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 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 Na2O Doping on the Surface and Catalytic Properties of the Mn2O3/Al2O3 System

1995 ◽  
Vol 12 (2) ◽  
pp. 119-128 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.M. Ghozza ◽  
S. Hammad
Keyword(s):  
Catalytic Activity ◽  
Active Sites ◽  
Catalytic Properties ◽  
Xrd Analysis ◽  
Manganese Carbonate ◽  
Oxidation Of Co ◽  
Mechanical Mixing ◽  
Catalytic Activities ◽  
Specific Catalytic Activity ◽  
Catalytically Active

Manganese/aluminium mixed oxide solids having the formula 0.2MnCO3/Al2O3 were prepared by mechanical mixing of a known weight of finely powdered manganese carbonate and aluminium hydroxide. The solids obtained were treated with NaNO3 (0.75–6 mol%) solution and dried at 110°C, then calcined in air at 500°C and 800°C for 6 h. The phases produced were identified by XRD analysis. The surface properties (SBET, Vp and r̄) of the pure and doped solids were studied by using N2 adsorption at – 196°C and their catalytic activities were determined by studying the oxidation of CO by O2at 125–300°C. The results obtained reveal that pure and doped mixed solids preheated in air at 500°C and 800°C consist of Mn2O3 (partridgite) and a poorly crystalline γ-alumina. Doping with sodium oxide at 500°C and 800°C resulted in a small decrease (14–19%) in the SBET value of the treated solids. However, this treatment brought about a significant modification in the catalytic activity of the doped solids. Doping with 0.75% Na2O at 500°C led to an increase of about 30–50% in the specific catalytic activity which was found to decrease on increasing the percentage of Na2O above this limit, falling to values smaller than that measured for the undoped catalyst. Doping at 800°C led to a progressive decrease in the activity of the treated solid to an extent proportional to the amount of dopant present. The doping process at 500°C and 800°C did not modify the mechanism of the catalytic reaction but altered the number of catalytically-active sites contributing in the catalysis of CO oxidation by O2 without changing their energetic nature.

scholarly journals Physicochemical Surface and Catalytic Properties of the Na2O-doped CuO–ZnO/Al2O3 System

1998 ◽  
Vol 16 (2) ◽  
pp. 77-86 ◽  
Author(s):  
G.A. El-Shobaky ◽  
G.A. Fagal ◽  
A.S. Ahmed ◽  
M. Mokhtar
Keyword(s):  
Catalytic Activity ◽  
Catalytic Properties ◽  
Nitrogen Adsorption ◽  
Nominal Composition ◽  
Impregnation Method ◽  
Maximum Increase ◽  
Oxide Support ◽  
Co Oxidation Reaction ◽  
Catalytically Active ◽  
Metal Oxide Support

In order to investigate the effect of Na2O doping (0.75–4.5 mol%) on metal oxide-support interactions, the surface and catalytic properties of the CuO–ZnO/Al2O3 system have been studied using XRD, nitrogen adsorption at -196°C and the catalytic oxidation of CO by O2 at 150–200°C. Pure and doped mixed oxide solid samples were prepared via the wet impregnation method using Al(OH)3, NaNO3. Zn(NO3)2 and Cu(NO3)2 solutions, followed by drying and calcination at 600°C and 700°C.The nominal composition of the solids thus prepared was 0.25CuO:0.06ZnO: Al2O3. The results obtained showed that Na2O doping followed by heating in air at 600°C leads to enhanced crystallization of the CuO crystallites to an extent proportional to the amount of dopant present, while doping followed by heating in air at 700°C hinders the solid–solid interactions between CuO andA12O3, and leads to the production of CuAl2O4. The specific surface area was found to increase progressively as a function of the dopant concentration for the solid calcined at 700°C. The catalytic activity was also found to increase progressively on increasing the amount of dopant added. The maximum increase in the catalytic activity measured at 150, 175 and 200°C over solids calcined at 700°C was 114, 102 and 82%. respectively. The doping process did not modify the mechanism of the catalyzed reaction but rather increased the concentration of catalytically active constituents (surface CuO crystallites) involved in the chemisorption and catalysis of the CO oxidation reaction without affecting their energetic nature.

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 Effect of Li2O Doping on the Surface and Catalytic Properties of the Fe2O3–NiO/Al2O3 System

1998 ◽  
Vol 16 (1) ◽  
pp. 21-32 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.M. Ghozza ◽  
N.M. Deraz
Keyword(s):  
Activation Energy ◽  
Catalytic Activity ◽  
Mixed Oxide ◽  
Active Sites ◽  
Catalytic Properties ◽  
Surface Characteristics ◽  
Appreciable Change ◽  
Surface Areas ◽  
Catalytically Active ◽  
Specific Surface Areas

Ferric–nickel/aluminium mixed oxide solids have the formula Fe2O3–0.42NiO/Al2O3 were treated with Li2O (0.75–3 mol%) and heated in air for 4 h at 500°C and 800°C, respectively. The effects of this treatment on the surface characteristics of these solids and their catalytic properties in relation to CO oxidation by O2 have been investigated. The results reveal that Li2O doping at 0.75 mol% concentration resulted in an increase of 24% and 18%, respectively, in the value of the specific surface areas, SBET, of the solids precalcined at 500°C and 800°C, while the addition of 3 mol% Li2O led to a slight decrease of ca. 10% in the SBET value of the same solids. In contrast, irrespective of whether the doping process involved solids precalcined at 500°C or 800°C, a significant decrease of 37% and 78%, respectively, was observed in the catalytic activity of these materials. This decrease in catalytic activity was not accompanied by any appreciable change in the magnitude of the activation energy for the catalytic reaction, i.e. Li2O doping brings about a decrease in the concentration of catalytically active sites without changing their energetic nature.

scholarly journals Morphology Effect of Ceria Supports on Gold Nanocluster Catalyzed CO Oxidation

2021 ◽  
Author(s):  
Zhiming Li ◽  
Xinyu Zhang ◽  
Quanquan Shi ◽  
Xia Gong ◽  
Hui Xu ◽  
...  
Keyword(s):  
Co Oxidation ◽  
Chemical Reactions ◽  
Active Sites ◽  
Gold Nanocluster ◽  
Catalytically Active ◽  
Morphology Effect

Interfacial perimeter is generally viewed as the catalytically active sites for a number of chemical reactions over the oxide-supported nanogold catalysts. Here, the well-defined CeO2 of nanocube, nanorod and nanopolyhedra...

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.

Novel nanoparticle catalysts for catalytic gas sensing

2016 ◽  
Vol 6 (2) ◽  
pp. 339-348 ◽  
Author(s):  
Eva Morsbach ◽  
Sebastian Kunz ◽  
Marcus Bäumer
Keyword(s):  
Active Sites ◽  
Gas Sensing ◽  
Catalytic Properties ◽  
Hydrogen Sensor ◽  
Colloidal Nanoparticles ◽  
Nanoparticle Catalysts ◽  
Porous Networks ◽  
Bifunctional Ligands ◽  
Catalytically Active ◽  
Total Heat Capacity

Applications such as catalytic gas sensing require a high density of catalytically active sites at low total heat capacity. One way to achieve this goal is the molecular linkage of colloidal nanoparticles with bifunctional ligands resulting in 3D-porous networks. The catalytic properties of such structures were investigated in a thermoelectric hydrogen sensor.

scholarly journals Structural, Surface and Catalytic Properties of Nano-Sized Ceria Catalysts

2009 ◽  
Vol 27 (4) ◽  
pp. 413-422 ◽  
Author(s):  
N.M. Deraz ◽  
A. Alarifi
Keyword(s):  
Cerium Oxide ◽  
Active Sites ◽  
Catalytic Properties ◽  
Heating Temperature ◽  
Nitrogen Adsorption ◽  
Structural Surface ◽  
Oxide Particles ◽  
Ceria Catalysts ◽  
20 Nm ◽  
Xrd And Tem

Well-dispersed uniform spheres of crystalline CeO2 were prepared by calcining precursor particles obtained by heating ammonium cerium nitrate for 4 h. These spherical substrates were examined using XRD and TEM methods, and by nitrogen adsorption studies at −196 °C. Subsequently, such cerium oxide particles prepared by calcination at 400–600 °C were used as catalysts for the conversion of isopropanol at 250–450 °C, using a flow method. The results obtained showed that increasing the heating temperature of the system investigated from 400 °C to 600 °C stimulated the formation of a well-crystallized CeO2 phase having a crystallite size varying between 10 and 20 nm. Both the surface area and catalytic activity of cerium oxide were found to decrease on increasing the calcination temperature. All solids investigated behaved as dehydrogenation catalysts which were selective towards the formation of acetone. The heat treatment did not alter the mechanism of dehydrogenation of isopropanol, but changed the concentration of active sites involved in the catalyzed reaction without altering their energetic nature.

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