scholarly journals Effect of γ-Irradiation on Some Surface and Catalytic Properties of Cr2O3/Al2O3 Solids Precalcined at 700°C

1998 ◽  
Vol 16 (3) ◽  
pp. 163-174 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.M. Ghozza ◽  
G.M. Mohamed
Keyword(s):  
Catalytic Activity ◽  
Active Sites ◽  
Opposite Effect ◽  
Catalytic Properties ◽  
Surface Characteristics ◽  
Mechanical Mixing ◽  
Γ Irradiation ◽  
Untreated Sample ◽  
Surface Parameters ◽  
Catalytically Active

The effects of γ-irradiation (20–160 Mrad) on the surface characteristics (SBET, VP and r) and catalytic properties (in CO oxidation by O2) of chromia/ alumina solids have been investigated. The solids were prepared by mechanical mixing of CrO3 with finely powdered Al(OH)3, followed by drying at 120°C and calcination in air at 700°C. The amounts of chromia in the samples were 8.2 wt% and 27.1 wt%, respectively. The results obtained show that doses of 20–40 Mrad brought about a measurable increase in the surface characteristics (SBET, 46%; VP, 93%; r, 31%) of the sample containing 27.1 wt% Cr2O3 but doses above this limit had the opposite effect. However, the various surface parameters of the sample treated with 160 Mrad were still higher than those of the untreated sample. With the sample containing 8.2 wt% Cr2O3, varying the dosage of γ-irradiation in the range 20–160 Mrad led to smaller variations in the surface parameters. The catalytic activities of both types of sample were decreased by γ-irradiation, with the decrease being more pronounced for samples rich in chromia. Curves relating catalytic activity to dosage exhibited minima at 40 Mrad. The observed decrease in catalytic activity with γ-irradiation was attributed to a decrease in the concentration of catalytically active sites taking part in chemisorption and catalysis of the oxidation of CO by O2 without any change in their energetic nature.

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 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 Surface and Catalytic Properties of NiO and Fe2O3 Solids

1997 ◽  
Vol 15 (8) ◽  
pp. 593-607 ◽  
Author(s):  
A. Abd. El-Aal ◽  
A.M. Ghozza ◽  
G.A. El-Shobaky
Keyword(s):  
Catalytic Activity ◽  
Calcination Temperature ◽  
Active Sites ◽  
Pore Radius ◽  
Total Pore Volume ◽  
Surface Characteristics ◽  
Oxidation Of Co ◽  
Catalytic Activities ◽  
Catalytically Active ◽  
The Mean

The surface characteristics, viz., the specific surface area SBET, the total pore volume Vp and the mean pore radius r̄, of NiO and Fe2O3 were determined from N2 adsorption isotherms conducted at −196°C for the different adsorbents preheated in air at temperatures in the range 300–800°C. The catalytic activities exhibited in CO oxidation by O2 on the various solids were investigated at temperatures varying between 150°C and 400°C. The effect of heating the NiO and Fe2O3 solids in CO and O2 atmospheres at 175–275°C on their catalytic activities was also studied. The results showed that increasing the calcination temperature in the range 300–800°C resulted in a progressive decrease in the SBET value of NiO and Fe2O3. The computed values of the apparent activation energy for the sintering of the oxides were 71 and 92 kJ/mol, respectively. The sintering of NiO and Fe2O3 took place mainly via a particle adhesion mechanism. The catalytic activity of NiO decreased progressively on increasing its calcination temperature from 300°C to 800°C, due to a decrease in its SBET value and the progressive removal of excess O2 which was present as non-stoichiometric NiO. This treatment also decreased the catalytic activity of Fe2O3. The decrease was, however, more pronounced when the temperature increased from 300°C to 400°C which was a result of the crystallization of the ferric oxide into the α-Fe2O3 phase. An increase in the calcination temperature for both oxides from 300°C to 800°C did not modify the mechanism of oxidation of CO by O2 over the various solids but rather changed the concentration of catalytically active sites. Heating NiO and Fe2O3 in CO and O2 atmospheres at 175–275°C modified their catalytic activities, with Fe2O3 being influenced to a greater extent than NiO.

Hydrogen peroxide decomposition on a two-component CuO-Cr2O3 catalyst

1988 ◽  
Vol 53 (8) ◽  
pp. 1636-1646 ◽  
Author(s):  
Viliam Múčka ◽  
Kamil Lang
Keyword(s):  
Hydrogen Peroxide ◽  
Catalytic Activity ◽  
Extreme Values ◽  
Catalytic Properties ◽  
Active Components ◽  
Catalytic Systems ◽  
Heterogeneous Catalytic ◽  
Peroxide Decomposition ◽  
Two Component ◽  
Catalytically Active

Some physical and catalytic properties of the two-component copper(II)oxide-chromium(III)oxide catalyst with different content of both components were studied using the decomposition of the aqueous solution of hydrogen peroxide as a testing reaction. It has been found that along to both basic components, the system under study contains also the spinel structure CuCr2O4, chromate washable by water and hexavalent ions of chromium unwashable by water. The soluble chromate is catalytically active. During the first period of the reaction the equilibrium is being established in both homogeneous and heterogeneous catalytic systems. The catalytic activity as well as the specific surface area of the washed solid is a non-monotonous function of its composition. It seems highly probable that the extreme values of both these quantities are not connected with the detected admixtures in the catalytic system. The system under study is very insensitive with regard to the applied doses of gamma radiation. Its catalytic properties are changed rather significantly after the thermal treatment and particularly after the partial reduction to low degree by hydrogen. The observed changes of the catalytic activity of the system under study are very probably in connection with the changes of the valence state of the catalytically active components of the catalyst.

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.

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 Catalytic Decomposition of H2O2 over a γ-Irradiated CuO–ZnO/Al2O3 System

1998 ◽  
Vol 16 (5) ◽  
pp. 381-390 ◽  
Author(s):  
Gehan A. Fagal ◽  
Amina A. Attia ◽  
Hala G. El-Shobaky
Keyword(s):  
Catalytic Activity ◽  
Mixed Oxide ◽  
Catalytic Decomposition ◽  
Nitrogen Adsorption ◽  
Surface Characteristics ◽  
Copper Nitrate ◽  
Oxide Material ◽  
Γ Irradiation ◽  
Exponential Factor ◽  
Γ Rays

A CuO–ZnO/Al2O3, catalyst sample was prepared by wet impregnation methods using Al(OH)3, zinc and copper nitrate solutions followed by drying at 110°C and calcination at 600°C. The nominal molar composition of the resulting material was calculated to be 0.25CuO · 0.03ZnO/Al2O3 Samples of this solid were exposed to varying dosages of γ-irradiation (20–160 Mrad) and the effect of such treatment on their surface characteristics and catalytic activity investigated using nitrogen adsorption studies at −196°C and studies of the decomposition of H2O2 at 30–50°C. The results obtained indicate that doses of γ-rays up to 80 Mrad had no significant effect on the specific surface area. SBET, of the supported mixed oxide material although this quantity increased by 20% when the solid was exposed to γ-irradiation doses of 160 Mrad. In contrast, such treatment brought about a progressive decrease in the catalytic activity of the treated catalyst samples. Thus, the reaction rate constant (k) of the catalyzed reaction measured at 50°C diminished from 8 × 10−2 min−1 to 0.3 × 10−2 min−1 on exposure of the supported mixed oxide material to a dose of 160 Mrad. What was surprising was that the activation energy (δE) of the catalytic reaction decreased as a function of the dose employed whereas it should have been expected to increase in the light of the observed decrease in the catalytic activity. This apparent discrepancy was resolved by recalculating the values of ΔE taking into account any possible changes in the pre-exponential factor of the Arrhenius equation brought about by γ-irradiation. The observed decrease in the catalytic activity due to treatment with γ-rays was attributed, mainly, to the enhanced removal of Brönsted acid centres by the action of such irradiation.

scholarly journals Catalytic Ozonation of 4-Nitrophenol in the Presence of Magnetically Separable Titanium Dioxide – Magnetite Composite

2016 ◽  
Vol 17 (4) ◽  
pp. 309 ◽  
Author(s):  
D.A. Kazakov ◽  
V.V. Vol’khin ◽  
K. Kaczmarski ◽  
Yu.O. Gulenova ◽  
M.N. Obirina ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Active Sites ◽  
Fine Particles ◽  
Aqueous Media ◽  
Composite Catalyst ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Catalytically Active ◽  
Magnetite Particles ◽  
Magnetically Separable

<p>This paper deals with determining catalytic activities of titania (TiO<sub>2</sub>) with various crystalline structures and magnetite (Fe<sub>3</sub>O<sub>4</sub>) during mineralization of 4-nitrophenol in aqueous media by ozonation. Among the titania samples under study, amorphized TiO<sub>2</sub> was shown to have the highest catalytic activity, while magnetite was characterized by the lowest catalytic activity. A procedure is proposed to synthesize a magnetically separable composite (TiO<sub>2</sub>/Fe<sub>3</sub>O<sub>4</sub>) including amorphized titania and magnetite phases, which involves deposition of a catalytically active titania phase on preformed magnetite particles. We also studied the effect of mass ratio of titania and magnetite phases in the composite on its catalytic activity during 4-nitrophenol mineralization by ozonation. It was found that catalytic activity of composite increased as the amorphized titania phase was doped with magnetite phase up to 30% wt but as the magnetite portion in the composite catalyst was further increased, its activity decreased. According to Fourier transform infrared (FTIR) spectroscopy, content of catalytically active sites (hydroxyl groups of titania) in the composite catalyst decreases as compared to the pure phase of amorphized titania. Increase in catalytic activity of the composite as its magnetite content increases to 30% wt can be attributed to increase of accessibility of catalytically active sites (OH groups) for ozone, because specific surface area and total pore volume of the composite catalyst as determined by BET increase as compared to amorphized TiO<sub>2</sub> and catalytically active titania phase is located mostly on surface of magnetite particles which is indicated by scanning electron microscopy (SEM) results and electrophoretic light scattering (ELS) data. It was shown that the obtained composite catalyst of optimized composition, in spite of its fine particles, can be easily recovered from aqueous phase by magnetic field and used repeatedly in ozonation in order to promote water purification process.</p>

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