John Regalbuto - Academia.edu (original) (raw)
Papers by John Regalbuto
The point of zero charge (PZC) of common oxide catalyst supports such as alumina and silica can b... more The point of zero charge (PZC) of common oxide catalyst supports such as alumina and silica can be altered by doping with anions such as Cl ÿ , which lower the ZPC, or cations such as Na þ or K þ , which raise the PZC. In a prior work it was shown that such alterations did not influence the properties of either support toward the adsorption of either cationic amine or anionic chloride complexes of Pt(IV) [1]. This follow-up work explored the hypothesis that in the pH range of interest (low pH over cation-doped silica, high pH over anion-doped alumina) the dopant is dissolved and the surface behaves as pure. The PZCs of doped silica and alumina washed in acidic, neutral, and basic solutions was measured by the EpHL (equilibrium pH at high loading) technique. Repeated acid washes of K þ-doped, PZC-raised silica quickly brought the PZC back to that of the pure oxide, and the same was observed for basic washed, PZC-lowered Cl ÿ-doped alumina. Thus, ion doping of silica and alumina does not appear to create irreversible changes in the materials' PZC and cannot be used to influence adsorptive properties.
Journal of Colloid and Interface Science, 2014
In this study we have developed a 2-surface model with the EPHL (''Equilibrium pH at high oxide l... more In this study we have developed a 2-surface model with the EPHL (''Equilibrium pH at high oxide loading'') method for mixed and composite oxides. Oxide charging parameters, namely the protonation and deprotonation constants and the hydroxyl surface densities, can be established from measurements of the pure oxides and used in the 2-surface model to predict the point of zero charges (PZC) of mixed and composite oxides. The accuracy of these predictions has been demonstrated with diverse control samples of known surface composition (physical mixtures of silica and alumina of high and low surface area). The EPHL method has been extended to composite materials (bound catalysts) and can explain correlations of reactivity with catalyst surface composition. The ''apparent surface coverage'' (ASC) of a particular mixed or composite oxide sample may then be determined by comparing the PZC of the material to either the 2-surface model results, using parameters of the individual oxides, or a calibration curve of EPHL measurements of physical mixtures of the individual ingredients.
Journal of Materials Chemistry A
To stabilize carbon supported gold nanoparticles which sinter rapidly in a corrosive environment,... more To stabilize carbon supported gold nanoparticles which sinter rapidly in a corrosive environment, bimetallic Ru@Au and Pt@Au core–shell supported nanoparticles were prepared by anchoring shells of Au onto higher surface free energy cores of Pt and Ru.
Journal of Catalysis, 2016
Several series of metal-acid bifunctional catalysts with controlled metal:acid ratios and metal s... more Several series of metal-acid bifunctional catalysts with controlled metal:acid ratios and metal site-acid site proximity were evaluated for n-heptane isomerization. Through the study of metal deposition reported in the companion paper, proximity could be achieved at four distinct scales; atomic, nano-, micro-, and millimeter scales. In the first two catalyst series, atomic and nanometer scale intimacy was obtained by depositing Pt onto acidic silica-alumina supports (Pt/Al-Si). It is demonstrated that poorly dispersed Pt/silica-alumina catalysts with nanometerscale proximity displayed a greater degree of bifunctionality than highly dispersed catalysts with atomic-scale proximity. In the latter two series of catalysts the scale of intimacy was stretched to micrometers using physical mixtures, and to millimeters by separating layers of nonacidic Pt/silica and metal free silica-alumina. Good bifunctionality is maintained at micrometer-scale intimacy and breaks down only at the millimeter scale. The best bifunctionality is achieved at very high acid to metal site ratios; results indicated that a single metal site can supply several hundred acid sites. Optimized bifunctional performance of Pt/silica-alumina catalysts for n-heptane isomerization requires a high acid-to-metal site ratio with nanometer to micrometer scale site proximity. The control of the numbers and proximities of metal and acid sites achieved in this work can be extended to many other metal-acid bifunctional reactions.
Advanced Materials Research, Feb 7, 2012
We have obtained relatively unambiguous evidence that validates a simple, predictive model descri... more We have obtained relatively unambiguous evidence that validates a simple, predictive model describing the uptake of noble metal coordination complexes from aqueous solutions onto oxide surfaces. The results confirm that the metal-oxide interaction is essentially electrostatic in nature. The evidence has been obtained by applying extended x-ray absorption fine structure (EXAFS) analysis to noble metal adsorption systems in which the effect of surface-localized pH has been isolated and quantified. The model has applications ranging from catalysts preparation to heavy metal pollution abatement and precious metal recovery.
Catalysts, 2016
Carbon-supported bimetallic Pt-Co cathode catalysts have been previously identified as higher act... more Carbon-supported bimetallic Pt-Co cathode catalysts have been previously identified as higher activity alternatives to conventional Pt/C catalysts for fuel cells. In this work, a series of Pt-Co/C catalysts were synthesized using electroless deposition (ED) of Pt on a Co/C catalyst prepared by modified charge enhanced dry impregnation. X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) characterization of the base catalyst showed highly dispersed particles. A basic ED bath containing PtCl 6 2´a s the Pt precursor, dimethylamine borane as reducing agent, and ethylenediamine as stabilizing agent successfully targeted deposition of Pt on Co particles. Simultaneous action of galvanic displacement and ED resulted in Pt-Co alloy formation observed in XRD and energy dispersive X-ray spectroscopy (XEDS) mapping. In addition, fast deposition kinetics resulted in hollow shell Pt-Co alloy particles while particles with Pt-rich shell and Co-rich cores formed with controlled Pt deposition. Electrochemical evaluation of the Pt-Co/C catalysts showed lower active surface but much higher mass and surface activities for oxygen reduction reaction compared to a commercial Pt/C fuel cell catalyst.
Langmuir, 1994
... Strength? Amal M. Shah and John R. Regalbuto' Department ... known. One such intrigu... more ... Strength? Amal M. Shah and John R. Regalbuto' Department ... known. One such intriguing phenomenon, observed in fundamental studies of noble metal adsorption onto alumina, is the retardation of metal adsorption at low pH. A ...
Catalysts, 2016
Pd/C and CoPd/C heterogeneous catalysts have been synthesized by adopting Charge Enhanced Dry Imp... more Pd/C and CoPd/C heterogeneous catalysts have been synthesized by adopting Charge Enhanced Dry Impregnation (CEDI). The particles size distribution, their high metal surface-to-bulk ratios, and synthesis feasibility are unmatchable to any known noble metal bimetallic heterogeneous catalyst preparation techniques. Next generation Fuel Cells and Fischer-Tropsch catalytic processes economy will be benefited from the proposed methodology.
Journal of Colloid and Interface Science, Aug 15, 2010
The procurement of oxide surface charging parameters has been a widely researched topic in recent... more The procurement of oxide surface charging parameters has been a widely researched topic in recent years [1-30]. In this study, a one-site, two-pK surface charging mechanism is used in combination with a diffuse double-layer description of the electric double-layer to fit pH shift data over silica and alumina. From these fits of pH data, with no further adjustment of parameters, metal adsorption can be predicted over both supports to a reasonable degree of accuracy. A multi-dimensional optimization procedure employing a Nelder-Mead simplex algorithm is used to optimize the DeltapK (pK(2)-pK(1)) parameter to obtain a best fit of the pH shift data with fixed PZC and hydroxyl density (N(s)). The resulting set of parameters is then used with no adjustment in a purely electrostatic adsorption model (the Revised Physical Adsorption or RPA model) in order to predict anionic chloroplatinic acid (CPA, [PtCl(6)](-2)) adsorption on alumina and cationic platinum tetraammine (PTA, [Pt(NH(3))(4)](+2)) adsorption on alumina and silica. The optimization procedure developed in this study gives reasonable values of the DeltapK compared to other values reported in the literature, with fits to the pH shift data at various oxide loadings with relative errors below 2.8%.
Applied Catalysis B: Environmental, 2016
The Journal of Physical Chemistry, 1995
The point of zero charge (PZC) of common oxide catalyst supports such as alumina and silica can b... more The point of zero charge (PZC) of common oxide catalyst supports such as alumina and silica can be altered by doping with anions such as Cl ÿ , which lower the ZPC, or cations such as Na þ or K þ , which raise the PZC. In a prior work it was shown that such alterations did not influence the properties of either support toward the adsorption of either cationic amine or anionic chloride complexes of Pt(IV) [1]. This follow-up work explored the hypothesis that in the pH range of interest (low pH over cation-doped silica, high pH over anion-doped alumina) the dopant is dissolved and the surface behaves as pure. The PZCs of doped silica and alumina washed in acidic, neutral, and basic solutions was measured by the EpHL (equilibrium pH at high loading) technique. Repeated acid washes of K þ-doped, PZC-raised silica quickly brought the PZC back to that of the pure oxide, and the same was observed for basic washed, PZC-lowered Cl ÿ-doped alumina. Thus, ion doping of silica and alumina does not appear to create irreversible changes in the materials' PZC and cannot be used to influence adsorptive properties.
Journal of Colloid and Interface Science, 2014
In this study we have developed a 2-surface model with the EPHL (''Equilibrium pH at high oxide l... more In this study we have developed a 2-surface model with the EPHL (''Equilibrium pH at high oxide loading'') method for mixed and composite oxides. Oxide charging parameters, namely the protonation and deprotonation constants and the hydroxyl surface densities, can be established from measurements of the pure oxides and used in the 2-surface model to predict the point of zero charges (PZC) of mixed and composite oxides. The accuracy of these predictions has been demonstrated with diverse control samples of known surface composition (physical mixtures of silica and alumina of high and low surface area). The EPHL method has been extended to composite materials (bound catalysts) and can explain correlations of reactivity with catalyst surface composition. The ''apparent surface coverage'' (ASC) of a particular mixed or composite oxide sample may then be determined by comparing the PZC of the material to either the 2-surface model results, using parameters of the individual oxides, or a calibration curve of EPHL measurements of physical mixtures of the individual ingredients.
Journal of Materials Chemistry A
To stabilize carbon supported gold nanoparticles which sinter rapidly in a corrosive environment,... more To stabilize carbon supported gold nanoparticles which sinter rapidly in a corrosive environment, bimetallic Ru@Au and Pt@Au core–shell supported nanoparticles were prepared by anchoring shells of Au onto higher surface free energy cores of Pt and Ru.
Journal of Catalysis, 2016
Several series of metal-acid bifunctional catalysts with controlled metal:acid ratios and metal s... more Several series of metal-acid bifunctional catalysts with controlled metal:acid ratios and metal site-acid site proximity were evaluated for n-heptane isomerization. Through the study of metal deposition reported in the companion paper, proximity could be achieved at four distinct scales; atomic, nano-, micro-, and millimeter scales. In the first two catalyst series, atomic and nanometer scale intimacy was obtained by depositing Pt onto acidic silica-alumina supports (Pt/Al-Si). It is demonstrated that poorly dispersed Pt/silica-alumina catalysts with nanometerscale proximity displayed a greater degree of bifunctionality than highly dispersed catalysts with atomic-scale proximity. In the latter two series of catalysts the scale of intimacy was stretched to micrometers using physical mixtures, and to millimeters by separating layers of nonacidic Pt/silica and metal free silica-alumina. Good bifunctionality is maintained at micrometer-scale intimacy and breaks down only at the millimeter scale. The best bifunctionality is achieved at very high acid to metal site ratios; results indicated that a single metal site can supply several hundred acid sites. Optimized bifunctional performance of Pt/silica-alumina catalysts for n-heptane isomerization requires a high acid-to-metal site ratio with nanometer to micrometer scale site proximity. The control of the numbers and proximities of metal and acid sites achieved in this work can be extended to many other metal-acid bifunctional reactions.
Advanced Materials Research, Feb 7, 2012
We have obtained relatively unambiguous evidence that validates a simple, predictive model descri... more We have obtained relatively unambiguous evidence that validates a simple, predictive model describing the uptake of noble metal coordination complexes from aqueous solutions onto oxide surfaces. The results confirm that the metal-oxide interaction is essentially electrostatic in nature. The evidence has been obtained by applying extended x-ray absorption fine structure (EXAFS) analysis to noble metal adsorption systems in which the effect of surface-localized pH has been isolated and quantified. The model has applications ranging from catalysts preparation to heavy metal pollution abatement and precious metal recovery.
Catalysts, 2016
Carbon-supported bimetallic Pt-Co cathode catalysts have been previously identified as higher act... more Carbon-supported bimetallic Pt-Co cathode catalysts have been previously identified as higher activity alternatives to conventional Pt/C catalysts for fuel cells. In this work, a series of Pt-Co/C catalysts were synthesized using electroless deposition (ED) of Pt on a Co/C catalyst prepared by modified charge enhanced dry impregnation. X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) characterization of the base catalyst showed highly dispersed particles. A basic ED bath containing PtCl 6 2´a s the Pt precursor, dimethylamine borane as reducing agent, and ethylenediamine as stabilizing agent successfully targeted deposition of Pt on Co particles. Simultaneous action of galvanic displacement and ED resulted in Pt-Co alloy formation observed in XRD and energy dispersive X-ray spectroscopy (XEDS) mapping. In addition, fast deposition kinetics resulted in hollow shell Pt-Co alloy particles while particles with Pt-rich shell and Co-rich cores formed with controlled Pt deposition. Electrochemical evaluation of the Pt-Co/C catalysts showed lower active surface but much higher mass and surface activities for oxygen reduction reaction compared to a commercial Pt/C fuel cell catalyst.
Langmuir, 1994
... Strength? Amal M. Shah and John R. Regalbuto' Department ... known. One such intrigu... more ... Strength? Amal M. Shah and John R. Regalbuto' Department ... known. One such intriguing phenomenon, observed in fundamental studies of noble metal adsorption onto alumina, is the retardation of metal adsorption at low pH. A ...
Catalysts, 2016
Pd/C and CoPd/C heterogeneous catalysts have been synthesized by adopting Charge Enhanced Dry Imp... more Pd/C and CoPd/C heterogeneous catalysts have been synthesized by adopting Charge Enhanced Dry Impregnation (CEDI). The particles size distribution, their high metal surface-to-bulk ratios, and synthesis feasibility are unmatchable to any known noble metal bimetallic heterogeneous catalyst preparation techniques. Next generation Fuel Cells and Fischer-Tropsch catalytic processes economy will be benefited from the proposed methodology.
Journal of Colloid and Interface Science, Aug 15, 2010
The procurement of oxide surface charging parameters has been a widely researched topic in recent... more The procurement of oxide surface charging parameters has been a widely researched topic in recent years [1-30]. In this study, a one-site, two-pK surface charging mechanism is used in combination with a diffuse double-layer description of the electric double-layer to fit pH shift data over silica and alumina. From these fits of pH data, with no further adjustment of parameters, metal adsorption can be predicted over both supports to a reasonable degree of accuracy. A multi-dimensional optimization procedure employing a Nelder-Mead simplex algorithm is used to optimize the DeltapK (pK(2)-pK(1)) parameter to obtain a best fit of the pH shift data with fixed PZC and hydroxyl density (N(s)). The resulting set of parameters is then used with no adjustment in a purely electrostatic adsorption model (the Revised Physical Adsorption or RPA model) in order to predict anionic chloroplatinic acid (CPA, [PtCl(6)](-2)) adsorption on alumina and cationic platinum tetraammine (PTA, [Pt(NH(3))(4)](+2)) adsorption on alumina and silica. The optimization procedure developed in this study gives reasonable values of the DeltapK compared to other values reported in the literature, with fits to the pH shift data at various oxide loadings with relative errors below 2.8%.
Applied Catalysis B: Environmental, 2016
The Journal of Physical Chemistry, 1995