Ibrahim A. Salem

Recent Studies on the Catalytic Activity of Titanium, Zirconium, and Hafnium Oxides

This review article deals with the recent work published on the catalytic activity of transition metal oxides of group IV of the periodic table. These oxides are mainly in the form of MO2, where M refers to either titanium, zirconium, or hafnium. The preparation of the pure, mixed, and supported oxides, as well as the characterization of their physicochemical properties, are briefly reviewed. However, their catalytic performance in various chemical reactions have been presented in detail. The photocatalytic activity of TiO2 in many photochemical degradation and conversion processes has been also discussed. Strong emphasis is put on discussion such as the nature and strength of active sites, adsorption of target compounds, kinetic parameters, and reaction mechanisms.

Activity of silica-alumina surface modified with some transition metal ions

Abstract Kinetics of H 2 O 2 decomposition have been investigated in the presence of a silica-alumina surface (25% Al 2 O 3 ) modified with transition metal ions including Cu(II), Co(II), and Fe(III). The decomposition reaction proceeded with first-order kinetics with respect to the peroxide concentration. The rate of reaction depends upon the type of ions. The reaction rate and the energy of activation decrease in the order Cu(II) > Co(II) > Fe(III). The initial concentration of H 2 O 2 has a great influence on the reaction rate and the coloration of the surface. The decomposition reaction involved the generation of free radical species as confirmed by using the reference chromogen 2,2′-azino-bis(3-ethylbenzthiazoline)-6-sulphonate diammonium salt as a probe. An isokinetic relationship indicates that the reaction is entropy-controlled. A probable mechanism has been suggested for the decomposition process which agrees with the results obtained.

Kinetics of heterogeneous decomposition of hydrogen peroxide with some transition metal complexes supported on silica-alumina in aqueous medium

Abstract Silica-alumina in the form of diethylamine (deam)-, dimethylamine (dmam)-, ethylamine (eam)-, ammonia (amm)- and aniline (an) -copper(II) complexes as well as deam-cobalt (II) complex have been used as potentially active catalysts for H2O2 decomposition in an aqueous medium. The reaction was first order with respect to the H2O2 concentration and the rate constants (per g of dry silica-alumina) were determined. A coloured compound, a peroxo-metal complex, which formed at the beginning of the reaction in each case, was found to contain the catalytically active species. The activation energy and the change in the entropy of activation increased with the basicity of the ligands in the following order: an

Role of aliphatic diamine ligands in hydrogen peroxide decomposition with Dowex-50W resin as transition metal complex ions

Abstract Dowex-50W resin, as the aliphatic diamine—transition metal ion (FeIII, CUII, COII) complexes, has been used as a potentially active catalyst for H2O2 decomposition in an aqueous medium. The rate constant, k (per g of dry resin) was evaluated over the temperature range 25–40°C. The reaction was first order with respect to [H2O2 in all cases. With 1,6-hexamethylenediamine as a ligand, the rate constant k decreased in the following order; CuII&>;CoII&>;FeIII. Also, with FeIII-complexes the value of k decreased with increasing the length of the methylene chain between the two amino groups of the ligand. The activation parameters were calculated and a reaction mechanism is proposed.

Catalytic decomposition of hydrogen peroxide in the presence ofN, N′-bis(salicylidene)-o-phenylenediamineiron(III) sorbed on to Dowex-50W resin

SummaryThe tetradentate Schiff-base ligandN, N′-bis(salicylidene)-o-phenylenediamine (salph) is very strongly sorbed by cation exchange materials with transition metal counter ions, forming stable complexes. The kinetics of catalytic decomposition of H2O2 in the presence of (salph)-FeIII sorbed on Dowex-50W resin has been studied in aqueous medium. The reaction is first order with respect to [H2O2]. The rate constant, k (per g of dry resin) decreased with increasing degree of resin cross-linkage due to a salting out effect. The activation parameters were calculated and a reaction mechanism is proposed.

Electrolytic recovery of antimony from natural stibnite ore

Abstract Stibnite ore at Wadi Abu Quraiya, situated in the central Eastern Desert of Egypt has been subjected to petrographical, mineralogical, infrared, X-ray diffraction, chemical and spectral analyses. Hydrometallurgical treatment based on leaching with acids, precipitation and electro-deposition of metal values from the ore have been developed. Studies to investigate suitable electrolytic baths for the cathodic deposition of metallic antimony either directly from the leach liquor or in the presence of complexing agents have been carried out. The influence of various factors on the electrodeposition process of the element from its electrolyte solutions is discussed. Advantages of the flowsheet and various approaches depending on convenient electrolytes for the deposition of antimony from the stibnite ore have been investigated. The results of spectrophotometric and chemical analyses revealed that the purity of the metal is > 99%.

The catalytic effect of transition metal-ion ammine complexes on the decomposition of hydrogen peroxide in the presence of Dower-50W resin in aqueous medium

SummaryThe kinetics of the catalytic decomposition of hydrogen peroxide was studied in the presence of Dowex-50W resin in the form of some transition metal-ion ammine complexes in an aqueous medium. The transition metal-ions, Co2+, Ag+, Cd2+ and Zn2+ were chosen in this study and the rate constants (per gram of dry resin) were evaluated at various resin weights in the 25–40°C range. A coloured compound (peroxo-metal complex), which formed at the beginning of the reaction in each case, was found to contain the catalytic active species. Probable mechanisms for the reactions are proposed. The activation energy and the change in the entropy of activation increased in the following sequence: [Ag(NH3]2]+< [Cd(NH3)6]2+<[Co(NH3)6]2+<[Zn(NH3)6]2+, which is also the probability sequence for the formation of the activated complex.

A kinetic approach for the homogeneous reaction between N,N'-propylenebis (salicylideneiminato)manganese(III) complex and hydrogen peroxide in aqueous solution

Abstract The kinetics of the homogeneous reaction between the [Mn III (saltm)Br] complex [saltm: N,N′-bis (salicylidene) propylenediamine] and hydrogen peroxide was studied in the pH range 5.05–7.29 in both aqueous and micellar sodium dodecyl sulphate solution. The reaction showed a first-order dependence in both the hydrogen peroxide and the complex. The rate of reaction was decreased with increasing acidity of the medium, as well as with increasing the concentration of the surfactant. The second-order rate constants and the activation parameters were evaluated. A mechanism involving manganese-(IV) and a peroxo-intermediate is proposed with the subsequent release of OH radicals as the rate-determining step.

Mineralogy and geochemistry of Gabal El-Ineigi Granite and associated fluorite veins, Central Eastern Desert, Egypt: application of fluid inclusions to fluorite genesis

Abstract Geological, mineralogical, geochemical and fluid inclusion studies were carried out on both the granitic rocks at the Gabal El-Ineigi Pluton and associated fluorite veins in order to examine their genetic relations. Gabal El-Ineigi rocks range from adamellite to granite composition. They originated from metaluminus calc-alkaline magma having strong alkaline tendencies. They have similar characteristics to I-type granites and were probably generated within an extensional environment due to crustal relaxation during a post-collision episode ( Studies of fluid inclusions from vein fluorite and quartz show that they are aqueous with phases (L + V) and that secondary inclusions predominate. The fluorite mineralisation probably took place at temperatures of > 250°C; the fluid salinites ranged up to 21.4 equiv. wt% NaCl. The quartz veins were formed at lower temperatures (∼ 120°C) and fluid salinites ranging up to 10.36 equiv. wt% NaCl. Rare earth element abundances in fluorite are variable and the relation between Tb/Ca versus Tb/La confirms a hydrothermal origin for fluorite. The negative Ce anamolies indicate high O fugacities at the source of the hydrothermal fluids. The negative Eu anomalies suggest equilibration of the hydrothermal fluids with the host granites.

The catalytic effect of some transition metal hexamethylenetetramine complexes in hydrogen peroxide decomposition

Abstract The kinetics of the catalytic decomposition of H2O2 with Wofatit KPS resin (4% DVB, 40–80 μm) in the form of 1:1 copper(II)-, manganese (II)-, cobalt(II)- and nickel(II)-hexamine complexes was studied in an aqueous medium. The decomposition reaction was first order with respect to [H2O2] and the rate constant, k (per g of dry resin) increased in the following sequence: Mn (II) &>; Co (II) &>; Cu (II) &>; Ni (II). The active species, formed as an intermediate at the beginning of the reaction, had an inhibiting effect on the reaction rate. An anionic surfactant, sodium dodecyl sulphate (SDS), considerably inhibited the reaction rate. A probable mechanism for the decomposition process has been suggested, which is consistent with the results obtained.