Alan Weimer - Academia.edu (original) (raw)

Papers by Alan Weimer

Research paper thumbnail of Stabilization of Supported Metal Nanoparticles Using an Ultrathin Porous Shell

ACS Catalysis, 2011

ABSTRACT Supported Pt nanoparticles (<2 nm) were stabilized by a highly porous, alumina na... more ABSTRACT Supported Pt nanoparticles (<2 nm) were stabilized by a highly porous, alumina nanofilm that was deposited on the Pt and its high surface area silica support. The alumina film with subnanometer thickness control resulted from thermal decomposition of an aluminum alkoxide layer that was deposited by molecular layer deposition (MLD). A catalyst with a porous ultrathin alumina layer was much more stable to calcination in air, even at 800 °C. The alumina-coated Pt nanoparticles were less catalytically active, most likely because of the small size of the pores in the alumina layer.

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Research paper thumbnail of Time-dependent behavior of bubble volume in fluidized beds

Industrial & Engineering Chemistry Fundamentals, 1985

Although a number of steady-state fluidized-bed hydrodynamic models are available (Davidson and H... more Although a number of steady-state fluidized-bed hydrodynamic models are available (Davidson and Harrison, 1963; Kunii and Levenspiel, 1968; Fryer and Potter, 1972), detailed time-dependent studies of gas flow have not been carried out to date. Murray (1965a, b), ...

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Research paper thumbnail of Design considerations for a multiple tube solar reactor

Solar Energy, 2013

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Research paper thumbnail of Solvent Control of Surface Plasmon-Mediated Chemical Deposition of Au Nanoparticles from Alkylgold Phosphine Complexes

ACS applied materials & interfaces, Jan 24, 2015

Bottom-up approaches to nanofabrication are of great interest because they can enable structural ... more Bottom-up approaches to nanofabrication are of great interest because they can enable structural control while minimizing material waste and fabrication time. One new bottom-up nanofabrication method involves excitation of the surface plasmon resonance (SPR) of a Ag surface to drive deposition of sub-15 nm Au nanoparticles from MeAuPPh3. In this work we used density functional theory to investigate the role of the PPh3 ligands of the Au precursor and the effect of adsorbed solvent on the deposition process, and to elucidate the mechanism of Au nanoparticle deposition. In the absence of solvent, the calculated barrier to MeAuPPh3 dissociation on the bare surface is <20 kcal/mol, making it facile at room temperature. Once adsorbed on the surface, neighboring MeAu fragments undergo ethane elimination to produce Au adatoms that cluster into Au nanoparticles. However, if the sample is immersed in benzene, we predict that the monolayer of adsorbed solvent blocks the adsorption of MeAuP...

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Research paper thumbnail of II.I.3 Solar-Thermal Hydrogen Production Using a Metal-Oxide Based Thermochemical Water Splitting Cycle

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Research paper thumbnail of Thermodynamic Considerations for the Design of Solar-Thermal Chemical Processes

ASME 2009 3rd International Conference on Energy Sustainability, Volume 2, 2009

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Research paper thumbnail of Near-isothermal Ferrite/Alumina (“Hercynite Cycle”) Two-step Red/Ox Cycle for Solar-thermal Water Splitting

Light, Energy and the Environment, 2014

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Research paper thumbnail of Dynamics of particle size/conversion distributions in fluidized beds: application to char gasification

Powder Technology, 1980

Dynamic relations are given which describe the time-dependent behavior of the distribution of rea... more Dynamic relations are given which describe the time-dependent behavior of the distribution of reacting particles which are distributed in both size and in their.

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Research paper thumbnail of Fast Switches Formed by a Low Temperature Direct Ink Writing Process

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Research paper thumbnail of An investigation of a fluidized bed solids feeder for an aerosol flow reactor

Powder Technology, 2010

Feeding a dispersed cloud of powder into an aerosol flow reactor, particularly on a laboratory sc... more Feeding a dispersed cloud of powder into an aerosol flow reactor, particularly on a laboratory scale, presents challenges. In this study, a fluid bed feeder was developed. With this feeder, fluidizing gas and brass milling media were the key means to disperse and break apart particle aggregates. Particle size distributions were measured with a laser imaging system and the dispersing

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Research paper thumbnail of Thermochemical production of fuels with concentrated solar energy

Optics express, Jan 26, 2010

This review article develops some of the underlying science for converting concentrated solar ene... more This review article develops some of the underlying science for converting concentrated solar energy into chemical fuels and presents examples of solar thermochemical processes and reactors.

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Research paper thumbnail of Rapid solar-thermal dissociation of natural gas in an aerosol flow reactor

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Research paper thumbnail of Atomic layer deposition on particles using a fluidized bed reactor with in situ mass spectrometry

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Research paper thumbnail of Aggregation behavior of nanoparticles in fluidized beds

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Research paper thumbnail of Engineered particle processing

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Research paper thumbnail of Manganese oxide dissociation kinetics for the Mn2O3 thermochemical water-splitting cycle. Part 1: Experimental

ABSTRACT It is shown that the dissociation of Mn2O3 to MnO in a short residence time aerosol flow... more ABSTRACT It is shown that the dissociation of Mn2O3 to MnO in a short residence time aerosol flow reactor can achieve high conversions approaching 75% when the concentration of oxygen is kept below 0.25%. Significant recombination reaction occurs when the oxygen content exceeds ∼0.25% by volume. A dual reaction mechanism for Mn2O3 dissociation was found: RAvrami−Erofeev=−A1e−Ea,1/RTn(1−X)[−ln(1−X)](n−1)/nROrder_of_reaction=−A2e−Ea,2/RT(1−X)n with the transition from one mechanism to the other occurring at an extent of reaction of approximately 0.6. Rate constants for the two mechanisms were calculated to be 1.8×107±1.3×107 and 5.6×103±4.1×103s−1, respectively, for oxygen concentration

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Research paper thumbnail of Atomic layer deposition on particles using a fluidized bed reactor with in situ mass spectrometry

Surface and Coatings Technology, 2007

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Research paper thumbnail of Modeling of a Multi-Tube Solar Reactor for Hydrogen Production at High Temperatures

ASME 2007 Energy Sustainability Conference, 2007

... Sophia Haussener, David Hirsch, Christopher Perkins, Alan Weimer, Allan Lewandowski, Aldo Ste... more ... Sophia Haussener, David Hirsch, Christopher Perkins, Alan Weimer, Allan Lewandowski, Aldo Steinfeld. ... allowed the successful demonstration of the zinc oxide dissociation in the temperature range 1500–2100 K at the High-Flux Solar Furnace (HFSF) at NREL in Golden, CO. ...

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Research paper thumbnail of Individual Nanoparticle Coating Using Atomic Layer Deposition

Luis F. Hakim, University of Colorado at Boulder, 1111 Engineering Drive ECCH 111 UCB 424, Boulde... more Luis F. Hakim, University of Colorado at Boulder, 1111 Engineering Drive ECCH 111 UCB 424, Boulder, CO 80309, Steven M. George, Chemistry and Biochemistry, University of Colorado at Boulder, Ekeley W145B, Boulder, CO 80309, and Alan W. Weimer, University ...

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Research paper thumbnail of Investigation of the Water Reduction with Zinc Powder Aerosol to Form Hydrogen Fuel

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Research paper thumbnail of Stabilization of Supported Metal Nanoparticles Using an Ultrathin Porous Shell

ACS Catalysis, 2011

ABSTRACT Supported Pt nanoparticles (&lt;2 nm) were stabilized by a highly porous, alumina na... more ABSTRACT Supported Pt nanoparticles (&lt;2 nm) were stabilized by a highly porous, alumina nanofilm that was deposited on the Pt and its high surface area silica support. The alumina film with subnanometer thickness control resulted from thermal decomposition of an aluminum alkoxide layer that was deposited by molecular layer deposition (MLD). A catalyst with a porous ultrathin alumina layer was much more stable to calcination in air, even at 800 °C. The alumina-coated Pt nanoparticles were less catalytically active, most likely because of the small size of the pores in the alumina layer.

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Research paper thumbnail of Time-dependent behavior of bubble volume in fluidized beds

Industrial & Engineering Chemistry Fundamentals, 1985

Although a number of steady-state fluidized-bed hydrodynamic models are available (Davidson and H... more Although a number of steady-state fluidized-bed hydrodynamic models are available (Davidson and Harrison, 1963; Kunii and Levenspiel, 1968; Fryer and Potter, 1972), detailed time-dependent studies of gas flow have not been carried out to date. Murray (1965a, b), ...

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Research paper thumbnail of Design considerations for a multiple tube solar reactor

Solar Energy, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Solvent Control of Surface Plasmon-Mediated Chemical Deposition of Au Nanoparticles from Alkylgold Phosphine Complexes

ACS applied materials & interfaces, Jan 24, 2015

Bottom-up approaches to nanofabrication are of great interest because they can enable structural ... more Bottom-up approaches to nanofabrication are of great interest because they can enable structural control while minimizing material waste and fabrication time. One new bottom-up nanofabrication method involves excitation of the surface plasmon resonance (SPR) of a Ag surface to drive deposition of sub-15 nm Au nanoparticles from MeAuPPh3. In this work we used density functional theory to investigate the role of the PPh3 ligands of the Au precursor and the effect of adsorbed solvent on the deposition process, and to elucidate the mechanism of Au nanoparticle deposition. In the absence of solvent, the calculated barrier to MeAuPPh3 dissociation on the bare surface is <20 kcal/mol, making it facile at room temperature. Once adsorbed on the surface, neighboring MeAu fragments undergo ethane elimination to produce Au adatoms that cluster into Au nanoparticles. However, if the sample is immersed in benzene, we predict that the monolayer of adsorbed solvent blocks the adsorption of MeAuP...

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Research paper thumbnail of II.I.3 Solar-Thermal Hydrogen Production Using a Metal-Oxide Based Thermochemical Water Splitting Cycle

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Thermodynamic Considerations for the Design of Solar-Thermal Chemical Processes

ASME 2009 3rd International Conference on Energy Sustainability, Volume 2, 2009

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Near-isothermal Ferrite/Alumina (“Hercynite Cycle”) Two-step Red/Ox Cycle for Solar-thermal Water Splitting

Light, Energy and the Environment, 2014

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Research paper thumbnail of Dynamics of particle size/conversion distributions in fluidized beds: application to char gasification

Powder Technology, 1980

Dynamic relations are given which describe the time-dependent behavior of the distribution of rea... more Dynamic relations are given which describe the time-dependent behavior of the distribution of reacting particles which are distributed in both size and in their.

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Research paper thumbnail of Fast Switches Formed by a Low Temperature Direct Ink Writing Process

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Research paper thumbnail of An investigation of a fluidized bed solids feeder for an aerosol flow reactor

Powder Technology, 2010

Feeding a dispersed cloud of powder into an aerosol flow reactor, particularly on a laboratory sc... more Feeding a dispersed cloud of powder into an aerosol flow reactor, particularly on a laboratory scale, presents challenges. In this study, a fluid bed feeder was developed. With this feeder, fluidizing gas and brass milling media were the key means to disperse and break apart particle aggregates. Particle size distributions were measured with a laser imaging system and the dispersing

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Thermochemical production of fuels with concentrated solar energy

Optics express, Jan 26, 2010

This review article develops some of the underlying science for converting concentrated solar ene... more This review article develops some of the underlying science for converting concentrated solar energy into chemical fuels and presents examples of solar thermochemical processes and reactors.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Rapid solar-thermal dissociation of natural gas in an aerosol flow reactor

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Atomic layer deposition on particles using a fluidized bed reactor with in situ mass spectrometry

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Aggregation behavior of nanoparticles in fluidized beds

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Engineered particle processing

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Manganese oxide dissociation kinetics for the Mn2O3 thermochemical water-splitting cycle. Part 1: Experimental

ABSTRACT It is shown that the dissociation of Mn2O3 to MnO in a short residence time aerosol flow... more ABSTRACT It is shown that the dissociation of Mn2O3 to MnO in a short residence time aerosol flow reactor can achieve high conversions approaching 75% when the concentration of oxygen is kept below 0.25%. Significant recombination reaction occurs when the oxygen content exceeds ∼0.25% by volume. A dual reaction mechanism for Mn2O3 dissociation was found: RAvrami−Erofeev=−A1e−Ea,1/RTn(1−X)[−ln(1−X)](n−1)/nROrder_of_reaction=−A2e−Ea,2/RT(1−X)n with the transition from one mechanism to the other occurring at an extent of reaction of approximately 0.6. Rate constants for the two mechanisms were calculated to be 1.8×107±1.3×107 and 5.6×103±4.1×103s−1, respectively, for oxygen concentration

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Research paper thumbnail of Atomic layer deposition on particles using a fluidized bed reactor with in situ mass spectrometry

Surface and Coatings Technology, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modeling of a Multi-Tube Solar Reactor for Hydrogen Production at High Temperatures

ASME 2007 Energy Sustainability Conference, 2007

... Sophia Haussener, David Hirsch, Christopher Perkins, Alan Weimer, Allan Lewandowski, Aldo Ste... more ... Sophia Haussener, David Hirsch, Christopher Perkins, Alan Weimer, Allan Lewandowski, Aldo Steinfeld. ... allowed the successful demonstration of the zinc oxide dissociation in the temperature range 1500–2100 K at the High-Flux Solar Furnace (HFSF) at NREL in Golden, CO. ...

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Research paper thumbnail of Individual Nanoparticle Coating Using Atomic Layer Deposition

Luis F. Hakim, University of Colorado at Boulder, 1111 Engineering Drive ECCH 111 UCB 424, Boulde... more Luis F. Hakim, University of Colorado at Boulder, 1111 Engineering Drive ECCH 111 UCB 424, Boulder, CO 80309, Steven M. George, Chemistry and Biochemistry, University of Colorado at Boulder, Ekeley W145B, Boulder, CO 80309, and Alan W. Weimer, University ...

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Research paper thumbnail of Investigation of the Water Reduction with Zinc Powder Aerosol to Form Hydrogen Fuel

Bookmarks Related papers MentionsView impact