S.E. Samra

Surface and acidic properties of some mixed oxide catalysts in relation to their catalytic activities

Abstract A series of silica-alumina catalysts were prepared to contain different proportions of alumina. The catalysts were calcined at 773–973 K. Another series of silica-titania catalysts of different chemical compositions were prepared and calcined between 773 and 973 K. The textural properties (surface area and pore structure) of the catalysts were determined by low-temperature nitrogen adsorption at 77 K. The surface acidity (acid amount and acid strength) was determined for each catalyst by thermal programmed desorption (TPD) of pyridine. The catalytic cracking of cumene at 673–773 K and the catalytic conversion of isopropanol at 473–593 K were investigated using microcatalytic technique. Cracking of cumene is a first-order catalytic reaction which takes place on relatively strong acid sites and the reaction is structurally sensitive. Dehydration of isopropanol on mixed oxide catalysts is a zero-order reaction and proceeds on most of the acid sites. Dehydration of isopropanol is related to the surface acid density and is structurally insensitive.

Effect of thermal treatment on the various properties of iron(III) -aluminum(III) coprecipitated hydroxide system

Five samples of Fe O -Al O binary system containing 10, 20, 30, 50 and 80 wt.% Fe O were prepared by 23 2 3 23 coprecipitation method, followed by calcination in the temperature range 723-1273 K. The structural characterization was examined by using XRD, DTA and TGA techniques. The textural parameters for the investigated samples, e.g., surface area, total pore volume, mean pore radius and the pore volume distribution, were calculated from the low-temperature nitrogen adsorption isotherms at 77 K. The dehydration and dehydrogenation activities of ethanol, 1-propanol, and 2-propanol in samples were followed up with the aid of microcatalytic pulse technique. The assignments of different phases by XRD and DTA techniques revealed the presence of binary system from a-Fe O and a-Al O as a final product at 1273 K. The 23 2 3 inter-conversion between the polymorphic modifications of iron oxide and aluminium oxide was observed at lower temperature. The results also indicated that the textural, acidic properties and the catalytic activities were affected by the thermal treatments and the ratio of iron oxide to aluminium oxide in the prepared samples. q 2000 Elsevier Science B.V. All rights reserved. . .

Removal of Copper(II) from Aqueous Solutions by Flotation Using Limestone Fines as the Sorbent and Oleic Acid as the Surfactant

The removal of toxic copper(II) from aqueous solutions was investigated using limestone fines (LS), which are inexpensive and widespread over the globe, as the effective inorganic sorbent with oleic acid (HOL) as the surfactant. The main parameters (i.e. initial solution pH, sorbent, surfactant and copper concentrations, stirring times, temperature and presence of foreign ions) influencing the sorption and flotation processes were examined. The results obtained showed the removal of more than 98% CuII at pH 7. It was also found that the addition of sodium and magnesium ions as activators enhanced the efficiency of copper separation. The procedure was successfully applied to recover copper spiked to some natural water samples. A mechanism for sorption and flotation is suggested.

Kinetic investigation of the removal of aluminum from water samples by adsorption onto powdered marble wastes

Abstract Batch adsorption experiments were conducted in the laboratory, aiming to the removal of aluminum from aqueous solutions onto powdered marble wastes (PMW) as an effective inorganic sorbent, which is inexpensive, widespread, and may represent an environmental problem. The main parameters (i.e., initial solution pH, sorbent and Al3+ ions concentrations, stirring times and temperature) influencing the sorption process in addition to the effect of some foreign ions was examined. The results obtained revealed that the sorption of Al3+ ions onto PMW is endothermic in nature and followed first‐order kinetics. The adsorption data were well described by the Langmuir, Freundlich and Dubinin‐Radushkevich (D‐R) adsorption models over the concentration range studied. Under the optimum experimental conditions employed, the removal of ca. 100% of Al3+ions was attained. The procedure was successfully applied to the removal of aluminum from aqueous and different natural water samples with an RSD (%), does not exceed 2.12%. Moreover, the adsorption mechanism is suggested.

Sorptive–Flotation of Copper(II) from Water Using Different Types of Powdered Activated Carbons as Sorbents and Oleic Acid as Surfactant

Different types of powdered activated carbon, viz. charcoal (PACh), graphite (PG) and three samples (PACI, PACII and PACIII) prepared from olive stones generated as plant wastes and modified with aqueous oxidizing agents, viz. H2O2, HNO3 and (NH4)2S2O8, were separated from aqueous solution by flotation using oleic acid (HOL) as a surfactant. The effects of initial temperature, initial pH of the suspension, initial carbon and surfactant concentrations, stirring times and the presence of foreign ions on the flotation efficiency of the carbon samples were investigated. Under optimum conditions, separation of the carbon samples was almost complete (~100%). The separation of CuII-loaded carbon was also examined in the presence and absence of sulphide ions as activators. Nearly 100% CuII was removed at pH 7 after stirring for 30 min or on raising the temperature of the solution to 30°C or higher. In addition, CuII may be separated quantitatively at pH 3 and room temperature if sulphide ions are used as activators. The procedure was extended to the recovery of CuII added to some natural water samples. On the basis of IR analyses and neutralization titrations of the surface groups, a mechanism for the sorption and flotation processes is advanced.

Textural, Structural and Catalytic Properties of Cr2O3/SiO2 Catalysts

Four chromia/silica samples containing 5–30 wt% CrIII were prepared by impregnation methods and calcined at 773–1173 K. Nickel, molybdenum and vanadium oxide-impregnated Cr2O3/SiO2 samples were also prepared by impregnation and were subjected to the same thermal treatment. The textural parameters of all the samples prepared were determined from the adsorption of nitrogen at 77 K, while X-ray diffraction (XRD) and differential thermal analysis (DTA) techniques were used to elucidate their structures. The catalytic properties of the solids so prepared in the catalytic cracking of cumene were investigated using a pulse microcatalytic technique. The surface areas evaluated for the various Cr2O3/SiO2 samples studied were found to decrease gradually on increasing their CrIII content, the calcination temperature and on addition of Ni, Mo and V oxides. DTA and XRD studies demonstrated the absence of any interaction between the SiO2 and Cr2O3, with the latter being the only phase capable of detection by these techniques. Samples impregnated with Ni, Mo and V ions also showed no interaction between these ions and Cr2O3 and SiO2, with only the corresponding oxides being detected. The results obtained for the catalysis studies also indicated that the cracking of cumene depended on the metal content, impregnant cations and thermal treatment of the solids employed.

Methanation activity in relation to the textural and catalytic parameters of Ni/Al2O3 catalysts

A range of NiO/Al2O3, solids (4.0–12.0 wt% Ni) was prepared by the impregnation technique. The textural properties of these solids were determined from nitrogen adsorption measurements at 77 K. Reduction of the solids with hydrogen was carried out 650, 675, 700 and 725 K. Some catalytic parameters for these reduced materials were determined from studies of the adsorption of hydrogen at 400 K. The methanation of carbon monoxide over these reduced materials used as catalysts was followed between 550 K and 600 K using a steady-state flow reactor. The surface area of the NiO/Al2O3 solids decreased and their mean pore radius increased with increasing content of NiO. Increasing the temperature employed for their reduction led to increased diffusion of Ni atoms to the surface with a consequent increase in their catalytic activity. A direct relationship was found between % methanation and the surface area of the reduced catalytic material expressed as m2/g (catalyst).

Removal of Copper(II) Ions from Aqueous Solutions. I. Adsorption Studies Using Powdered Marble Wastes as Sorbent

Batch adsorption experiments of copper(II) ions from aqueous solutions on to powdered marble wastes (PMW) have been performed. The latter is an effective inorganic sorbent which is inexpensive, widespread and may represent an environmental problem. The main parameters influencing the sorption process, i.e. initial solution pH, sorbent and Cu2+ ion concentrations, stirring times and temperature, were examined. The results obtained revealed that the sorption of Cu2+ ions on to PMW was endothermic in nature and followed first-order kinetics. Moreover, it was well described by the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) adsorption models over the concentration range studied. Under the optimum experimental conditions employed, the removal of ca. 100% Cu2+ ions was attained.

Some Surface and Catalytic Properties of V2O5-Cr2O3/SiO2, MoO3-Cr2O3/SiO2 and NiO-Cr2O3/SiO2 Ternary Solid Catalysts

Ternary vanadia–chromia/silica, molybdena–chromia/silica and nickel oxide–chromia/silica solid catalysts were prepared by the impregnation method. Their structural characteristics were examined using differential thermal analysis (DTA) and X-ray diffraction techniques. The catalytic activities of the prepared samples towards the conversion of isopropanol and cyclohexanol and the kinetics of these catalytic conversions were studied with the aid of a microcatalytic pulse technique. In addition, the surface acidities of selected samples were measured from the percentage of propene produced by the poisoned catalysts. X-Ray diffraction and differential thermal analysis revealed that the only detectable phase was α-Cr2O3 with the presence of all other phases or spinel not being confirmed. The order of the surface acidities was found to lie in the sample sequence: 3 wt% V2O5–20 wt% Cr2O3/SiO2 > 3 wt% MoO3–20 wt% Cr2O3/SiO2 > 20 wt% Cr2O3/SiO2 > 3 wt% NiO-20 wt% Cr2O3/SiO2, all samples having been precalcined at 500°C. Catalytic conversion of isopropanol gave propene and acetone, whereas cyclohexene, cyclohexanone and methylcyclopentene (as an isomerization product) were produced from the catalytic conversion of cyclohexanol. The catalytic activity was found to be influenced considerably by the type of impregnating ion employed and by the precalcination temperature, and hence by the surface acidity of the examined catalysts. On the other hand, the Bassett–Habgood and Kiperman equations could be applied in a satisfactory manner to the generation of the various reaction products. The calculated activation energies for the catalytic conversion of isopropanol and cyclohexanol were compared.

Synthesis of sulfamic acid supported on Cr-MIL-101 as a heterogeneous acid catalyst and efficient adsorbent for methyl orange dye

Typical highly porous metal–organic framework (MOFs) materials based on chromium benzenedicarboxylates (Cr-BDC) were prepared through a one-pot hydrothermal synthesis, and were then modified by loading the appropriate ratio of sulfamic acid (SA) using a simple impregnation technique. Pure and modified MIL-101 was characterized by XRD, TEM, SEM and FT-IR measurements. TEM and SEM measurements confirmed that the MIL-101 particles preserved their regular octahedral structure after loading with different weight contents of sulfamic acid. The total number of acid sites and Bronsted to Lewis acid sites ratio (B/L) were examined using potentiometric titration and pyridine adsorption. The acid strength and surface acidity of SA/MIL-101 gradually increased after the modification of Cr-MIL-101 by sulfamic acid crystals up to 55 wt%, then decreased again. The catalytic performance of the solid catalysts was confirmed in the synthesis of 14-phenyl-14H-dibenzo [a,j] xanthene and 7-hydroxy-4-methyl coumarin. In the two reactions, the sample with 55% sulfamic acid loaded on MIL-101 displayed the highest catalytic activity and acidity. The adsorption behaviors of sulfamic acid loaded on MIL-101 materials for methyl orange (MO) as an anionic dye were studied, and were exceptionally suitable for the Langmuir adsorption isotherm. All loaded adsorbents showed high adsorption capacity for methyl orange at 25 °C. The results indicate that the adsorption capacity was modified by changing the amount of sulfamic acid loaded on MIL-101.