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Papers by Chris Bauer

J. Chris Bauer J. Beth Sanderson, Cristiano Trionfetti Jaime R. Blanton and Stefan D. Wieland 515... more J. Chris Bauer J. Beth Sanderson, Cristiano Trionfetti Jaime R. Blanton and Stefan D. Wieland 5150 Gilbertsville Highway, Calvert City, KY (USA) Rodenbacher Chaussee 4, Hanau-Wolfgang (Germany) chris.bauer@evonik.com Introduction Vinyl acetate monomer (VAM) is an intermediate chemical and is used in the manufacture of many different types of products such as paints, adhesives, textiles, etc. VAM is typically synthesized by the reaction of ethylene with acetic acid using a silica supported bimetallic Au-Pd catalyst promoted with potassium acetate. The amount and composition of Au and Pd can influence the activity and selectivity of the reaction. Thus, monitoring this parameter to keep the metal loading within a specified range during the manufacturing process is extremely important. A commercial interest also exists to accurately measure the amount of Au and Pd contained on the catalyst. This task is quite challenging because silica is a difficult material to digest.

Journal of the American Chemical Society, 2005

Intermetallic compounds and alloys are traditionally synthesized by heating mixtures of metal pow... more Intermetallic compounds and alloys are traditionally synthesized by heating mixtures of metal powders to high temperatures for long periods of time. A low-temperature solution-based alternative has been developed, and this strategy exploits the enhanced reactivity of nanoparticles and the nanometer diffusion distances afforded by binary nanocomposite precursors. Prereduced metal nanoparticles are combined in known ratios, and they form nanomodulated composites that rapidly transform into intermetallics and alloys upon heating at low temperatures. The approach is general in terms of accessible compositions, structures, and morphologies. Multiple compounds in the same binary system can be readily accessed; e.g., AuCu, AuCu 3, Au3Cu, and the AuCu-II superlattice are all accessible in the Au-Cu system. This concept can be extended to other binary systems, including the intermetallics FePt3, CoPt, CuPt, and Cu3-Pt and the alloys Ag-Pt, Au-Pd, and Ni-Pt. The ternary intermetallic Ag2Pd3S can also be rapidly synthesized at low temperatures from a nanocomposite precursor comprised of Ag2S and Pd nanoparticles. Using this low-temperature solution-based approach, a variety of morphologically diverse nanomaterials are accessible: surface-confined thin films (planar and nonplanar supports), free-standing monoliths, nanomesh materials, inverse opals, and dense gram-scale nanocrystalline powders of intermetallic AuCu. Importantly, the multimetallic materials synthesized using this approach are functional, yielding a roomtemperature Fe-Pt ferromagnet, a superconducting sample of Ag 2Pd3S (Tc) 1.10 K), and a AuPd4 alloy that selectively catalyzes the formation of H2O2 from H2 and O2. Such flexibility in the synthesis and processing of functional intermetallic and alloy materials is unprecedented.

Journal of Solid State Chemistry, 2008

The concept of nanocrystal conversion chemistry, which involves the use of pre-formed nanoparticl... more The concept of nanocrystal conversion chemistry, which involves the use of pre-formed nanoparticles as templates for chemical transformation into derivative solids, has emerged as a powerful approach for designing the synthesis of complex nanocrystalline solids. The general strategy exploits established synthetic capabilities in simple nanocrystal systems and uses these nanocrystals as templates that help to define the composition, crystal structure, and morphology of product nanocrystals. This article highlights key examples of ''conversion chemistry'' approaches to the synthesis of nanocrystalline solids using a variety of techniques, including galvanic replacement, diffusion, oxidation, and ion exchange. The discussion is organized according to classes of solids, highlighting the diverse target systems that are accessible using similar chemical concepts: metals, oxides, chalcogenides, phosphides, alloys, intermetallic compounds, sulfides, and nitrides.

Chemistry of Materials, 2006

For each of the binary oxide nanoparticle precursors shown below, the simulated XRD pattern for t... more For each of the binary oxide nanoparticle precursors shown below, the simulated XRD pattern for the binary oxide is shown at the bottom, the room-temperature (as-prepared) nanoparticle sample is shown in the middle, and the nanoparticle sample heated to 500 C in air for 1-2 h is shown at the top. (CoO is not shown, because of its low signal due to fluorescence. For the Cu-O system, Cu 2 O forms initially, but converts to CuO open heating in air. For NiO, the assynthesized sample is a mixture of NiO and several nickel oxide hydroxide phases, but converts cleanly to NiO when heated to 500 °C in air.

Advanced Functional Materials, 2011

Mesoporous carbon materials do not have sufficient ordering at the atomic scale to exhibit good e... more Mesoporous carbon materials do not have sufficient ordering at the atomic scale to exhibit good electronic conductivity. To date, mesoporous carbons having uniform mesopores and high surface areas have been prepared from partially‐graphitizable precursors in the presence of templates. High temperature thermal treatments above 2000 °C, which are usually required to increase conductivity, result in a partial or total collapse of the mesoporous structures and reduced surface areas induced by growth of graphitic domains, limiting their applications in electric double layer capacitors and lithium‐ion batteries. In this work, we successfully implemented a “brick‐and‐mortar” approach to obtain ordered graphitic mesoporous carbon nanocomposites with tunable mesopore sizes below 850 °C without using graphitization catalysts or high temperature thermal treatments. Phenolic resin‐based mesoporous carbons act as mortar to highly conductive carbon blacks and carbon onions (bricks). The capacitan...

Journal of Materials Chemistry, 2012

Journal of the American Chemical Society, 2009

Pt and Pt-containing alloys are important industrial catalysts and have many interesting properti... more Pt and Pt-containing alloys are important industrial catalysts and have many interesting properties and practical applications, particularly as nanoparticles. 1-5 For example, Pt nanoparticles are efficient catalysts for CO oxidation and steam reforming reactions. Pt-M alloys (M) Fe, Co, Ni) have also been found to exhibit useful magnetic properties. 6-8 From a catalysis perspective, Pt is Figure 2. TEM images of CuPt nanorods with average lengths of (A) 12.6 (1.9, (B) 27.8 (4.4, (C) 37.1 (10.1, and (D) 55.5 (7.8 nm (histograms of lengths are shown in the corresponding insets) and of (E) CuPt cubes and (F) the γ-Al 2 O 3-supported CuPt nanorod catalyst prior to reaction.

Catalysis Letters, 2009

In an effort to determine the active state of supported palladium for the direct formation of H 2... more In an effort to determine the active state of supported palladium for the direct formation of H 2 O 2 from H 2 and O 2 , the catalytic behavior of Pd 0 /SiO 2 , PdO/SiO 2 and partially reduced PdO/SiO 2 was determined. The results obtained in an ethanol slurry, with chloride ions and H 2 SO 4 being present, showed that the PdO/SiO 2 catalyst was almost completely inactive for the formation of H 2 O 2 at 10°C. The Pd 0 /SiO 2 catalyst exhibited the highest activity for H 2 O 2 formation, and the PdO/SiO 2 material, reduced under very mild conditions, exhibited an intermediate activity. The state of Pd on the three catalysts was characterized by XRD, TEM and XPS methods. Only Pd 0 (the metal phase) and PdO were observed on Pd 0 /SiO 2 and PdO/SiO 2 , respectively. As expected, with the partially reduced PdO/SiO 2 catalyst, both Pd 0 and PdO phases were evident. The TEM results revealed that the Pd 0 particles decorated the larger PdO particles. The results reported here support the role of metallic palladium, rather than the oxide, as the active phase for the direct formation of H 2 O 2 .

Applied Catalysis A: General, 2008

The effect of adding Pt to a Pd/SiO2 catalyst for the direct formation of H2O2 in ethanol that co... more The effect of adding Pt to a Pd/SiO2 catalyst for the direct formation of H2O2 in ethanol that contains H2SO4 and halide ions (Cl− or Br−) has been investigated. The addition of only 5atom% Pt to a catalyst that contained 0.5wt.% Pd resulted in a 2.5-fold increase in the rate of peroxide formation with only a small decrease in selectivity.

Angewandte Chemie, Aug 4, 2008

Angewandte Chemie, Jul 4, 2008

Applied Catalysis A-general, May 1, 2008

The effect of adding Pt to a Pd/SiO2 catalyst for the direct formation of H2O2 in ethanol that co... more The effect of adding Pt to a Pd/SiO2 catalyst for the direct formation of H2O2 in ethanol that contains H2SO4 and halide ions (Cl− or Br−) has been investigated. The addition of only 5atom% Pt to a catalyst that contained 0.5wt.% Pd resulted in a 2.5-fold increase in the rate of peroxide formation with only a small decrease in selectivity.

Journal of Materials Chemistry, 2008

ABSTRACT Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful c... more ABSTRACT Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful catalysts for a variety of chemical transformations. Supported intermetallic nanoparticle catalysts are usually prepared by depositing precursors onto a support followed by high-temperature annealing, which is necessary to generate the intermetallic compound but causes sintering and minimizes surface area. Here we show that solution chemistry methods for converting metal nanoparticles into intermetallic compounds are applicable to supported nanoparticle catalyst systems. Unsupported nanocrystalline Pt can be converted to nanocrystalline PtSn, PtPb, PtBi, and FePt3 by reaction with appropriate metal salt solutions under reducing conditions. Similar reactions convert Al2O3, CeO2, and carbon-supported Pt nanoparticles into PtSn, PtPb, PtSb, Pt3Sn, and Cu3Pt. These reactions generate supported alloy and intermetallic nanoparticles directly in solution without the need for high temperature annealing or additional surface stabilizers. These supported intermetallic nanoparticles are catalytically active for chemical transformations such as formic acid oxidation (PtPb/Vulcan) and CO oxidation (Pt3Sn/graphite). Notably, PtPb/Vulcan XC-72 was found to electrocatalytically oxidize formic acid at a lower onset potential (0.1 V) than commercial PtRu/Vulcan XC-72 (0.4 V).

Angewandte Chemie International Edition, 2008

Physical Chemistry Chemical Physics, 2011

Supported gold nanoparticles have generated an immense interest in the field of catalysis due to ... more Supported gold nanoparticles have generated an immense interest in the field of catalysis due to their extremely high reactivity and selectivity. Recently, alloy nanoparticles of gold have received a lot of attention due to their enhanced catalytic properties. Here we report the synthesis of silica supported AuCu nanoparticles through the conversion of supported Au nanoparticles in a solution of Cu(C(2)H(3)O(2))(2) at 300 °C. The AuCu alloy structure was confirmed through powder XRD (which indicated a weakly ordered alloy phase), XANES, and EXAFS. It was also shown that heating the AuCu/SiO(2) in an O(2) atmosphere segregated the catalyst into a Au-CuO(x) heterostructure between 150 °C to 240 °C. Heating the catalyst in H(2) at 300 °C reduced the CuO(x) back to Cu(0) to reform the AuCu alloy phase. It was found that the AuCu/SiO(2) catalysts were inactive for CO oxidation. However, various pretreatment conditions were required to form a highly active and stable Au-CuO(x)/SiO(2) catalyst to achieve 100% CO conversion below room-temperature. This is explained by the in situ FTIR result, which shows that CO molecules can be chemisorbed and activated only on the Au-CuO(x)/SiO(2) catalyst but not on the AuCu/SiO(2) catalyst.

J. Chris Bauer J. Beth Sanderson, Cristiano Trionfetti Jaime R. Blanton and Stefan D. Wieland 515... more J. Chris Bauer J. Beth Sanderson, Cristiano Trionfetti Jaime R. Blanton and Stefan D. Wieland 5150 Gilbertsville Highway, Calvert City, KY (USA) Rodenbacher Chaussee 4, Hanau-Wolfgang (Germany) chris.bauer@evonik.com Introduction Vinyl acetate monomer (VAM) is an intermediate chemical and is used in the manufacture of many different types of products such as paints, adhesives, textiles, etc. VAM is typically synthesized by the reaction of ethylene with acetic acid using a silica supported bimetallic Au-Pd catalyst promoted with potassium acetate. The amount and composition of Au and Pd can influence the activity and selectivity of the reaction. Thus, monitoring this parameter to keep the metal loading within a specified range during the manufacturing process is extremely important. A commercial interest also exists to accurately measure the amount of Au and Pd contained on the catalyst. This task is quite challenging because silica is a difficult material to digest.

Journal of the American Chemical Society, 2005

Intermetallic compounds and alloys are traditionally synthesized by heating mixtures of metal pow... more Intermetallic compounds and alloys are traditionally synthesized by heating mixtures of metal powders to high temperatures for long periods of time. A low-temperature solution-based alternative has been developed, and this strategy exploits the enhanced reactivity of nanoparticles and the nanometer diffusion distances afforded by binary nanocomposite precursors. Prereduced metal nanoparticles are combined in known ratios, and they form nanomodulated composites that rapidly transform into intermetallics and alloys upon heating at low temperatures. The approach is general in terms of accessible compositions, structures, and morphologies. Multiple compounds in the same binary system can be readily accessed; e.g., AuCu, AuCu 3, Au3Cu, and the AuCu-II superlattice are all accessible in the Au-Cu system. This concept can be extended to other binary systems, including the intermetallics FePt3, CoPt, CuPt, and Cu3-Pt and the alloys Ag-Pt, Au-Pd, and Ni-Pt. The ternary intermetallic Ag2Pd3S can also be rapidly synthesized at low temperatures from a nanocomposite precursor comprised of Ag2S and Pd nanoparticles. Using this low-temperature solution-based approach, a variety of morphologically diverse nanomaterials are accessible: surface-confined thin films (planar and nonplanar supports), free-standing monoliths, nanomesh materials, inverse opals, and dense gram-scale nanocrystalline powders of intermetallic AuCu. Importantly, the multimetallic materials synthesized using this approach are functional, yielding a roomtemperature Fe-Pt ferromagnet, a superconducting sample of Ag 2Pd3S (Tc) 1.10 K), and a AuPd4 alloy that selectively catalyzes the formation of H2O2 from H2 and O2. Such flexibility in the synthesis and processing of functional intermetallic and alloy materials is unprecedented.

Journal of Solid State Chemistry, 2008

The concept of nanocrystal conversion chemistry, which involves the use of pre-formed nanoparticl... more The concept of nanocrystal conversion chemistry, which involves the use of pre-formed nanoparticles as templates for chemical transformation into derivative solids, has emerged as a powerful approach for designing the synthesis of complex nanocrystalline solids. The general strategy exploits established synthetic capabilities in simple nanocrystal systems and uses these nanocrystals as templates that help to define the composition, crystal structure, and morphology of product nanocrystals. This article highlights key examples of ''conversion chemistry'' approaches to the synthesis of nanocrystalline solids using a variety of techniques, including galvanic replacement, diffusion, oxidation, and ion exchange. The discussion is organized according to classes of solids, highlighting the diverse target systems that are accessible using similar chemical concepts: metals, oxides, chalcogenides, phosphides, alloys, intermetallic compounds, sulfides, and nitrides.

Chemistry of Materials, 2006

For each of the binary oxide nanoparticle precursors shown below, the simulated XRD pattern for t... more For each of the binary oxide nanoparticle precursors shown below, the simulated XRD pattern for the binary oxide is shown at the bottom, the room-temperature (as-prepared) nanoparticle sample is shown in the middle, and the nanoparticle sample heated to 500 C in air for 1-2 h is shown at the top. (CoO is not shown, because of its low signal due to fluorescence. For the Cu-O system, Cu 2 O forms initially, but converts to CuO open heating in air. For NiO, the assynthesized sample is a mixture of NiO and several nickel oxide hydroxide phases, but converts cleanly to NiO when heated to 500 °C in air.

Advanced Functional Materials, 2011

Mesoporous carbon materials do not have sufficient ordering at the atomic scale to exhibit good e... more Mesoporous carbon materials do not have sufficient ordering at the atomic scale to exhibit good electronic conductivity. To date, mesoporous carbons having uniform mesopores and high surface areas have been prepared from partially‐graphitizable precursors in the presence of templates. High temperature thermal treatments above 2000 °C, which are usually required to increase conductivity, result in a partial or total collapse of the mesoporous structures and reduced surface areas induced by growth of graphitic domains, limiting their applications in electric double layer capacitors and lithium‐ion batteries. In this work, we successfully implemented a “brick‐and‐mortar” approach to obtain ordered graphitic mesoporous carbon nanocomposites with tunable mesopore sizes below 850 °C without using graphitization catalysts or high temperature thermal treatments. Phenolic resin‐based mesoporous carbons act as mortar to highly conductive carbon blacks and carbon onions (bricks). The capacitan...

Journal of Materials Chemistry, 2012

Journal of the American Chemical Society, 2009

Pt and Pt-containing alloys are important industrial catalysts and have many interesting properti... more Pt and Pt-containing alloys are important industrial catalysts and have many interesting properties and practical applications, particularly as nanoparticles. 1-5 For example, Pt nanoparticles are efficient catalysts for CO oxidation and steam reforming reactions. Pt-M alloys (M) Fe, Co, Ni) have also been found to exhibit useful magnetic properties. 6-8 From a catalysis perspective, Pt is Figure 2. TEM images of CuPt nanorods with average lengths of (A) 12.6 (1.9, (B) 27.8 (4.4, (C) 37.1 (10.1, and (D) 55.5 (7.8 nm (histograms of lengths are shown in the corresponding insets) and of (E) CuPt cubes and (F) the γ-Al 2 O 3-supported CuPt nanorod catalyst prior to reaction.

Catalysis Letters, 2009

In an effort to determine the active state of supported palladium for the direct formation of H 2... more In an effort to determine the active state of supported palladium for the direct formation of H 2 O 2 from H 2 and O 2 , the catalytic behavior of Pd 0 /SiO 2 , PdO/SiO 2 and partially reduced PdO/SiO 2 was determined. The results obtained in an ethanol slurry, with chloride ions and H 2 SO 4 being present, showed that the PdO/SiO 2 catalyst was almost completely inactive for the formation of H 2 O 2 at 10°C. The Pd 0 /SiO 2 catalyst exhibited the highest activity for H 2 O 2 formation, and the PdO/SiO 2 material, reduced under very mild conditions, exhibited an intermediate activity. The state of Pd on the three catalysts was characterized by XRD, TEM and XPS methods. Only Pd 0 (the metal phase) and PdO were observed on Pd 0 /SiO 2 and PdO/SiO 2 , respectively. As expected, with the partially reduced PdO/SiO 2 catalyst, both Pd 0 and PdO phases were evident. The TEM results revealed that the Pd 0 particles decorated the larger PdO particles. The results reported here support the role of metallic palladium, rather than the oxide, as the active phase for the direct formation of H 2 O 2 .

Applied Catalysis A: General, 2008

The effect of adding Pt to a Pd/SiO2 catalyst for the direct formation of H2O2 in ethanol that co... more The effect of adding Pt to a Pd/SiO2 catalyst for the direct formation of H2O2 in ethanol that contains H2SO4 and halide ions (Cl− or Br−) has been investigated. The addition of only 5atom% Pt to a catalyst that contained 0.5wt.% Pd resulted in a 2.5-fold increase in the rate of peroxide formation with only a small decrease in selectivity.

Angewandte Chemie, Aug 4, 2008

Angewandte Chemie, Jul 4, 2008

Applied Catalysis A-general, May 1, 2008

The effect of adding Pt to a Pd/SiO2 catalyst for the direct formation of H2O2 in ethanol that co... more The effect of adding Pt to a Pd/SiO2 catalyst for the direct formation of H2O2 in ethanol that contains H2SO4 and halide ions (Cl− or Br−) has been investigated. The addition of only 5atom% Pt to a catalyst that contained 0.5wt.% Pd resulted in a 2.5-fold increase in the rate of peroxide formation with only a small decrease in selectivity.

Journal of Materials Chemistry, 2008

ABSTRACT Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful c... more ABSTRACT Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful catalysts for a variety of chemical transformations. Supported intermetallic nanoparticle catalysts are usually prepared by depositing precursors onto a support followed by high-temperature annealing, which is necessary to generate the intermetallic compound but causes sintering and minimizes surface area. Here we show that solution chemistry methods for converting metal nanoparticles into intermetallic compounds are applicable to supported nanoparticle catalyst systems. Unsupported nanocrystalline Pt can be converted to nanocrystalline PtSn, PtPb, PtBi, and FePt3 by reaction with appropriate metal salt solutions under reducing conditions. Similar reactions convert Al2O3, CeO2, and carbon-supported Pt nanoparticles into PtSn, PtPb, PtSb, Pt3Sn, and Cu3Pt. These reactions generate supported alloy and intermetallic nanoparticles directly in solution without the need for high temperature annealing or additional surface stabilizers. These supported intermetallic nanoparticles are catalytically active for chemical transformations such as formic acid oxidation (PtPb/Vulcan) and CO oxidation (Pt3Sn/graphite). Notably, PtPb/Vulcan XC-72 was found to electrocatalytically oxidize formic acid at a lower onset potential (0.1 V) than commercial PtRu/Vulcan XC-72 (0.4 V).

Angewandte Chemie International Edition, 2008

Physical Chemistry Chemical Physics, 2011

Supported gold nanoparticles have generated an immense interest in the field of catalysis due to ... more Supported gold nanoparticles have generated an immense interest in the field of catalysis due to their extremely high reactivity and selectivity. Recently, alloy nanoparticles of gold have received a lot of attention due to their enhanced catalytic properties. Here we report the synthesis of silica supported AuCu nanoparticles through the conversion of supported Au nanoparticles in a solution of Cu(C(2)H(3)O(2))(2) at 300 °C. The AuCu alloy structure was confirmed through powder XRD (which indicated a weakly ordered alloy phase), XANES, and EXAFS. It was also shown that heating the AuCu/SiO(2) in an O(2) atmosphere segregated the catalyst into a Au-CuO(x) heterostructure between 150 °C to 240 °C. Heating the catalyst in H(2) at 300 °C reduced the CuO(x) back to Cu(0) to reform the AuCu alloy phase. It was found that the AuCu/SiO(2) catalysts were inactive for CO oxidation. However, various pretreatment conditions were required to form a highly active and stable Au-CuO(x)/SiO(2) catalyst to achieve 100% CO conversion below room-temperature. This is explained by the in situ FTIR result, which shows that CO molecules can be chemisorbed and activated only on the Au-CuO(x)/SiO(2) catalyst but not on the AuCu/SiO(2) catalyst.