S.A.A. Mansour

Bio: S.A.A. Mansour is an academic researcher from Minia University. The author has contributed to research in topics: Thermal decomposition & Differential thermal analysis. The author has an hindex of 17, co-authored 37 publications receiving 749 citations. Previous affiliations of S.A.A. Mansour include Yahoo!.

Ceria on silica and alumina catalysts: dispersion and surface acid-base properties as probed by X-ray diffractometry, UV-Vis diffuse reflectance and in situ IR absorption studies

Abstract: X-ray diffractometry and UV-Vis diffuse reflectance spectroscopy revealed that fluorite-structured CeO 2 crystallites (mean size 22.3 nm) are dispersed on silica surfaces (CeSi) into microcrystallites (11.2-8.1 nm) and dispersed further on alumina surfaces (CeAl) into nanocrystallites ( x monolayers. Consequently, IR spectroscopy of adsorbed pyridine found Lewis acid sites to be far more strengthened on CeAl. Bronsted acid sites (proton-donors) were probed exclusively on CeAl. On the other hand, IR spectroscopy of adsorbed deuterated chloroform (CDCl 3 ) showed the originally moderate Lewis base sites (low-coordinated OH − and O 2− ) to be weakened on CeSi, but markedly strengthened on CeAl. Lewis base sites exposed on ceria surfaces assume a strong nucleophilic reactivity.

Adsorption and surface reactions of pyridine on pure and doped ceria catalysts as studied by infrared spectroscopy

Abstract: Pyridine (Py) adsorption on ceria surfaces, prepared by thermal decomposition of diammonium hexanitratocerate at 400 °C, was studied by infrared spectroscopy and gravimetric techniques. At room temperature, Py was irreversibly adsorbed via coordination to Lewis sites of different acid strengths. High temperature calcination (at 800 °C) of ceria greatly reduced the Py adsorption capacity of the surface. Upon thermoevacuation at 100–400 °C, Py cracking occurred with formation of various surface species (among these caboxylates and nitrites) deriving from cleavage of the ring via attack of surface oxygen on adsorbed Py. Doping of ceria with Na + , Al 3+ and Cr 3+ ions (at 1 atom dopant per Ce atom) largely modified the Py adsorption capacity and surface reactions, thus revealing disparate impacts on acid/base properties of the surface.

Characterization of the thermal genesis course of manganese oxides from inorganic precursors

Abstract: NH4MnO4, Mn3O4 and Mn(NO3)2·6H2O were used as precursor compounds for the thermal genesis (at 150–600°C) of manganese oxides. Thermal events occurring during the genesis course were monitored by means of thermogravimetry and differential thermal analysis, in oxidizing and non-oxidizing atmospheres. Intermediate and final solid-phase products were characterized using X-ray diffractometry and infrared spectroscopy. Model manganese oxides were subjected to similar examinations for reference purposes. The results indicated that NH4MnO4 is almost completely decomposed near 120°C, giving rise to predominantly α-Mn2O3. The presence of K+ contaminant supports an oxidative conversion of α-Mn2O3 into KMn8O16+ at ⩾300°C. In contrast, the genesis of pure α-Mn2O3 from Mn(NO3)2·6H2O is not achieved unless the calcination temperature exceeds 500°C; β-MnO2 was the only detectable intermediate. Mn3O4, obtained at room temperature by the addition of aqueous Mn2+ to ammonia solution, was converted into α-Mn2O3 via the formation and subsequent decomposition of Mn5O8 at ⩾300°C.

Surface characterization of silica-supported cobalt oxide catalysts

Abstract: Silica supported cobalt oxides were prepared by the impregnation method, using an aqueous solution of cobalt nitrate hexahydrate (Co(NO3)2 · 6H2O), then calcined at different temperatures (510, 620 and 870 K). Characterization of the samples was carried out by X-ray diffraction, N2-adsorption at −196°C, UV–Vis diffuse reflectance spectroscopy and KBr-IR spectroscopy of the calcination products. The surface acidity was studied by IR spectroscopy of adsorbed pyridine at different temperatures (300, 370, 470 and 570 K). Results indicated that Co3O4 is the stable phase on silica, however, dispersion of minor amount of cobalt oxide could not be ruled out. Results also indicated that the crystallinity of the formed Co3O4 increased by increasing the loading level and/or the calcination temperature. Furthermore, the surface area of the support was decreased by increasing the loading level and the calcination temperatures. It has been also found that the surface of the supported catalysts exposed strong different Lewis acid sites.

Thermal decomposition of calcium citrate tetrahydrate

Abstract: The thermal decomposition of calcium citrate tetrahydrate in dynamic air or dry nitrogen has been studied thoroughly. Thermal events encountered throughout the decomposition range (room temperature to 1000°C) have been monitored by TG, DTA and DSC. The encountered events have been characterized by analysing the decomposition solid products using X-ray diffractometry, IR spectroscopy and scanning electron microscopy (SEM). Non-isothermal kinetic and thermodynamic parameters (A, k, ΔE, ΔH, Cp and ΔS) have been determined. The results show that Ca3(C6H5O7)2·4H2O dehydrates in two successive steps at 60–140°C and 140–190°C each involving release of two moles of water. The ultimate decomposition product has been found to be CaO which formed above 640°C in air or dry nitrogen flow. SEM examinations indicate the formation of fusion nuclei accompanying the second dehydration step. Decomposition pathways in air and nitrogen are proposed.

Oxygen Evolution Reaction Dynamics, Faradaic Charge Efficiency, and the Active Metal Redox States of Ni–Fe Oxide Water Splitting Electrocatalysts

Abstract: Mixed Ni–Fe oxides are attractive anode catalysts for efficient water splitting in solar fuels reactors. Because of conflicting past reports, the catalytically active metal redox state of the catalyst has remained under debate. Here, we report an in operando quantitative deconvolution of the charge injected into the nanostructured Ni–Fe oxyhydroxide OER catalysts or into reaction product molecules. To achieve this, we explore the oxygen evolution reaction dynamics and the individual faradaic charge efficiencies using operando differential electrochemical mass spectrometry (DEMS). We further use X-ray absorption spectroscopy (XAS) under OER conditions at the Ni and Fe K-edges of the electrocatalysts to evaluate oxidation states and local atomic structure motifs. DEMS and XAS data consistently reveal that up to 75% of the Ni centers increase their oxidation state from +2 to +3, while up to 25% arrive in the +4 state for the NiOOH catalyst under OER catalysis. The Fe centers consistently remain in the +3 sta...

IR study of polycrystalline ceria properties in oxidised and reduced states

Abstract: Surface properties of high surface area ceria samples, either in the reduced or unreduced state, have been investigated using FT-IR spectroscopy. Upon reduction, detailed features in the background spectrum of unreduced samples, which may be assigned to surface or multiphonon modes, vanish while weak bands due to electronic transitions appear. One of these bands is assignable to Ce3+ as point defect in the core. Adsorption of probe molecules is used to characterise the Lewis acid–base strength of surface sites. Adsorption of a proton donor (pyrrole) or an electronic acceptor (CO2) is indicative of the high basicity of surface O2− ions for ceria either reduced or not. The acid strength of cerium ions is weak; its decrease upon reduction may be shown by adsorbing weak Lewis bases (CO, acetonitrile) but not by stronger ones (pyridine, dimethylether). Superoxide (O−2) or peroxide (O2−2) surface species are produced when O2 is adsorbed on surface reduced defects. In the case of samples with a higher degree of reduction, the electron donor power is shown by tetracyanoethylene adsorption. Surface hydroxy and methoxy species from H2 and methanol dissociations, respectively, are very sensitive probes in differentiating one, two and threefold co-ordinatively unsaturated cationic sites and their reduction state. The use of methoxy species allows to quantify the ceria reduction degree through the addition of known amounts of oxygen. Adsorbed formate species are also sensitive to ceria reduction state.

Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides.

Abstract: Focuses on the surface chemistry and spectroscopy of chromium in inorganic oxides. Characterization of the molecular structures of chromium; Mechanics of hydrogenation-dehydrogenation reactions; Mobility and reactivity on oxidic surfaces.

In situ FTIR spectra of pyridine adsorbed on SiO2-Al2O3, TiO2, ZrO2 and CeO2: general considerations for the identification of acid sites on surfaces of finely divided metal oxides

Abstract: Exposure of strong Lewis (coordinatively unsaturated metal atoms) and Bronsted (proton donor OH-groups) acid sites on solid surfaces is a prime demand for potential adsorptive and catalytic applications. In situ FTIR spectroscopy of small adsorbed base molecules, often NH 3 , pyridine, CH 3 CN, NO or CO molecules, has been well established as a powerful surface analytical technique for characterization of nature, strength and concentration of acid sites. Pyridine (Py) has been preferred as an IR probe molecule of finely divided metal oxide surfaces at room (RT) and higher temperature regimes, since it is (i) more selective and stable than NH 3 ; (ii) much more strongly adsorbed than CO and CH 3 CN; and (iii) relatively more sensitive to the strength of Lewis acid sites than NO. In the present work, in situ IR spectra of Py adsorbed at ≥RT on characterized alumina, silica, silica–alumina, titania, zirconia and ceria were measured, and compared with RT-spectra of liquid and gas phase Py obtained under identical spectroscopic conditions, in order to characterize spectral consequences of mutual Py–Py interactions in the adsorbed phase. It has been concluded that the availability of Lewis acid sites can be unequivocally monitored by formation of coordinated Py molecules giving rise to IR-absorption(s) due to the ν 8a mode of ν CCN vibrations at 1630–1600 cm −1 , where the higher the frequency assumed, the stronger the acidity of the site. Formation of pyridinium surface species (PyH + ) is identifiable by (i) an ν 8a -absorption at ≥1630 cm −1 ; (ii) an ν 19b -absorption at 1550–1530 cm −1 ; as well as (iii) ν N + H and δ N + H absorptions occurring, respectively, near 2450 and 1580 cm −1 , and, thus, the availability of Bronsted acid sites. Moreover, products and IR-characteristics of Py surface reactions at >RT have been identified, and used to imply nature of surface base sites (OH − and O 2− ) involved in formation of acid–base site pairs.

Ni/CeO2-ZrO2 catalysts for the dry reforming of methane

Abstract: Nickel catalysts supported on binary CeO 2 –ZrO 2 carriers (28–100% CeO 2 molar content) were prepared and evaluated regarding their catalytic performance for the CO 2 reforming of CH 4 (Dry Reforming of Methane, DRM). The textural and structural properties of catalysts and supports were studied in their calcined, reduced and used state by N 2 adsorption–desorption, XRD, UV–vis DRS, TPR, SEM–EDS and TPH. Zirconium improves the textural properties of the CeO 2 –ZrO 2 supports and the corresponding catalysts and enhances their textural stability under thermal reductive treatment. XRD analysis shows the formation of Ce x Zr 1− x O 2 solid solution for all Ce/(Ce + Zr) ratios. Considerable alterations in the electronic environment of the cations and increased lattice defects in the binary solid solutions were detected by UV–vis DR spectroscopy. A significant increase in the reducibility of both supports and catalysts is observed in the presence of Zr. Compared to the zirconia-free sample, the Ni/CeO 2 -ZrO 2 catalysts exhibited much higher activity for the title reaction, accredited to the increase of the surface concentration of the active sites. However, the amount of carbonaceous deposits is not straightforward related to the activity but depends on the Ce/Zr ratio. Among the zirconium containing catalysts, the zirconium-rich one exhibited the higher activity and the stronger resistance to the formation of carbonaceous deposits.