The catalytic conversion of isopropanol was conducted over a poorly crystalline -alumina irradiated with different doses of -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. -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.
The results obtained showed that the addition of small amounts of LiNO3 to the reacting mixed solids, consisting of equimolar proportion of Fe2O3 and basic MgCO3 much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO3 (6 mol% Li2O) decreased the decomposition temperature of MgCO3 from 525.5 to362C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800C yielding MgFe2O4. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the
completion of this reaction required prolonged heating at elevated temperature above 1100C. Doping with Li2O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe2O4 phase at temperatures starting from 700C. The addition of 6 mol% Li2O to the mixed solids followed by precalcination at 1050C for 4 h resulted in complete conversion of the reacting oxides
into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050C effected the disappearance of most of IR
transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe2O4 structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility
of the various reacting cations. The activation energy of formation (ΔE) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61
kJ mol−1 for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li2O, respectively.
A copper, zinc and aluminium mixed oxides sample having the nominal composition 0.25 CuO/0.03 ZnO/Al2O3 was prepared by impregnating Al(OH)3 with copper and zinc nitrate solutions, drying at 100 °C then heating in air at 600 °C. The obtained solid was exposed to different doses of -rays (20–160 Mrad). The surface characteristics namelySBETVP andr of different treated adsorbents were determined from N2 adsorption isothems measured at –196 °C. The catalytic activity of various irradiated solids was determined by following up the kinetics of CO-oxidation by O2 at 150–200 °C. The results showed that the doses up to 80 Mrad resulted in no significant change in theSBET but increased slightly theVP (20%) of the treated adsorbents. The irradiation at 160 Mrad caused an increase of 20% in theSBET of the irradiated solid sample. The catalytic activity increased progressively by increasing the dose, a dose of 160 Mrad brought about an increase of 140% in the catalyst's activity. The apparent activation energy of the catalytic reaction decreased monotonically by increasing the absorbed dose of -rays which was attributed to a parallel induced decrease in the value of pre-exponential term of the Arrhenius equation. The observed increase in the catalytic activity due to -irradiation has been interpreted as a result of increasing the concentration of catalytically-active sites contributing in chemisorption and catalysis of CO-oxidation via a possible fragmentation of CuO crystallites.
Authors:G. A. El-Shobaky, A. S. Ahmad, A. N. Al-Noaimi, and H. G. El-Shobaky
Basic cobalt and copper carbonates were prepared by precipitation from solutions of their nitrates using KHCO3 at room temperature in CO2 atmosphere. The thermal decomposition of the prepared basic carbonates was studied by means of TG and DTA techniques and the phases produced were identified by XRD measurements. The products obtained at 400‡C were subjected to different doses of gamma-rays (40–160 M rad) and the thermal stabilities of these solids were investigated.
Authors:G. El-Shobaky, M. Doheim, A. Turky, and H. El-Boohy
NiO-doped Co3O4 samples precalcined at 500 °C were subjected to various doses of -rays within the range 0.2-1.6 MGy. The particle size and BET-surface areas of different samples were determined using XRD and nitrogen adsorption at -196 °C. The catalytic reactions studied were conversion of ethanol and isopropanol at 250-400 °C using a micropulse technique and H2O2 decomposition in aqueous solution at 30-50 °C. The results revealed that the -irradiation brought a significant decrease in the particle size of Co3O4 phase with subsequent increase in the SBET surface areas. The treatment brought also a progressive decrease in the total conversion of both alcohol (dehydration and dehydrogenation) falling to a minimum value (about 20% of its initial activity) at a dose of 0.8 MGy. The catalysts retain their initial activity upon exposure to a dose of 1.6 MGy. On the other hand, the catalytic activity in H2O2 decomposition of the investigated system decreased progressively by increasing the dose of -rays and the catalysts lost more than 90% of their initial activity upon exposure to a dose of 1.6 MGy.
Copper and nickel oxide samples supported on MgO were prepared by wet impregnation method. The obtained solids were heated
at 350 °C and 450 °C. The extent of copper and nickel oxides was fixed at 16.7 mol%. The effect of g-irradiation (0.2-1.6
MGy) on the surface and catalytic properties of the solids were investigated. The techniques employed were XRD, nitrogen adsorption
at -196 °C and H2O2 decomposition. The results revealed that the g-irradiation up to 0.8 MGy of CuO/MgO-450 °C effected a measurable decrease
in the crystallite size of CuO phase with subsequent increase in its degree of ordering. Irradiation at a dose of 1.6 MGy
brought about a complete conversion of MgO into Mg(OH)2 during its cooling from 450 °C to room temperature via interacting with atmospheric water vapor. The SBET and total pore volume of CuO/MgO precalcined at 350 °C and 450 °C increased progressively as a function of g-ray dose reached
a maximum limit at 0.8 MGy. Gamma-irradiation of NiO/MgO-450 °C solids up to 0.8 MGy increased the degree of ordering of MgO
and NiO phases without changing their crystallite size. The exposure of these solids to 1.6 MGy led to an effective transformation
of some of NiO (not dissolved in MgO lattice) into Ni(OH)2 via interacting with atmospheric water vapor during cooling from 450 °C to room temperature. Gamma-irradiation led to a measurable
increase in the SBET and Vp of NiO/MgO system. Gamma-irradiation of the two investigated systems resulted in both increase and decrease in their catalytic
activities in H2O2 decomposition depending mainly on the irradiation dose and calcination temperature. This treatment, however, did not modify
the mechanism of the catalytic reaction, but changed the catalytic active sites without changing their energetic nature.
Authors:M. Doheim, A. Ahmed, H. El-Boohy, and G. El-Shobaky
Manganese oxide samples obtained from thermal decomposition of manganese carbonate at 400 and 600 °C were subjected to different doses of g-irradiation within the range 0.2 to 1.6 MGy. The surface and catalytic properties of the above samples were studied using nitrogen adsorption isotherms measured at -196 °C and catalytic conversion of ethanol and isopropanol at 300-400 °C using micropulse technique. The results obtained revealed that manganese oxides obtained at 400 °C consisted of a mixture of Mn2O3 and MnO2 while the samples calcined at 600 °C composed entirely of Mn2O3. Gamma-irradiation resulted in a decrease in the particle size of manganese oxide phases with subsequent increase in their specific surface areas. Gamma-irradiation with 0.2 and 0.8 MGy effected a measurable progressive decrease in the catalytic activity in dehydration and dehydrogenation of both alcohols. However, the treated catalyst retained their initial activity upon exposure to a dose of 1.6 MGy. Also, g-irradiation increased the selectivities of the investigated solids towards dehydrogenation of both alcohols. The catalyst samples precalcined at 600 °C exhibited higher catalytic activities than those precalcined at 400 °C.
Authors:A. Al-Noaimi, G. El-Shobaky, A. Ahmad, and H. El-Shobaky
The effects of -irradiation (20–160 Mrad) and lithium oxide doping (0.75–6 mol%) on the surface and catalytic properties of unloaded Co3O4 solid have been investigated. The surface characteristics of various solids were determined from nitrogen adsorption isothems taken at –196 °C and their catalytic activities were measured by following the kinetics of CO-oxidation by O2 at 100–150 °C using a static method. The results showed that -rays brough about a decrease of 21% inSBET of Co3O4 due to widening of its pores and led also to a considerable increase in its catalytic activity. A maximum increase of 91% was observed upon exposure to a dose of 80 Mrad. Lithium oxide-doping at at 500 °C resulted in an increase of 150% inSBET of treated solid without changing its mean pore radius. This treatment was also accompanied by an increase of about 50% in its catalytic activity measured at 150 °C. Gamma-irradiation and Li2O-doping of unloaded Co3O4 did not change the magnitude of apparent activation energy of catalysis of CO-oxidation by O2 but increased the concentration of catalytically active sites contributing in the catalytic process. In other words, -rays and lithium oxide doping did not alter the mechanism of catalytic oxidation of CO by O2 over unloaded cobaltic oxide solid.
Authors:M. A. Fahmey, M. A. Zayed, and H. G. El-Shobaky
This paper describes the use of the mass spectrometry (MS), thermal analyses (TA) and other physico-chemical methods to investigate
the structure of two newly synthesized phenolic-iodine derivative polymeric products. These two products are formed as a result
of redox-interaction of adrenaline hydrogen tartrate (AHT, I) with iodate (IO-3) and periodate (IO-4). The characterization of the two products were achieved satisfactorily by using the above tools and their proposed general
formulae, were found to be C52H67O36N4I (AHT- IO-3, II) and C26H34O18N2I2(AHT- IO-4, III). The fragmentation behavior of the main compound (AHT) in MS and TA (TG and DTA) techniques was investigated and compared.
The results obtained were used to explain the fragmentation of the products AHT- IO-3and AHT- IO-4in mass spectrometry and thermal analyses techniques. The stabilities of different fragments were discussed. The results indicate
that the two techniques are supporting each other in which the mass spectrometry provides the structural information in gas
phase while the thermal analyses provides the quantitative fragmentation in the solid-state.