Nanocatalysis

2017 ◽  
Author(s):  
R.T. Vang ◽  
S. Wendt ◽  
F. Besenbacher
Keyword(s):  
Surface Characterization ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Scale ◽  
Scanning Tunnelling Microscope ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Transmission Electron ◽  
Elementary Surface ◽  
And Diffusion

This article discusses nanocatalysis and especially the interrelation between the structure, composition and properties of catalysts. It begins with a review of techniques that have been developed and employed for surface characterization, which can be divided intothree main areas: spectroscopy, diffraction, and microscopy. After describing the nanocharacterization tools, the article considers the theoretical underpinnings of catalysts and catalytic processes. It also examines how detailed atomic-scale insight into elementary surface processes relevant to catalysis can be obtained mainly by means of high-resolution scanning tunnelling microscope studies on single-crystal surfaces. More specifically, it explores the surface structure, adsorption, dissociation and diffusion, and surface chemical reactions of catalysts. The article also looks at the design of new catalysts from first principles and concludes with an assessment of nanocatalysts and transmission electron microscope studies of nanoclusters on high surface area supports.

Electron holography of catalysts

1995 ◽  
Vol 53 ◽  
pp. 416-417
Author(s):  
A. K. Datye ◽  
D. S. Kalakkad ◽  
L. F. Allard ◽  
E. Völkl
Keyword(s):  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Scale ◽  
Nano Particles ◽  
Phase Image ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Phase Information ◽  
Particle Structure

The active phase in heterogeneous catalysts consists of nanometer-sized metal or oxide particles dispersed within the tortuous pore structure of a high surface area matrix. Such catalysts are extensively used for controlling emissions from automobile exhausts or in industrial processes such as the refining of crude oil to produce gasoline. The morphology of these nano-particles is of great interest to catalytic chemists since it affects the activity and selectivity for a class of reactions known as structure-sensitive reactions. In this paper, we describe some of the challenges in the study of heterogeneous catalysts, and provide examples of how electron holography can help in extracting details of particle structure and morphology on an atomic scale.Conventional high-resolution TEM imaging methods permit the image intensity to be recorded, but the phase information in the complex image wave is lost. However, it is the phase information which is sensitive at the atomic scale to changes in specimen thickness and composition, and thus analysis of the phase image can yield important information on morphological details at the nanometer level.

scholarly journals Pd Nanoparticles Stabilized on the Cross-Linked Melamine-Based SBA-15 as a Catalyst for the Mizoroki–Heck Reaction

2021 ◽  
Author(s):  
Ayat Nuri ◽  
Abolfazl Bezaatpour ◽  
Mandana Amiri ◽  
Nemanja Vucetic ◽  
Jyri-Pekka Mikkola ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Inductively Coupled Plasma ◽  
High Surface ◽  
High Surface Area ◽  
Coupling Reaction ◽  
Pd Nanoparticles ◽  
Significant Activity ◽  
Inductively Coupled ◽  
Transmission Electron ◽  
Ft Ir

AbstractMesoporous SBA-15 silicate with a high surface area was prepared by a hydrothermal method, successively modified by organic melamine ligands and then used for deposition of Pd nanoparticles onto it. The synthesized materials were characterized with infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), nitrogen physisorption, scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR) and inductively coupled plasma (ICP-OES). The catalyst was effectively used in the Mizoroki–Heck coupling reaction of various reactants in the presence of an organic base giving the desired products in a short reaction time and with small catalysts loadings. The reaction parameters such as the base type, amounts of catalyst, solvents, and the temperature were optimized. The catalyst was easily recovered and reused at least seven times without significant activity losses. Graphic Abstract

High Cr(VI) Adsorption Performance of Coal-Based Activated Carbon in Aqueous Solution

2013 ◽  
Vol 798-799 ◽  
pp. 1123-1127
Author(s):  
Hua Lei Zhou ◽  
Qiong Qiong Zhu ◽  
Dong Hua Huang
Keyword(s):  
Aqueous Solution ◽  
Activated Carbon ◽  
Pore Structure ◽  
Ph Value ◽  
High Surface ◽  
High Surface Area ◽  
Koh Activation ◽  
Transmission Electron ◽  
Mesoporous Adsorbent ◽  
Initial Ph

The activated carbon with high surface area was prepared by KOH activation from anthracite and used as adsorbent for removal of Cr (VI) from aqueous solution. The pore structure and surface properties were characterized by N2 adsorption at 77K, transmission electron microscope (TEM) and Fourier transform infrared spectroscopy ( FTIR). Effect of pH and isotherms at different temperature were investigated. Results show that the prepared carbon is a microporous-and mesoporous-adsorbent with developed pore structure and abundant surface oxygen-containing groups. PH value of the solution plays key function on the adsorption. The chemical adsorption dominates the adsorption process. The activated carbon exhibits much higher Cr adsorption capacity than the commercial activated carbon at initial pH of ~3. The equilibrium adsorption data are fitted by both Freundlich model and Langmuir model well.

Texture Evaluation of Sol-Gel Derived Mesoporous Bioactive Glass

2013 ◽  
Vol 284-287 ◽  
pp. 230-234
Author(s):  
Yu Jen Chou ◽  
Chi Jen Shih ◽  
Shao Ju Shih
Keyword(s):  
Surface Area ◽  
Calcination Temperature ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Nitrogen Adsorption ◽  
Bioactive Glasses ◽  
Transmission Electron ◽  
Sol Gel Process ◽  
Adsorption Desorption

Recent years mesoporous bioactive glasses (MBGs) have become important biomaterials because of their high surface area and the superior bioactivity. Various studies have reported that when MBGs implanted in a human body, hydroxyl apatite layers, constituting the main inorganic components of human bones, will form on the MBG surfaces to increase the bioactivity. Therefore, MBGs have been widely applied in the fields of tissue regeneration and drug delivery. The sol-gel process has replaced the conventional glasses process for MBG synthesis because of the advantages of low contamination, chemical flexibility and lower calcination temperature. In the sol-gel process, several types of surfactants were mixed with MBG precursor solutions to generate micelle structures. Afterwards, these micelles decompose to form porous structures after calcination. Although calcination is significant for contamination, crystalline and surface area in MBG, to the best of the authors’ knowledge, only few systematic studies related to calcination were reported. This study correlated the calcination parameters and the microstructure of MBGs. Microstructure evaluation was characterized by transmission electron microscopy and nitrogen adsorption/desorption. The experimental results show that the surface area and the pore size of MBGs decreased with the increasing of the calcination temperature, and decreased dramatically at 800°C due to the formation of crystalline phases.

Nanostructured Pt/WOx-C Solids as Electrocatalyst for PEMFC

2012 ◽  
Vol 15 (3) ◽  
pp. 165-170 ◽  
Author(s):  
M.L. Hernández-Pichardo ◽  
R.G. González-Huerta ◽  
P. Del Angel ◽  
E. Palacios-González ◽  
S.P. Paredes-Carrera
Keyword(s):  
Proton Exchange Membrane ◽  
High Surface ◽  
High Surface Area ◽  
Proton Exchange ◽  
Synthesis Methods ◽  
Co Tolerance ◽  
Transmission Electron ◽  
Anode Electrocatalysts ◽  
Exchange Membrane ◽  
Nanostructured Pt

Platinum nanoparticles supported on high surface area carbon black (e.g., Vulcan XC-72) are the most commonly used catalysts for both cathode and anode in proton exchange membrane fuel cells (PEMFCs), however, some other catalysts such as Pt/MoOx and Pt/WOx are also considered promising, due to their higher activity, stability and enhanced CO tolerance. This work is focused on the synthesis and characterization of nanostructured Pt/WOx-C as both cathode and anode electrocatalysts for PEMFCs. The Pt deposit on the surface of the support is a crucial step in the synthesis of the catalytic materials. Because of this, different synthesis methods were probed in order to find the conditions for the higher dispersion and accessibility of Platinum over the WOx-C support and to improve the PEMFC cathode stability. The catalysts were prepared by UV and ultrasound assisted approaches, and characterized by Transmission Electron Microscopy as well as lineal and cyclic voltammetry.

Magnetic Fe3O4@C nanoparticles as adsorbents for removal of amoxicillin from aqueous solution

2013 ◽  
Vol 69 (1) ◽  
pp. 147-155 ◽  
Author(s):  
Babak Kakavandi ◽  
Ali Esrafili ◽  
Anoushiravan Mohseni-Bandpi ◽  
Ahmad Jonidi Jafari ◽  
Roshanak Rezaei Kalantary
Keyword(s):  
Electron Microscopy ◽  
Activated Carbon ◽  
Kinetic Models ◽  
High Surface ◽  
High Surface Area ◽  
Order Kinetic ◽  
Magnetic Composites ◽  
Factors Affecting ◽  
Transmission Electron ◽  
Pseudo Second Order

In the present study, powder activated carbon (PAC) combined with Fe3O4 magnetite nanoparticles (MNPs) were used for the preparation of magnetic composites (MNPs-PAC), which was used as an adsorbent for amoxicillin (AMX) removal. The properties of magnetic activated carbon were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunaeur, Emmett and Teller and vibrating sample magnetometer. The operational factors affecting adsorption such as pH, contact time, adsorbent dosage, initial AMX concentration and temperature were studied in detail. The high surface area and saturation magnetization for the synthesized adsorbent were found to be 671.2 m2/g and 6.94 emu/g, respectively. The equilibrium time of the adsorption process was 90 min. Studies of adsorption equilibrium and kinetic models revealed that the adsorption of AMX onto MNPs-PAC followed Freundlich and Langmuir isotherms and pseudo-second-order kinetic models. The calculated values of the thermodynamic parameters, such as ΔG°, ΔH° and ΔS° demonstrated that the AMX adsorption was endothermic and spontaneous in nature. It could be concluded that MNPs-PAC have a great potential for antibiotic removal from aquatic media.

Smoothening by Self-Diffusion of Silicon during Annealing in a Rapid Processing Chamber

2013 ◽  
Vol 205-206 ◽  
pp. 364-369
Author(s):  
Pablo Eduardo Acosta-Alba ◽  
Christophe Gourdel ◽  
Oleg Kononchuk
Keyword(s):  
Atomic Scale ◽  
Crystal Surfaces ◽  
Surface Evolution ◽  
Origin And Evolution ◽  
Self Diffusion ◽  
Diffusion Parameters ◽  
Power Spectral ◽  
Rapid Processing ◽  
And Diffusion ◽  
Good Agreement

Atomic-scale mechanisms of thermal activated self-diffusion on crystal surfaces are investigated through AFM images. Surface evolution is studied by means of the Power Spectral Density (PSD) function over a large spatial bandwidth. We propose a parametric model based on the Mullins-Herring (MH) diffusion equation by adding two stochastic terms. Then, surface evolution during high temperature annealing in reducing ambient can be predicted. Very good agreement between experimental and theoretical roughness and diffusion parameters was observed. Origin and evolution of the stochastic terms, describing conservative and non-conservative noises, are discussed.

Enhanced Specific Heat of Silica Nanofluid

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Donghyun Shin ◽  
Debjyoti Banerjee
Keyword(s):  
Electron Microscopy ◽  
Specific Heat ◽  
Unit Volume ◽  
High Surface ◽  
High Surface Area ◽  
Lithium Carbonate ◽  
Sem Image ◽  
Surface Energies ◽  
Transmission Electron ◽  
The Stability

Silica nanoparticles (1% by weight) were dispersed in a eutectic of lithium carbonate and potassium carbonate (62:38 ratio) to obtain high temperature nanofluids. A differential scanning calorimeter instrument was used to measure the specific heat of the neat molten salt eutectic and after addition of nanoparticles. The specific heat of the nanofluid was enhanced by 19–24%. The measurement uncertainty for the specific heat values in the experiments is estimated to be in the range of 1–5%. These experimental data contradict earlier experimental results reported in the literature. (Notably, the stability of the nanofluid samples was not verified in these studies.) In the present study, the dispersion and stability of the nanoparticles were confirmed by using scanning electron microscopy (SEM). Percolation networks were observed in the SEM image of the nanofluid. Furthermore, no agglomeration of the nanoparticles was observed, as confirmed by transmission electron microscopy. The observed enhancements are suggested to be due to the high specific surface energies that are associated with the high surface area of the nanoparticles per unit volume (or per unit mass).

scholarly journals Synthesis and Characterization of Hierarchical Porousα-FeOOH for the Adsorption and Photodegradation of Rhodamine B

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Jianliang Cao ◽  
Gaojie Li ◽  
Yan Wang ◽  
Guang Sun ◽  
Hari Bala ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Rhodamine B ◽  
Uv Light ◽  
Low Cost ◽  
High Surface ◽  
High Surface Area ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Hierarchical Porous ◽  
Templated Method

Hierarchical porousα-FeOOH nanoparticles were controlled and prepared via a facile polystyrene (PS) microspheres-templated method. Theα-Fe2O3was obtained by the calcination of the as-preparedα-FeOOH. The resulting nanoparticles were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2-sorption techniques. The adsorption and photodegradation of Rhodamine B performance were evaluated under UV light at room temperature. The results indicated that the photocatalytic activity of theα-FeOOH nanoparticles is superior toα-Fe2O3-200 andα-Fe2O3-300 due to the hierarchically multiporous structure and high surface area. This convenient and low-cost process provides a rational synthesis alternative for the preparation of multiporous materials and the as-synthesis products have great foreground applications in many aspects.

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