scholarly journals Continuous synthesis of TiO2-supported noble metal NPs and their application in ammonia borane hydrolysis

2021 ◽  
Author(s):  
Lamei Luo ◽  
Mei Yang ◽  
Guangwen Chen
Keyword(s):  
Particle Size ◽  
Metal Nanoparticles ◽  
Noble Metal ◽  
Active Sites ◽  
Average Particle Size ◽  
Ammonia Borane ◽  
Noble Metal Nanoparticles ◽  
Average Particle ◽  
Batch Method ◽  
Continuous Synthesis

A stabilizer-free method based on segmented flow for the continuous synthesis of TiO2 supported noble metal nanoparticles (M/TiO2-MR, M = Pd, Pt or Au) was proposed. Due to the enhanced mixing performance arising from the internal convection in the discrete plugs, the particle size of noble metal nanoparticles could be well controlled by reducing the metal precursors with NaBH4 just in the presence of TiO2 without using any stabilizer. In comparison with the batch method, the as-prepared M/TiO2-MR had smaller noble metal particle size and better dispersity. Experimental results showed that adjusting the oil-to-water phase ratio or increasing the total volume flow rate and synthetic temperature could lead to smaller average particle size with narrower distribution. The as-prepared M/TiO2-MR possessed higher catalytic activities in the hydrolysis of ammonia borane than those prepared by the batch method, which could be ascribed to smaller noble metal nanoparticles, exposing more active sites.

scholarly journals Ni Nanoparticles on CeO2 (111): Energetics, Electron Transfer and Structure by Ni Adsorption Calorimetry, Spectroscopies and DFT

2020 ◽  
Author(s):  
Zhongtian Mao ◽  
Pablo Lustemberg ◽  
John R. Rumptz ◽  
M. V. Ganduglia-Pirovano ◽  
Charles T. Campbell
Keyword(s):  
Particle Size ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Density Functional ◽  
Average Particle Size ◽  
Heat Of Adsorption ◽  
Low Energy ◽  
Average Particle ◽  
Adsorption Calorimetry ◽  
Ni Clusters

<div>The morphology, interfacial bonding energetics and charge transfer of Ni clusters and nanoparticles on slightly-reduced CeO<sub>2-x</sub> (111) surfaces at 100 to 300 K have been studied using single crystal adsorption calorimetry (SCAC), low-energy ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and density functional theory (DFT). The initial heat of adsorption of Ni vapor decreased with the extent of pre-reduction (x) of the CeO<sub>2-x</sub> (111), showing that stoichiometric ceria adsorbs Ni more strongly than oxygen vacancies. On CeO<sub>1.95</sub> (111) at 300 K, the heat dropped quickly with coverage in the first 0.1 ML, attributed to nucleation of Ni clusters on stoichiometric steps, followed by the Ni particles spreading onto less favorable terrace sites. At 100 K, the clusters nucleate on terraces due</div><div>to slower diffusion. Adsorbed Ni monomers are in the +2 oxidation state, and they bind by ~45 kJ/mol more strongly to step sites than terraces. The measured heat of adsorption versus average particle size on terraces is favorably compared to DFT calculations. The Ce 3d XPS lineshape</div><div>showed an increase in Ce<sup>3+</sup>/Ce<sup>4+</sup> ratio with Ni coverage, providing the number of electrons donated to the ceria per Ni atom. The charge transferred per Ni is initially large but strongly decreases with increasing cluster size for both experiments and DFT, and shows large differences between clusters at steps versus terraces. This charge is localized on the interfacial Ni and Ce atoms in their atomic layers closest to the interface. This knowledge is crucial to understanding the nature of the active sites on the surface of Ni-CeO<sub>2</sub> catalysts for which metal-oxide interactions play a very important role in the activation of O−H and C−H bonds. The changes in these interactions with Ni particle size (metal loading) and the extent of reduction of the ceria help to explain how previously reported catalytic activity and selectivity change with these same structural details.</div>

Strategy for stabilizing noble metal nanoparticles without sacrificing active sites

2019 ◽  
Vol 55 (48) ◽  
pp. 6846-6849 ◽  
Author(s):  
Weikang Ji ◽  
Xuyu Wang ◽  
Minni Tang ◽  
Le Yang ◽  
Zebao Rui ◽  
...  
Keyword(s):  
Metal Nanoparticles ◽  
Noble Metal ◽  
Active Sites ◽  
Noble Metal Nanoparticles ◽  
Electronic Interaction ◽  
Pt Nanoparticle ◽  
Support Interaction ◽  
Metal Support Interaction ◽  
Metal Support ◽  
Surface Fluorination

We report a facile surface fluorination strategy for restricting Pt nanoparticle sintering through providing anchoring sites on the TiO2 support and enhancing metal–support interaction via improved electronic interaction without sacrificing the active sites.

Noble metal enhanced photocatalytic activity of heterostructured TiO2 spheres with tunable interiors and shells

2020 ◽  
Vol 13 (08) ◽  
pp. 2050039
Author(s):  
Bo Qiu ◽  
Xin Xiao ◽  
Min Zhang ◽  
Yue Mao ◽  
Xiaoheng Liu
Keyword(s):  
Metal Nanoparticles ◽  
Noble Metal ◽  
Precious Metal ◽  
Active Sites ◽  
Inner Core ◽  
Catalytic Performance ◽  
Noble Metal Nanoparticles ◽  
Oxide Support ◽  
Metal Support Interaction ◽  
Metal Support

Heterostructured TiO2 spheres with tunable interiors and shells were prepared by self-template technology. This structure is composed of a hollow shell and an inner core which can enhance light scattering in the hollow space and provide a large surface to generate sufficient active sites. Besides, the nanosheets grown on the shell layer not only increased their specific surface area, but also exposed more surface-active sites. The performance of photocatalysts was estimated by the RhB decolorization, and experimental results show that the photoactivity can be greatly improved by depositing noble metal nanoparticles. It improves the efficiency of charge utilization and enhances the overall catalytic performance from the three stages of charge carrier generation, separation and surface reaction. The strong metal–support interaction (SMSI) between the noble metal nanoparticles and the oxide support has been proven to inhibit the supported precious metal, one strategy for nanoparticle aggregation and growth. On the one hand, the nanoshells isolate the precious metal nanoparticles from each other, preventing the aggregation of metal nanoparticles.

scholarly journals Ni Nanoparticles on CeO2 (111): Energetics, Electron Transfer and Structure by Ni Adsorption Calorimetry, Spectroscopies and DFT

2020 ◽  
Author(s):  
Zhongtian Mao ◽  
Pablo Lustemberg ◽  
John R. Rumptz ◽  
M. V. Ganduglia-Pirovano ◽  
Charles T. Campbell
Keyword(s):  
Particle Size ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Density Functional ◽  
Average Particle Size ◽  
Heat Of Adsorption ◽  
Low Energy ◽  
Average Particle ◽  
Adsorption Calorimetry ◽  
Ni Clusters

<div>The morphology, interfacial bonding energetics and charge transfer of Ni clusters and nanoparticles on slightly-reduced CeO<sub>2-x</sub> (111) surfaces at 100 to 300 K have been studied using single crystal adsorption calorimetry (SCAC), low-energy ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and density functional theory (DFT). The initial heat of adsorption of Ni vapor decreased with the extent of pre-reduction (x) of the CeO<sub>2-x</sub> (111), showing that stoichiometric ceria adsorbs Ni more strongly than oxygen vacancies. On CeO<sub>1.95</sub> (111) at 300 K, the heat dropped quickly with coverage in the first 0.1 ML, attributed to nucleation of Ni clusters on stoichiometric steps, followed by the Ni particles spreading onto less favorable terrace sites. At 100 K, the clusters nucleate on terraces due</div><div>to slower diffusion. Adsorbed Ni monomers are in the +2 oxidation state, and they bind by ~45 kJ/mol more strongly to step sites than terraces. The measured heat of adsorption versus average particle size on terraces is favorably compared to DFT calculations. The Ce 3d XPS lineshape</div><div>showed an increase in Ce<sup>3+</sup>/Ce<sup>4+</sup> ratio with Ni coverage, providing the number of electrons donated to the ceria per Ni atom. The charge transferred per Ni is initially large but strongly decreases with increasing cluster size for both experiments and DFT, and shows large differences between clusters at steps versus terraces. This charge is localized on the interfacial Ni and Ce atoms in their atomic layers closest to the interface. This knowledge is crucial to understanding the nature of the active sites on the surface of Ni-CeO<sub>2</sub> catalysts for which metal-oxide interactions play a very important role in the activation of O−H and C−H bonds. The changes in these interactions with Ni particle size (metal loading) and the extent of reduction of the ceria help to explain how previously reported catalytic activity and selectivity change with these same structural details.</div>

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