Iron oxide particles were deposited in an ordered mesoporous material (SBA-15) with the aim of st... more Iron oxide particles were deposited in an ordered mesoporous material (SBA-15) with the aim of studying its behavior in the catalytic hydrogenation of CO (Fischer-Tropsch Synthesis). Bulk iron oxide, and iron supported on porous silica with different textural properties (Aerosil ® -200) were used for comparison. The characterization of the materials showed that in the Fe@SBA-15 material, iron nanoparticles were confined inside the mesopores of the SBA-15 support (pore diameter ~ 8 nm), and Fe@Aerosil ® -200 material also presented iron oxide nanoparticles highly dispersed on the material. In situ Synchrotron radiation XRD studies were performed in order to study the evolution of iron phases in the Fe@SBA-15 and the bulk iron oxide under hydrogen and hydrogen/carbon monoxide conditions. DFT calculations were performed on bare Fe(100) and a Fe 16 cluster in CO activation and C x H y hydrogenation. Catalytic microactivity tests, performed at conversions of ~ 6-8%, showed important differences in the selectivity of the materials. Higher selectivity to methane and light hydrocarbons were observed in the supported catalysts (Fe@SBA-15 and Fe@Aerosil ® -200) than in bulk Fe catalyst. Moreover, the supported catalysts showed selectivity to ethylene (Fe@SBA-15) and propylene (Fe@Aerosil ® -200), products that were not observed in the bulk iron catalyst. On the other hand, bulk iron showed a major selectivity to higher hydrocarbons (C 5 -C 9 ) and oxygenates.
HIGHLIGHTS Carbos foams were prepared employing sucrose as the carbon source. Porosity and mo... more HIGHLIGHTS Carbos foams were prepared employing sucrose as the carbon source. Porosity and morphology of the materials was controlled using different metallic nitrates. Nitrates of aluminum, iron and silver were used as blowing agents. The synthesized carbon foams have interesting CO2 adsorption capacities.
Three different designs for adsorption calorimeters are presented, which use sensors based on the... more Three different designs for adsorption calorimeters are presented, which use sensors based on the Seebeck effect. The noises of signals with respect to the baseline are evaluated on each one of the builded equipment and the detection limit of the thermal effects is expressed in µWatt. It was determined that the different designs and working conditions affect the baseline noise and the detection limit. Values of the noise in the baseline are between ± 100 µV and ± 0,5 µV and between 887,2 and 24 µWatt. These values allow making measures in the solid-gas interphase with very good precision.
Tesis doctoral inédita de la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento d... more Tesis doctoral inédita de la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de lectura: 19-6-199
Density-functional theory calculations based on the GGA-PBE (generalized gradient approximation P... more Density-functional theory calculations based on the GGA-PBE (generalized gradient approximation Perdew-Burke-Ernzerhof) exchange correlation functional were used to investigate the effect of hydrogen on the diffusion of adsorbed carbon, oxygen and hydrogen on the surface of Fe(100). The diffusion energy barrier was calculated for both clean surfaces and those with hydrogen, and it was found that hydrogen produced binding energies for carbon and oxygen. These bonds stabilized the binding of hydrogen with the Fe(100) surface. For all of the surface species studied here, the energy barrier was increased when hydrogen was coadsorbed, from 1.29 eV to 1.46 eV for C, from 0.33 eV to 0.53 eV for O and from 0.11 eV to 0.15 eV for H. An approximation of the diffusion coefficient was obtained from energy barrier calculations and a pre-exponential factor of diffusion was calculated. Carbon exhibited low diffusion at the surface under experimental temperatures, while oxygen diffusion was activated above 450 K and hydrogen was diffused in all the temperature ranges investigated.
Adsorption of co 2 on mixed oxides derived from hydrotalcites at several temperatures and high pr... more Adsorption of co 2 on mixed oxides derived from hydrotalcites at several temperatures and high pressures, Chemical Engineering
A raw montmorillonite (MMT) and three organomontmorillonites (OMMTs) with different amounts of he... more A raw montmorillonite (MMT) and three organomontmorillonites (OMMTs) with different amounts of hexadecyltrimethylammonium bromide (HDTMABr), and further silver loading (MMTeAg or OMMTeAg) were used to study their surface and structural changes and fungicidal activity. For OMMT and OMMTeAg samples, the specific surface area and micropore amount decreased with the increase in surfactant loading, whereas textural properties remained constant. Surfactant entrance into the interlayer with the increase in surfactant loading was irrespective of Ag loading, whereas a decreasing number of stacked clay platelets and loss of surfactant were found after Ag incorporation. Ag nanoparticles of different sizes and large silver aggregates found in OMMTeAg altered the electric surface charge as compared with the OMMT samples. Although the surfactant loading up to actual 100% of the MMT cation exchange capacity decreased silver retention, for MH2eAg sample (with 200% HDTMA loaded with respect to the MMT's cation exchange capacity, and further Ag loading) silver retention was close to that of MMT and null silver lixiviation could be assigned to the HDTMAeAg complex and AgBr formation. Fungicidal activity was correlated with surfactant loading, increasing with Ag addition.
Contamination of water with arsenic is a major global health problem. The use of adsorbent materi... more Contamination of water with arsenic is a major global health problem. The use of adsorbent materials for the removal of As from aqueous systems is a plausible solution to this problem. In this work, the use of commercial bentonites (purified and modified with iron (III)) for the removal of As from water was studied. The samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier Transformed Infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nitrogen adsorption / desorption isotherms to determine their physicochemical properties. The arsenic removal capacities of adsorbent materials were studied from 1 mg/L solutions of As (III) using the colorimetric technique of molybdenum blue. High adsorption capacity (0.33 mg / g) of As (III) was obtained in aqueous systems after 1 hour of treatment with unmodified bentonite. The incorporation of iron improved the removal performance in short times. The obtained results could be the starting point for the development of a low-cost filtration system that contributes to solve the problem of arsenic in water.
Natural zeolites are low in cost and exhibit interesting properties for applications in adsorptio... more Natural zeolites are low in cost and exhibit interesting properties for applications in adsorption and catalysis. However, the fact that they are natural materials, not obtained in pure form, and can incorporate various compensating ions can compromise their properties and restrict their use. As their textural and chemical properties are of great relevance for adsorption and catalysis applications, this work aims to study the modification of the natural zeolite clinoptilolite to obtain materials with better physicochemical properties. Clinoptilolite was treated with NaOH under various conditions. The treated material was characterized by X-ray diffraction, X-ray fluorescence, N 2 adsorption and desorption at 77 K, CO 2 adsorption at 273 K, and pyridine adsorption. The treatment allowed the removal of silicon from the material, improving the textural properties and preserving the structural Al. With the removal of Si, the Si/Al ratio decreased, and consequently, the number of acid and adsorptive sites increased. In addition, statistical planning revealed that the concentration of NaOH is the parameter that most influences the improvement of the textural properties.
The present work investigates the synthesis of iron-cobalt based nanocomposites supported on SBA-... more The present work investigates the synthesis of iron-cobalt based nanocomposites supported on SBA-15 and shows a detailed study of their porosity and the photocatalytic activity in methylene blue degradation as a model dye. The textural characterization indicated the presence of interconnected pores after the impregnation process and insertion of Fe and Co on SBA-15. TEM images confirmed that the SBA-15 mesopores were partially filled by Fe and Co species after the addition of metals and an average particle size of 11 nm. The diffractograms revealed the formation of the Fe 2 SiO 4 and CoFe 2 O 4 phases for the O-SBA-15 sample (oxide supported on SBA-15) and the presence of the Fe 7 Co 3 structure for the solid A-SBA-15 (alloy dispersed in mesoporous silica), indicating the phases that are partially blocking the mesopores. The photocatalysis results confirmed that the silica support is essential to optimize the photocatalytic activity of the Fe and Co species in the dye degradation, favoring the accessibility of active sites. The presence of the phase mixture, Fe 2 SiO 4, and Fe 7 Co 3 , in OAM-SBA-15 (oxide and alloy supported on SBA-15) sample, favors the photocatalytic activity of methylene blue (MB) due to the synergistic effect between Fe 2+ and Fe 0. The degradation of the MB occur through a sequence of reactions both on the solid surface and on the solution.
Materials Research-ibero-american Journal of Materials, Dec 1, 2008
A series of activated carbons (AC) were prepared from waste of the olive oil production in the Cu... more A series of activated carbons (AC) were prepared from waste of the olive oil production in the Cuyo Region, Argentine by two standard methods: a) physical activation by steam and b) chemical activation with ZnCl 2. The AC samples were characterized by nitrogen adsorption at 77 K and evaluated for natural gas storage purposes through the adsorption of methane at high pressures. The activated carbons showed micropore volumes up to 0.50 cm 3 .g-1 and total pore volumes as high as 0.9 cm 3 .g-1. The BET surface areas reached, in some cases, more than 1000 m 2 .g-1. The methane adsorption-measured in the range of 1-35 bar-attained values up to 59 V CH4 /V AC and total uptakes of more than 120 cm 3 .g-1 (STP). These preliminary results suggest that Cuyo's olive oil waste is appropriate for obtaining activated carbons for the storage of natural gas.
Iron oxide particles were deposited in an ordered mesoporous material (SBA-15) with the aim of st... more Iron oxide particles were deposited in an ordered mesoporous material (SBA-15) with the aim of studying its behavior in the catalytic hydrogenation of CO (Fischer-Tropsch Synthesis). Bulk iron oxide, and iron supported on porous silica with different textural properties (Aerosil ® -200) were used for comparison. The characterization of the materials showed that in the Fe@SBA-15 material, iron nanoparticles were confined inside the mesopores of the SBA-15 support (pore diameter ~ 8 nm), and Fe@Aerosil ® -200 material also presented iron oxide nanoparticles highly dispersed on the material. In situ Synchrotron radiation XRD studies were performed in order to study the evolution of iron phases in the Fe@SBA-15 and the bulk iron oxide under hydrogen and hydrogen/carbon monoxide conditions. DFT calculations were performed on bare Fe(100) and a Fe 16 cluster in CO activation and C x H y hydrogenation. Catalytic microactivity tests, performed at conversions of ~ 6-8%, showed important differences in the selectivity of the materials. Higher selectivity to methane and light hydrocarbons were observed in the supported catalysts (Fe@SBA-15 and Fe@Aerosil ® -200) than in bulk Fe catalyst. Moreover, the supported catalysts showed selectivity to ethylene (Fe@SBA-15) and propylene (Fe@Aerosil ® -200), products that were not observed in the bulk iron catalyst. On the other hand, bulk iron showed a major selectivity to higher hydrocarbons (C 5 -C 9 ) and oxygenates.
HIGHLIGHTS Carbos foams were prepared employing sucrose as the carbon source. Porosity and mo... more HIGHLIGHTS Carbos foams were prepared employing sucrose as the carbon source. Porosity and morphology of the materials was controlled using different metallic nitrates. Nitrates of aluminum, iron and silver were used as blowing agents. The synthesized carbon foams have interesting CO2 adsorption capacities.
Three different designs for adsorption calorimeters are presented, which use sensors based on the... more Three different designs for adsorption calorimeters are presented, which use sensors based on the Seebeck effect. The noises of signals with respect to the baseline are evaluated on each one of the builded equipment and the detection limit of the thermal effects is expressed in µWatt. It was determined that the different designs and working conditions affect the baseline noise and the detection limit. Values of the noise in the baseline are between ± 100 µV and ± 0,5 µV and between 887,2 and 24 µWatt. These values allow making measures in the solid-gas interphase with very good precision.
Tesis doctoral inédita de la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento d... more Tesis doctoral inédita de la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de lectura: 19-6-199
Density-functional theory calculations based on the GGA-PBE (generalized gradient approximation P... more Density-functional theory calculations based on the GGA-PBE (generalized gradient approximation Perdew-Burke-Ernzerhof) exchange correlation functional were used to investigate the effect of hydrogen on the diffusion of adsorbed carbon, oxygen and hydrogen on the surface of Fe(100). The diffusion energy barrier was calculated for both clean surfaces and those with hydrogen, and it was found that hydrogen produced binding energies for carbon and oxygen. These bonds stabilized the binding of hydrogen with the Fe(100) surface. For all of the surface species studied here, the energy barrier was increased when hydrogen was coadsorbed, from 1.29 eV to 1.46 eV for C, from 0.33 eV to 0.53 eV for O and from 0.11 eV to 0.15 eV for H. An approximation of the diffusion coefficient was obtained from energy barrier calculations and a pre-exponential factor of diffusion was calculated. Carbon exhibited low diffusion at the surface under experimental temperatures, while oxygen diffusion was activated above 450 K and hydrogen was diffused in all the temperature ranges investigated.
Adsorption of co 2 on mixed oxides derived from hydrotalcites at several temperatures and high pr... more Adsorption of co 2 on mixed oxides derived from hydrotalcites at several temperatures and high pressures, Chemical Engineering
A raw montmorillonite (MMT) and three organomontmorillonites (OMMTs) with different amounts of he... more A raw montmorillonite (MMT) and three organomontmorillonites (OMMTs) with different amounts of hexadecyltrimethylammonium bromide (HDTMABr), and further silver loading (MMTeAg or OMMTeAg) were used to study their surface and structural changes and fungicidal activity. For OMMT and OMMTeAg samples, the specific surface area and micropore amount decreased with the increase in surfactant loading, whereas textural properties remained constant. Surfactant entrance into the interlayer with the increase in surfactant loading was irrespective of Ag loading, whereas a decreasing number of stacked clay platelets and loss of surfactant were found after Ag incorporation. Ag nanoparticles of different sizes and large silver aggregates found in OMMTeAg altered the electric surface charge as compared with the OMMT samples. Although the surfactant loading up to actual 100% of the MMT cation exchange capacity decreased silver retention, for MH2eAg sample (with 200% HDTMA loaded with respect to the MMT's cation exchange capacity, and further Ag loading) silver retention was close to that of MMT and null silver lixiviation could be assigned to the HDTMAeAg complex and AgBr formation. Fungicidal activity was correlated with surfactant loading, increasing with Ag addition.
Contamination of water with arsenic is a major global health problem. The use of adsorbent materi... more Contamination of water with arsenic is a major global health problem. The use of adsorbent materials for the removal of As from aqueous systems is a plausible solution to this problem. In this work, the use of commercial bentonites (purified and modified with iron (III)) for the removal of As from water was studied. The samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier Transformed Infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nitrogen adsorption / desorption isotherms to determine their physicochemical properties. The arsenic removal capacities of adsorbent materials were studied from 1 mg/L solutions of As (III) using the colorimetric technique of molybdenum blue. High adsorption capacity (0.33 mg / g) of As (III) was obtained in aqueous systems after 1 hour of treatment with unmodified bentonite. The incorporation of iron improved the removal performance in short times. The obtained results could be the starting point for the development of a low-cost filtration system that contributes to solve the problem of arsenic in water.
Natural zeolites are low in cost and exhibit interesting properties for applications in adsorptio... more Natural zeolites are low in cost and exhibit interesting properties for applications in adsorption and catalysis. However, the fact that they are natural materials, not obtained in pure form, and can incorporate various compensating ions can compromise their properties and restrict their use. As their textural and chemical properties are of great relevance for adsorption and catalysis applications, this work aims to study the modification of the natural zeolite clinoptilolite to obtain materials with better physicochemical properties. Clinoptilolite was treated with NaOH under various conditions. The treated material was characterized by X-ray diffraction, X-ray fluorescence, N 2 adsorption and desorption at 77 K, CO 2 adsorption at 273 K, and pyridine adsorption. The treatment allowed the removal of silicon from the material, improving the textural properties and preserving the structural Al. With the removal of Si, the Si/Al ratio decreased, and consequently, the number of acid and adsorptive sites increased. In addition, statistical planning revealed that the concentration of NaOH is the parameter that most influences the improvement of the textural properties.
The present work investigates the synthesis of iron-cobalt based nanocomposites supported on SBA-... more The present work investigates the synthesis of iron-cobalt based nanocomposites supported on SBA-15 and shows a detailed study of their porosity and the photocatalytic activity in methylene blue degradation as a model dye. The textural characterization indicated the presence of interconnected pores after the impregnation process and insertion of Fe and Co on SBA-15. TEM images confirmed that the SBA-15 mesopores were partially filled by Fe and Co species after the addition of metals and an average particle size of 11 nm. The diffractograms revealed the formation of the Fe 2 SiO 4 and CoFe 2 O 4 phases for the O-SBA-15 sample (oxide supported on SBA-15) and the presence of the Fe 7 Co 3 structure for the solid A-SBA-15 (alloy dispersed in mesoporous silica), indicating the phases that are partially blocking the mesopores. The photocatalysis results confirmed that the silica support is essential to optimize the photocatalytic activity of the Fe and Co species in the dye degradation, favoring the accessibility of active sites. The presence of the phase mixture, Fe 2 SiO 4, and Fe 7 Co 3 , in OAM-SBA-15 (oxide and alloy supported on SBA-15) sample, favors the photocatalytic activity of methylene blue (MB) due to the synergistic effect between Fe 2+ and Fe 0. The degradation of the MB occur through a sequence of reactions both on the solid surface and on the solution.
Materials Research-ibero-american Journal of Materials, Dec 1, 2008
A series of activated carbons (AC) were prepared from waste of the olive oil production in the Cu... more A series of activated carbons (AC) were prepared from waste of the olive oil production in the Cuyo Region, Argentine by two standard methods: a) physical activation by steam and b) chemical activation with ZnCl 2. The AC samples were characterized by nitrogen adsorption at 77 K and evaluated for natural gas storage purposes through the adsorption of methane at high pressures. The activated carbons showed micropore volumes up to 0.50 cm 3 .g-1 and total pore volumes as high as 0.9 cm 3 .g-1. The BET surface areas reached, in some cases, more than 1000 m 2 .g-1. The methane adsorption-measured in the range of 1-35 bar-attained values up to 59 V CH4 /V AC and total uptakes of more than 120 cm 3 .g-1 (STP). These preliminary results suggest that Cuyo's olive oil waste is appropriate for obtaining activated carbons for the storage of natural gas.
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