Sabri S. Mahmoud

In situ UV‐VIS diffuse reflectance spectroscopy of reduction–reoxidation of heteropoly compounds by methanol and ethanol: a correlation between spectroscopic and catalytic data

The degree of reduction/oxidation of H4PVMo11O40 (HPA) and Cs2H2PVMo11O40 (CsPA) was studied during reduction and reoxidation by methanol, ethanol and mixtures with oxygen, respectively. The peak intensity of the intervalence charge transfer (IVCT) band, the apparent band gap energy (Eg*) and catalytic data were obtained by in situ UV‐VIS diffuse reflectance spectrosccopy (UV‐VIS‐DRS) and on‐line gas chromatography (GC), respectively. The peak intensity of the IVCT band and Eg* increase during the reduction of heteropoly compounds by the alcohols. The spectroscopic and catalytic data (conversion, selectivity) correlate in the transient state during the reoxidation process. It is shown that isolated Keggin anions act as precursors for the active states of the catalysts, which molecular structure cannot be deduced from UV‐VIS spectroscopy alone. UV‐VIS spectroscopy, however, can serve as a tool to determine the degree of reduction in future combined in situ UV‐VIS/Raman/XRD studied.

The Kinetics of Tenoxicam Photodegradation in Solution

Photodegradation of tenoxicam was investigated under different reaction conditions. After 60 min of exposure to UV light, the photodegradation was extensive, and the maximum and minimum in the UV-visible spectrum were shifted to shorter and longer wavelengths, respectively. Ethanol exerted a photostabilizing effect on tenoxicam. Tenoxicam is more stable in acidic and basic media than in neutral solution. Increasing light intensity or temperature causes an increase in the rate of photodegradation. The photodegradation of tenoxicam was found to follow first-order kinetics under all these conditions.

Catalytic debutylation oftert-butylphenols by some natural clays

In the catalytic debutylation oftert-butylphenols by some Jordanian, Bulgarian and Turkish natural clays, Jordanian kaolin and bentonite were found to be the most active catalysts among the clays studied. The activity of these clays to converto-tert-butylphenol to phenol,p-tert-butylphenol and other minor products is in the following order: Jordanian kaolin >Jordanian bentonite>Turkish bentonite> Bulgarian bentonite. While for the conversion ofp-tert-butylphenols, Jordanian clays showed moderate activity, with bentonite being the most active, the other clays were not active. Also, all the clays studied were ineffective towards conversion ofm-tert-butylphenol. As to the debutylation selectivity of theortho isomer, Jordanian bentonite proved to be slightly debutylation selective, whereas Jordanian kaolin showed a relatively high selectivity toardsortho topara isomerization. Thepara isomer produced only debutylation products and none of the other isomers.

PRETREATMENT EFFECTS ON THE CATALYTIC ACTIVITY OF JORDANIAN BENTONITE

De-tert-butylation of 2-tert-butylphenol was carried out over thermally-treated and acid-treated Jordanian bentonite clay samples. This reaction was found to follow first-order kinetics for all clay samples with different pretreatment procedures. The apparent rate constant, k, was also determined, and found to depend on the pretreatment. Thermal pretreatment at temperatures up to 250°C has an enhancing effect on surface acid sites. The total surface acidity (Ho <4.8) and the concentration of strong acid sites peaked at 250°C. Also, as a result, the maximum catalyst activity was obtained with samples treated at this temperature. Acid pretreatment with 0.10 M HCl, 1.0 M H2SO4 or 1.0 M H3PO4, followed by thermal treatment at 250°C produced the best enhancement effect on the surface acidity and catalytic activity.

The kinetics and molecular modeling of the complexation of tenoxicam with cyclodextrins in solution

The effect of cyclodextrins on photodegradation of tenoxicam (TEN) was studied at pH 4, 7 and 10. After 60 min of irradiation with UV light, the photodegradation was extensive. All cyclodextrins (alpha, beta, or gamma) stabilize TEN and reduce the rate of photodegradation. The largest effect of cyclodextrins is at pH 7. Molecular modeling results help to explain and manipulate the results. The results are discussed and compared with other results from previous studies.

Mössbauer spectroscopy of Fe60Ni40 alloy films

Abstract Films of the alloy Fe60Ni40 are prepared by thermal evaporation of the alloy powder onto Al foils. Mossbauer spectra of the films on the Al substrate show a dominent central paramagnetic line during the first month after their preparation, which is attributed to the Fe-rich γ′ f.c.c. phase. The spectrum collected four months after preparation shows a 25% decrease in the relative intensity of the paramagnetic signal. However, the paramagnetic intensity drops by 65% upon removal of the film from the substrate, reaching a value close to that for the original alloy powder. This is interpreted as due to the atomic diffusion of Fe atoms from Fe-rich clusters into the surrounding FeNi matrix, and the occurrence of a phase relaxation to a state similar to that of the original powder, implying that the relative proportion of the γ′ phase could be dictated by the chemical composition of the alloy.

Selective Hydrogenation of Cinnamaldehyde Catalyzed by Ruthenium (II) Complexes Based on Azoimine Ligands

In this work, four Ru (II) complexes based on azoimine ligands were tested with respect to their catalytic behavior in the liquid phase hydrogenation of cinnamaldehyde. The introduction of a thiophenyl substitution in the azoimine ligand was found to enhance significantly the catalytic activity and selectivity of the Ru complex. The catalytic behavior of the most active complex in this work was studied with respect to the effect of the co-catalyst KOH, the Ru complex and the cinnamaldehyde (CALD) concentrations as well as with respect to the effect of the reaction temperature. KOH is needed to transform the Ru complex into a reactive form and the higher the KOH concentration in the system, the higher is the efficiency of the catalytic system. The order of this activation process with respect to KOH and with respect to the Ru complex was found to be one in both cases. With a CALD-to-Ru ratio of 84:1 at T=86 o C, pH2=4 bar and [KOH]= 5.82×10 -3 M, a complete conversion could be accomplished in only 90 minutes with selectivity to cinnamyl alcohol approaching 95%. Increasing the initial concentration of cinnamaldehyde has, under the reaction conditions investigated in this work, a negative effect on the rate of hydrogenation with an order decreasing with increased concentration from -1 to -3. Based on our results, an outer-sphere mechanism is ruled out to operate in this system.

Hydrocatalytic Reduction of Nitrate in Aqueous Solution over Titania Supported Pd-Au Catalysts

Some Pd and/or Au containing catalysts supported on TiO2 were prepared by impregnation (I) and incipient witness (IW) methods. These catalysts that include Au3%/TiO2-I, Au1.5%/TiO2-I, Au1.5%Pd1.5%/TiO2-I, Pd1.5%/TiO2-I, Pd3%/TiO2-I and Au6.0%Pd0.2%/TiO2/IW were characterized by means of XRD. The supported metal was thereby determined to have a particle size around 50 nm. All catalysts were tested in the reduction of nitrate ions in aqueous solution and in the presence of hydrogen gas. All tested catalysts were found to be of relatively high activity and with high dinitrogen selectivity in this respect. Pd-Au/TiO2 catalysts were found to have high selectivity but slightly lower activity than Pd-catalysts. Incorporation of Au into Pd catalysts has improved their selectivity. Au1.5%Pd1.5%/TiO2-I produces less nitrite than Pd3%/TiO2I, indicating that alloying has positive effects on the reduction of nitrate. The alloying effects were much more pronounced in the case of Au6%Pd0.2%/TiO2/IW where more than 87% nitrate conversion was achieved with ~100% dinitrogen selectivity in 30 min. of reaction and without any detectable nitrogen fixation.