scholarly journals Surface and Catalytic Properties of γ-Irradiated Fe2O3/Al2O3 Solids

1996 ◽  
Vol 13 (3) ◽  
pp. 153-163 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.S. Ahmad ◽  
A.M. Ghozza ◽  
S.M. El-Khouly
Keyword(s):  
Co Oxidation ◽  
Surface Area ◽  
Catalytic Reaction ◽  
Active Sites ◽  
Catalytic Properties ◽  
Nitrogen Adsorption ◽  
Ferric Nitrate ◽  
Unit Surface Area ◽  
Γ Irradiation ◽  
Co Oxidation Reaction

Two specimens of Fe2O3/Al2O3 solids were prepared by impregnating a known mass of finely-powdered Al(OH)3 with calculated amounts of ferric nitrate solutions followed by drying at 120°C and calcination in air at 400°C for 4 h. The mixed solids thus prepared had the nominal molar compositions 0.06Fe2O3/Al2O3 and 0.125Fe2O3/Al2O3 (FeAl-I and FeAl-II). The surface and catalytic properties of various irradiated solids (15–200 Mrad) were studied using nitrogen adsorption at −196°C and catalysis of CO oxidation by O2 at 150–280°C using a static method. The results obtained revealed that γ-irradiation at doses between 15 and 80 Mrad resulted in a progressive decrease (7–22%) in the surface area of the treated solids. Treatment with doses above this limit exerted an opposite effect. γ-Irradiation also resulted in a widening of the pores of the irradiated adsorbents. The catalytic activity of the FeAl-I solid was influenced slightly by γ-rays while the FeAl-II catalyst was significantly modified by this treatment. The reaction rate constant per unit surface area of the catalytic reaction conducted at 280°C over the FeAl-II solid decreased (65%) by exposure to doses up to 120 Mrad, then increased on increasing the dose above this limit. This did not modify the mechanism of the catalytic reaction, but changed the number of catalytically-active sites taking part in chemisorption and catalysis of the CO oxidation reaction without affecting their energetic nature.

scholarly journals Effect of Li2O Doping on the Surface and Catalytic Properties of the Cr2O/Al2O3 System

1998 ◽  
Vol 16 (6) ◽  
pp. 415-429 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.M. Ghozza ◽  
H.G. El-Shobaky
Keyword(s):  
Co Oxidation ◽  
Catalytic Reaction ◽  
Active Sites ◽  
Catalytic Properties ◽  
Nitrogen Adsorption ◽  
Maximum Increase ◽  
Exponential Factor ◽  
Catalytic Activities ◽  
Catalytically Active ◽  
Maximum Decrease

Two Cr2O3/Al2O3 samples with the nominal compositions 0.06Cr2O2/Al2O3 and 0.125Cr2O3/Al2O3 (AlCr-I and AlCr-II, respectively) were prepared by mixing a known amount of finely powdered Al(OH)3 with calculated amounts of CrO3, followed by drying at 120°C and calcination at 700°C and 800°C. Doped solid specimens were prepared by treating Al(OH)3 samples with known amounts of LiNO3 dissolved in the minimum amount of distilled water prior to mixing with CrO3. Dopant concentrations of 0.75, 1.50, 3.00 and 6.00 mol% Li2O were employed. The surface and catalytic properties of the pure and doped solids thus prepared were investigated using nitrogen adsorption at −196°C and studies of the catalysis of CO oxidation by O2 over the solid specimens at 300–400°C. The results of such studies showed that Li2O doping followed by calcination at 700°C led to a maximum increase in the specific surface area, SBET, of 26% for AlCr-I and of 55% for AlCr-II when these samples were doped with 3.00 mol% Li2O. The reverse effect was found when the calcination temperature was increased to 800°C, where a decrease of 34% in the SBET value of the AlCr-II sample doped with 3.00 mol% Li2O was detected. The catalytic activities measured at 350°C over the pure and doped solids decreased on increasing the dopant concentration, the maximum decrease in such activity being ca. 33% and 50%, respectively, for the AlCr-I and AlCr-II samples calcined at 700°C. Doping led to noticable changes in the magnitude of the activation energy for the catalytic reaction. Such changes were accompanied by parallel changes in the value of the pre-exponential factor in the Arrhenius equation. These results may indicate that Li2O doping has no effect on the mechanism of the catalytic reaction but modifies (decreases) the concentration of catalytically active sites taking part in chemisorption during the catalysis of CO oxidation by O2.

scholarly journals Surface and Catalytic Properties of γ-Irradiated Cr2O3/Al2O3 Solids

1997 ◽  
Vol 15 (6) ◽  
pp. 465-476 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.M. Ghozza ◽  
G.M. Mohamed
Keyword(s):  
Catalytic Activity ◽  
Co Oxidation ◽  
Surface Area ◽  
Pore Volume ◽  
Active Sites ◽  
Catalytic Properties ◽  
Total Pore Volume ◽  
Bet Surface Area ◽  
Two Samples ◽  
Γ Rays

Two samples of Cr2O3/Al2O3 were prepared by mixing a known mass of finely powdered Al(OH)3 with a calculated amount of CrO3 solid followed by drying at 120°C and calcination at 400°C. The amounts of chromium oxide employed were 5.66 and 20 mol% Cr2O3, respectively. The calcined solid specimens were then treated with different doses of γ-rays (20–160 Mrad). The surface and catalytic properties of the different irradiated solids were investigated using nitrogen adsorption at −196°C and the catalysis of CO oxidation by O2 at 300–400°C. The results revealed that γ-rays brought about a slight decrease in the BET surface area, SBET (15%), and in the total pore volume, Vp (20%), of the adsorbent containing 5.66 mol% Cr2O3. The same treatment increased the total pore volume, Vp (36%), and the mean pore radius, r̄ (43%), of the other adsorbent sample without changing its BET surface area. The catalytic activities of both catalyst samples were found to increase as a function of dose, reaching a maximum value at 80–160 Mrad and 40 Mrad for the solids containing 5.66 and 20 mol% Cr2O3, respectively. The maximum increase in the catalytic activity measured at 300°C was 59% and 100% for the first and second catalyst samples, respectively. The induced effect of γ-irradiation on the catalytic activity was an increase in the concentration of catalytically active sites taking part in chemisorption and in the catalysis of CO oxidation by O2 without changing their energetic nature. This was achieved by a progressive removal of surface hydroxy groups during the irradiation process.

scholarly journals Effects of γ-Irradiation on the Surface and Catalytic Properties of Co3O4/MgO Systems Aged for One Year

2002 ◽  
Vol 20 (10) ◽  
pp. 1037-1049 ◽  
Author(s):  
G.A. El-Shobaky ◽  
S.A. El-Molla ◽  
S.A. Ismail
Keyword(s):  
Catalytic Activity ◽  
Surface Area ◽  
Rate Constant ◽  
Reaction Rate ◽  
Catalytic Properties ◽  
Reaction Rate Constant ◽  
Unit Surface Area ◽  
Γ Irradiation ◽  
Γ Rays ◽  
One Year

The effects of γ-rays (20–160 Mrad) on the surface and catalytic properties of two Co3O4/MgO systems were investigated. The formulae of the investigated solids were 0.05Co3O4/MgO and 0.2Co3O4/MgO, respectively, both prepared by the impregnation method and calcined at 500°C. The irradiated samples were left for one year in sealed tubes before any measurements were undertaken. γ-Irradiation of the investigated solids resulted in a progressive decrease in the particle size of the Co3O4 and MgO phases. This treatment also led to a measurable increase in the specific surface area of the treated solids to an extent proportional to the γ-ray dosage. Treatment of the Co3O4/MgO system with different doses of γ-rays brought about a significant increase in the catalytic activity expressed both as the reaction rate constant and as the reaction rate constant per unit surface area. However, the curve relating to the catalytic activity and dosage of γ-rays showed maxima located at 40 and 80 Mrad for samples having the formula 0.05Co3O4/MgO and 0.2Co3O4/MgO, respectively. Furthermore, samples exposed to 160 Mrad showed a larger catalytic activity than the unirradiated samples. The results demonstrate the role of γ-rays in inhibiting the deterioration of the catalytic activity of the investigated systems as a function of aging time. The irradiation process did not modify the activation energy of the catalyzed reaction but altered the concentration of active centres on the surfaces of the solids without changing their energetic nature.

SURFACE CHEMISTRY AND CATALYTIC PROPERTIES OF BORON PHOSPHATE: 1. SURFACE AREA AND ACIDITY

1965 ◽  
Vol 43 (6) ◽  
pp. 1680-1688 ◽  
Author(s):  
J. B. Moffat ◽  
H. L. Goltz
Keyword(s):  
Surface Area ◽  
Active Sites ◽  
Elevated Temperatures ◽  
Catalytic Properties ◽  
Nitrogen Adsorption ◽  
Weight Changes ◽  
Kcal Mole ◽  
Boron Phosphate ◽  
Surface Areas ◽  
Nitrogen Adsorption Isotherms

Surface properties of the dehydration catalyst, boron phosphate (BP), prepared by the reaction of triethyl borate and phosphoric acid, were investigated by the use of a microbalance system. During evacuation at elevated temperatures, weight changes of the BP were obtained. Nitrogen adsorption isotherms were measured after each treatment. Surface areas appear to increase, and reach a maximum in the range 200–300 °C. Weight changes are initially large but begin to level off as the temperature is increased. Ammonia isotherms were obtained at 25.00 °C on aliquots of the same BP sample after various pretreatments. Amounts of ammonia remaining adsorbed after evacuation overnight were taken as the quantity chemisorbed. An approximate value of 8.9 kcal/mole of ammonia was obtained for the heat of chemisorption of ammonia by measuring the pressure and weight change as the amount of chemisorbed ammonia is decreased on heating the BP to various temperatures in a closed system. Results are interpreted in terms of change of number of active sites with surface area and the deactivation of sites on loss of water.

Bound Rubber and Elastomer-Filler Interaction

1995 ◽  
Vol 68 (2) ◽  
pp. 297-310 ◽  
Author(s):  
B. Meissner
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Active Sites ◽  
Quantitative Description ◽  
Interfacial Area ◽  
Active Surface ◽  
Unit Surface Area ◽  
Bound Rubber ◽  
The Difference ◽  
High Structure

Abstract The statistical theory of bound rubber and the polymer-filler gel formation theory are shown to offer a satisfactory quantitative description of a set of experimental bound-rubber data recently obtained by Wolff, Wang, Tan (Rubber Chem. Technol. 66, 163 (1993)) on SBR compounds filled with 17 furnace blacks covering the whole range of rubber grades. The observed decrease of bound-rubber content per unit of interfacial area with increasing loading and/or specific surface area of carbon black is explained by the theory as being due to the statistical nature of the adsorption process. A correlation was found to exist between specific surface activity of filler D (adjustable parameter of the theory, number of active sites per unit surface area) and filler structure, the latter being characterized by the difference between DBP absorption and crushed DBP absorption. Also, D was found to increase with loading of a high-structure black. The two effects are ascribed to filler aggregates breakdown during mixing, which leads to a new active surface formation for polymer bonding.

scholarly journals Kinetics and Thermodynamics of CO Oxidation by (TiO2)6

2021 ◽  
Author(s):  
Navjot Kaur ◽  
Neetu Goel ◽  
Michael Springborg ◽  
Mohammad Molayem
Keyword(s):  
Co Oxidation ◽  
Active Sites ◽  
Density Functional ◽  
Harmonic Approximation ◽  
Oxidation Mechanism ◽  
Structural Isomers ◽  
Reactivity Descriptors ◽  
Co Oxidation Reaction ◽  
Adsorption Of Co ◽  
Global And Local

Molecular level insights into the mechanism and thermodynamics of CO oxidation by a (TiO) cluster have been obtained through density functional calculations. Thereby, we have considered as an example, two different structural isomers of (TiO) with the purpose of understanding the interplay between local structure and activity for the CO oxidation reaction. Active sites in the two isomeric forms were identified on the basis of global and local reactivity descriptors. For the oxidation of CO to CO2 we considered both sequential and simultaneous adsorption of CO and O2 on (TiO2)6 cluster through the ER and LH mechanisms, respectively. Three different pathways were obtained for CO oxidation by (TiO2)6 cluster, and the mechanistic route of each pathway were identified by locating the transition-state and intermediate structures. The effects of temperature on the rate of the reaction was investigated within the harmonic approximation. The structure-dependent activity of the cluster was rationalized through reactivity descriptors and analysis of the frontier orbitals. Finally, we also considered the effects of a support, i.e., graphene, on the oxidation mechanism.

scholarly journals Effect of Mo Dispersion on the Catalytic Properties and Stability of Mo–Fe Catalysts for the Partial Oxidation of Methanol

Molecules ◽  
2020 ◽  
Vol 25 (10) ◽  
pp. 2410
Author(s):  
Shuai Zhang ◽  
Minghan Han
Keyword(s):  
Surface Layer ◽  
Surface Area ◽  
Partial Oxidation ◽  
Active Sites ◽  
Oxygen Vacancies ◽  
Catalyst Surface ◽  
Catalytic Properties ◽  
Oxidation Of Methanol ◽  
Partial Oxidation Of Methanol ◽  
Fe Catalysts

Mo–Fe catalysts with different Mo dispersions were synthesized with fast (Cat-FS, 600 r·min−1) or slow stirring speed (Cat-SS, 30 r·min−1) by the coprecipitation method. Improving the stirring speed strengthened the mixing of the solution and increased the dispersion of particles in the catalyst, which exhibited favorable activity and selectivity. The byproduct (dimethyl ether (DME)) selectivity increased from 2.3% to 2.8% with Cat-SS, while it remained unchanged with Cat-FS in a stability test. The aggregation of particles and thin Mo-enriched surface layer decreased the catalyst surface area and slowed down the reoxidation of reduced active sites with Cat-SS, leaving more oxygen vacancies which promoted the formation of DME by the nonoxidative channel.

Synthesis of High Surface Area Silicon Carbide and Its Application in CO Oxidation Reaction

2008 ◽  
Vol 24 (01) ◽  
pp. 171-175 ◽  
Author(s):  
ZHAN Ying-Ying ◽  
◽  
◽  
CAI Guo-Hui ◽  
ZHENG Yong ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Co Oxidation ◽  
Surface Area ◽  
Oxidation Reaction ◽  
High Surface ◽  
High Surface Area ◽  
Co Oxidation Reaction

scholarly journals Synthesis and characterization of Cu-MFI catalyst for the direct medium temperature range NO decomposition

2016 ◽  
Vol 34 (1) ◽  
pp. 177-184 ◽  
Author(s):  
Karolina Maduna Valkaj ◽  
Vesna Tomašić ◽  
Andrea Katović ◽  
ElżBieta Bielańska
Keyword(s):  
Ion Exchange ◽  
Active Sites ◽  
Catalytic Properties ◽  
Direct Synthesis ◽  
Copper Acetate ◽  
Nitrogen Adsorption ◽  
No Decomposition ◽  
Medium Temperature ◽  
Exchange Method ◽  
Mfi Zeolites

AbstractIn this study the physico-chemical and catalytic properties of copper bearing MFI zeolites (Cu-MFI) with different Si/Al and Si/Cu ratios were investigated. Two different methods for incorporation of metal ions into the zeolite framework were used: the ion exchange from the solution of copper acetate and the direct hydrothermal synthesis. Direct synthesis of a zeolite in the presence of copper-phosphate complexes was expected to generate more active copper species necessary for the desired reaction than the conventional ion exchange method. Direct decomposition of NO was used as a model reaction, because this reaction still offers a very attractive approach to NOX removal. The catalytic properties of zeolite samples were studied using techniques, such as XRD, SEM, EPR and nitrogen adsorption/desorption measurements at 77 K. Results of the kinetic investigation revealed that both methods are applicable for the preparation of the catalysts with active sites capable of catalyzing the NO decomposition. It was found out that Cu-MFI zeolites obtained through direct synthesis are promising catalysts for NO decomposition, especially at lower reaction temperatures. The efficiency of the catalysts prepared by both methods is compared and discussed.

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