scholarly journals Surface Characteristics of the Pure and Li2O-doped MoO3/Al2O3 System

1998 ◽  
Vol 16 (2) ◽  
pp. 127-134 ◽  
Author(s):  
G.A. El-Shobaky ◽  
Kh.A. Khalil
Keyword(s):  
Activation Energy ◽  
Calcination Temperature ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Surface Characteristics ◽  
Ammonium Molybdate ◽  
Lithium Oxide ◽  
Sintering Process ◽  
The Mean ◽  
Nitrogen Adsorption Isotherms

Two series of MoO3/Al2O3 solids, having the nominal compositions 0.2MoO3: Al2O3 and 0.5MoO3:A12O3, were prepared by impregnating finely powdered Al(OH)3 samples with calculated amounts of ammonium molybdate solutions. The solids thus obtained were dried at 120°C and then calcined in air at temperatures varying between 400°C and 1000°C. The doped samples were prepared by treating Al(OH)3 with LiNO3 solutions prior to impregnation with ammonium molybdate. The dopant concentrations employed were 1.5 and 6.0 mol% Li2O, respectively. The surface characteristics, viz. the specific surface area (SBET), the total pore volume (VP) and the mean pore radius (r) of the various pure and doped solids were measured from nitrogen adsorption isotherms conducted at -196°C. The SBET data measured for different adsorbents calcined at various temperatures enabled the apparent activation energy for sintering (ΔE3) to be determined for all the adsorbents investigated. The results obtained reveal that the SBET value of the pure and doped solids decreased on increasing the calcination temperature in the range 400–1000°C. The decrease was, however, more pronounced when the calcination temperature increased from 500°C to 700°C due to the formation of Al2(MoO4)3. Lithium oxide doping decreased the SBET value of the solid samples investigated and also decreased the activation energy for sintering to an extent proportional to the amount of dopant present. The sintering process for the pure and doped solids proceeds, mainly, via a particle adhesion mechanism.

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 The Effect of Calcium Doping on the Surface and Catalytic Properties of Cobaltic Oxide Catalysts

2003 ◽  
Vol 21 (3) ◽  
pp. 229-243 ◽  
Author(s):  
Nasr-Allah M. Deraz
Keyword(s):  
Activation Energy ◽  
Calcination Temperature ◽  
Calcium Oxide ◽  
Total Pore Volume ◽  
Textural Properties ◽  
Peroxide Decomposition ◽  
Cobaltic Oxide ◽  
Adsorption Of Nitrogen ◽  
Activation Energy Of Sintering ◽  
Calcium Doping

The effects of calcium oxide doping (0.75, 1.5 and 3 mol% CaO) and calcination temperature (400, 500, 600 and 700°C) on different surface properties of Co3O4 were investigated. The structural properties of pure and doped oxide samples were determined by XRD methods, the textural properties were investigated via the adsorption of nitrogen at −196°C while the hydrogen peroxide decomposition activity of the investigated solids was determined by oxygen gasometric measurement of the reaction kinetics at 20–40°C. The dissolution of calcium ions in the Co3O4 lattice at temperatures in the range 400–600°C was accompanied by a marked decrease in the mean hydraulic radii (rh) and an increase in the surface area (SBET) and total pore volume (Vp) of the prepared oxide samples. In contrast, doping at 700°C brought about a decrease in the SBET and Vp values of the investigated solids. The catalytic activity for H2O2 decomposition on cobaltic oxide calcined at 400–700°C was found to decrease considerably on doping with CaO. The activation energy for sintering (ΔEs) of the pure and doped solids was determined from the variation in their SBET values as a function of the calcination temperature of these solids. Calcium oxide treatment resulted in a 50% increase in the activation energy of sintering of cobaltic oxide solid calcined at 400–600°C. This increase reflects the role of CaO doping in hindering the sintering of cobaltic oxide.

scholarly journals Surface Characteristics of Hardened Slag–Lime Pastes

1995 ◽  
Vol 12 (4) ◽  
pp. 323-334 ◽  
Author(s):  
Anwar Amin
Keyword(s):  
Surface Area ◽  
Chemical Nature ◽  
Weight Ratio ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Surface Characteristics ◽  
Hydraulic Radius ◽  
Initial Water ◽  
Granulated Blast Furnace Slag ◽  
Furnace Slag

Two types of slag–lime pastes were prepared from granulated blast furnace slag and calcium hydroxide in a weight ratio of 80:20 and using initial water/solid (W/C) ratios of 0.25 and 0.4, respectively, to produce low and normal porosity pastes. After being hydrated for various lengths of time, the pastes were examined for surface area and pore structure using the nitrogen adsorption technique. The results of surface area, total pore volume and mean hydraulic radius measurements were related as far as possible to the chemical nature and physical state of the hydration products formed.

scholarly journals Surface Characteristics Change of Zinc Modified H-ZSM-5 Zeolites in Methanol to Hydrocarbons Transformation Process

2020 ◽  
Vol 6 (11) ◽  
pp. 23-30
Author(s):  
A. Sidorov ◽  
V. Molchanov ◽  
L. Mushinskii ◽  
R. Brovko
Keyword(s):  
Surface Properties ◽  
Catalyst Deactivation ◽  
Catalyst Activity ◽  
Nitrogen Adsorption ◽  
Surface Characteristics ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Transformation Process ◽  
Methanol To Hydrocarbons ◽  
Nitrogen Adsorption Isotherms

The t-plot method is a well-known method for determining the volumes of micro- and/or mesoporous materials and the specific surface area of a sample by comparison with a reference adsorption isotherm of a non-porous material having a similar surface chemical composition. The article describes the applicability of the t-graph method to the analysis of the surface properties of zinc modified samples of zeolite H-ZSM-5 before and after the reactions of methanol transformation into hydrocarbons occur on them. Zeolites are widely used as catalysts in the petrochemical and refining industries. These materials contain active Bronsted acid sites, distributed within the microporous structure of zeolites, which leads to selective catalysis due to the difference in the pore shape of the zeolites used. The size, shape of the zeolite catalyst determines the catalytic performance in terms of both product selectivity and catalyst deactivation. In most zeolite catalyzed hydrocarbon conversion reactions, catalyst activity is lost due to carbon deposition. In this connection, the determination of the surface properties of zeolites is an important task that contributes to the disclosure of the physicochemical essence of the process of deactivation of zeolites. The recalculation of nitrogen adsorption isotherms using the t-plot model made it possible to determine the volume of micro and mesopores. Based on the t-graph data, it can be concluded that during the transformation of methanol into hydrocarbons, carbon accumulates on the surface of the zeolite. In this case, the predominant deposition of carbon on the surface of mesopores, due to the fact that in the process of decontamination, from 61 to 73% of the volume of mesopores is lost. The number of micropores also decreases, but the share of losses is 42–54%, which is 10–15% lower compared to the loss of mesopore volume.

scholarly journals Synthesis of bimodally porous titania powders by hydrolysis of titanium tetraisopropoxide

2000 ◽  
Vol 15 (11) ◽  
pp. 2322-2329 ◽  
Author(s):  
Ki Chang Song ◽  
Sotiris E. Pratsinis
Keyword(s):  
Phase Composition ◽  
Calcination Temperature ◽  
Water Concentration ◽  
Nitrogen Adsorption ◽  
Molar Ratio ◽  
Titanium Tetraisopropoxide ◽  
X Ray Diffraction ◽  
Porous Titania ◽  
Nitrogen Adsorption Isotherms ◽  
Hydrolysis Of

Bimodally porous titania powders with controlled phase composition and porosity were made by hydrolysis of titanium tetraisopropoxide (TTIP) and calcination. The extent of calcination was followed by thermogravimetric differential thermal analysis and Fourier transform infrared spectroscopy. The specific surface area (SSA) of the powders ranged from 10 to 500 m2/g as determined by nitrogen adsorption. The SSA increased by decreasing either the water concentration during hydrolysis or the calcination temperature. The pore size distribution was bimodal with fine intraparticle pore diameters at 1–6 nm and larger interparticle pore diameters at 30–120 nm as determined by nitrogen adsorption isotherms. The particle phase composition as determined by x-ray diffraction ranged from amorphous to crystalline anatase and rutile largely proportional to the calcination temperature and to a lesser extent on the initial H2O/TTIP molar ratio.

scholarly journals Effects of Li2O Doping on the Surface and Catalytic Properties of Co3O4–Fe2O3 Solids Precalcined at Different Temperatures

2000 ◽  
Vol 18 (3) ◽  
pp. 243-260 ◽  
Author(s):  
G.A. El-Shobaky ◽  
M.A. Shouman ◽  
M.N. Alaya
Keyword(s):  
Activation Energy ◽  
Catalytic Activity ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Nitrogen Adsorption ◽  
Surface Characteristics ◽  
Oxidation Of Co ◽  
Surface Areas ◽  
Different Temperatures ◽  
Activation Energy Of Sintering

The effects of Li2O treatment on the solid–solid interactions and the surface and catalytic properties of the Co3O4–Fe2O3 system have been studied using TG, DTA and XRD methods, nitrogen adsorption studies at −196°C and the catalytic oxidation of CO by O2 at 150–350°C. The results obtained showed that Li2O doping followed by precalcination at 500–1000°C enhanced the formation of cobalt ferrite to an extent proportional to the amount of dopant added (0.52–6.0 mol% Li2O). The solid–solid interaction leading to the formation of CoFe2O4 took place at temperatures ≥700°C in the presence of the Li2O dopant. Lithia doping modified the surface characteristics of the Co3O4–Fe2O3 solids, both increasing and decreasing their BET surface areas depending on the amount of dopant added and the precalcination temperature employed for the treated solids. The activation energy of sintering (ΔES) of cobalt/ferric mixed oxides was determined for the pure and doped solids from the variation in their specific surface areas as a function of the precalcination temperature. Both an increase and a decrease in the value of ΔES due to Li2O doping occurred depending on the amount of lithia added. The doping of Co3O4–FeO solids, followed by precalcination at 500°C, effected a significant increase (144%) in their catalytic activity towards CO oxidation by O2. Precalcination at 700–1000°C of the mixed oxide solids doped with Li2O (0.52 and 0.75 mol%) resulted in an increase in their catalytic activity which decreased upon increasing the amount of Li2O added above this limit. The activation energy of the catalyzed reaction was determined for the pure and variously doped solids studied.

Low Temperature Sintering Studies of Ammonium Molybdate, Nickel Hydroxide and Nickel Molybdate

1994 ◽  
Vol 59 (4) ◽  
pp. 875-884 ◽  
Author(s):  
Samih A. Halawy ◽  
Khalaf Alla M. Abd El-Salaam ◽  
Hesham M. Ragih
Keyword(s):  
Activation Energy ◽  
Nickel Hydroxide ◽  
Thermal Process ◽  
Arrhenius Plot ◽  
Isothermal Condition ◽  
Ammonium Molybdate ◽  
Sintering Process ◽  
Different Temperatures ◽  
Tg And Dtg ◽  
Mixture Sample

The thermal decomposition of ammonium molybdate, nickel hydroxide and MoO3-NiO 50 mole % mixture were studied by means of TG and DTG non-isothermally, in a dynamic atmosphere of N2. The activation energy of the thermal process of such samples, also, were evaluated using Maple's theory, in isothermal condition. The variation of SBET with time, during heating ammonium molybdate, nickel hydroxide and MoO3-NiO 50 mole % mixture at different temperatures, in the range 200 - 400 °C, was monitored, and the activation energy for the sintering process of each compound were calculated from the Arrhenius plot. The final products of heating each sample at the sintering temperatures after 6 h, were characterized by IR and XRD analyses. MoO3 was formed clearly at 350 °C, while Ni forms a mixture of nickel(II) and -(III) oxides at the same temperature. NiMoO4 was produced, also, at 350 °C in MoO3-NiO 50 mole % mixture sample.

scholarly journals HIGHLY EFFICIENT REMOVAL OF COPPER(II) IONS FROM AQUEOUS SOLUTION BY NICKEL 2-ETHYLIMIDAZOLATE

2021 ◽  
Vol 64 (5) ◽  
pp. 24-29
Author(s):  
Victoria A. Fufaeva ◽  
Dmitry V. Filippov
Keyword(s):  
Experimental Data ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Sorption Kinetics ◽  
Average Pore ◽  
Average Pore Radius ◽  
Sample Characterization ◽  
Exchange Adsorption ◽  
Sorbent Solution ◽  
Nitrogen Adsorption Isotherms

Nickel 2-ethylimidazolate was obtained and characterized, which is used in this work as a sorbent for the removal of copper (II) ions. The sample characterization was carried out by scanning electron microscopy, low-temperature nitrogen adsorption. It was found that the obtained sorbent is a microheterogeneous material with the size of individual particles in the range of 0.4-0.7 μm. Nitrogen adsorption isotherms in the pores of nickel 2-ethylimidazolate were obtained. It was found that when processing the experimental data in linear coordinates of TVFM, linearization is reached in coordinates lnV-lnPs/P, which indicates the predominance of mesopores in the structure of nickel 2-ethylimidazolate. The total pore volume was determined from the TVFM linear coordinates. It was 0.21 cm3/g. According to obtained differential pore size distribution, the most probable average pore radius corresponds to 7.5 nm. One of the main characteristics of nickel 2-ethylimidazolate as a sorbent, the surface area was determined by the A.V. Kiselev method and amounted to 703.56 m2/g. The efficiency verification of using nickel 2-ethylimidazolate in the heavy metal ions sorption processes was carried out by removal of copper(II) ions from aqueous solutions by the limited solution volume method at different contact times. The copper(II) sorption kinetics in the presence of nickel 2-ethylimidazolate was studied by processing experimental data in the first and second orders linear coordinates. It was found that the adsorption kinetics of copper(II) ions is described by a second order model, which indicated ion-exchange adsorption. Equilibrium adsorption capacity in the sorbent-solution system is reached at a contact time of 90-120 min.

Synthesis of dispersed mesoporous powders solid solution Zr0.88Ce0.12O2 for catalyst carrier of the conversion of methane to synthesis –gas

2020 ◽  
pp. 73-83
Author(s):  
L. V. Morozova ◽  
◽  
I. A. Drozdova ◽  
Keyword(s):  
Solid Solution ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Primary Crystal ◽  
X Ray ◽  
Catalyst Carrier ◽  
Conversion Of Methane ◽  
Deposition Processes ◽  
Zirconia Oxide ◽  
Coprecipitation Of Hydroxides

The xerogels in the system 0.88 mol.% ZrO2 − 0.12 mol.% CeO2 were obtained by the method of coprecipitation in a neutral (pH = 7) and slightly alkaline (pH = 9) medium under the influence of ultrasound with the size of the agglomerates 70 – 230 nm. It is shown that the coprecipitation of hydroxides of zirconium and cerium at pH = 9 with the use of ultrasonic treatment facilitates the formation of a primary crystal is symbolic of the particles in the xerogel, whose size is ~ 5 nm, whereas the xerogel synthesized in a neutral environment consists only of the x-ray amorphous phase. The effect of pH-precipitation on deposition processes of dehydration of the xerogels and crystallization solid solution based on zirconia oxide in the metastable pseudocubic modification (с′-ZrO2) was discovered. It was found that in the temperature range 500 – 800 °C there is a phase transition с′-ZrO2 → t-ZrO2, the size of the crystallites of the formed tetragonal solid solutions is 8 and 11 nm. The method of low-temperature nitrogen adsorption were investigated dispersion properties and characteristics of the pore structure of the powders of the solid solution Zr0.88Ce0.12O2. It is determined that the specific surface area of t-ZrO2 samples obtained after firing at 800 °C is 117 and 178 m2/g, the total pore volume reaches 0.300 − 0.325 cm3/g, the pore size distribution is monomodal and is in the range of 2 − 8 nm. The effect of thermal “aging” at a temperature of 800 °C (40 h) on the structure and dispersion of the solid solution t-ZrO2 powders was studied.

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