The Specific Activity of Silica Supported Platinum for the Catalysis of Hydrogen – Water Deuterium Exchange

1971 ◽  
Vol 49 (21) ◽  
pp. 3411-3417 ◽  
Author(s):  
N. H. Sagert ◽  
R. M. L. Pouteau
Keyword(s):  
Particle Size ◽  
Specific Activity ◽  
Deuterium Exchange ◽  
Hydrogen Chemisorption ◽  
Unit Surface Area ◽  
Particle Sizes ◽  
X Ray Diffraction ◽  
Hydrogen Water ◽  
Surface Areas ◽  
Platinum Particles

Some rate data are reported for deuterium exchange between water and hydrogen using series of platinum–silica catalysts. Three different methods of preparing catalysts were used to give different series of metal particle sizes. Within each series, the particle size was increased by sintering batches in air, at temperatures up to 700 °C. These methods produced platinum particles ranging from 5 to 250 Å in diameter. Metal surface areas and particle sizes were measured by hydrogen chemisorption, X-ray diffraction, and electron microscopy.The specific rates, i.e., rates per unit surface area of platinum varied by a factor of three within each series, reaching a maximum for sintering temperatures of about 500 °C. These maximum rates, measured at 127 °C with a water-to-hydrogen ratio of 0.31, varied from 1.9 × 10−8 to 5 × 10−8 mol D2 cm−2 s−1. Thus no effect of particle size on rate was observed, and the differences noted are ascribed to other effects of the methods of preparing the catalysts.

The Specific Activity of Silica Supported Platinum for the Catalysis of Hydrogen–Methane Deuterium Exchange

1973 ◽  
Vol 51 (21) ◽  
pp. 3588-3595 ◽  
Author(s):  
Norman Henry Sagert ◽  
Rita Mary Louise Pouteau
Keyword(s):  
Particle Size ◽  
Rate Coefficient ◽  
Specific Activity ◽  
Particle Size Effect ◽  
Rate Coefficients ◽  
Hydrogen Chemisorption ◽  
Specific Rate ◽  
Unit Surface Area ◽  
Surface Areas ◽  
Platinum Particles

Rate data are reported as a function of temperature for the exchange of D2 with CH4 over a number of platinum–silica catalysts. Two different methods of preparing catalysts, impregnation and ion exchange, were used to get two series of metal particle sizes. Within each series, the particle size was increased by sintering batches in air at temperatures to 800 °C. These methods produced platinum particles ranging from 0.9 to 10 nm diameter. The metal surface areas were measured by hydrogen chemisorption and, where possible, by X-ray diffraction and electron microscopy.The specific rate coefficients or rate coefficients per unit surface area of platinum varied by a factor of up to 40 within each series and reached a maximum for sintering temperatures of about 500 °C. The maximum specific rate coefficients for CH4 conversion at 200 °C, and total pressure of 60 kN m−2, were 1.3 and 1.9 × 10−6 mol CH4 m−2 s−1 for the ion-exchanged and impregnated catalysts respectively. Activation energies were in the range 60 to 100 kJ mol−1. Since a relatively small change in specific rate coefficient was noted between the two series as compared to the changes within each series, no large effect of particle size on the specific rate coefficient was demonstrated. The different specific rate coefficients within the series are ascribed to other effects of sintering, particularly the formation of the lower energy Pt(111) surface. Some evidence was noted for a particle size effect in the distribution of products, with more multiple exchange being observed for the smallest particles.

scholarly journals The Evaluation of Meloxicam Nanocrystals by Oral Administration with Different Particle Sizes

Molecules ◽  
2022 ◽  
Vol 27 (2) ◽  
pp. 421
Author(s):  
Yao Yu ◽  
Yang Tian ◽  
Hui Zhang ◽  
Qingxian Jia ◽  
Xuejun Chen ◽  
...  
Keyword(s):  
Particle Size ◽  
Water Solubility ◽  
Cell Model ◽  
Particle Sizes ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Laser Scattering ◽  
Transport Studies ◽  
Transmission Electron ◽  
Transmission And Absorption

Meloxicam (MLX) is a non-steroidal anti-inflammatory drug used to treat rheumatoid arthritis and osteoarthritis. However, its poor water solubility limits the dissolution process and influences absorption. In order to solve this problem and improve its bioavailability, we prepared it in nanocrystals with three different particle sizes to improve solubility and compare the differences between various particle sizes. The nanocrystal particle sizes were studied through dynamic light scattering (DLS) and laser scattering (LS). Transmission electron microscopy (TEM) was used to characterize the morphology of nanocrystals. The sizes of meloxicam-nanocrystals-A (MLX-NCs-A), meloxicam-nanocrystals-B (MLX-NCs-B), and meloxicam-nanocrystals-C (MLX-NCs-C) were 3.262 ± 0.016 μm, 460.2 ± 9.5 nm, and 204.9 ± 2.8 nm, respectively. Molecular simulation was used to explore the distribution and interaction energy of MLX molecules and stabilizer molecules in water. The results of differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) proved that the crystalline state did not change in the preparation process. Transport studies of the Caco-2 cell model indicated that the cumulative degree of transport would increase as the particle size decreased. Additionally, plasma concentration–time curves showed that the AUC0–∞ of MLX-NCs-C were 3.58- and 2.92-fold greater than those of MLX-NCs-A and MLX-NCs-B, respectively. These results indicate that preparing MLX in nanocrystals can effectively improve the bioavailability, and the particle size of nanocrystals is an important factor in transmission and absorption.

Particle Size Analysis of the Synthesized Al2O3 by Dissolution and Alkali Fusion-Coprecipitation Methods

2020 ◽  
Vol 860 ◽  
pp. 128-134
Author(s):  
Cahyaning Fajar Kresna Murti ◽  
Malik Anjelh Baqiya ◽  
Endarko ◽  
Triwikantoro
Keyword(s):  
Particle Size ◽  
Ammonium Hydroxide ◽  
Particle Size Analysis ◽  
Fusion Product ◽  
Size Analysis ◽  
Particle Sizes ◽  
X Ray Diffraction ◽  
Bottom Up ◽  
Alkali Fusion ◽  
Transmission Electron

Particle size analysis of synthesized Al2O3 by dissolution and alkali fusion-coprecipitation methods has been conducted. The formation of nano- or microparticles can be synthesized by the top-down (physically) and bottom-up (chemically) methods. In this study, the commercial alumina (Merck) with the particle size of 63 µm was synthesized through the bottom-up method. The dissolution method was done by reacting to alumina with ammonium hydroxide (NH4OH). The alkali fusion method was carried out by reacting alumina with sodium hydroxide (NaOH) and it obtained by coprecipitation of the alkali fusion product with HCl and NH4OH. The result from both methods were calcined at 600°C. The phase of synthesized Al2O3 was identified by using X-ray diffraction (XRD), whereas the morphology observed using a transmission electron microscope (TEM), and the particle sizes measured by particle sizes analyzer (PSA). The XRD pattern shows the γ-Al2O3 phases with particle sizes of ~33 nm and ~25 nm from TEM observations, while the PSA results revealed agglomerated particles with particle sizes of 1263 nm and 477 nm for the dissolution and alkali fusion-coprecipitation method, respectively. Therefore, both methods can be used to reduce the particle size of γ-Al2O3.

scholarly journals Effects of Size and Dispersity of Microcrystalline Celluloses on Size, Structure and Stability of Nanocrystalline Celluloses Extracted by Acid Hydrolysis

Nano LIFE ◽  
2014 ◽  
Vol 04 (04) ◽  
pp. 1441014 ◽  
Author(s):  
Qi Liu ◽  
Weiping Hao ◽  
Yongguang Yang ◽  
Aurore Richel ◽  
Canbin Ouyang ◽  
...  
Keyword(s):  
Particle Size ◽  
Acid Hydrolysis ◽  
Size Structure ◽  
Particle Sizes ◽  
X Ray Diffraction ◽  
X Ray ◽  
Force Microscopy ◽  
Atomic Force ◽  
Transmission Electron ◽  
Sonication Treatment

Nanocrystalline celluloses (NCCs) were separated from four commercial microcrystalline celluloses (MCCs) by an acid hydrolysis–sonication treatment. Transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectrum, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were conducted to investigate the NCCs. MCCs with different morphologies and particle sizes showed different aggregation degrees. The aggregation of MCCs followed the order MCC1 > MCC3 > MCC2 > MCC4, which is the same order of the heights of the resulting NCCs. The best uniformity and thermal stability were characterized for NCC3, which was produced by MCC3 with smallest original particle size and good dispersity among the four MCCs. This result suggests that both the original particle size and dispersity of MCCs had significant effects on separated NCCs.

scholarly journals Size Effects on Magnetic Properties ofNi0.5Zn0.5Fe2O4Prepared by Sol-Gel Method

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Min Zhang ◽  
Zhenfa Zi ◽  
Qiangchun Liu ◽  
Peng Zhang ◽  
Xianwu Tang ◽  
...  
Keyword(s):  
Particle Size ◽  
Magnetic Measurements ◽  
Sol Gel ◽  
Domain Wall Motion ◽  
Blocking Temperature ◽  
Particle Sizes ◽  
X Ray Diffraction ◽  
Gel Method ◽  
Sol Gel Method ◽  
Cation Redistribution

Ni0.5Zn0.5Fe2O4particles with different particle sizes have been synthesized by sol-gel method. X-ray diffraction results show that all the samples are pure cubic spinel structure with their sizes ranging from 9 to 96 nm. The lattice constant significantly decreases with further increasing annealing temperature. The magnetic measurements show superparamagnetic nature below the particle size of 30 nm, while others show ferrimagnetic nature above the corresponding blocking temperature. The blocking temperature increases with the increase in particle size, which can be explained by Stoner-Wohlfarth theory. The saturation magnetization increases as the particle size increases, which can be explained by the cation redistribution on tetrahedral A and octahedral B sites and the domain wall motion. The variation of coercivity as a function of particle size is based on the domain structure.

Preparation and characterization of alumina membranes and alumina–titania composite membranes

1999 ◽  
Vol 14 (9) ◽  
pp. 3599-3603 ◽  
Author(s):  
Li Shi ◽  
Ning-Bew Wong
Keyword(s):  
Thermal Analysis ◽  
Particle Size ◽  
Differential Thermal Analysis ◽  
Sol Gel ◽  
Composite Membranes ◽  
Particle Sizes ◽  
Pore Sizes ◽  
Surface Areas ◽  
Alumina Membranes

Supported and unsupported γ-alumina membranes and alumina–titania composite membranes were prepared using the sol-gel method. In the course of preparation, effects of acid concentration, type of acid, alkoxide, and binder on the particle size of the sols and pore size of the membranes were investigated by thermogravimetry and differential thermal analysis, N2 physisorption, and light scattering. It was observed that the particle sizes of all the sols had only a small affect on the pore sizes of the membranes. Qualities of the membranes were improved by addition of polyvinyl alcohol as binder to the boehmite precursor. This resulted in less critical but more controllable drying and calcining procedures. Composite membranes with different pore sizes from 3.2 to 4.8 nm and surface areas retained above 100 m2/g could be regulated by different alumina-to-titania ratios.

scholarly journals Particle Size Dependence of TiO2Electrodes in Rechargeable Lithium Battery

1996 ◽  
Vol 19 (3) ◽  
pp. 189-198 ◽  
Author(s):  
S. Y. Huang ◽  
G. Campet ◽  
N. Treuil ◽  
J. Porter ◽  
K. Chhor
Keyword(s):  
Particle Size ◽  
Lithium Battery ◽  
Size Dependence ◽  
Storage Capacity ◽  
Xrd Analysis ◽  
Structural Defects ◽  
Particle Sizes ◽  
Nanosized Particles ◽  
Rechargeable Lithium Battery ◽  
Surface Areas

Particle size effects in five anatase TiO2pellet electrodes with different particle sizes (4 ∼ 300nm) and surface areas (8 ∼ 380m2/g) were studied by XRD analysis, chronopotentiometry and chronoamperometry in Li/LiN(CF3SO2)2+ EC:DME/TiO2cells. Nanosized TiO2electrodes showed by 22% larger storage capacity, 50% lower overvoltage loss at the same current density, and 75% higher charge density for a given time than microsized ones; electric storage capacity enhances more rapidly with decreasing particle size and increasing surface area in a nanoscale region than in a microscale region. The particle size dependence may be explained by surface morphology of electrodes and existence of structural defects or distortion in the surface layer of TiO2nanosized particles.

The Effects of Particle Size and Morphology of Raw Materials on the Properties of MoSi2 Synthesized by SHS

2013 ◽  
Vol 319 ◽  
pp. 213-218 ◽  
Author(s):  
Ying Zhou ◽  
Cai Li Wei ◽  
Guo Tian Ye ◽  
Chen Yong Liu
Keyword(s):  
Particle Size ◽  
Raw Materials ◽  
Secondary Phase ◽  
Combustion Products ◽  
Particle Sizes ◽  
X Ray Diffraction ◽  
High Temperature Synthesis ◽  
Particle Size And Morphology ◽  
Size And Morphology ◽  
Grinding Time

In this work, the influences of the particle size and morphology of raw materials on the formation of MoSi2 by self-propagating high-temperature synthesis (SHS) were investigated. A series of Si powders with different particle sizes and Mo powders with different morphologies were obtained by grinding for 1, 5 and 10 hours, respectively. X-ray diffraction pattern characterization (XRD) and scanning electron microscopy (SEM) were used to characterize the samples. It was found that, the phase compositions and morphologies of the combustion products depended on the particle size and morphology of the raw materials. The particle sizes of Si powders decreased with increasing the grinding time, and a secondary phase of Mo5Si3 was detected in the obtained MoSi2 powders when the smallest particle size of Si powders was about 1μm. While, the particle sizes of Mo powders increased with increasing the grinding times, and the obtained MoSi2 showed massive flaky structures, which were similar to the morphologies of Mo particles.

scholarly journals Comparative Study of Pore Structure Characteristics between Mudstone and Coal under Different Particle Size Conditions

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8435
Author(s):  
Jianguo Zhang ◽  
Xiyuan Li ◽  
Jihong Jiao ◽  
Jianbao Liu ◽  
Feng Chen ◽  
...  
Keyword(s):  
Particle Size ◽  
Pore Structure ◽  
Mercury Intrusion Porosimetry ◽  
Coal Bed ◽  
Particle Sizes ◽  
N2 Adsorption ◽  
Structure Characteristics ◽  
Surface Areas ◽  
The Difference ◽  
And Migration

In order to investigate the difference of pore structure characteristics between mudstone and coal under different particle size conditions, samples acquired from Henan province were smashed and screened into three different particle sizes (20–40, 80–100, and >200 mesh) to conduct the experiments, using the high-pressure mercury intrusion porosimetry (MIP) and low-temperature N2 adsorption (LT-N2A) techniques. The results demonstrated that the proportion of open pores or semi-enclosed pores increased, and the pores became preferable contacted each other for both mudstone and coal during the crushing process. These variations of pore structure characteristics in the coal were beneficial to methane storage and migration. The total specific surface areas and pore volumes all showed a tendency of increasing continually for both mudstone and coal, as the particle sizes decreased from the LT-N2A test. The mudstone and coal were non-rigid aggregates with micropores, plate-shaped pores, and slit-shaped pores developed inside. The effect of the crushing process on the pore shape for the mudstone and coal was inappreciable. Moreover, the influence of the particle sizes on the mesopore was the most significant, followed by the macropore; and on the micropore, the influence was negligible for both mudstone and coal. The crushing process only had a significant impact on the pore structure of mudstone with a particle size of less than 100 mesh, while it could still alter the pore structure of coal with a particle size of larger than 100 mesh. It is believed that this work has a significant meaning to explore the diffusion and migration rules of coal-bed methane in coal.

Investigation of Mg2Si formation from Si and Mg by using spark plasma sintering synthesis

2015 ◽  
Vol 1735 ◽  
Author(s):  
Kota Sunohara ◽  
Koya Arai ◽  
Tomoyuki Nakamura ◽  
Kenjiro Fujimoto ◽  
Yuki Yamaguchi ◽  
...  
Keyword(s):  
Particle Size ◽  
Spark Plasma Sintering ◽  
Inert Gas ◽  
Particle Sizes ◽  
X Ray Diffraction ◽  
X Ray ◽  
Plasma Sintering ◽  
Spark Plasma

AbstractIn this study, we fabricated Mg2Si from metal Mg and Si with different particle sizes (425 - 300, 300 - 180, and 75 μm or less) using spark plasma sintering (SPS) equipment. Additionally, the Mg2Si formation was investigated. A sieved Si powder was mixed with metal Mg powder in an inert gas (Ar) atmosphere. The mixture was placed in a graphite die while still in an Ar atmosphere and subjected to SPS at 923 K and 1113 K. The obtained sintering bodies were Mg2Si particles with a size of about 5 μm. Then, the sintered bodies were evaluated by X-ray diffraction (XRD). As a result, it was confirmed that generation of Mg2Si increased with decreasing Si particle size.

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