Nabil H. Amin

Effect of γ-irradiation on the catalytic activity and selectivity of γ-alumina II. Conversion of isopropanol

The catalytic conversion of isopropanol was conducted over a poorly crystalline γ-alumina irradiated with different doses of γ-rays (25–150 Mrad). The catalytic reaction was carried out at 180–400°C in a flow technique under atmospheric pressure. The results showed that the dose of 25 Mrad resulted in a decrease of about 50% of the dehydration activity which suffered a further slight decrease upon irradiation at a dose of 50 Mrad. Increasing the dose in the range of 50–150 Mrad effected an increase in the dehydration activity reaching a maximum limit at 100 Mrad, then decreased abruptly by a dose of 150 Mrad. γ-irradiation led also to creation of some active sites contributing in dehydrogenation of isopropanol to producing acetone. These results were discussed in terms of removal of Brönsted acidity (25–50 Mrad), responsible for the dehydration reaction and to transformation of Lewis to Brönsted acidity (100 Mrad) by the action of liberated water from the dehydration reaction. The drop in dehydration activity due to irradiation at 150 Mrad might result from an efficient removal of the Brönsted acid sites created. The induced dehydrogenation activity of irradiated aluminas was attributed to creation of some electron-donor centers.

Effect of gamma-irradiation on the catalytic activity and selectivity of gamma-alumina

Methanol conversion reaction was carried out in contact with a poorly crystalline γ-alumina pre-irradiated with different doses of γ-rays. The reaction was conducted at 140–440°C using a flow technique under atmospheric pressure. The results obtained revealed that γ-irradiation of Al2O3 resulted in drastic modifications of its activity and selectivity in methanol conversion reaction. The dose of 15 Mrad was sufficient to suppress completely the formation of dimethyl ether (DME) and stimulated the formation of methane, which started at 200°C instead of 300°C in the case of the unirradiated alumina specimen. However, the rate of CH4 formation was found to decrease as a function of the dose employed. When the dose reached 140 Mrad, DME was reproduced with a rate comparable to that measured for the unirradiated catalyst sample. These results permitted us to conclude that DME is produced on the weak acidic sites (Brönsted acidity of Al2O3) and is not necessarily an intermediate compound for methane formation that takes place directly from methanol on strong acidic sites (Lewis acidity). The doses of 15–75 Mrad expelled completely the Brönsted acidic sites from Al2O3 surface, and the doses above this limit brought about a transformation of Lewis acidic sites into Brönsted acidity that is responsible for dimethyl ether formation. This transformation occurs by the action of liberated water from the dehydration of methyl alcohol.

Thermal solid-solid interaction between CuO and pure Al2O3 solids

Abstract Pure finely powdered aluminium hydroxide specimens were treated with solutions containing different proportions of cupric nitrate, followed by drying at 100 ° C and roasting in air at temperatures varying between 500 and 1100° C. The solid-solid interactions between the resulting mixed oxides were investigated using DTA, TG, DTG and X-ray diffraction techniques. The results obtained revealed that cupric nitrate and aluminium hydroxide decompose readily at 250 and 320° C respectively, to produce CuO and Al 2 O 3 solids. The mixed oxides formed begin to interact at 650° C, yielding CuAl 2 O 4 . The crystallinity of the resulting aluminate increases with increasing firing temperature up to 1000° C, and remains thermally stable up to 1100 ° C in the presence of excess alumina, then partially decomposes to CuAlO 2 , in the case of a stoichiometric mixture of CuO and Al 2 O 3 . When the Al(OH) 3 specimen was roasted in air at 1000° C, it yielded a mixture of κ- and θ-Al 2 O 3 of moderate crystallinity; when fired at 1100° C, a mixture of κ-, θ- and α-Al 2 O 3 phases is produced. However, the presence of CuO (16.3 wt.%) results in the formation of well crystallized α-Al 2 O 3 (corrundum) at a temperature of about 1000° C. The transformation of different aluminas into α-Al 2 O 3 was found to be accompanied by an exothermic peak in the DTA curve at 975° C.

Decomposition of H2O2 on Pure and ZnO-Treated Co3O4/Al2O3 Solids

The effects of Co3O4 loading, precalcination temperature and ZnO treatment on the catalytic properties of the Co3O4/Al2O3 system were investigated. The amounts of Co3O4 were varied between 5.57 wt% and 32.0 wt% and the resulting solids subjected to heat treatment at temperatures in the range 400–600°C. The amounts of ZnO were varied between 0.36 wt% and 2.12 wt%. The results obtained indicated that ZnO treatment of Co3O4/Al2O3 solids followed by precalcination at 400°C resulted in a progressive decrease in the particle size of the Co3O4 crystallites in the resulting samples. The catalytic activity of such solids towards H2O2 decomposition decreased progressively as the precalcination temperature employed was increased in the range 400–600°C. The relationship between the catalytic activity expressed as a plot of the reaction rate constant, k, versus the amount of Co3O4 in the samples showed a progressive increase in the range 5.6–17.7 wt% followed by an abrupt increase when the extent of loading exceeded this limit. Treatment with ZnO effected a measurable increase (42%) in the specific surface area (SBET) of the treated solids. However, such treatment also resulted in a considerable increase in the value of the reaction rate constant for the catalyzed reaction. Thus, the maximum increase in the value of k20°C due to doping with 2.12 wt% ZnO attained a value of 543% while the corresponding increase in the value of the reaction rate constant per unit surface area, k̄20°C, was 331%. Precalcination at 400–600°C of Co3O4/Al2O3 solids subjected to ZnO treatment did not modify the mechanism whereby the catalytically active constituents (surface cobalt species) were involved in the reaction although their concentration was altered without affecting their energetic nature.

Potentiodynamic and cyclic voltammetric behaviour of a lead electrode in NaOH solution@@@Potentiodynamisches und cyclovoltammetrisches Verhalten einer Bleielektrode in NaOH-Lösung

SummaryThe electrochemical behaviour of lead in NaOH solution was studied by potentiodynamic and cyclic voltammetric techniques in combination with X-ray diffraction analysis. The active dissolution of lead involves a small shoulderA1′ followed by a peakA1 prior to a passive region. The shoulderA1′ is assigned to the electroformation of a Pb(OH)2 film, whereas peakA1 is due to the formation of PbO. Beyond the passive region, the current density increases again, forming a small shoulderA2′ and a peakA2 prior to the oxygen evolution potential. The shoulderA2′ and the peakA2 are correlated to the electrooxidation of PbO to Pb3O4 and PbO2, respectively. The intensity of the anodic peaks increases with increasing alkali concentration, temperature and scan rate. In cyclic voltammetry, the reverse scan shows two cathodic peaksC1 andC2 which are correlated to the electroreduction of PbO and PbO2 respectively, to Pb.ZusammenfassungDas elektrochemische Verhalten von Blei in NaOH wurde mittels potentiodynamischer und cyclovoltammetrischer Techniken unter Zuhilfenahme der Röntgenbeugungsanalyse untersucht. Die aktive Auflösung von Blei verläuft über eine SchulterA1′, die von einem einer passiven Region vorgelagerten PeakA1 gefolgt wird. Die SchulterA1′ wird der elektrochemischen Bildung eines Pb(OH)2-Films, der PeakA1 der Bildung von PbO zugeschrieben. Jenseits der passiven Region steigt die Stromdichte wieder an, und vor Erreichen des Sauerstoffpotentials treten eine kleine SchulterA2′ und ein PeakA2 auf, die mit der Elektrooxidation von PbO zu Pb3O4 und PbO2 korrelieren. Analog dazu beobachtet man in der cyclischen Voltammetrie zwei kathodische PeaksC1 undC2, die der Elektroreduktion von PbO und PbO2 zu Pb entsprechen. Die Intensität der anodischen Peaks steigt mit steigender Alkalikonzentration, Temperatur und Scangeschwindigkeit.

Effect of Ag-doping of nanosized FeMgO system on its structural, surface, spectral, and catalytic properties

The effects of Ag-doping on the physico-chemical, spectral, surface, and catalytic properties of the FeMgO system with various Fe2O3 loadings were investigated. The dopant (Ag) molar ratio varied between 0.01 % and 0.05 %. The techniques employed for characterisation of catalysts were TG/DTG, XRD, ESR, N2 adsorption at −196°C, and catalytic decomposition of H2O2 at 25–35°C. The results obtained revealed that the investigated catalysts consisted of nanosized MgO as the major phase, apart from the MgFe2O4 and/or Fe3O4 phases. ESR result of the FeMgO system revealed the presence of paramagnetic species as a result of Ag-doping. The textural properties including SBET, porosity and St were modified by Ag-doping. The doping process with Ag-species improved the catalytic activity of the FeMgO system. Increasing the calcination temperature from 400°C to 800°C increased the catalytic activity (k*30 °C) of 0.05 AgFeMgO in H2O2 decomposition by 21.2 times.

Surface and Catalytic Properties of the CuO/Al2O3 System Treated with Different Proportions of ZnO

The effects of ZnO treatment on the surface and catalytic properties of CuO/Al2O3 were investigated. All the samples studied contained a fixed amount of CuO (13.5 wt%) while the amount of ZnO dopant was varied in the range 0.68–6.46 wt%. The pure and variously doped solids were subjected to heat treatment (precalcination) in the temperature range 400–600°C. The samples obtained were investigated by XRD methods, nitrogen adsorption at −196°C and studies of their catalytic influence on the decomposition of H2O2 at 20–40°C. The results obtained indicated that ZnO treatment of CuO/Al2O3 followed by precalcination at 500°C led to a progressive decrease in the degree of crystallinity of the CuO phase to an extent proportional to the amount of ZnO present in the system. This suggests that such treatment led to a significant decrease in the particle size of the CuO crystallites produced. The BET surface areas of the treated solids increased on increasing the amount of ZnO present in the system. Similarly, the catalytic activity, as expressed in terms of the reaction rate constant for the decomposition of H2O2, increased on increasing the amount of dopant added to reach a maximum value (ca. 67%) when 1.7 wt% ZnO had been added to the system, and then subsequently decreased on further addition of dopant. It was found that ZnO treatment of CuO/Al2O3 did not modify the activation energy of the catalyzed reaction but rather changed the concentration of catalytically active constituents without changing their energetic nature.

Effect of Ag-doping of Nanosized FeAlO System on its Structural, Surface and Catalytic Properties

The effects of Ag2O-doping on the physicochemical, surface and catalytic properties FeAlO system with various extent of Fe2O3 loading have been investigated. The dopant concentration was changed between 1.5 and 4.0 mol % Ag2O. Pure and variously doped solids were subjected to heat treatment at 400-800?C. The techniques employed for characterization of catalysts were TG/DTG, XRD, N2-adsorption at ?196?C and the catalytic decomposition of H2O2 at 25-40?C. The obtained results revealed that, the investigated catalysts consisted of nanosized ?-Al2O3 phase. The textural properties including SBET, porosity and St were modified by Ag2O-doping. The doping process with Ag-species improved the catalytic activity of FeAlO system. Increasing the precalcination temperature from 400 to 800?C increased the catalytic activity (k30°C) of 3.5 % AgFeAlO with 1.9 fold towards H2O2 decomposition. Furthermore, the maximum increase in the k30°C value due to doping with 3.5 mol% Ag2O attained about 15.1 fold for the solids calcined at 800°C.

Some physicochemical, surface and catalytic properties of the MoO3/Al2O3 system

The effects of MoO3 doping on the solid–solid interactions, surface and catalytic properties of Al2O3 solid were investigated using DTA, TG and XRD methods, N2 adsorption at −196°C and the catalytic conversion of isopropanol at 150–400°C using a flow technique under atmospheric pressure. The nominal composition of the mixed solid was 0.5MoO3:Al2O3. Pure and Mo oxide-treated solids were subjected to thermal treatment at 500–1000°C prior to surface and catalytic measurements. The results showed that the Al2O3 support material when precalcined at 500°C exhibited the highest catalytic activity and selectivity towards isopropanol conversion (100% selective towards propylene formation). Moreover, loading MoO3 on Al2O3, followed by precalcination at 500°C, resulted in the formation of an active catalyst towards dehydration and dehydrogenation, especially for the reaction carried out below 200°C. Further increase in the precalcination temperature of Al2O3 from 500°C to 900°C resulted in a dramatic decrease in its dehydration activity due to the decrease in its surface area and surface acidity. The solids precalcined at 1000°C showed a maximum dehydrogenation activity for the catalytic reaction when the latter was carried out at 400°C.