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

ABSTRACT

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