Jacinto Sa - Academia.edu (original) (raw)
Papers by Jacinto Sa
Catalysis Letters, 2005
Bimetallic Pd–Sn catalysts were synthesized by incipient-wetness impregnation of the metals on al... more Bimetallic Pd–Sn catalysts were synthesized by incipient-wetness impregnation of the metals on alumina and employed for the reduction of nitrates from aqueous solutions. The catalysts were characterized by FTIR spectroscopy of adsorbed CO, X-ray diffraction (XRD), transmission electron microscopy (TEM), and H2 chemisorption. The influence of the metal ratio was evaluated in reaction measurements. The bimetallic Pd–Sn catalysts exhibited high selectivity for nitrate removal forming less NO 2− and NH 4+ than the Pd–Cu catalysts.
Journal of Catalysis, 2005
Monometallic palladium catalysts were synthesized using different titanium supports and tested fo... more Monometallic palladium catalysts were synthesized using different titanium supports and tested for the reduction of nitrates from aqueous solutions using hydrogen as a reductant. The Pd/TiO 2 catalysts were characterized by electron paramagnetic resonance (EPR), lowtemperature Fourier transform infrared (FTIR) spectroscopy of adsorbed CO, and X-ray diffraction (XRD). The catalysts studied exhibited a high activity for nitrate removal with a lower tendency for nitrite formation than the conventional bimetallic Pd catalysts. Although ammonium formation was greater than desired, the use of a monometallic catalyst for this two-step reduction process is significant and suggests that a single site may be responsible for both reduction stages. The titanium support (particularly the Ti 3+ centers generated during prereduction in the presence of Pd) appear to play an important role in the nitrate degradation process. The potential role of Pd β-hydride in generating these Ti 3+ centers is discussed.
Applied Catalysis A-general, 2005
Bimetallic (Pd/Cu) catalysts supported on alumina were used for the degradation of nitrates in wa... more Bimetallic (Pd/Cu) catalysts supported on alumina were used for the degradation of nitrates in water. The reduction temperature strongly affects the surface and oxidation states of the metals on the catalysts. These significant changes were characterized by FT-IR, XPS, TEM with EDX and H 2 chemisorption. Migration of superficial copper on top of palladium and towards the support during the reducing steps was observed, moreover palladium particles free of copper were found. With increasing reduction temperature the activity of the bimetallic catalysts passes through a maximum whereas the selectivity to nitrogen increases. #
Applied Catalysis B-environmental, 2007
A Pd/SnO2 catalyst was doped with low concentrations of Bi in order to induce selective poisoning... more A Pd/SnO2 catalyst was doped with low concentrations of Bi in order to induce selective poisoning of sites on the Pd surface in order to test a hypothesis that specific surface sites are responsible for ammonium formation during the catalytic hydrogenation of nitrates ...
Applied Catalysis B-environmental, 2011
Catalytic hydrogenation of nitrates has been studied since the beginning of the nineties. Despite... more Catalytic hydrogenation of nitrates has been studied since the beginning of the nineties. Despite the encouraging initial results the problematic of ammonium by-product formation is yet to be solved. This manuscript aims to be an overview of past and present research in the field and propose some key areas, which should be addressed to improve current and newly developed systems.
Catalysis Communications, 2008
Detection of mobile charge carriers consistent with a process involving electron transfer from Ti... more Detection of mobile charge carriers consistent with a process involving electron transfer from TiO 2 to metal particle was measured by EPR and FTIR in the presence of a hole scavenger and under UV irradiation. The main role of the metal (Ag, Au or Cu) was to scavenge the ...
Journal of Physical Chemistry B, 2006
A sample containing Pd nanoparticles deposited on TiO 2 was subjected to a series of different th... more A sample containing Pd nanoparticles deposited on TiO 2 was subjected to a series of different thermal pretreatments. The range of these treatments was selected to provide a palladium surface in a number of different states, including a form where TiO x overlayers had been formed. Experiments were conducted to determine how the state of the Pd surface influenced the formation of Pd hydride. The amount of hydrogen released during a temperature-programmed experiment was used to quantify the extent of Pd -hydride formation following room-temperature exposure to hydrogen. Samples were characterized by HAADF (highangle annular dark-field) electron microscopy with EDX (energy-dispersive X-ray) analysis and CO pulse chemisorption and FTIR (Fourier transform infrared spectroscopy) of adsorbed CO. The amount and the ease with which Pd -hydride was formed was found to be dependent on the metal surface area, the presence of titania overlayers, and the Pd surface roughness/defect concentration.
Catalysis Letters, 2007
Pd/TiO2 catalysts were found to enter an strong metal support interaction (SMSI) state after redu... more Pd/TiO2 catalysts were found to enter an strong metal support interaction (SMSI) state after reduction at temperatures as low as 473 K. This was identified as a significant loss in the CO uptake as monitored by low temperature FTIR. Electron microscopy provides direct evidence of the presence of ordered, reduced titanium oxide layers over palladium (SMSI state) for Pd/TiO2 catalysts following reduction at temperature 623 K. The crystal phase was identified as Ti4O7 and this phase, once formed, was found to be stable even after exposure to atmospheric conditions.
Applied Catalysis B-environmental, 2009
Applied Catalysis B-environmental, 2008
The interactions between Pd/TiO 2 catalyst and the reactants and potential reaction intermediates... more The interactions between Pd/TiO 2 catalyst and the reactants and potential reaction intermediates present during aqueous nitrate reduction, including NO 3 À , NO 2 À and NO in the presence of H 2 and H 2 O were studied by infrared spectroscopy. Adsorbed forms of NO, nitrite and nitrate could all be detected in the presence of water. In the presence of water/H 2 , nitrate was the most stable surface species followed by nitrite and then highly reactive NO, suggesting that the reduction of nitrate to nitrite is the rate-limiting step. High concentrations of adsorbed nitrite appear to be linked to the detection of gaseous N 2 O while the formation of ammonia is related to reactions on the Pd surface and the extent of formation is linked to high levels of adsorbed NO in addition to the surface hydrogen availability and the presence of water. #
Catalysis Letters, 2005
Bimetallic Pd–Sn catalysts were synthesized by incipient-wetness impregnation of the metals on al... more Bimetallic Pd–Sn catalysts were synthesized by incipient-wetness impregnation of the metals on alumina and employed for the reduction of nitrates from aqueous solutions. The catalysts were characterized by FTIR spectroscopy of adsorbed CO, X-ray diffraction (XRD), transmission electron microscopy (TEM), and H2 chemisorption. The influence of the metal ratio was evaluated in reaction measurements. The bimetallic Pd–Sn catalysts exhibited high selectivity for nitrate removal forming less NO 2− and NH 4+ than the Pd–Cu catalysts.
Journal of Catalysis, 2005
Monometallic palladium catalysts were synthesized using different titanium supports and tested fo... more Monometallic palladium catalysts were synthesized using different titanium supports and tested for the reduction of nitrates from aqueous solutions using hydrogen as a reductant. The Pd/TiO 2 catalysts were characterized by electron paramagnetic resonance (EPR), lowtemperature Fourier transform infrared (FTIR) spectroscopy of adsorbed CO, and X-ray diffraction (XRD). The catalysts studied exhibited a high activity for nitrate removal with a lower tendency for nitrite formation than the conventional bimetallic Pd catalysts. Although ammonium formation was greater than desired, the use of a monometallic catalyst for this two-step reduction process is significant and suggests that a single site may be responsible for both reduction stages. The titanium support (particularly the Ti 3+ centers generated during prereduction in the presence of Pd) appear to play an important role in the nitrate degradation process. The potential role of Pd β-hydride in generating these Ti 3+ centers is discussed.
Applied Catalysis A-general, 2005
Bimetallic (Pd/Cu) catalysts supported on alumina were used for the degradation of nitrates in wa... more Bimetallic (Pd/Cu) catalysts supported on alumina were used for the degradation of nitrates in water. The reduction temperature strongly affects the surface and oxidation states of the metals on the catalysts. These significant changes were characterized by FT-IR, XPS, TEM with EDX and H 2 chemisorption. Migration of superficial copper on top of palladium and towards the support during the reducing steps was observed, moreover palladium particles free of copper were found. With increasing reduction temperature the activity of the bimetallic catalysts passes through a maximum whereas the selectivity to nitrogen increases. #
Applied Catalysis B-environmental, 2007
A Pd/SnO2 catalyst was doped with low concentrations of Bi in order to induce selective poisoning... more A Pd/SnO2 catalyst was doped with low concentrations of Bi in order to induce selective poisoning of sites on the Pd surface in order to test a hypothesis that specific surface sites are responsible for ammonium formation during the catalytic hydrogenation of nitrates ...
Applied Catalysis B-environmental, 2011
Catalytic hydrogenation of nitrates has been studied since the beginning of the nineties. Despite... more Catalytic hydrogenation of nitrates has been studied since the beginning of the nineties. Despite the encouraging initial results the problematic of ammonium by-product formation is yet to be solved. This manuscript aims to be an overview of past and present research in the field and propose some key areas, which should be addressed to improve current and newly developed systems.
Catalysis Communications, 2008
Detection of mobile charge carriers consistent with a process involving electron transfer from Ti... more Detection of mobile charge carriers consistent with a process involving electron transfer from TiO 2 to metal particle was measured by EPR and FTIR in the presence of a hole scavenger and under UV irradiation. The main role of the metal (Ag, Au or Cu) was to scavenge the ...
Journal of Physical Chemistry B, 2006
A sample containing Pd nanoparticles deposited on TiO 2 was subjected to a series of different th... more A sample containing Pd nanoparticles deposited on TiO 2 was subjected to a series of different thermal pretreatments. The range of these treatments was selected to provide a palladium surface in a number of different states, including a form where TiO x overlayers had been formed. Experiments were conducted to determine how the state of the Pd surface influenced the formation of Pd hydride. The amount of hydrogen released during a temperature-programmed experiment was used to quantify the extent of Pd -hydride formation following room-temperature exposure to hydrogen. Samples were characterized by HAADF (highangle annular dark-field) electron microscopy with EDX (energy-dispersive X-ray) analysis and CO pulse chemisorption and FTIR (Fourier transform infrared spectroscopy) of adsorbed CO. The amount and the ease with which Pd -hydride was formed was found to be dependent on the metal surface area, the presence of titania overlayers, and the Pd surface roughness/defect concentration.
Catalysis Letters, 2007
Pd/TiO2 catalysts were found to enter an strong metal support interaction (SMSI) state after redu... more Pd/TiO2 catalysts were found to enter an strong metal support interaction (SMSI) state after reduction at temperatures as low as 473 K. This was identified as a significant loss in the CO uptake as monitored by low temperature FTIR. Electron microscopy provides direct evidence of the presence of ordered, reduced titanium oxide layers over palladium (SMSI state) for Pd/TiO2 catalysts following reduction at temperature 623 K. The crystal phase was identified as Ti4O7 and this phase, once formed, was found to be stable even after exposure to atmospheric conditions.
Applied Catalysis B-environmental, 2009
Applied Catalysis B-environmental, 2008
The interactions between Pd/TiO 2 catalyst and the reactants and potential reaction intermediates... more The interactions between Pd/TiO 2 catalyst and the reactants and potential reaction intermediates present during aqueous nitrate reduction, including NO 3 À , NO 2 À and NO in the presence of H 2 and H 2 O were studied by infrared spectroscopy. Adsorbed forms of NO, nitrite and nitrate could all be detected in the presence of water. In the presence of water/H 2 , nitrate was the most stable surface species followed by nitrite and then highly reactive NO, suggesting that the reduction of nitrate to nitrite is the rate-limiting step. High concentrations of adsorbed nitrite appear to be linked to the detection of gaseous N 2 O while the formation of ammonia is related to reactions on the Pd surface and the extent of formation is linked to high levels of adsorbed NO in addition to the surface hydrogen availability and the presence of water. #