hydrocarbons were studied. Crystalline phase transformation from anatase to rutile occurred at 700°C for P25. Results indicate that samples with higher anatase/rutile ratios presented higher intrinsic activities for the photodegradation of a propane/isobutane/butane (40/35/25 %V) mixture. However, the activity did not totally disappear after complete crystalline transformation from anatase to rutile, indicating that the pure rutile phase also presents photoactivity. During the photocatalytic reaction of TiO2 samples, a linear dependence was found between the inverse of the intrinsic reaction rate constant (k intrinsic) and the water adsorption capacity in the surface (WAPS) of the synthesize...

International Journal of Chemical Reactor Engineering, 2007

A redox reaction scheme consisting of two steps as an alternate to the partial oxidation of metha... more A redox reaction scheme consisting of two steps as an alternate to the partial oxidation of methane (POX) for synthesis gas production is proposed. With the use of a thermodynamic analysis the CoWO4 spinel was introduced as a new oxygen carrier material, capable to be reduced with methane (15% CH4/Ar) and reoxidized with steam (30% H2O/Ar) to produce syngas and hydrogen in each redox step, respectively. H2 production is feasible during the regeneration of CoWO4 by oxidation of reduced species (Co and W) with steam. CoWO4 synthesis was performed using the solid state reaction. Characterization included: XRD, SEM and particle size determination. Redox-cycle performance was followed by TGA. Thermal stability of CoWO4 was tested by exposing the material to ten consecutive reduction/oxidation (H2/Ar, H2O/Ar) cycles at 850°C and after. Results indicate that CoWO4 showed no significant loss of activity. This stable behavior is associated to its crystalline structure, which allows the fixat...

International Journal of Chemical Reactor Engineering, 2008

Nanostructured manganese oxides were synthesized towards the catalytic decomposition of hydrogen ... more Nanostructured manganese oxides were synthesized towards the catalytic decomposition of hydrogen peroxide. The effect of the type of precipitant (Na2CO3 and NH4OH) over the particle size and crystallographic phase was determined. Also, the influence of particle size and crystal phase over the catalytic activity was established. Characterization of the obtained nanoparticles was performed through XRD analysis, BET surface area and TEM microscopy. Catalytic activity was followed through gasometry of the oxygen evolution [H2O2(l) ? H2O(l) + O2 (g)] at 25°C. Na2CO3 (Mn-1) and NH4OH (Mn-2) precipitants produced nanoparticles with average sizes of 5-10 nm and 20 nm, respectively. This result was attributed to higher pH stability of precipitant Na2CO3 during the synthesis process. XRD results revealed the presence of ß-MnO2, Mn5O8 and Mn3O4 crystal phase mixture for Mn-1 and Mn5O8 for Mn-2 catalyst. Catalytic activity resulted in intrinsic rate constants (kint = min-1m-2) of 5.2 and 2.3 fo...

Chemical Engineering Communications, 2000

ABSTRACT Noncatalytic gas-solid reactions should exhibit strong temperature dependence when the r... more ABSTRACT Noncatalytic gas-solid reactions should exhibit strong temperature dependence when the rate is controlled by surface kinetics. However, there are a number of examples in the literature where apparent activation energies less than 10 kcal/mol have been reported as being representative of intrinsic kinetics. This conclusion is often based on electrobalance data in which large gas Row rates were used to eliminate mass transfer resistance and the fact that fractional conversion-time results are consistent with the surface kinetics control version of a gas-solid reaction model.

International Journal of Chemical Reactor Engineering, 2005

Novel proposed processes for H2 production and energy generation such as partial oxidation of hyd... more Novel proposed processes for H2 production and energy generation such as partial oxidation of hydrocarbons (POX-MeO) and chemical looping process (CLP), respectively require the use of solid oxides as oxygen carriers. In POX-MeO the required oxygen for the partial oxidation of methane is provided by a transition metal oxide (MeO). First, H2 is produced through CH4+MeO = CO+H2+Me. Secondly, Me is re-oxidized through Me+O2 = MeO to regenerate the oxygen carrier. In the CL process, CH4 is being completely oxidized through CH2 + MeO = CO2 + H2O + Me producing heat and CO2 ready for sequestration. Finally, Me is re-oxidized using air to regenerate the Me back to MeO. In both processes the regenerated MeO is sent back to the initial step to result in a cyclic operation. Continuous exposure of MeO to Redox cycles frequently produces sinterization and MeO stabilization is needed to avoid loss of activity. The objective of this study is to investigate the stabilization effect of TiO2 in Co3O...

Spain Arbitration Review Revista Del Club Espanol Del Arbitraje, 2010

International Journal of Chemical Reactor Engineering, 2000

∗Centro de Investigacion en Materiales Avanzados SC, miguel.escobedo@ujed.mx †Centro de Investiga... more ∗Centro de Investigacion en Materiales Avanzados SC, miguel.escobedo@ujed.mx †Centro de Investigacion en Materiales Avanzados SC, manuel.delgado@cimav.edu.mx ‡Centro de Investigación en Materiales Avanzados SC, virginia.collins@cimav.edu.mx ∗∗Centro de ...