Hesham S. Abdel-Samad

Catalytic Behavior of Cobalt (II) Phthalocyanine Immobilized on Bentonite Clay in Bulk Polymerization of Methyl Methacrylate

The catalytic behavior of cobalt (II) phthalocyanine (CoPc) immobilized on bentonite clay, with different complex loadings ranging between 0.2 and 2.2 wt%, in the presence of n-butyl amine solvent, was investigated in bulk polymerization of methyl methacrylate without using an activator or cocatalyst. The interaction of CoPc molecules with a bentonite surface, encouraged by the amine, involved the inclined stacking model, i.e., interaction between N-atoms of the macro-ring system and OHs of the support. Two different mechanistic pathway regions could be suggested, depending on complex loadings. The first was in the range, 0.2−1.0 wt% CoPc, behaving in ionic fashion as the bare bentonite. Isolated oriented molecules probably activated bentonite through the exposure of new internal acid sites during intercalation. The second, in the range of 1.4−2.2 wt% CoPc, proceeded via combined mechanisms, ionic functioned by bentonite support and free radical functioned by complex packed oriented stacks, staggered in clay galleries to cover a fraction of internal active acid sites. The number of polymer chains formed per one CoPc center (reaction turnovers) was >2–∼10 with diluted catalyst samples. With higher loadings, one chain was formed per active site. Such behaviors, without a detectable effect on polymer characteristics or enchainment sequence, were studied in light of intercalation, orientation and accessibility models.

Rare earth oxides doped NiO/γ-Al2O3 catalyst for oxidative dehydrogenation of cyclohexane

Abstract The effect of rare earth oxides (RE=Ce, La, Gd, and Dy) doping of alumina support in NiO/γ-Al 2 O 3 system was investigated on its catalytic performance in oxidative dehydrogenation (ODH) of cyclohexane. The physicochemical properties of various samples were followed up through N 2 physisorption, temperature programmed reduction (H 2 -TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and potentiometric acid-base titration techniques. In the parent NiO/γ-Al 2 O 3 catalyst, Ni species were found to be strongly interacted with alumina surface. Addition of rare earth dopants to γ-Al 2 O 3 in the catalyst system affected the nickel-alumina interaction and resulted in significant modifications in the catalytic performances in the ODH reaction. The results revealed the beneficial role of both La 2 O 3 and Gd 2 O 3 doping in enhancing the ODH catalytic activity and selectivity to cyclohexene. H 2 -TPR and XPS results indicated that majority of Ni species in NiO/La 2 O 3 modified γ-Al 2 O 3 were more weakly interacted with La 2 O 3 and alumina whereas both NiO like species and nickel aluminate were present on the surface. Doping with cerium or dysprosium increased the nickel-support interaction and led to a decrease in surface nickel concentration. In case of doping with Ce, surface concentration of cerium oxide was higher than those of the other RE oxides; the doped catalyst reached its steady state activity faster than the other catalysts. The acid-base results suggested that RE metals were interacted most likely with acidic surface hydroxyl groups. The degree of nickel-alumina interaction decreased in the following order: LaAl>GdAl>CeAl>DyAl.

Redox-Initiated Bulk Polymerization of Methyl Methacrylate Using a CuO/TiO2 Catalyst System

Catalytic bulk polymerization of methyl methacrylate (MMA) has been carried out at 80°C over pure titania (anatase), and supported CuO/TiO2 catalyst system of different CuO % loadings (ranged between 0.5–20 wt%), without using an initiator or cocatalyst. The produced polymers were characterized via hydrogen nuclear magnetic resonance (1HNMR) and gel permeation chromatography (GPC). The prepared catalyst samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2-adsorption-desorption. The polymer yield (%) was shown to increase by increasing the CuO content up to 8.0 wt%, and then decreased. All polymers were of high molecular weights with low % of pentads. They were almost of syndiotactic-rich structure, produced mainly through a chain-end control mechanism. The polymerization process was suggested to be catalyst-dependent, redox-initiated and following a free radical mechanism. The sample of 8.0% CuO loading (above the monolayer coverage) was the most active; a fraction of loaded CuO existed on the titania external surface, while a larger fraction seemed to be inserted into the support pore system.

Surface functionality and electrochemical investigations of a graphitic electrode as a candidate for alkaline energy conversion and storage devices.

Graphite is a typical electrocatalyst support in alkaline energy conversion and storage devices such as fuel cells, supercapacitores and lithium ion batteries. The electrochemical behaviour of a graphite electrode in 0.5 M NaOH was studied to elucidate its surface structure/electrochemical activity relationship. Graphite voltammograms are characterized by an anodic shoulder AI and a cathodic peak CI in addition to the oxygen reduction reaction plateaus, PI and PII. AI and CI were attributed to oxidation and reduction of some graphite surface function groups, respectively. Rotating ring disk electrode (RRDE) study revealed two different oxygen types assigned as inner and outer oxygen. The inner oxygen was reduced via the more efficient 4-electron pathway. The outer oxygen reduction proceeded with a lower efficient 2-electron pathway. The calculated percentages of the 4-electron pathway were ranged from 70% to 90%. A full mechanism for the graphite surface function groups changes over the studied potential window was suggested through the combination between the voltammetric, FT-IR and Raman results.

Pitting Corrosion of Zn Peculiarly Caused by Acetate Anions

Abstract The corrosion behaviour of zinc metal was studied in acetate solutions. The potentiodynamic polarization curve in 0.1 M acetate solution displays an anodic peak (A1) owing to the anodic dissolution of zinc followed by a passive layer formation region. Breakdown of the passive film and the initiation of pitting corrosion were observed beyond the pitting potential (Epit) and confirmed by SEM images. The reverse scan of the cyclic voltammogram shows three cathodic peaks; CI, CII and CIII. CI was attributed to the reduction of the pitting corrosion product formed at potentials more anodic than Epit, while the overlapped CII and CIII peaks were attributed to the reduction of the exterior and the interior passive layers, respectively. The potentiostatic current time transients at different applied potentials (around the pitting potential) for different electrolyte concentrations involved three stages. The first stage exhibited rapid current decrease with time till a minimum value (im) at the incubation time (ti). The second and the third stages, where the current increases again linearly with time through two different slopes, are correlated to the pit nucleation and growth, respectively. An increase of the pit nucleation rate and a decrease in its growth were observed with increasing the anodic potential limit (Ea). Electrochemical impedance spectroscopy (EIS) measurements, at different potentials before and after Epit were performed. The effect of the acetate concentration was studied as well. A suggested equivalent circuit was used to fit the EIS data. The impedance results confirmed that the thickness of the formed passive layer increases with proceeding of the anodic potential reaching a maximum value at Epit. The passive film thickness decreased again at more anodic potentials.