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.
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), ...
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...
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.
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
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.
A solar-thermal aerosol flow reactor process is being developed to dissociate natural gas (NG) to... more A solar-thermal aerosol flow reactor process is being developed to dissociate natural gas (NG) to hydrogen (H 2 ) and carbon black at high rates. Concentrated sunlight approaching 10 kW heats a 9:4 cm long  2:4 cm diameter graphite reaction tube to temperatures~2000 K using a 74% theoretically efficient secondary concentrator. Pure methane feed has been dissociated to 70% for residence times less than 0.1 s. The resulting carbon black is 20-40 nm in size, amorphous, and pure. A 5 million (M) kg/yr carbon black/1.67 M kg/yr H 2 plant is considered for process scale-up. The total permanent investment (TPI) of this plant is $12.7 M. A 15% IRR after tax is achieved when the carbon black is sold for $0.66/ kg and the H 2 for $13.80/GJ. This plant could supply 0.06% of the world carbon black market. For this scenario, the solar-thermal process avoids 277 MJ fossil fuel and 13.9 kg-equivalent CO 2 /kg H 2 produced as compared to conventional steam-methane reforming and furnace black processing. #
A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to ... more A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to particle surfaces to functionalize particles at large scale using atomic layer deposition (ALD). Nano-and micron-sized particles were effectively fluidized using an inert carrier gas assisted by mechanical agitation of the powder bed. The gas-solid contacting properties of fluidized bed reactors are beneficial for ALD surface reactions, while the frequent solid-solid collisions do not disrupt the self-limiting behavior of ALD reactant gases. Films can be deposited with monolayer control on individual particles of various substrate types, including metals, ceramics and polymers. In situ mass spectrometry was used for realtime monitoring of gaseous product(s) and reactants throughout the ALD reaction. Alumina (Al 2 O 3 ) ALD on particles demonstrates the process control capabilities of this unique, scalable configuration. The applications of Al 2 O 3 ALD films on particles are widely varying but typically involve core substrate surface passivation, which includes thermal oxidation resistance, photocatalytic activity mitigation and the fabrication of electrically insulative metal particles. Particle functionalization is achievable to nanoscale precision on a wide range of substrate types and sizes with minimal waste of costly ALD precursors and process time.
The fluidization behavior of fumed silica, zirconia, and iron oxide nanopowders was studied at at... more The fluidization behavior of fumed silica, zirconia, and iron oxide nanopowders was studied at atmospheric and reduced pressures. Using a high-speed laser imaging system, the characteristics of fluidized aggregates of nanoparticles were studied in real time. The effect of different particle interactions such as London -van der Waals, liquid bridging and electrostatic on different fluidization parameters was studied at atmospheric pressure. The reduction of interparticle forces resulted in a reduced aggregate size and minimum fluidization velocity (U mf ) and an increased bed expansion. Nanoparticles were also fluidized at reduced pressure (¨16 Pa) with vibration to study the effect of low pressure on the minimum fluidization velocity. Aggregate properties (size, density) instead of primary nanoparticle properties were found to govern the minimum fluidization velocity and expansion of the fluidized bed. An important consideration is the relative strength of intra-aggregate interparticle forces (forces within the aggregate holding nanoparticles together) to inter-aggregate interparticle forces (forces between aggregates). This relative strength may be inferred from the sphericity of the aggregates during fluidization. D
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
A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to ... more A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to particle surfaces to functionalize particles at large scale using atomic layer deposition (ALD). Nano-and micron-sized particles were effectively fluidized using an inert carrier gas assisted by mechanical agitation of the powder bed. The gas-solid contacting properties of fluidized bed reactors are beneficial for ALD surface reactions, while the frequent solid-solid collisions do not disrupt the self-limiting behavior of ALD reactant gases. Films can be deposited with monolayer control on individual particles of various substrate types, including metals, ceramics and polymers. In situ mass spectrometry was used for realtime monitoring of gaseous product(s) and reactants throughout the ALD reaction. Alumina (Al 2 O 3 ) ALD on particles demonstrates the process control capabilities of this unique, scalable configuration. The applications of Al 2 O 3 ALD films on particles are widely varying but typically involve core substrate surface passivation, which includes thermal oxidation resistance, photocatalytic activity mitigation and the fabrication of electrically insulative metal particles. Particle functionalization is achievable to nanoscale precision on a wide range of substrate types and sizes with minimal waste of costly ALD precursors and process time.
... 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. ...
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 ...
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.
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), ...
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...
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.
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
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.
A solar-thermal aerosol flow reactor process is being developed to dissociate natural gas (NG) to... more A solar-thermal aerosol flow reactor process is being developed to dissociate natural gas (NG) to hydrogen (H 2 ) and carbon black at high rates. Concentrated sunlight approaching 10 kW heats a 9:4 cm long  2:4 cm diameter graphite reaction tube to temperatures~2000 K using a 74% theoretically efficient secondary concentrator. Pure methane feed has been dissociated to 70% for residence times less than 0.1 s. The resulting carbon black is 20-40 nm in size, amorphous, and pure. A 5 million (M) kg/yr carbon black/1.67 M kg/yr H 2 plant is considered for process scale-up. The total permanent investment (TPI) of this plant is $12.7 M. A 15% IRR after tax is achieved when the carbon black is sold for $0.66/ kg and the H 2 for $13.80/GJ. This plant could supply 0.06% of the world carbon black market. For this scenario, the solar-thermal process avoids 277 MJ fossil fuel and 13.9 kg-equivalent CO 2 /kg H 2 produced as compared to conventional steam-methane reforming and furnace black processing. #
A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to ... more A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to particle surfaces to functionalize particles at large scale using atomic layer deposition (ALD). Nano-and micron-sized particles were effectively fluidized using an inert carrier gas assisted by mechanical agitation of the powder bed. The gas-solid contacting properties of fluidized bed reactors are beneficial for ALD surface reactions, while the frequent solid-solid collisions do not disrupt the self-limiting behavior of ALD reactant gases. Films can be deposited with monolayer control on individual particles of various substrate types, including metals, ceramics and polymers. In situ mass spectrometry was used for realtime monitoring of gaseous product(s) and reactants throughout the ALD reaction. Alumina (Al 2 O 3 ) ALD on particles demonstrates the process control capabilities of this unique, scalable configuration. The applications of Al 2 O 3 ALD films on particles are widely varying but typically involve core substrate surface passivation, which includes thermal oxidation resistance, photocatalytic activity mitigation and the fabrication of electrically insulative metal particles. Particle functionalization is achievable to nanoscale precision on a wide range of substrate types and sizes with minimal waste of costly ALD precursors and process time.
The fluidization behavior of fumed silica, zirconia, and iron oxide nanopowders was studied at at... more The fluidization behavior of fumed silica, zirconia, and iron oxide nanopowders was studied at atmospheric and reduced pressures. Using a high-speed laser imaging system, the characteristics of fluidized aggregates of nanoparticles were studied in real time. The effect of different particle interactions such as London -van der Waals, liquid bridging and electrostatic on different fluidization parameters was studied at atmospheric pressure. The reduction of interparticle forces resulted in a reduced aggregate size and minimum fluidization velocity (U mf ) and an increased bed expansion. Nanoparticles were also fluidized at reduced pressure (¨16 Pa) with vibration to study the effect of low pressure on the minimum fluidization velocity. Aggregate properties (size, density) instead of primary nanoparticle properties were found to govern the minimum fluidization velocity and expansion of the fluidized bed. An important consideration is the relative strength of intra-aggregate interparticle forces (forces within the aggregate holding nanoparticles together) to inter-aggregate interparticle forces (forces between aggregates). This relative strength may be inferred from the sphericity of the aggregates during fluidization. D
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
A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to ... more A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to particle surfaces to functionalize particles at large scale using atomic layer deposition (ALD). Nano-and micron-sized particles were effectively fluidized using an inert carrier gas assisted by mechanical agitation of the powder bed. The gas-solid contacting properties of fluidized bed reactors are beneficial for ALD surface reactions, while the frequent solid-solid collisions do not disrupt the self-limiting behavior of ALD reactant gases. Films can be deposited with monolayer control on individual particles of various substrate types, including metals, ceramics and polymers. In situ mass spectrometry was used for realtime monitoring of gaseous product(s) and reactants throughout the ALD reaction. Alumina (Al 2 O 3 ) ALD on particles demonstrates the process control capabilities of this unique, scalable configuration. The applications of Al 2 O 3 ALD films on particles are widely varying but typically involve core substrate surface passivation, which includes thermal oxidation resistance, photocatalytic activity mitigation and the fabrication of electrically insulative metal particles. Particle functionalization is achievable to nanoscale precision on a wide range of substrate types and sizes with minimal waste of costly ALD precursors and process time.
... 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. ...
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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