Mohamed Zaki | Minia University (original) (raw)

Papers by Mohamed Zaki

Thermochimica Acta, 1998

Molybdena (MoO 3 ) and molybdates of bismuth (Bi 2 Mo 3 O 12 ), chromium (Cr 2 Mo 3 O 12 ), bariu... more Molybdena (MoO 3 ) and molybdates of bismuth (Bi 2 Mo 3 O 12 ), chromium (Cr 2 Mo 3 O 12 ), barium (BaMoO 4 ), manganese (MnMoO 4 ) and copper (Cu 3 Mo 2 O 9 ) were synthesized and characterized by X-ray powder diffractometry and infrared spectroscopy. They were then assessed as`loose contact' catalysts for soot deep oxidation (combustion) in air by thermogravimetry. A similar assessment was carried out on commercial chromia (Cr 2 O 3 ) and tungsta (WO 3 ). Observed high oxidation activity of MoO 3 , as compared to both Cr 2 O 3 and WO 3 , is attributed to the higher volatility (mobility) of MoO x species. On similar grounds, observed high activity of MoO 3 and Cu 3 Mo 2 O 9 , as compared to the other test molybdates, is explained. Relatively speaking, however, a higher activity was observed for Cu 3 Mo 2 O 9 than MoO 3 , whereby soot ignition temperature decreased from 5718C (uncatalyzed oxidation) to 4308C, to occur within the temperature range of diesel exhaust (200±4508C). This observation is ascribed to copper-promoted redox conduct of Mo(VI) in the oxidation reaction of soot. Kinetics of the reaction was studied non-isothermally, and the kinetic parameters (A, k, ÁE and the reaction order) were calculated. # 1998 Elsevier Science B.V.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2000

Pure d-MnO 2 materials were prepared by calcination at 250 -700°C for 3 h of a parent gel obtaine... more Pure d-MnO 2 materials were prepared by calcination at 250 -700°C for 3 h of a parent gel obtained by (i) a sol -gel synthesis involving a mild reduction of KMnO 4 solution; (ii) drying at room temperature; (iii) calcination to 700 or 900°C; and (iv) a subsequent acid treatment at room temperature. The bulk crystalline structure of the d-MnO 2 materials was evidenced by thermogravimetry, X-ray powder diffractometry (XRD) and high-resolution transmission electron microscopy (HRTEM). Then, surface properties were determined by X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy, and N 2 sorptometry. The results revealed that the bulk structure is morphologically organized in the form of needle-like nanofibers. Surfaces thereon exposed were found to assume high specific area (74 m 2 g − 1 ) and heat of adsorption (BET-C =130), as well as a mesoporous texture, when initially calcined to 700°C. These surface properties were also found to withstand subsequent calcination at up to 350°C for 3 h.

Journal of Colloid and Interface Science, 1996

Journal of Chemical Technology & Biotechnology, 2000

Aluminium dross tailings (ADT), a chemical waste from a factory producing aluminium in Egypt, was... more Aluminium dross tailings (ADT), a chemical waste from a factory producing aluminium in Egypt, was used for the recovery of the aluminium content in the form of alumina (Al 2 O 3 ). Extraction of the aluminium was carried out via atmospheric-and high-pressure leaching with caustic soda. Then, it was separated from the sodium aluminate solutions thus obtained, using six different precipitation methods. The precipitates were ®ltered, washed, dried and calcined at 600°C to produce the test aluminas. The precipitates and the calcination products were analysed for their chemical and crystalline phase compositions. The calcination products (aluminas) were subjected to sorpometry for surface area determination, and to particle sizing. The results indicated that highly pure (SiO 2`0 .53% and Na 2 O`0.14%), well-de®ned crystalline g-aluminas of high surface areas (b200 m 2 g À1 ) and uniform small crystallite sizes (60±70 A Ê ) could be ef®ciently recovered from ADT. Optimal recovery conditions were examined and determined.

Applied Catalysis A: General, 2000

Boehmite, ␥-AlO(OH), recovered from aluminium dross tailings (ADT) and steel-pickling chemical wa... more Boehmite, ␥-AlO(OH), recovered from aluminium dross tailings (ADT) and steel-pickling chemical waste (SPW) were used to prepare 1-10 wt.% FeO x /Al 2 O 3 catalysts. Surface and bulk properties of the catalysts were characterized by nitrogen sorptometry, thermogravimetry (TG) of adsorbed pyridine, X-ray photoelectron spectroscopy and X-ray powder diffractometry. The results have shown the catalysts to consist of highly dispersed ␣-Fe 2 O 3 particles on high-surface area ␥-Al 2 O 3 , but cannot exclude the coexistence of monolayer species of Fe(II)-O and/or Fe(III)-O, as well as Fe(III) incursions into the support bulk structure. Activity tests of the catalysts towards ethanol dehydration (at 140-250 • C) in the gas phase, have revealed that increasing amounts of supported FeO x species could turn ␥-Al 2 O 3 from being diethyl ether selective to ethene selective, without changing its originally high dehydration activity towards the alcohol. Consequent modifications of the surface acid site density have been correlated to observed changes in the alcohol dehydration rate. Hence, the switching of the catalyst selectivity to ethene formation has been suggested to follow suppression (or elimination) of bi-molecular reaction mechanism necessary for ether formation due to Fe(III) incursion into the support, and/or ether decomposition on Fe 2 O 3 particles.

Non-isothermal decomposition of chromium chromate hexahydrate, Cr 2 (CrO 4 ) 3 ⋅6H 2 O, was studi... more Non-isothermal decomposition of chromium chromate hexahydrate, Cr 2 (CrO 4 ) 3 ⋅6H 2 O, was studied on heating up to 600°C in different dynamic atmospheres of N 2 , O 2 and H 2 , using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). The results obtained at various heating rates (2-20°C min -1 ) were used to derive kinetic (E a and lnA) and thermodynamic (∆H, C p and ∆S) parameters.

Metal Powder Report, 1998

Transmission electron microscopy (TEM) studies and nitrogen gas adsorption data were used to inve... more Transmission electron microscopy (TEM) studies and nitrogen gas adsorption data were used to investigate textural characteristics of titanias prepared via calcination, at 400°C/3 h, of the hydrolysis products of titanium(IV) isopropoxide in n-heptane or isopropanol solvent. A variety of titanias (anatase form) were produced with different textural characteristics. The nature of these products was controlled largely by the synthesis parameters such as water ratio, the addition of acetic acid, and the solvent used during the hydrolysis. The resultant microstructure of the solids is correlated with the pertinent preparative conditions.

Applied Catalysis A: General, 1998

The present investigation presents and correlates observed and reported characterization results ... more The present investigation presents and correlates observed and reported characterization results of calcined, supported and unsupported chromias obtained via various precursor compounds. Studies performed employed a range of surface and bulk analytical techniques, in hopes of a proper assessment of the stability of surface chromate (Cr(VI)±O) species thus generated to thermal decomposition, hydrolysis and reduction. Impacts on the redox catalytic activity were probed towards the decomposition of H 2 O 2 solutions and the CO oxidation in the gas phase. The results have revealed that chromate species established on bulk and dispersed -Cr 2 O 3 particles enjoy high stability against thermal and chemical treatments, and yet contribute to the formation of surface sites that are catalytically active in redox reactions. This should help lessening environmental reservations about the industrial application of calcined chromia catalysts. #

Materials Research Bulletin, 2008

Chemical interactions in mixed, aqueous solutions of NH 4 HCO 3 and M(NO 3 ) 3 Á9H 2 O, where M s... more Chemical interactions in mixed, aqueous solutions of NH 4 HCO 3 and M(NO 3 ) 3 Á9H 2 O, where M stands for Ho, Sm, or La, were facilitated under various hydrothermal treatment conditions (pH 8-12 and temperature = 75-135 8C). The solution chemistry established did not make available necessary concentrations of soluble HCO 3 À and MO(OH) 2 À species for the formation of dawsonite-type ammonium hydroxymetalocarbonates, NH 4 M(CO 3 )(OH) 2 , but, alternatively, high concentrations of soluble CO 3 2À , and M(H 2 O) n 3+ or M(H 2 O) nÀ1 (OH) 2+ facilitating, respectively, precipitation of corresponding hydrated carbonate, M 2 (CO 3 ) 2 Á2H 2 O, or carbonate hydroxide, MCO 3 (OH). X-ray powder diffractometry, infrared spectroscopy, and thermal analyses proved alternative formation of Ho 2 (CO 3 ) 3 Á2H 2 O or LaCO 3 (OH) under the whole set of hydrothermal treatment conditions probed, and Sm 2 (CO 3 ) 3 Á2H 2 O at pH < 10 or SmCO 3 (OH) at pH ! 10, thus implying dependence of the composition of the product carbonate compound on the hydrolysability of the initial M(H 2 O) n 3+ species and, hence, the metal ionic size (La > Sm > Ho). Calcination of the various hydrothermal treatment products at !600 8C resulted in the thermal genesis of the corresponding sesquioxides (M 2 O 3 ). Bulk and surface characterization studies of the product oxides, employing N 2 sorptiometry and scanning electron microscopy, in addition to the above analytical techniques, revealed overall strong crystallinity, large average crystallite size, and well-defined particle morphology. They revealed, moreover, surfaces, though of limited accessibilities ( 13 m 2 /g), exposing OH groups of various coordination symmetries and, hence, acid-base properties, thus furnishing promising surface catalytic attributes. #

Journal of Thermal Analysis and Calorimetry, 2010

The formation of Barium monotungstate (BaWO 4 ) particles in equimolar powder mixtures of BaCO 3 ... more The formation of Barium monotungstate (BaWO 4 ) particles in equimolar powder mixtures of BaCO 3 and WO 3 was examined under isothermal and nonisothermal conditions upon heating in air at 25-1200°C, using thermogravimetry. Concurrence of the observed mass loss (due to the release of CO 2 ) to the occurrence of the formation reaction was evidenced. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The x-t and x-T data thus obtained were processed using well established mathematical apparatus and methods, in order to characterize nature of reaction rate-determining step, and derive isothermal and non-isothermal kinetic parameters. Moreover, the reaction mixture quenched at various temperatures (600-1,000°C) in the reaction course was analyzed by various spectroscopic and microscopic techniques, for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional diffusion of WO 3 species across the product layer (BaWO 4 ), which was implied to form on the barium carbonate particles. The isothermally determined activation energy (118-125 kJ/mol) was found to be more credible than that (245 kJ/mol) determined nonisothermally.

Chemistry of Materials, 2005

Preparation of dawsonite-type compounds, NH 4 M(CO 3 )(OH) 2 , was attempted for M ) Al, Cr, or F... more Preparation of dawsonite-type compounds, NH 4 M(CO 3 )(OH) 2 , was attempted for M ) Al, Cr, or Fe, using a hydrothermal method under various basicity and thermal conditions. Crystalline structure and chemical composition verification studies, employing X-ray diffractometry, infrared spectroscopy, and elemental analyses, revealed that a successful preparation is critically dependent on the availability of MO(OH)and HCO 3reaction species, which is facilitated at pH value in the vicinity of 10 and temperature e100°C. Accordingly, it was possible to prepare dawsonite-type compounds for Al and Cr, but not for Fe. In the latter case, the sparingly soluble FeOOH compound was the eventual product. Thermal analyses of the hydrothermal products helped define the temperature regime at which they decompose into the corresponding M(III)-oxides. Bulk and surface characterization studies of the oxides thus produced revealed that dawsonite-type compounds are feasible precursors for catalytic-grade Al 2 O 3 and Cr 2 O 3 .

Adsorption Science & Technology, 2009

The adsorptive interactions of 2-propanol (2-PrOH) molecules with silica surfaces were investigat... more The adsorptive interactions of 2-propanol (2-PrOH) molecules with silica surfaces were investigated using ab initio and density functional calculations. Two cluster models of silica were chosen to represent the terminal ≡SiOH groups and the siloxane bridges ≡Si-(O) 2 -Si≡ on the silica surface. The Hartree-Fock (HF) and Density Functional Theory (DFT) approaches, employing a 6-31G(d) basis set, were used to calculate the geometries, electronic structures, vibrational frequencies and adsorption energies of the adsorption complexes formed. The calculated adsorption energies were corrected for zero-point vibrational energies (ZPVE) and basis set superposition errors (BSSE). The results favoured a most likely surface configuration for the physisorbed species in which 2-PrOH molecules are bound to exposed silanol groups via two hydrogen bonds, with the alcoholic -OH group acting simultaneously as a proton acceptor and donor. Moreover, bonding of 2-PrOH with strained surface siloxane bridges (≡Si-O-Si≡) was shown to lead to chemisorption of the alcohol molecule. These findings have been shown to help interpreting reported infrared spectroscopic results of in-situ experimental studies. (SP4) (SP5)

Journal of Analytical and Applied Pyrolysis, 1997

Ti(OPr'), vapor was pyrolyzed in dry nitrogen atmosphere using a simple tubular flow reactor at 4... more Ti(OPr'), vapor was pyrolyzed in dry nitrogen atmosphere using a simple tubular flow reactor at 400 and 800°C. Well-defined spheroidal anatase TiO, particles showing mesoporous surfaces of 30 m2 g-r and assuming two different morphologies (fused and composite) were produced at the low temperature (ca. 4OO"Q whereas deformed spheroidal particles of rutile-structured TiO, and surfaces of 12 mZ g ~' were obtained at the high temperature (ca. SOO'C). Particles of the high-temperature product were distinguished by a low porosity and a uniform morphology (composite). The heat-induced modifications at 800°C may be ascribed to enhancements in (a) hydrolysis of Ti(OPr'),, by a possible generation of water vapor as a secondary pyrolysis product of the alkoxide. (b) particle growth via coalescence rather than by vapor deposition, and (c) particle sintering. The pyrolysis products were characterized by X-ray diffrdctometry, high-resolution transmission electron microscopy, and volumetry of nitrogen adsorption at liquid nitrogen temperature. C 1997 Elsevier Science B.V.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998

Powder Technology, 1997

TiO2 powders were obtained by calcination of base hydrolysis products of titanium(IV) isopropoxid... more TiO2 powders were obtained by calcination of base hydrolysis products of titanium(IV) isopropoxide, Ti(OPr~)a at 400°C for 3 h. The hydrolysis was carded out at room temperature in two different solvents, namely isopropanol and n-heptane, and in the presence of low and high ammonia contents. X-ray powder diffractometry showed the resulting TiO2 powders to consist of anatase crystallites, irrespective of the hydrolysis conditions applied. In contrast, N2 adsorption isotherms (determined at liquid nitrogen temperature) probed notably different surface textures for the test powders, depending on the amount of base added and the solvent used. These results were confirmed by transmission electron microscopy, and attributed to the solvent-permitted ammonia interactions with the titania precursors formed during the course of the alkoxide hydrolysis. Accordingly, preparative conditions can be resolved for producing titania powders of higher specific surface area (67-73 m2/g) than the commercial titanias described by manufacturers as being high surface area powders ( ~ 50 m2/g).

Thermochimica Acta, 2009

BaCO3 and Cr2O4 powder mixture Thermochemical interactions Topochemical interactions Influence of... more BaCO3 and Cr2O4 powder mixture Thermochemical interactions Topochemical interactions Influence of the surrounding gas atmosphere Product analysis a b s t r a c t Occurrence and products of solid/solid interactions in equimolar-mixed BaCO 3 and Cr 2 O 3 powders were examined isothermally (700-1000 • C) and non-isothermally (25-1200 • C) under different gas atmospheres, employing thermogravimetry, X-ray diffractometry, infrared and Raman spectroscopies, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Irrespective of the gas atmosphere, a noncatalytic decomposition of the barium carbonate commenced at 570 • C, a temperature that is much less than the decomposition temperature (≥970 • C) of separate BaCO 3 . Characteristics and distribution of the yielding products were found to be quite sensitive to the surrounding gas atmosphere. Under N 2 atmosphere, the interactions were thermochemical in nature, leading eventually to the formation of barium chromite (BaCr 2 O 4 ) spinel as the sole detectable product. Under O 2 atmosphere, however, the oxygen molecules contributed oxidatively to the chromite thermal genesis course, thus imposing a topochemical nature to the reaction, leading to formation of BaCrO 4 , as the major product, and barium chromites (BaCr 2 O 4 and Ba 3 Cr 2 O 6 ), as minor products. Proposed reaction pathways and characteristics of products have been presented and discussed.

Journal of Materials Science Letters, 1999