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Papers by Krisztian Niesz

Research paper thumbnail of Hydrothermal growth of mesoporous SBA-15 silica in the presence of PVP-stabilized Pt nanoparticles: Synthesis, characterization, and catalytic properties

Journal of The American Chemical Society, 2006

Research paper thumbnail of Radial anisotropic growth of rhodium nanoparticles

Nano Letters, 2004

In this contribution, we report the synthesis of rhodium multipods that result from a homogeneous... more In this contribution, we report the synthesis of rhodium multipods that result from a homogeneous seeded growth mechanism. Small Rh nanocrystal seeds were synthesized by the reduction of RhCl3 in ethylene glycol in the presence of PVP. These seed particles could be subsequently used, without isolation, to form larger rhodium nanoparticles. A reaction temperature of 190 degrees C led to isotropic cubic Rh particles. Lowering the reaction temperature resulted in more anisotropic growth, which gave Rh cubes with horns at 140 degrees C, and Rh multipods at 90 degrees C. The anisotropic growth occurred in the (111) direction, as determined by high-resolution TEM (HRTEM). Anisotropic growth proceeds via a seeded growth mechanism, and not by oriented attachment.

Research paper thumbnail of Rhodium nanoparticles from cluster seeds: Control of size and shape by precursor addition rate

Nano Letters, 2007

The size-tunable synthesis of poly(vinylpyrrolidone)-stabilized cuboctahedral rhodium nanoparticl... more The size-tunable synthesis of poly(vinylpyrrolidone)-stabilized cuboctahedral rhodium nanoparticles with mean diameters ranging between 3-7 nm and multipod structures was accomplished using seeded growth methods. Isotropic PVP-capped 2.9 nm seeds were prepared by ligand exchange on rhodium-triphenylphosphine metal-organic clusters. Quantitative investigation of reaction parameters in ethylene glycol revealed that size and shape could be controlled at a single reaction temperature of 120 degrees C. The rate of rhodium monomer addition was found to be critical for monodispersity and shape control, regardless of thermodynamic factors. Solvent viscosity, varied by changing the polyol solvents, indicated that autocatalytic addition kinetics are responsible for isotropic versus anisotropic growth.

Research paper thumbnail of Precise control of the Pt nanoparticle size by seeded growth using EO13PO30EO13 triblock copolymers as protective agents

Research paper thumbnail of End morphology of ball milled carbon nanotubes

Research paper thumbnail of Mechanical and chemical breaking of multiwalled carbon nanotubes

Research paper thumbnail of Sol-gel synthesis of ordered mesoporous alumina

Chemical Communications, 2004

Research paper thumbnail of Monodisperse platinum nanoparticles of well-defined shape: synthesis, characterization, catalytic properties and future prospects

Topics in Catalysis, 2006

Monodisperse platinum nanoparticles with well-defined faceting have been synthesized by a modifie... more Monodisperse platinum nanoparticles with well-defined faceting have been synthesized by a modified polyol process with the addition of silver ions. Pt nanoparticles are encapsulated in mesoporous silica during in situ hydrothermal growth of the high surface area support. Removal of the surface regulating polymer, poly(vinylpyrrolidone), was achieved using thermal oxidation-reduction treatments. Catalysts were active for ethylene hydrogenation after polymer removal. Rates for ethylene hydrogenation decreased in accordance with the amount of Ag retained in the Pt nanoparticles after purification. Ag is most likely present on the Pt particle surface as small clusters. Future prospects for these catalysts for use in low temperature selective hydrogenation reactions are discussed.

Research paper thumbnail of High-efficiency aminocarbonylation by introducing CO to a pressurized continuous flow reactor

Organic Letters, 2008

Halogenated aryl carboxylic acids were efficiently converted to the corresponding dicarboxylic ac... more Halogenated aryl carboxylic acids were efficiently converted to the corresponding dicarboxylic acid monoamides by a one-step Pd-catalyzed aminocarbonylation in a micro/meso fluidic continuous flow reactor (X-Cube) operated at high pressure and high temperature with CO gas introduction. Reaction parameters (solvent, base, catalyst, pressure, temperature) were rapidly optimized in the reactions, which required less than 2 min. The method gave improved results over comparable batch techniques and is also suited to automated parallel syntheses of compound libraries.

Research paper thumbnail of Kinetics and mechanism of ethylene hydrogenation poisoned by CO on silica-supported monodisperse Pt nanoparticles

Journal of Catalysis, 2007

Research paper thumbnail of STM investigation of carbon nanotubes connected by functional groups

Materials Science and Engineering: C, 2003

Chemical functionalization of carbon nanotubes (CNTs) is essential for many applications. Attachm... more Chemical functionalization of carbon nanotubes (CNTs) is essential for many applications. Attachment of functional groups to nanotubes can dramatically increase the solubility of the nanotube material. Sidewall functional groups should react with polymers and improve the mechanical properties of nanocomposites. Tubes interconnected by chemical bonds will have a reduced contact resistance and can be used for interconnection purposes in nanoscale circuits. Carbon nanotubes covered with functional groups attached to their exterior wall were analyzed using scanning tunneling microscopy (STM) and TEM. The functionalization was carried out in three steps: acid treatment in H2SO4/HNO3 (3:1) mixture, reaction with SOCl2 and reaction with diaminopropanol (DAP). The binding force between the nanotubes connected by functional groups and the mechanical stability of the connection was investigated.

Research paper thumbnail of Pre-prepared platinum nanoparticles supported on SBA-15–preparation, pretreatment conditions and catalytic properties

Research paper thumbnail of Fabrication of two-and three-dimensional model catalyst systems with monodispersed platinum nanoparticles as active metal building blocks

Inorganica Chimica Acta, 2006

Research paper thumbnail of Structure sensitivity of vibrational spectra of mesoporous silica SBA-15 and Pt/SBA-15

Journal of Physical Chemistry B, 2005

Research paper thumbnail of Production of carbon nanotubes on different metal supported catalysts

Reaction Kinetics and Catalysis Letters, 2001

Research paper thumbnail of Functional groups generated by mechanical and chemical breaking of multiwall carbon nanotubes

Since the discovery of carbon nanotubes several attempts were made to modify them by various phys... more Since the discovery of carbon nanotubes several attempts were made to modify them by various physical and chemical methods. Applying a ball-milling system mechanical cutting of nanotubes can be achieved. TEM, surface area and porosity measurements are used to follow these changes on the nanotubes. Using different reagents and methods functional groups can be generated on the nanotubes. To prove the existence of these groups infrared spectroscopy is used. Finally, it will be shown that the physical and chemical breaking processes complete each other very well. .

Research paper thumbnail of Sonication-accelerated catalytic synthesis of oxide nanoparticles

Research paper thumbnail of Large-scale engineered synthesis of BaTiO3 nanoparticles using low-temperature bioinspired principles

Research paper thumbnail of Adsorption and co-adsorption of ethylene and carbon monoxide onsilica-supported monodisperse Pt nanoparticles. Volumetric adsorption andinfrared spectroscopy studies

Langmuir, 2008

The adsorption of carbon monoxide and ethylene, and their sequential adsorption, was studied over... more The adsorption of carbon monoxide and ethylene, and their sequential adsorption, was studied over a series of Pt/SBA-15 catalysts with monodisperse particle sizes ranging from 1.7 to 7.1 nm by diffuse-reflectance infrared spectroscopy and chemisorption. Gas adsorption was dependent on the Pt particle size, temperature, and sequence of gas exposure. Adsorption of CO at room temperature on Pt/SBA-15 gives rise to a spectroscopic feature assigned to the C-O stretch: nu(CO) = 2075 cm-1 (1.9 nm); 2079 cm-1 (2.9 nm); 2082 cm-1 (3.6 nm); and 2090 cm-1 (7.1 nm). The intensity of the signal decreased in a sigmoidal fashion with increasing temperature, thereby providing semiquantitative surface coverage information. Adsorption of ethylene on Pt/SBA-15 gave rise to spectroscopic features at approximately 1340, approximately 1420, and approximately 1500 cm-1 assigned to ethylidyne, di-sigma-bonded ethylene, and pi-bonded ethylene, respectively. The ratio of these surface species is highly dependent on the Pt particle size. At room temperature, Pt particles stabilize ethylidyne as well as di-sigma- and pi-bonded ethylene; however, ethylidyne predominated on the surfaces of larger particles. Ethylidyne was the only identifiable species at 403 K, with its formation being more facile on larger particles. Co-adsorption experiments reveal that the composition of the surface layer is dependent on the order of exposure to gases. Exposure of a C2H4-covered Pt surface to CO resulted in an approximately 50% decrease in chemisorbed CO compared to a fresh Pt surface. The nu(CO) appeared at 2050 cm-1 on Pt/SBA-15 pretreated with C2H4 at room temperature. The di-sigma-bonded and pi-bonded species are the most susceptible to displacement from the surface by CO. The formation of ethylidyne appeared to be less sensitive to the presence of adsorbed carbon monoxide, especially on larger particles. Upon exposure of C2H4 to a CO-covered Pt surface, little irreversible uptake occurred due to nearly 100% site blocking. These results demonstrate that carbon monoxide competes directly with ethylene for surface sites, which will have direct implications on the poisoning of the heterogeneously catalyzed conversion of hydrocarbons.

Research paper thumbnail of Engineering grain size and electrical properties of donor-doped barium titanate ceramics

Ceramics International, 2011

ABSTRACT A semiconducting lanthanum-doped barium titanate ceramic has been fabricated for battery... more ABSTRACT A semiconducting lanthanum-doped barium titanate ceramic has been fabricated for battery safety applications by simple means from nanoparticles prepared at room temperature by kinetically controlled vapor diffusion catalysis. The material, characterized by electron microscopy, X-ray diffraction and electrical measurements, exhibits a difficult to achieve combination of submicron grain size (∼500nm) and attractive electrical properties of room temperature resistivity below 100Ωcm and a 12-fold increase in resistivity through the Curie temperature (positive thermal coefficient of resistivity, PTCR). Systematic investigation of sintering conditions revealed that a short period of heating at 1350°C under air is necessary to suppress abnormal grain growth, while precise control of the cooling rate is needed to achieve the targeted electrical properties. Cooling must be sufficiently fast to avoid complete back-oxidation, yet slow enough to facilitate oxygen adsorption at the grain boundaries to produce the thin oxide layer apparently responsible for the observed PTCR.

Research paper thumbnail of Hydrothermal growth of mesoporous SBA-15 silica in the presence of PVP-stabilized Pt nanoparticles: Synthesis, characterization, and catalytic properties

Journal of The American Chemical Society, 2006

Research paper thumbnail of Radial anisotropic growth of rhodium nanoparticles

Nano Letters, 2004

In this contribution, we report the synthesis of rhodium multipods that result from a homogeneous... more In this contribution, we report the synthesis of rhodium multipods that result from a homogeneous seeded growth mechanism. Small Rh nanocrystal seeds were synthesized by the reduction of RhCl3 in ethylene glycol in the presence of PVP. These seed particles could be subsequently used, without isolation, to form larger rhodium nanoparticles. A reaction temperature of 190 degrees C led to isotropic cubic Rh particles. Lowering the reaction temperature resulted in more anisotropic growth, which gave Rh cubes with horns at 140 degrees C, and Rh multipods at 90 degrees C. The anisotropic growth occurred in the (111) direction, as determined by high-resolution TEM (HRTEM). Anisotropic growth proceeds via a seeded growth mechanism, and not by oriented attachment.

Research paper thumbnail of Rhodium nanoparticles from cluster seeds: Control of size and shape by precursor addition rate

Nano Letters, 2007

The size-tunable synthesis of poly(vinylpyrrolidone)-stabilized cuboctahedral rhodium nanoparticl... more The size-tunable synthesis of poly(vinylpyrrolidone)-stabilized cuboctahedral rhodium nanoparticles with mean diameters ranging between 3-7 nm and multipod structures was accomplished using seeded growth methods. Isotropic PVP-capped 2.9 nm seeds were prepared by ligand exchange on rhodium-triphenylphosphine metal-organic clusters. Quantitative investigation of reaction parameters in ethylene glycol revealed that size and shape could be controlled at a single reaction temperature of 120 degrees C. The rate of rhodium monomer addition was found to be critical for monodispersity and shape control, regardless of thermodynamic factors. Solvent viscosity, varied by changing the polyol solvents, indicated that autocatalytic addition kinetics are responsible for isotropic versus anisotropic growth.

Research paper thumbnail of Precise control of the Pt nanoparticle size by seeded growth using EO13PO30EO13 triblock copolymers as protective agents

Research paper thumbnail of End morphology of ball milled carbon nanotubes

Research paper thumbnail of Mechanical and chemical breaking of multiwalled carbon nanotubes

Research paper thumbnail of Sol-gel synthesis of ordered mesoporous alumina

Chemical Communications, 2004

Research paper thumbnail of Monodisperse platinum nanoparticles of well-defined shape: synthesis, characterization, catalytic properties and future prospects

Topics in Catalysis, 2006

Monodisperse platinum nanoparticles with well-defined faceting have been synthesized by a modifie... more Monodisperse platinum nanoparticles with well-defined faceting have been synthesized by a modified polyol process with the addition of silver ions. Pt nanoparticles are encapsulated in mesoporous silica during in situ hydrothermal growth of the high surface area support. Removal of the surface regulating polymer, poly(vinylpyrrolidone), was achieved using thermal oxidation-reduction treatments. Catalysts were active for ethylene hydrogenation after polymer removal. Rates for ethylene hydrogenation decreased in accordance with the amount of Ag retained in the Pt nanoparticles after purification. Ag is most likely present on the Pt particle surface as small clusters. Future prospects for these catalysts for use in low temperature selective hydrogenation reactions are discussed.

Research paper thumbnail of High-efficiency aminocarbonylation by introducing CO to a pressurized continuous flow reactor

Organic Letters, 2008

Halogenated aryl carboxylic acids were efficiently converted to the corresponding dicarboxylic ac... more Halogenated aryl carboxylic acids were efficiently converted to the corresponding dicarboxylic acid monoamides by a one-step Pd-catalyzed aminocarbonylation in a micro/meso fluidic continuous flow reactor (X-Cube) operated at high pressure and high temperature with CO gas introduction. Reaction parameters (solvent, base, catalyst, pressure, temperature) were rapidly optimized in the reactions, which required less than 2 min. The method gave improved results over comparable batch techniques and is also suited to automated parallel syntheses of compound libraries.

Research paper thumbnail of Kinetics and mechanism of ethylene hydrogenation poisoned by CO on silica-supported monodisperse Pt nanoparticles

Journal of Catalysis, 2007

Research paper thumbnail of STM investigation of carbon nanotubes connected by functional groups

Materials Science and Engineering: C, 2003

Chemical functionalization of carbon nanotubes (CNTs) is essential for many applications. Attachm... more Chemical functionalization of carbon nanotubes (CNTs) is essential for many applications. Attachment of functional groups to nanotubes can dramatically increase the solubility of the nanotube material. Sidewall functional groups should react with polymers and improve the mechanical properties of nanocomposites. Tubes interconnected by chemical bonds will have a reduced contact resistance and can be used for interconnection purposes in nanoscale circuits. Carbon nanotubes covered with functional groups attached to their exterior wall were analyzed using scanning tunneling microscopy (STM) and TEM. The functionalization was carried out in three steps: acid treatment in H2SO4/HNO3 (3:1) mixture, reaction with SOCl2 and reaction with diaminopropanol (DAP). The binding force between the nanotubes connected by functional groups and the mechanical stability of the connection was investigated.

Research paper thumbnail of Pre-prepared platinum nanoparticles supported on SBA-15–preparation, pretreatment conditions and catalytic properties

Research paper thumbnail of Fabrication of two-and three-dimensional model catalyst systems with monodispersed platinum nanoparticles as active metal building blocks

Inorganica Chimica Acta, 2006

Research paper thumbnail of Structure sensitivity of vibrational spectra of mesoporous silica SBA-15 and Pt/SBA-15

Journal of Physical Chemistry B, 2005

Research paper thumbnail of Production of carbon nanotubes on different metal supported catalysts

Reaction Kinetics and Catalysis Letters, 2001

Research paper thumbnail of Functional groups generated by mechanical and chemical breaking of multiwall carbon nanotubes

Since the discovery of carbon nanotubes several attempts were made to modify them by various phys... more Since the discovery of carbon nanotubes several attempts were made to modify them by various physical and chemical methods. Applying a ball-milling system mechanical cutting of nanotubes can be achieved. TEM, surface area and porosity measurements are used to follow these changes on the nanotubes. Using different reagents and methods functional groups can be generated on the nanotubes. To prove the existence of these groups infrared spectroscopy is used. Finally, it will be shown that the physical and chemical breaking processes complete each other very well. .

Research paper thumbnail of Sonication-accelerated catalytic synthesis of oxide nanoparticles

Research paper thumbnail of Large-scale engineered synthesis of BaTiO3 nanoparticles using low-temperature bioinspired principles

Research paper thumbnail of Adsorption and co-adsorption of ethylene and carbon monoxide onsilica-supported monodisperse Pt nanoparticles. Volumetric adsorption andinfrared spectroscopy studies

Langmuir, 2008

The adsorption of carbon monoxide and ethylene, and their sequential adsorption, was studied over... more The adsorption of carbon monoxide and ethylene, and their sequential adsorption, was studied over a series of Pt/SBA-15 catalysts with monodisperse particle sizes ranging from 1.7 to 7.1 nm by diffuse-reflectance infrared spectroscopy and chemisorption. Gas adsorption was dependent on the Pt particle size, temperature, and sequence of gas exposure. Adsorption of CO at room temperature on Pt/SBA-15 gives rise to a spectroscopic feature assigned to the C-O stretch: nu(CO) = 2075 cm-1 (1.9 nm); 2079 cm-1 (2.9 nm); 2082 cm-1 (3.6 nm); and 2090 cm-1 (7.1 nm). The intensity of the signal decreased in a sigmoidal fashion with increasing temperature, thereby providing semiquantitative surface coverage information. Adsorption of ethylene on Pt/SBA-15 gave rise to spectroscopic features at approximately 1340, approximately 1420, and approximately 1500 cm-1 assigned to ethylidyne, di-sigma-bonded ethylene, and pi-bonded ethylene, respectively. The ratio of these surface species is highly dependent on the Pt particle size. At room temperature, Pt particles stabilize ethylidyne as well as di-sigma- and pi-bonded ethylene; however, ethylidyne predominated on the surfaces of larger particles. Ethylidyne was the only identifiable species at 403 K, with its formation being more facile on larger particles. Co-adsorption experiments reveal that the composition of the surface layer is dependent on the order of exposure to gases. Exposure of a C2H4-covered Pt surface to CO resulted in an approximately 50% decrease in chemisorbed CO compared to a fresh Pt surface. The nu(CO) appeared at 2050 cm-1 on Pt/SBA-15 pretreated with C2H4 at room temperature. The di-sigma-bonded and pi-bonded species are the most susceptible to displacement from the surface by CO. The formation of ethylidyne appeared to be less sensitive to the presence of adsorbed carbon monoxide, especially on larger particles. Upon exposure of C2H4 to a CO-covered Pt surface, little irreversible uptake occurred due to nearly 100% site blocking. These results demonstrate that carbon monoxide competes directly with ethylene for surface sites, which will have direct implications on the poisoning of the heterogeneously catalyzed conversion of hydrocarbons.

Research paper thumbnail of Engineering grain size and electrical properties of donor-doped barium titanate ceramics

Ceramics International, 2011

ABSTRACT A semiconducting lanthanum-doped barium titanate ceramic has been fabricated for battery... more ABSTRACT A semiconducting lanthanum-doped barium titanate ceramic has been fabricated for battery safety applications by simple means from nanoparticles prepared at room temperature by kinetically controlled vapor diffusion catalysis. The material, characterized by electron microscopy, X-ray diffraction and electrical measurements, exhibits a difficult to achieve combination of submicron grain size (∼500nm) and attractive electrical properties of room temperature resistivity below 100Ωcm and a 12-fold increase in resistivity through the Curie temperature (positive thermal coefficient of resistivity, PTCR). Systematic investigation of sintering conditions revealed that a short period of heating at 1350°C under air is necessary to suppress abnormal grain growth, while precise control of the cooling rate is needed to achieve the targeted electrical properties. Cooling must be sufficiently fast to avoid complete back-oxidation, yet slow enough to facilitate oxygen adsorption at the grain boundaries to produce the thin oxide layer apparently responsible for the observed PTCR.