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.

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 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.

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.

Catalytic activity of Co-åkermanite and Co-pyroxene in oxidation reactions

2011 ◽  
Vol 89 (8) ◽  
pp. 939-947 ◽  
Author(s):  
Irena Mihailova ◽  
Dimitar Mehandjiev
Keyword(s):  
Catalytic Activity ◽  
Solid Phase ◽  
Sol Gel ◽  
Cobalt Content ◽  
Octahedral Coordination ◽  
Tetrahedral Coordination ◽  
Oxidation Reactions ◽  
Oxidation Of Co ◽  
Phase Synthesis ◽  
Catalytically Active

Two calcium–cobalt silicates were synthesized in which cobalt occupies different structural positions. The crystal phases belong to two main structural silicate types. In the Co-åkermanite structure (Ca2CoSi2O7), cobalt cations take tetrahedral coordination toward oxygen atoms. In the Co-pyroxene structure of CaCoSi2O6, cobalt displays octahedral coordination. Ca2CoSi2O7 was prepared by solid-phase synthesis and CaCoSi2O6 was prepared by sol–gel method. The synthesis of the phases was confirmed by XRD, FTIR, and EPR data. On the basis of the XPS analysis, it can be concluded that Co2+ cations exist in the studied silicates. Thus, it is possible to study the catalytic activity of two silicate phases containing Co2+ cations in different coordinations: tetrahedral and octahedral. It was found that cobalt silicates with crystal structures corresponding to pyroxene and åkermanite possess catalytic activity in the reactions of complete oxidation of CO and toluene. Co-pyroxene exhibits higher catalytic activity than Co-åkermanite, but the higher cobalt content on the surface of Co-pyroxene should also be taken into account. Then, it turns out that catalytically active complexes with Со2+ ions in tetrahedral coordination are more efficient than those with such ions in octahedral coordination when equal concentrations of cobalt were used on the surface of the catalysts.

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.

Controllable synthesis of Ni nanotube arrays and their structure-dependent catalytic activity toward dye degradation

CrystEngComm ◽  
2014 ◽  
Vol 16 (21) ◽  
pp. 4406-4413 ◽  
Author(s):  
Xiang-Zi Li ◽  
Kong-Lin Wu ◽  
Yin Ye ◽  
Xian-Wen Wei
Keyword(s):  
Catalytic Activity ◽  
Catalytic Properties ◽  
Dye Degradation ◽  
Nanotube Arrays ◽  
Nanorod Arrays ◽  
Growth Mechanisms ◽  
Controllable Synthesis ◽  
Catalytic Activities ◽  
One Step ◽  
The Relationship

Ni nanotube (nanorod) arrays are controllably fabricated by a one-step approach, the GDDATG and DDCG growth mechanisms are introduced. The Ni nanostructures present higher catalytic activities for dye degradation, the relationship between structures and catalytic properties is also studied.

scholarly journals Surface and Catalytic Properties of NiO–Fe2O3 Solids Supported on Al2O3

1996 ◽  
Vol 13 (5) ◽  
pp. 409-421 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.M. Ghozza ◽  
N.M. Deraz
Keyword(s):  
Rate Constant ◽  
Reaction Rate ◽  
Catalytic Properties ◽  
Unit Area ◽  
Surface Characteristics ◽  
Reaction Rate Constant ◽  
Oxidation Of Co ◽  
Catalytic Activities ◽  
Surface Areas ◽  
Specific Surface Areas

A series of NiO–Fe2O3 catalysts supported on γ-Al2O3 was prepared. The effect of the NiO and Fe2O3 contents and the precalcination temperature on the surface and catalytic properties of the various solids has been investigated. The surface characteristics, viz. SBET, Vp and r, were determined using N2 adsorption conducted at –196°C. The catalytic activities of the various solids were studied using the oxidation of CO by O2 at temperatures in the range between 150°C and 400°C. The prepared solids were preheated in air at various temperatures between 400°C and 1000°C. The results obtained revealed that the SBET values of the different solids decrease progressively on increasing the precalcination temperature above 400°C due to sintering. The specific surface areas were also found to decrease on increasing both the NiO and Fe2O3 contents. The catalytic activities, expressed as reaction rate constant (k) and reaction rate constant per unit area (k), were found to decrease on increasing the precalcination temperature in the range 400–1000°C. Furthermore, the amounts of NiO and Fe2O3 in the different solids modified their catalytic activities in different manners.

Composition, Surface Structure and Catalytic Properties of Manganese- and Cobalt-Containing Oxide Layers on Titanium

2014 ◽  
Vol 875-877 ◽  
pp. 351-355 ◽  
Author(s):  
M.S. Vasilyeva ◽  
V.S. Rudnev
Keyword(s):  
Surface Structure ◽  
Plasma Electrolytic Oxidation ◽  
Catalytic Properties ◽  
Oxidation Of Co ◽  
Oxide Layers ◽  
X Ray ◽  
Electrolytic Oxidation ◽  
Catalytically Active ◽  
Plasma Electrolytic ◽  
Scanning Electron

Silicon-containing oxide layers deposited on titanium using the plasma electrolytic oxidation (PEO) method were modified with manganese and cobalt compound through impregnation followed by annealing. The obtained manganese composites are catalytically active in the process of oxidation of CO at 100 оС, while cobalt-containing structures demonstrate this type of activity at temperatures above 200оС. The composition and surface structure of the obtained systems were investigated by means of X-ray phase and energy dispersive analyses and by high resolution scanning electron microscopy (SEM). Granule-like particles with diameters of a few dozens of nanometers were observed on the surface of oxide-cobalt layers on titanium, whereas the surface of oxide-manganese layers was coated by nano-whiskers of diameters <50 nm and length <1 μm. The presence of manganese-containing nano-whiskers substantially increases the catalyst specific surface, thus facilitating the attainment of higher degree of transformation of initial gaseous substances.

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