Ahmed K. H. Nohman - Academia.edu (original) (raw)

Papers by Ahmed K. H. Nohman

Research paper thumbnail of Surface active holmia/ γ-alumina nanocatalyst: Preparation and characterization

Main Group Chemistry, 2021

Holmia supported γ-alumina nanocatalyst was prepared by impregnation of γ-alumina with aqueous so... more Holmia supported γ-alumina nanocatalyst was prepared by impregnation of γ-alumina with aqueous solution of holmium acetate hydrate Ho(CH3COO)3.3.5 H2O. The physicochemical characteristics of the nanocatalyst calcined at 600°C were established by different techniques, using surface adsorption–desorption of N2 (SBET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (DRS). The recorded optical reflectance of the sample showed that the new self-assembled nanocatalyst is excellent as host material for advanced optical applications. Moreover, the catalyst showed enhanced catalytic activity toward Isopropyl alcohol decomposition.

Research paper thumbnail of Low-temperature synthesis of high-purity BiFeO3 via carbonized metal citrate xerogel

Journal of Alloys and Compounds, 2020

Abstract Bi/Fe-citrate xerogel, prepared by sol-gel processing, was first carbonized and, then, c... more Abstract Bi/Fe-citrate xerogel, prepared by sol-gel processing, was first carbonized and, then, calcined at 300–700 °C for 1 h. The gel and its calcination products were characterized by thermal analyses (TG/DTA), X-ray powder diffractometry (XRD), Fourier-transform infrared spectrophotometry (FTIR), BET-specific surface area measurement (SBET), and Ultraviolet–Visible diffuse reflectance spectrometry (UV–Vis DRS). It was found that the carbonization step helps to subside the effects of a glowing thermal decomposition event, thus suppressing the formation of parasitic phases (such as Fe2O3 and Bi2Fe4O9). Rhombohedral-BiFeO3 yielded at 500 °C was found to assume qualifying properties for photo-assisted applications.

Research paper thumbnail of Characterization of the thermal genesis course of manganese oxides from inorganic precursors

Thermochimica Acta, 1992

Abstract NH4MnO4, Mn3O4 and Mn(NO3)2·6H2O were used as precursor compounds for the thermal genesi... more 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.

Research paper thumbnail of Nitrogen Adsorption and Surface Texture of High-Area Manganese Oxides Derived from Potassium-Contaminated NH4MnO4

Adsorption Science & Technology

Nitrogen sorption isotherms have been determined at 77 K on pre-characterised MnOx bulk samples o... more Nitrogen sorption isotherms have been determined at 77 K on pre-characterised MnOx bulk samples obtained by calcination at 423–873 K of K+-contaminated NH4MnO4. The isotherms have been analysed for estimating the surface area and pore structure of the test samples adopting the αs-method and standard adsorption data determined on a local reference material (calcination product of the permanganate at 1273 K for 20 h). The most prominent result of the present investigation is that the presence of K+ leads to the formation of a channel-structured KMn8O16 bulk phase at 573 K and the following consequent textural modifications: (i) a considerable increase in the surface area to 205 m2/g, (ii) the construction of a uniform pore system consisting of slit-shaped pores with narrow entrances, and (iii) the evolution of energetically uniform internal surfaces of considerable area (= 92 m2/g). The results also reveal that the test surfaces generally exhibit a low heat towards N2 adsorption.

Research paper thumbnail of The Influence of Phosphate and Sulphate Ions on the Surface Texture of Alumina

Adsorption Science & Technology, 1999

Research paper thumbnail of Holmium and Uranium modified NiO/SiO2 and NiO/TiO2 Catalysts

Research paper thumbnail of Pyridine as a Probe for characterization of surface acid sites on chromium and zirconium oxides : a diffuse reflectance spectroscopic study

Research paper thumbnail of Mn/Al2O3 Systems: Structure and Activity

ABSTRACT a-Mn2O3 and KMn8O16 were detected on catalysts prepared by pore volume impregnation of ?... more ABSTRACT a-Mn2O3 and KMn8O16 were detected on catalysts prepared by pore volume impregnation of ?-alumina using manganous nitrate and ammonium permanganate, respectively. While the surface texture was not remarkably affected: decomposition activities towards H2O2 and 2-propanol were higher for the later.

Research paper thumbnail of Preparation of Manganese Oxide Catalysts Using Novel NH4MnO4 and Manganese Hydroxide Precursors. Comparison of Unsupported and Alumina Supported Catalysts

Studies in Surface Science and Catalysis, 1991

ABSTRACT Unsupported and Al2O3- supported Mn oxide catalysts were prepd. using Mn(NO3)2, Mn(OH)2,... more ABSTRACT Unsupported and Al2O3- supported Mn oxide catalysts were prepd. using Mn(NO3)2, Mn(OH)2, and NH4MnO4. They were bulk and surface characterized by thermal anal., x-ray diffraction, diffuse reflectance, IR and photoelectron spectroscopy, SBET and TPR.

Research paper thumbnail of Assessment of textural consequences of compacting calcined chromia gel by nitrogen sorption isotherms

Colloids and Surfaces, 1987

ABSTRACT Powd. chromia was obtained by calcination of a pentahydrated chromia gel at 573-973 K fo... more ABSTRACT Powd. chromia was obtained by calcination of a pentahydrated chromia gel at 573-973 K for 5 h. The calcination conditions were detd. on the basis of thermal anal. of the parent gel. There exists a considerable disparity in the degrees of oxidn., crystallinity, surface area and pore structure between different samples. The powders were compacted in a die at a series of known pressures (100-1000 GN m-2) encompassing com. conditions. Consequent textural modifications were detd. by a direct comparison between the N adsorption isotherms of the compacts and each resp. loose powder (viz., f-plots). The detailed outcome depends largely on the initial characteristics of the loose powder.

Research paper thumbnail of Surface texture of high-area manganese oxide powders versus compaction

Powder Technology, 1995

Three prepared manganese oxide powders from K+-contaminated NH4MnO4, of high surface area (43-340... more Three prepared manganese oxide powders from K+-contaminated NH4MnO4, of high surface area (43-340 m 2 g-X) were investigated for the assessment of the textural consequences of compaction. The powders were compacted in die at various pressures (1-15 ton in-2) encompassing technological conditions. Textural modifications were estimated by applying the fplots. Results indicated that compaction effects vary depending on the initial physicochemical characteristics of the powder. For industrial applications of pelleted catalysts, it is advisable to choose the appropriate compaction pressure to give optimal textural characteristics.

Research paper thumbnail of Thermal decomposition of holmium oxalate hexahydrate and formation of a catalyst for 2-propanol decomposition-Thermoanalytic and in-situ spectroscopic studies

Research paper thumbnail of Spectro-thermal investigation of the decomposition intermediates developed throughout reduction of ammonium paratungstate

Thermochimica Acta, 2000

The thermal decomposition course of ammonium paratungstate (APT) in hydrogen was studied using th... more The thermal decomposition course of ammonium paratungstate (APT) in hydrogen was studied using thermogravimetric and differential thermal analyses. X-ray diffractometry, infrared spectroscopy and diffuse re¯ectance spectroscopy were used to characterize and identify the intermediate solid products. It was found that ammonium paratungstate decomposes to tungsten metal W 0 through ®ve main steps encompassing different tungsten intermediate compounds. Ammonium tungsten bronze (NH 4) 0.33 WO 3 , which precedes the formation of WO 3 , is relatively the most stable intermediate (250±5508C) encountered through reduction of APT to tungsten metal W 0. The in¯uence of hydrogen spillover on the reduction behavior commences to be effective just after formation of the bronze intermediate.

Research paper thumbnail of Redox Catalysis on Manganese Oxides — Surface Attributes and Reaction Mechanisms

ChemInform, 2006

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Research paper thumbnail of Development of Catalytic Properties of Mordenite Zeolite via Chemical Modification

ChemInform, 2006

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Research paper thumbnail of Thermoanalytic resolution of hydrogen-influenced reductive events in the decomposition course of ammonium paratungstate

Thermochimica Acta, 1994

Hydrogen-influenced reductive events in the decomposition course of ammonium para-Zaki * 61519, E... more Hydrogen-influenced reductive events in the decomposition course of ammonium para-Zaki * 61519, Egypt tungstate (APT) were resolved by thermal analysis (TG and DTA) as a function of the heating atmosphere (air, N, and HZ) and rate (2-20°C mix'). A kinetic characterization of the events was carried out non-isothermally. The results indicated that the reductive events begin after the complete decomposition of APT into WO, near 400°C and lead eventually to the formation of W" at 700-800°C. Thus, it was concluded that a pre-calcination of APT-containing materials might develop upon reduction to monolayer-type W" catalysts.

Research paper thumbnail of Thermochemical adsorptive and catalytic events occurring during isopropanol decomposition over MnOx-modified aluminas. In situ infrared spectroscopic studies

Thermochimica Acta, 1996

Adsorptive and catalytic events occurring at gas/solid interfaces established during isopropanol ... more Adsorptive and catalytic events occurring at gas/solid interfaces established during isopropanol decomposition over pure and MnOx-modified aluminas were monitored and characterized by in situ infrared spectroscopic measurements. On pure alumina the alcohol adsorbs dissociatively and non-dissociatively at room temperature, giving rise respectively to isopropoxides coordinated to Lewis acid sites and isopropanol molecules hydrogen-bonded to hydroxyl (and oxide) sites. Those adsorbed species withstand outgassing at room temperature, but are completely eliminated near 200°C. Meanwhile, the alcohol catalytic dehydration is commenced at 150°C and gas-phase propene is thus released. Quantitative conversion into the alkene is effected near 225°C. The modification with MnO x stabilizes the isopropoxide species to thermo evacuation at well above 200°C, but activates their conversion into surface carboxylates at > 300°C. Moreover, the isopropanol dehydration selectivity of alumina is critically suppressed and acetone becomes the dominant gas-phase product. Thus, a strong dehydrogenation selectivity is generated. These and other MnO~-influenced alterations to the adsorptive and catalytic behaviours of alumina are discussed on the basis of available characterization results for the catalysts and mechanistic aspects established in the field.

Research paper thumbnail of Sulfated Alumina Catalysts: Consequences of Sulfate Content and Source

Monatshefte für Chemie - Chemical Monthly, 2005

Consequences of the loading level of sulfate ions (3, 6, and 10-wt%) as well as the source of sul... more Consequences of the loading level of sulfate ions (3, 6, and 10-wt%) as well as the source of sulfate (H 2 SO 4 or (NH 4) 2 SO 4) on the structural, textural, and surface acid-base properties as well as the impacts on catalytic activity towards 2-propanol conversions on-Al 2 O 3 and on aluminum hydroxide gel is described. Structural investigations of the catalysts by XRD revealed that the sulfation processes do not remarkably affect the-phase of alumina irrespective of the sulfate content or source. N 2-adsorption at 77 K indicated that sulfated gel catalysts exhibit the highest S BET areas and, in general, S BET for all catalysts were found to decrease with the increase of sulfate content, such a decrease is more pronounced for the 10% loaded catalysts. Pyridine adsorption as followed by FTIR indicated that sulfation of alumina increases the strength of its Lewis acid sites and creates Brønsted acidity in the case of highly loaded catalysts. The catalytic decomposition of 2-propanol in the gas phase indicated that, amongst all the catalysts investigated, the 6% loaded ones exhibited 100% activity (2-propanol conversion) and the highest propene (dehydration product) selectivity.

Research paper thumbnail of Phosphated Alumina Catalysts: Surface Properties and Reactivity towards 2-PrOH Decomposition

Monatshefte für Chemie - Chemical Monthly, 2007

The influence of the type of precursor, the phosphate content, as well as the source of phosphate... more The influence of the type of precursor, the phosphate content, as well as the source of phosphate ions on the surface texture, acidity, and catalytic activity of phosphated aluminas has been described. Phosphated alumina catalysts were prepared by impregnating two different precursors with two different sources of phosphate in different loading levels w ¼ 3, 6, and 10% PO 4 3À. The characterisation of the catalyst was performed using X-ray powder diffraction (XRD), thermal analysis (TG), and nitrogen adsorption-desorption methods at 77 K. The surface acidity of the catalysts has been studied by FT-IR spectroscopy of adsorbed pyridine at different temperatures. Moreover, the activity in the catalytic decomposition of isopropanol (2-PrOH) has been investigated at 520 K. Investigation of the surface properties shows that the addition of phosphate ions does not change the crystal phase (-phase) and the samples prepared from gel and phosphoric acid have the highest surface area. An FT-IR study of pyridine adsorption shows both Lewis and Brønsted acid sites on the surface of the samples prepared from gel, while only Lewis acid sites are detected on the samples prepared from crystalline oxide. The catalytic activity by 2-PrOH conversion shows that the conversion of 2-PrOH as well as the selectivity towards propene formation increases from w ¼ 3 to 6% followed by a decline for w ¼ 10%. Moreover, the strongest activity was detected in case of phosphated alumina gel with w ¼ 6% which gives 97.3% propene and 96.1% conversion of 2-PrOH.

Research paper thumbnail of Precursor-Support Interactions in Silica-Supported Manganese Oxide Catalysts

Monatshefte f�r Chemie / Chemical Monthly, 2004

Catalyst materials investigated in this study were obtained by calcination of impregnated silica ... more Catalyst materials investigated in this study were obtained by calcination of impregnated silica with Mn(CH 3 COO) 2 Á 4H 2 O and MnC 2 O 4 Á 2H 2 O, so as to yield 10 wt% Mn=SiO 2. The precursor compounds as well as pure and impregnated silica support were calcined at 600 and 1000 C in a static air atmosphere for 5 h. Structural characteristics of the catalysts thus obtained were investigated by DTA, TG, XRD, IR and DRS. N 2 adsorption at À195 C was used for the assessment of surface texture of the test materials. Results of structural characterisation of catalysts obtained by calcination of manganese acetate-impregnated silica at 1000 C indicated the presence of strong silica-precursor interactions. Species of manganese silicates were detectable. Moreover, the decomposition of manganese acetate enhanced the transformation of amorphous silica into well crystallised-quartz. In contrast, Mn 2 O 3 , Mn 3 O 4 , and minor proportions of MnO were detected in the catalysts derived from the manganese oxalate-impregnated silica. This has been ascribed to much weaker precursor=support interactions in the oxalate-impregnated silica than the acetate-impregnated one.

Research paper thumbnail of Surface active holmia/ γ-alumina nanocatalyst: Preparation and characterization

Main Group Chemistry, 2021

Holmia supported γ-alumina nanocatalyst was prepared by impregnation of γ-alumina with aqueous so... more Holmia supported γ-alumina nanocatalyst was prepared by impregnation of γ-alumina with aqueous solution of holmium acetate hydrate Ho(CH3COO)3.3.5 H2O. The physicochemical characteristics of the nanocatalyst calcined at 600°C were established by different techniques, using surface adsorption–desorption of N2 (SBET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (DRS). The recorded optical reflectance of the sample showed that the new self-assembled nanocatalyst is excellent as host material for advanced optical applications. Moreover, the catalyst showed enhanced catalytic activity toward Isopropyl alcohol decomposition.

Research paper thumbnail of Low-temperature synthesis of high-purity BiFeO3 via carbonized metal citrate xerogel

Journal of Alloys and Compounds, 2020

Abstract Bi/Fe-citrate xerogel, prepared by sol-gel processing, was first carbonized and, then, c... more Abstract Bi/Fe-citrate xerogel, prepared by sol-gel processing, was first carbonized and, then, calcined at 300–700 °C for 1 h. The gel and its calcination products were characterized by thermal analyses (TG/DTA), X-ray powder diffractometry (XRD), Fourier-transform infrared spectrophotometry (FTIR), BET-specific surface area measurement (SBET), and Ultraviolet–Visible diffuse reflectance spectrometry (UV–Vis DRS). It was found that the carbonization step helps to subside the effects of a glowing thermal decomposition event, thus suppressing the formation of parasitic phases (such as Fe2O3 and Bi2Fe4O9). Rhombohedral-BiFeO3 yielded at 500 °C was found to assume qualifying properties for photo-assisted applications.

Research paper thumbnail of Characterization of the thermal genesis course of manganese oxides from inorganic precursors

Thermochimica Acta, 1992

Abstract NH4MnO4, Mn3O4 and Mn(NO3)2·6H2O were used as precursor compounds for the thermal genesi... more 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.

Research paper thumbnail of Nitrogen Adsorption and Surface Texture of High-Area Manganese Oxides Derived from Potassium-Contaminated NH4MnO4

Adsorption Science & Technology

Nitrogen sorption isotherms have been determined at 77 K on pre-characterised MnOx bulk samples o... more Nitrogen sorption isotherms have been determined at 77 K on pre-characterised MnOx bulk samples obtained by calcination at 423–873 K of K+-contaminated NH4MnO4. The isotherms have been analysed for estimating the surface area and pore structure of the test samples adopting the αs-method and standard adsorption data determined on a local reference material (calcination product of the permanganate at 1273 K for 20 h). The most prominent result of the present investigation is that the presence of K+ leads to the formation of a channel-structured KMn8O16 bulk phase at 573 K and the following consequent textural modifications: (i) a considerable increase in the surface area to 205 m2/g, (ii) the construction of a uniform pore system consisting of slit-shaped pores with narrow entrances, and (iii) the evolution of energetically uniform internal surfaces of considerable area (= 92 m2/g). The results also reveal that the test surfaces generally exhibit a low heat towards N2 adsorption.

Research paper thumbnail of The Influence of Phosphate and Sulphate Ions on the Surface Texture of Alumina

Adsorption Science & Technology, 1999

Research paper thumbnail of Holmium and Uranium modified NiO/SiO2 and NiO/TiO2 Catalysts

Research paper thumbnail of Pyridine as a Probe for characterization of surface acid sites on chromium and zirconium oxides : a diffuse reflectance spectroscopic study

Research paper thumbnail of Mn/Al2O3 Systems: Structure and Activity

ABSTRACT a-Mn2O3 and KMn8O16 were detected on catalysts prepared by pore volume impregnation of ?... more ABSTRACT a-Mn2O3 and KMn8O16 were detected on catalysts prepared by pore volume impregnation of ?-alumina using manganous nitrate and ammonium permanganate, respectively. While the surface texture was not remarkably affected: decomposition activities towards H2O2 and 2-propanol were higher for the later.

Research paper thumbnail of Preparation of Manganese Oxide Catalysts Using Novel NH4MnO4 and Manganese Hydroxide Precursors. Comparison of Unsupported and Alumina Supported Catalysts

Studies in Surface Science and Catalysis, 1991

ABSTRACT Unsupported and Al2O3- supported Mn oxide catalysts were prepd. using Mn(NO3)2, Mn(OH)2,... more ABSTRACT Unsupported and Al2O3- supported Mn oxide catalysts were prepd. using Mn(NO3)2, Mn(OH)2, and NH4MnO4. They were bulk and surface characterized by thermal anal., x-ray diffraction, diffuse reflectance, IR and photoelectron spectroscopy, SBET and TPR.

Research paper thumbnail of Assessment of textural consequences of compacting calcined chromia gel by nitrogen sorption isotherms

Colloids and Surfaces, 1987

ABSTRACT Powd. chromia was obtained by calcination of a pentahydrated chromia gel at 573-973 K fo... more ABSTRACT Powd. chromia was obtained by calcination of a pentahydrated chromia gel at 573-973 K for 5 h. The calcination conditions were detd. on the basis of thermal anal. of the parent gel. There exists a considerable disparity in the degrees of oxidn., crystallinity, surface area and pore structure between different samples. The powders were compacted in a die at a series of known pressures (100-1000 GN m-2) encompassing com. conditions. Consequent textural modifications were detd. by a direct comparison between the N adsorption isotherms of the compacts and each resp. loose powder (viz., f-plots). The detailed outcome depends largely on the initial characteristics of the loose powder.

Research paper thumbnail of Surface texture of high-area manganese oxide powders versus compaction

Powder Technology, 1995

Three prepared manganese oxide powders from K+-contaminated NH4MnO4, of high surface area (43-340... more Three prepared manganese oxide powders from K+-contaminated NH4MnO4, of high surface area (43-340 m 2 g-X) were investigated for the assessment of the textural consequences of compaction. The powders were compacted in die at various pressures (1-15 ton in-2) encompassing technological conditions. Textural modifications were estimated by applying the fplots. Results indicated that compaction effects vary depending on the initial physicochemical characteristics of the powder. For industrial applications of pelleted catalysts, it is advisable to choose the appropriate compaction pressure to give optimal textural characteristics.

Research paper thumbnail of Thermal decomposition of holmium oxalate hexahydrate and formation of a catalyst for 2-propanol decomposition-Thermoanalytic and in-situ spectroscopic studies

Research paper thumbnail of Spectro-thermal investigation of the decomposition intermediates developed throughout reduction of ammonium paratungstate

Thermochimica Acta, 2000

The thermal decomposition course of ammonium paratungstate (APT) in hydrogen was studied using th... more The thermal decomposition course of ammonium paratungstate (APT) in hydrogen was studied using thermogravimetric and differential thermal analyses. X-ray diffractometry, infrared spectroscopy and diffuse re¯ectance spectroscopy were used to characterize and identify the intermediate solid products. It was found that ammonium paratungstate decomposes to tungsten metal W 0 through ®ve main steps encompassing different tungsten intermediate compounds. Ammonium tungsten bronze (NH 4) 0.33 WO 3 , which precedes the formation of WO 3 , is relatively the most stable intermediate (250±5508C) encountered through reduction of APT to tungsten metal W 0. The in¯uence of hydrogen spillover on the reduction behavior commences to be effective just after formation of the bronze intermediate.

Research paper thumbnail of Redox Catalysis on Manganese Oxides — Surface Attributes and Reaction Mechanisms

ChemInform, 2006

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Research paper thumbnail of Development of Catalytic Properties of Mordenite Zeolite via Chemical Modification

ChemInform, 2006

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Research paper thumbnail of Thermoanalytic resolution of hydrogen-influenced reductive events in the decomposition course of ammonium paratungstate

Thermochimica Acta, 1994

Hydrogen-influenced reductive events in the decomposition course of ammonium para-Zaki * 61519, E... more Hydrogen-influenced reductive events in the decomposition course of ammonium para-Zaki * 61519, Egypt tungstate (APT) were resolved by thermal analysis (TG and DTA) as a function of the heating atmosphere (air, N, and HZ) and rate (2-20°C mix'). A kinetic characterization of the events was carried out non-isothermally. The results indicated that the reductive events begin after the complete decomposition of APT into WO, near 400°C and lead eventually to the formation of W" at 700-800°C. Thus, it was concluded that a pre-calcination of APT-containing materials might develop upon reduction to monolayer-type W" catalysts.

Research paper thumbnail of Thermochemical adsorptive and catalytic events occurring during isopropanol decomposition over MnOx-modified aluminas. In situ infrared spectroscopic studies

Thermochimica Acta, 1996

Adsorptive and catalytic events occurring at gas/solid interfaces established during isopropanol ... more Adsorptive and catalytic events occurring at gas/solid interfaces established during isopropanol decomposition over pure and MnOx-modified aluminas were monitored and characterized by in situ infrared spectroscopic measurements. On pure alumina the alcohol adsorbs dissociatively and non-dissociatively at room temperature, giving rise respectively to isopropoxides coordinated to Lewis acid sites and isopropanol molecules hydrogen-bonded to hydroxyl (and oxide) sites. Those adsorbed species withstand outgassing at room temperature, but are completely eliminated near 200°C. Meanwhile, the alcohol catalytic dehydration is commenced at 150°C and gas-phase propene is thus released. Quantitative conversion into the alkene is effected near 225°C. The modification with MnO x stabilizes the isopropoxide species to thermo evacuation at well above 200°C, but activates their conversion into surface carboxylates at > 300°C. Moreover, the isopropanol dehydration selectivity of alumina is critically suppressed and acetone becomes the dominant gas-phase product. Thus, a strong dehydrogenation selectivity is generated. These and other MnO~-influenced alterations to the adsorptive and catalytic behaviours of alumina are discussed on the basis of available characterization results for the catalysts and mechanistic aspects established in the field.

Research paper thumbnail of Sulfated Alumina Catalysts: Consequences of Sulfate Content and Source

Monatshefte für Chemie - Chemical Monthly, 2005

Consequences of the loading level of sulfate ions (3, 6, and 10-wt%) as well as the source of sul... more Consequences of the loading level of sulfate ions (3, 6, and 10-wt%) as well as the source of sulfate (H 2 SO 4 or (NH 4) 2 SO 4) on the structural, textural, and surface acid-base properties as well as the impacts on catalytic activity towards 2-propanol conversions on-Al 2 O 3 and on aluminum hydroxide gel is described. Structural investigations of the catalysts by XRD revealed that the sulfation processes do not remarkably affect the-phase of alumina irrespective of the sulfate content or source. N 2-adsorption at 77 K indicated that sulfated gel catalysts exhibit the highest S BET areas and, in general, S BET for all catalysts were found to decrease with the increase of sulfate content, such a decrease is more pronounced for the 10% loaded catalysts. Pyridine adsorption as followed by FTIR indicated that sulfation of alumina increases the strength of its Lewis acid sites and creates Brønsted acidity in the case of highly loaded catalysts. The catalytic decomposition of 2-propanol in the gas phase indicated that, amongst all the catalysts investigated, the 6% loaded ones exhibited 100% activity (2-propanol conversion) and the highest propene (dehydration product) selectivity.

Research paper thumbnail of Phosphated Alumina Catalysts: Surface Properties and Reactivity towards 2-PrOH Decomposition

Monatshefte für Chemie - Chemical Monthly, 2007

The influence of the type of precursor, the phosphate content, as well as the source of phosphate... more The influence of the type of precursor, the phosphate content, as well as the source of phosphate ions on the surface texture, acidity, and catalytic activity of phosphated aluminas has been described. Phosphated alumina catalysts were prepared by impregnating two different precursors with two different sources of phosphate in different loading levels w ¼ 3, 6, and 10% PO 4 3À. The characterisation of the catalyst was performed using X-ray powder diffraction (XRD), thermal analysis (TG), and nitrogen adsorption-desorption methods at 77 K. The surface acidity of the catalysts has been studied by FT-IR spectroscopy of adsorbed pyridine at different temperatures. Moreover, the activity in the catalytic decomposition of isopropanol (2-PrOH) has been investigated at 520 K. Investigation of the surface properties shows that the addition of phosphate ions does not change the crystal phase (-phase) and the samples prepared from gel and phosphoric acid have the highest surface area. An FT-IR study of pyridine adsorption shows both Lewis and Brønsted acid sites on the surface of the samples prepared from gel, while only Lewis acid sites are detected on the samples prepared from crystalline oxide. The catalytic activity by 2-PrOH conversion shows that the conversion of 2-PrOH as well as the selectivity towards propene formation increases from w ¼ 3 to 6% followed by a decline for w ¼ 10%. Moreover, the strongest activity was detected in case of phosphated alumina gel with w ¼ 6% which gives 97.3% propene and 96.1% conversion of 2-PrOH.

Research paper thumbnail of Precursor-Support Interactions in Silica-Supported Manganese Oxide Catalysts

Monatshefte f�r Chemie / Chemical Monthly, 2004

Catalyst materials investigated in this study were obtained by calcination of impregnated silica ... more Catalyst materials investigated in this study were obtained by calcination of impregnated silica with Mn(CH 3 COO) 2 Á 4H 2 O and MnC 2 O 4 Á 2H 2 O, so as to yield 10 wt% Mn=SiO 2. The precursor compounds as well as pure and impregnated silica support were calcined at 600 and 1000 C in a static air atmosphere for 5 h. Structural characteristics of the catalysts thus obtained were investigated by DTA, TG, XRD, IR and DRS. N 2 adsorption at À195 C was used for the assessment of surface texture of the test materials. Results of structural characterisation of catalysts obtained by calcination of manganese acetate-impregnated silica at 1000 C indicated the presence of strong silica-precursor interactions. Species of manganese silicates were detectable. Moreover, the decomposition of manganese acetate enhanced the transformation of amorphous silica into well crystallised-quartz. In contrast, Mn 2 O 3 , Mn 3 O 4 , and minor proportions of MnO were detected in the catalysts derived from the manganese oxalate-impregnated silica. This has been ascribed to much weaker precursor=support interactions in the oxalate-impregnated silica than the acetate-impregnated one.