Effects of doping with CeO[2] and calcination temperature on physicohcemical properties of NiO/Al[2]O[3] system

The effects of doping with CeO[2] and calcinations temperature on physicochemical properties of NiO/Al[2]O[3] system have been investigated using DTA, XRD, nitrogen adsorption measurements at - 196 [degree sign] C techniques and decomposition of H[2]O[2] at 30-50 [degree sign] C. The pure and variously doped mixed solids were subjected to heat treatment at 300, 400, 700, 900 and 1000 [degree sign] C. The amounts of dopant were 0.75, 1.5 and 3 mol% CeO[2]. The results revealed that the presence of NiO with aluminium oxide much enhanced the degree of crystallinity of the gamma-Al[2]O[3] phase. In contrast, the presence of Al[2]O[3] much retarded the crystallization process of the NiO phase. The specific surface areas were found to increase with increasing calcinations temperature from 300 to 400 [degree sign] C and with doping of the system under investigation with CeO[2]. The pure and variously doped solids, calcined at 300 and 400 [degree sign] C, were constituted of amorphous NiO dispersed in gamma-Al[2]O[3] Heating at 700[degree sign] C resulted in formation of poorly crystalline NiO and gamma-Al[2]O[3] phases beside CeO[2] for the doped solids. Crystalline NiAl[2]O[4] phase was formed starting from 900[degree sign] C as a result of solid-solid interaction between the reacted oxides. The degree of crystallinity of NiAl[2]O[4] increased with increasing the calcinations temperature from 900 to 1000 [degree sign]. An opposite effect was observed upon doping with CeO[2]. NiO/Al[2]O[3] system calcined at 300 and 400 [degree sign] has catalytic activity higher than individual NiO obtained at the same calcinations temperature. The catalytic activity of NiO/Al[2]O[3] system increased, progressively, with increasing the amount of CeO[2] dopant. The doping process did not modify the mechanism of the catalyzed reaction but changed the concentration of active sties without changing their energetic nature

Surface and catalytic properties of Mn2O3/MgO system doped with ZnO

The effects of calcination temperature and doping of Mn2O3/MgO system with ZnO on its surface and catalytic properties were investigated. The techniques employed were nitrogen adsorption at -196°C. XRD and H2O2 decomposition at 30-50°C. Pure and variously doped solids were prepared by wet impregnation method using manganese nitrate, magnesium basic carbonate and zinc nitrate. The prepared solids were calcined at 400, 600, 700, 900 and 1000°C. The amount of Mn2O3 was fixed at 20 mol% for all solids. The dopant concentration was changed between 0.75 and 3 mol% ZnO. The results revealed that manganese oxides interacted with magnesium oxide to yield crystallized magnesium manganates at temperature starting from 400°C. Pure and doped solids precalcined at 400°C consisted of MgO and MgMnO3 phases. The degree of crystallinity of the detected phases increased with increasing the calcination temperature to 600°C with detection of poorly crystalline Mn2O3. Furthermore, ZnO-doping of the system investigated followed by calcination at 400°C and 600°C resulted in decreasing the intensity of the diffraction lines with subsequent decrease the detected phases, in their crystallite size and increases their surface areas [SBET] up to a certain extent of dopant added. ZnO doping hinders the formation of MgMnO3 phase at 400 and 600°C. At 700°C, Mn2O3, Mg6MnO8 and Mg2MnO4 phases were detected. At 900 and 1000°C, only, well crystalline Mg6MnO8 and Mg2MnO4 phases were detected for all the solids. The doping process carried out at 400 and 600°C increased effectively the catalytic activity of the system under investigation reaching a maximum limit at 1.5 mol% ZnO. The increase in dopant concentration above this limit decreased the catalytic activity which remained greater than those measured for the pure solids calcined at the same temperatures. The presence of 1.5 mol ZnO brought about an increase of 191% and 144% of the catalytic activity of the solids calcined at 400 and 600°C, respectively. The doping process did not affect the activation energy values of the catalyzed reaction but rather increased the concentration of active sites involved in the catalyzed reaction without changing their energetic nature

Thermal solid-solid interactions and physicochemical properties of NiO/Fe2O3 system treated with K2O

The effects of calcination temperature and doping with K2O on solid-solid interactions and physicochemical properties of NiO/Fe2O3 system were investigated using TG, DTA and XRD techniques. The amounts of potassium, expressed as mol% K2O were 0.62, 1.23, 2.44 and 4.76. The pure and variously doped mixed solids were thermally treated at 300, 500, 750, 900 and 1000°C. The catalytic activity was determined for each solid in H2O2 decomposition reaction at 30-50°C. The results obtained showed that the doping process much affected the degree of crystallinity of NiO and Fe2O3 detected for all solids calcined at 300 and 500°C. Fe2O3 interacted readily with NiO at temperature starting from 700°C producing crystalline NiFe2O4 phase. The degree of reaction propagation increased with calcination temperature. K2O-treatment stimulates the ferrite formation to an extent proportional to its amount added in the formation of KFe11O17