Heterogeneous Interactions of Methylamines on Porous Adsorbents. Part I. The Adsorption of Monomethylamine on Silica Gels and Silica–Alumina

1972 ◽  
Vol 50 (11) ◽  
pp. 1666-1674 ◽  
Author(s):  
W. G. Cook ◽  
R. A. Ross
Keyword(s):  
Nitrogen Adsorption ◽  
Silica Gels ◽  
Heats Of Adsorption ◽  
Surface Areas ◽  
Pore Size Distributions ◽  
Wide Range ◽  
Heat Curve ◽  
Silica Alumina ◽  
Adsorption Heats ◽  
Adsorption Desorption

The adsorption of monomethylamine has been studied near its boiling point, 266 °K, on silica–alumina and on a wide range of silica gels by measurement of adsorption–desorption isotherms and isothermal calorimetric heats of adsorption. In addition, surface areas and pore-size distributions have been determined by low-temperature nitrogen adsorption. Heats of adsorption on Davison "923" silica gel varied from around 33.0 kcal/mol at θ = 0.01 to 6.2 kcal/mol at monolayer completion. Maxima were observed in this heat curve in the regions of θ = 0.15, 0.28, and 0.40. These phenomena are believed to be related to interactions among the adsorbed species in pores of diameters approaching molecular dimensions. Heats of adsorption on silica–alumina fell smoothly from 39.5 kcal/mol at θ = 0.03 to 13.0 kcal/mol at θ = 1.00. Adsorption–desorption characteristics of methylamine were also examined on a series of silica gels with widely different pore structures. The variations in the heats of adsorption with surface coverage are discussed in terms of both the nature of the adsorbed surface species and lateral interactions among the adsorbed molecules.

Heterogeneous Interactions of Methylamines on porous Adsorbents Part II. Interactions on Silica–Alumina and Silica Gel Surfaces of Di- and Tri-methylamine in the Region of their Boiling Points

1972 ◽  
Vol 50 (15) ◽  
pp. 2451-2456 ◽  
Author(s):  
W. G. Cook ◽  
R. A. Ross
Keyword(s):  
Silica Gel ◽  
Surface Coverage ◽  
Adsorbed Layer ◽  
Silica Gels ◽  
Heats Of Adsorption ◽  
Boiling Points ◽  
Silica Alumina ◽  
Desorption Isotherms ◽  
Adsorption Desorption ◽  
Heterogeneous Interactions

The adsorption of di- and tri-methylamine has been studied at 280 and 276°K, respectively, on a range of silica gels and on silica–alumina. Adsorption–desorption isotherms and isothermal calorimetric heats of adsorption were measured. Heats of adsorption for di-methylamine on silica gel varied from 29.0 kcal/mol at θ = 0.05 to 12.0 kcal/mol at monolayer completion, while for silica–alumina the heats fell from 31.4 to 9.0 kcal/mol between these same values of surface coverage. For tri-methylamine on silica gel, heats fell from 21.0, θ = 0.05, to 10.3 kcal/mol, θ = 1.00, while heats of 21.4 and 9.9 kcal/mol, respectively, were found at these same surface coverages on silica–alumina. The values of the heats of adsorption are discussed in terms of interactions in the adsorbed layer which are believed to be influenced by the pore sizes in the adsorbent and by the basicity of the amine molecules.

The Effect of Heat Treatment of Silica Gels on the Calorimetric Heats of Adsorption of Sulfur Dioxide up to One-twentieth Monolayer Coverage at 423 °K

1972 ◽  
Vol 50 (8) ◽  
pp. 1241-1245 ◽  
Author(s):  
R. W. Glass ◽  
R. A. Ross
Keyword(s):  
Sulfur Dioxide ◽  
Nitrogen Adsorption ◽  
Silica Gels ◽  
Distribution Data ◽  
Heats Of Adsorption ◽  
Heat Treated ◽  
Adsorbed Complex ◽  
Adsorption Desorption ◽  
Limiting Values ◽  
Dual Site

Calorimetric heats of adsorption of sulfur dioxide have been determined at 423°K for a series of silica gels heat-treated at 240, 550, 700, 800, and 900 °C. At the lowest surface coverage of 0.01 μmol m−2, heats of 25 to 30 kcal mol−1 were observed. These values dropped rapidly with increasing coverage and approached "limiting" values of 6 to 7 and 12 kcal mol−1 for dehydroxylated and hydroxylated surfaces, respectively. To explain the results at lowest coverages an adsorbed complex involving multiple hydrogen bonds is proposed while at higher coverages it is suggested that single and dual site adsorbed species predominate for the dehydroxylated and hydroxylated surfaces, respectively. Sulfur dioxide adsorption isotherms on all gels at 423 °K obeyed the Langmuir equation.Adsorbents were characterized by nitrogen adsorption–desorption isotherms at 77 °K and pore size distribution data were calculated from the desorption branch.

Phase Stabilization of Mesoporous Mn-Promoted ZrO2: Influence of the Precursor

2010 ◽  
Vol 132 ◽  
pp. 68-75 ◽  
Author(s):  
Marcello L. Hernández-Pichardo ◽  
J.A. Montoya ◽  
P. Del Angel ◽  
S.P. Paredes
Keyword(s):  
Nitrogen Adsorption ◽  
Hydrolysis Rate ◽  
Ammonium Bromide ◽  
Preferential Formation ◽  
Surface Areas ◽  
Pore Size Distributions ◽  
Mesoporous Zirconia ◽  
Cetyl Trimethyl Ammonium ◽  
Adsorption Desorption ◽  
Mn Doped

Mesoporous zirconia-Mn oxides were prepared by surfactant-assisted precipitation using different zirconia precursors and cetyl-trimethyl-ammonium bromide (CTAB) as a synthetic template. The objective of this work was to find out the influence of the zirconia precursors over the structural and textural characteristics of Mn-doped mesoporous zirconia solids. A series of syntheses were carried out by two methods using different zirconia precursors, modifying the Zr:surfactant ratio and the hydrolysis rate of the precipitate. After calcination at 500 °C, the samples were characterized by XRD, DTA, TEM and nitrogen adsorption-desorption isotherm. The use of the zirconium nitrate leads to materials having higher surface areas and narrow pore size distributions in the range of mesoporous materials; however, the preferential formation of the zirconia in the metaestable tetragonal phase was identified as the effect of the particle size allowed by the preparation method rather than the effect of the precursor. It was also found that the Mn and surfactant addition enhances the stabilization of the tetragonal crystalline phase and porosity.

scholarly journals Action Time-Effect and Mechanism of Low-Calcium Fly Ash in Cement-Based Composites

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 681
Author(s):  
Na Yan ◽  
Qingqing Tang ◽  
Ying Zhang ◽  
Guowen Sun
Keyword(s):  
Fly Ash ◽  
Nitrogen Adsorption ◽  
Chemical Effect ◽  
Hydration Products ◽  
X Ray Diffraction ◽  
Degree Of Hydration ◽  
Surface Areas ◽  
Activity Effect ◽  
Low Calcium ◽  
Pore Size Distributions

This study was conducted in order to investigate when low-calcium fly ash plays a physical or chemical effect and what is the chemical effect proportion of low-calcium fly ash. Two types of low-calcium fly ash and quartz powder, with similar fineness as active and inert admixtures, were used as materials in this study. Under different water/binder ratios and hydration ages, the effects of the different types of admixtures and their dosages on the flexural and compressive strength of the composites were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption methods, in addition to an assessment of the degree of hydration of the fly ash, were employed to observe the hydration products at different ages, the microstructures of the hydration products, as well as their surface areas and pore size distributions. The results show that during the hydration period of 28 days, the low-calcium fly ash has a micro-aggregate filling physical effect. However, after 56 days, the hydration degree of fly ash begins to exceed 1%. This illustrates that the low-calcium fly ash has both the pozzolanic activity effect and micro-aggregate filling effect. In contrast, the low-calcium fly ash hydrated for 90 days is still dominated by the physical filling effect.

Structural and surface aspects of thermally treated copper aluminium mixed hydroxides

1991 ◽  
Vol 69 (10) ◽  
pp. 1511-1515 ◽  
Author(s):  
Awad I. Ahmed ◽  
S. E. Samra ◽  
S. A. El-Hakam
Keyword(s):  
Pore Structure ◽  
Copper Content ◽  
Textural Properties ◽  
Nitrogen Adsorption ◽  
Phase Changes ◽  
X Ray Diffraction ◽  
X Ray ◽  
Surface Areas ◽  
Structure Surface ◽  
Adsorption Desorption

CuO–Al2O3 catalysts containing various amounts of copper oxide have been prepared by precipitation. The phase changes were studied by X-ray diffraction. The results obtained revealed that the thermal treatment of solid CuO–Al2O3 at 700 °C produced only crystalline CuO. Heating to 900 °C led to the formation of copper alumina spinel together with unreacted CuO and γ-Al2O3. The spinel content was found to increase with increasing copper content. Nitrogen adsorption–desorption isotherms on the calcined samples have been measured. Surface areas have been calculated and the pore structure analysed. The textural properties of the system were found to depend on both the copper content and the calcination temperature. Key words: CuO, Al2O3 catalysts, structure, surface area, pore structure.

scholarly journals Surfactant-Free Solvothermal Method for Synthesis of Mesoporous Nanocrystalline TiO2Microspheres with Tailored Pore Size

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Yajing Zhang ◽  
Sujuan Zhang ◽  
Kangjun Wang ◽  
Fu Ding ◽  
Jing Wu
Keyword(s):  
Pore Size ◽  
Anatase Phase ◽  
Nitrogen Adsorption ◽  
Ethanol Solution ◽  
Tetrabutyl Titanate ◽  
Size Distributions ◽  
Pore Size Distributions ◽  
Structure Morphology ◽  
Mesoporous Microspheres ◽  
Adsorption Desorption

TiO2mesoporous microspheres self-assembled from nanoparticles were synthesized by a surfactant-free solvothermal route. The TiO2precursors were fabricated by tetrabutyl titanate, glacial acetic acid, and urea in the ethanol solution at 140°C for 20 h, and TiO2mesoporous microspheres were obtained by a postcalcination at temperatures of 450°C for promoting TiO2crystallization and the removal of residual organics. The phase structure, morphology, and pore nature were characterized by XRD, SEM, and nitrogen adsorption-desorption measurements. The as-prepared TiO2microspheres are in anatase phase, with 2-3 μm in diameter, and narrow pore distribution range is 3-4 nm. The adjustments of the synthetic parameters lead to the formation of the mesoporous TiO2microspheres with tuned pore size distributions and morphology.

Study of the catalytic activity of Al-Fe pillared clays in the Baeyer–Villiger oxidation

Clay Minerals ◽  
2012 ◽  
Vol 47 (2) ◽  
pp. 275-284 ◽  
Author(s):  
L. S. Belaroui ◽  
A. Bengueddach
Keyword(s):  
Textural Properties ◽  
Nitrogen Adsorption ◽  
Pillared Clays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Dissolved Iron ◽  
Surface Areas ◽  
Accessible Surface ◽  
Adsorption Desorption ◽  
Villiger Oxidation

AbstractThree types of AlFePILCs pillared clays have been prepared from Algerian clay precursors. They have been characterized and tested in the Baeyer–Villiger oxidation of cyclohexanone to caprolactone using benzaldehyde and oxygen as oxidant at room temperature. The structural and textural properties of the catalyst have been determined by X-ray diffraction, nitrogen adsorption-desorption isotherms and Mössbauer spectroscopy.The different activities of the clays have been related to their Fe contents and accessible surface areas. The induction period observed before the reaction started has been attributed to the dissolution of a portion of the Fe3+ cations, mediated by either the perbenzoic acid intermediate or the benzoic acid co-product. The reaction was indeed catalysed by a few ppm of dissolved iron cations and the catalysis of the Baeyer–Villiger oxidation reaction should mechanistically be considered as homogeneous.

MESOPOROUS CARBON ELECTRODE: SYNTHESIS, CHARACTERIZATION AND ELECTROCHEMICAL PROPERTIES

2010 ◽  
Vol 03 (03) ◽  
pp. 161-164 ◽  
Author(s):  
XI LONG ◽  
CHUNXIA ZHAO ◽  
WEN CHEN
Keyword(s):  
Cyclic Voltammetry ◽  
Electrochemical Properties ◽  
Mesoporous Carbon ◽  
Nitrogen Adsorption ◽  
Mesoporous Structure ◽  
Constant Current ◽  
Surface Areas ◽  
Constant Current Charge ◽  
Adsorption Desorption ◽  
Charge Discharge

The present paper studies a kind of mesoporous carbon (MC) with high electrochemical performance, which was prepared by vapor infiltration method. The microstructure and electrochemical properties of the mesoporous carbon were investigated by transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherms, cyclic voltammetry (CV), constant current charge–discharge cycling (CD), and the long-term stability test. The results indicated that the mesoporous carbon has an ordered mesoporous structure, with pore size of about 3.87 nm and surface areas of 1087 m2 ⋅ g-1. The cyclic voltammetry curve reveals typical electrical double-layer capacitor property. After 200 cycles, the CV curves can almost be overlapped, which indicates excellent cycling stability. From the charge/discharge cycling, the specific capacitance of MC is 117 F ⋅ cm-1 in 1.0 M KNO3 electrolyte media at a scan rate of 1.0 mV ⋅ s-1, which decays with increasing current density. The charge–discharge efficiency also decays with it.

Sorption of dimethyl ether on silica gel

1970 ◽  
Vol 48 (1) ◽  
pp. 13-16 ◽  
Author(s):  
E. Robinson ◽  
R. A. Ross
Keyword(s):  
Dimethyl Ether ◽  
Hysteresis Loops ◽  
Acid Sites ◽  
Silica Gels ◽  
Hydrogen Bond Formation ◽  
Heats Of Adsorption ◽  
Heat Treated ◽  
Ether Oxygen ◽  
Initial Adsorption ◽  
Adsorption Desorption

The adsorption of dimethyl ether has been studied at its boiling point on a range of silica gels by measurement of adsorption/desorption isotherms and isothermal calorimetric heats of adsorption. Data were determined on gels heat treated at 240, 500, 700, and 900 °C and also on gels impregnated with 0.274% w/w aluminum. On 240 °C gels, heats of adsorption varied from around 20 through 12 to 7 kcal/mole at θ = 0.01, 0.50, and 0.90, respectively. Hysteresis loops are analyzed and the initial adsorption trends explained by hydrogen bond formation between the ether oxygen and surface hydroxy groups. The enhanced amounts of ether adsorbed after aluminum impregnation are explained by the creation of either Brønsted acid sites on gels treated at 240 °C or Lewis acid sites on gels treated at the highest temperatures.

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