Effects of ferric and chormic salts in physicochemical, surface and catalytic properties of pure and doped Fe[2]O[3]-Cr[2]O[3] system

FERRIC/CHROMIC mixed oxides having the formula 0.85 Fe[2]O[3]: 0.15 Cr[2]O[3] were obtained by thermal decomposition of the mixed hydroxides prepared from mixed nitrate and sulphate solutions using NH[4]OH. Pure mixed hydroxides were heated at 500[degree sign] C. The doped solids were prepared by treating the precipitated hydroxides with different amounts of Li[2] and K[2]O [0.5, 0.75 and 1.5 mol%] followed by calcinations at 500 [degree sign] C. The techniques employed were XRD, N[2]-adsorption and oxidation of CO by O[2] at 200-300 [degree sign] C. The results revealed that pure and doped systems consisted of nanocrystalline phases having crystallite size varying between S-64 nm depending on the nature of ferric and chromic slats used and dopant concentration. Pure mixed solids consisted of a mixture of alpha and gamma-Fe[2]O[3] phase whose crystallite size decreases by increasing the dopant concentrations. K[2]O-doping of the investigated systems resulted in the formation of K[2]FeO[4] together with ferric oxide phases. Li[2]O-doping [0.5 and 0.75 mol%] led to the formation of LiFe[5]O[8] together with gamma-Fe[2]O[3] phase. However, the heavily Li[2]O-doped samples consisted entirely of LiFe[5]O[8]. The S[BET] of pure system prepared from ferric and chromic sulphates measured higher S[BET] values as compared to those prepared from mixed nitrates, whereas K[2]O-doping decreased the S[BET]. On the other hand, Li[2]O-doping exerted a measurable increase in the S[BET]. The increase was however, more pronounced in case of the system prepared by using mixed sulphate solutions. The catalytic activity was higher in case of the catalysts prepared by using mixed nitrates as compared to the catalysts prepared by using mixed nitrates as compared to the catalysts prepared by using mixed sulphate solutions. The doping process led to a progressive significant increase in the catalytic activity. The increase was, however, much more pronounced in case of the catalysts prepared from the mixed sulphates. The maximum increase in the K[200[degree sign] C] value due to doping with 1.5 mol% K[2]O attained 20.8% and 285% for the solids prepared from mixed nitrates and mixed sulphates, respectively. These values measured 27% and 241% in case of the catalysts prepared by using mixed nitrate and mixed sulphate solutions, respectively. The doping process did not affect the mechanism of the catalyzed reaction but increased the concentrations of active sites involved in catalytic reaction without changing their energetic nature

Studies on some physicochemical, surface and catalytic properties of CuO - ZnO/Al2O3 system prepared by coprecipitation

Four copper - zinc aluminium mixed oxides having different composition were prepared by coprecipitation method. The prepared solids were calcined at 400 - 800 degree C. Some physicochemical, surface and catalytic properties of the systems investigated were studied using XRD, EDX, nitrogen adsorption at 196 degree C and catalytic oxidation of CO by O2 at 100 - 200 degree C.The results revealed that all investigated solids consisted of nanocrystalline CuO and ZnO phases even those calcined at 800 degree C.The surface characteristics of different adsorbents were strongly dependent on their chemical composition and calcination temperature. The SBET decreased by increasing both the copper oxide content and calcination temperature. The value of 132m 2/g was computed for the system containing the smallest amount of CuO and being calcined at 400 degree C. The activation energies of sintering for different solids were determined from the values of SBET as being influenced by calcination temperature. The catalytic activities, in CO - oxidation by O 2, for all solids were found to increase by increasing both CuO content and calcination temperature. The activation energies of the reaction have been determined

Effects of pH and temperature of coprecipitation and thermal treatment on some physicochemical, surface and catalytic properties of nano-sized zinc ferrite

Zinc ferrite nanoparticles were prepared via thermal treatment of zinc-iron mixed hydroxides at 400-600 [degree sign] C. The mixed hydroxides were coprecipitated from their nitrates solutions using NaOH as precipitating agent. The effects of pH and temperature of coprecipitation and calcination temperature on some physicochemical, surface and catalytic properties of the prepared ferrites were studied. The prepared systems were characterized using TG, DTG, DTA, chemical analysis, atomic absorption spectroscopy [AAS], X-ray diffraction [XRD], energy dispersive X-ray [EDX] as well as texture properties based on nitrogen adsorption-desorption isotherms. The results revealed that solid- solid interaction between ZnO and Fe[2]O[3] took place at temperature starting from 400[degree sign] C to produce ZnFe[2]O[3] phase. The surface and catalytic properties of the produced ferrite phase were strongly dependent on coprecipitation conditions of the mixed hydroxides and on their calcinations temperature

Thermal decomposition of cobalt nitrate supported on Gamma Alumina

The effect of A1[2]O[3] on the thermal decomposition of cobalt nitrate and its interaction with the produced cobal oxides were investigated using DTA, TG, DTG, X-ray diffraction and IR absorption spectometry techniques. The results obtained evealed that, A1[2]O[3] enhanced the thermal decomposition of cobalt nitrate and decreased its decomposition temperature from 230 to 200C. The produced CoO reacted simultaneously with the evolved NO[2] gas and atmospheric O[2] giving Co[3]O[4] whichremained thermally stable up to about 900C due to dissolution of some of AL[2]O[3] in its lattice resulting in an increase of its oxidation state. Co[3]O[4] interacted with AL[2]O[3] at about 1000C yielding wellcrystalline CoAL[2]O[4] spinel. The AL[2]O[3] employed was poorly crystalline gamma-alumina, being treated with small amount of Co[3]O[4] [.05 mole] and heated in air at 1000C it crystallized to well-crystalline alpha-corrundum which was found to be mostly converted to well-crystalline delta -AL[2]O[3] when subjected to slow cooling [25C/min] to room temperature

Effect of calcination temperature and chemical composition on the surface properties of Co3 O4 supported on gamma-Al2O3

A series of Co[3]O[4] supported on gamma-AL[2]O[3] was prepared by impregnating a finely powdered poorly crystalline gamma-alumina samples with cobalt nitrate solution containing different proportions of Co[No3][2] using a pore-filling method. The obtained solids were dried at 100C then roasted at temperatures between 450 and 750C. The cobalt content was varied between 10.5 to 37.1 Wt.% Co[3] O[4]. The surface charateristics namely, specific surface area, total pore volume and mean pore radius of various supported catalysts were determined from N[2] adsorption isotherms measured at 77CK. The results obtained revealed that both specific surface area and total pore volume of the employed alumina support display an important decrease by loading with cobalt oxide. The SBET of certain of the investigated solids decrease progressively by increasing the roasting temperature from 450 to 750C. The SBET of all samples decreases at 750C. This decrease becomes more pronounced on increasing the Co[3]O[4] content from 0.05 to 0.1 mole/mole AL[2]O[3] and less pronounced thereafter. The surface area is largely stabilized in the samples with 0.25 Co[3] O[4] alumina

Effect of method of preparation and calcination temperature on the catalytic activity of NiO/Al2O3 solids

Two series of NiO/AL[2]O[3] solids of different composition were prepared by both coprecipitation and impregnation of - delta -AL[2]O[3]. The catalytic activity of various solids, heated in air at 250-300C were determined under the oxidation of CO by O[2] at 250-300C under static conditions and the magnitudes of the catalytic reaction rate constant perunit surface area [k] were calculated for the different catalysts. Both bilk and surface concentration of nickel ions for each solid was determined using atomic absorption spectrometry and ESCA techniques, respectively. The obtained results revealed that, surface concentration of Ni[2+] ions [sni] was much greater than that in the bulk and decreased regularly by increasing the calcination temperature through an inward diffusion of nickel ions into the interior of the grains of the solid. Such activated diffusion was, however, less pronounced for the solids rich in NiO content. The catalysts prepared by coprecipitation, although, measured higher specific surface areas than those obtained by impregnation, yet they exhibited lower specific catalytic activities. This discrepency was explained in terms of actual surface concentration of nickel ions. This was much larger [3-fold] for the solids obtained by impregnation than those prepared by copreciptation and having the same composition. On this basis, the surface concentration of nickel ions played the most important role in determining the catalytic activity of NiO/AL[2]O[3] solids