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ABSTRACT:The effects of doping CuO/Al 2 O 3 solids with Li 2 O on their surface and catalytic properties were investigated using nitrogen adsorption at -196ºC, the decomposition of H 2 O 2 at 20-40ºC and the oxidation of CO by O 2 at 175ºC. The pure solids were prepared by wet impregnation of finely powdered solid Al(OH) 3 which had been precalcined at 400ºC; the resulting material was then dried and calcined at 500ºC with copper nitrate dissolved in the least amount of distilled water. The amount of copper oxide in such solids was fixed at 13.5 wt% while the amounts of Li 2 O added varied between 0.19 wt% and 3.80 wt%.The results obtained showed that such Li 2 O doping enhanced the crystallization of the CuO phase to an extent proportional to the amount of dopant added and increased the concentration of surface OH groups. This treatment led to a progressive small increase in the BET surface areas (S BET ) of the treated solids, which attained a maximum limit at 0.76 wt% Li 2 O but decreased upon increasing the dopant concentration above this limit. The addition of 0.76 wt% Li 2 O effected an increase of 14.6% in the S BET values of the treated solids while the addition of 3.80 wt% Li 2 O led to a corresponding decrease of 38.5% in this value.Doping with Li 2 O resulted in a progressive decrease in the catalytic activity of the solids towards CO oxidation by O 2 while the presence of 3.80 wt% Li 2 O effected a decrease of 72.5% in the value of the reaction rate constant measured at 175ºC. In contrast, such treatment of CuO/Al 2 O 3 solids with Li 2 O brought about a progressive increase in their catalytic activity towards H 2 O 2 decomposition, which reached a maximum limit in the presence of 1.90 wt% Li 2 O and then decreased when the amount of Li 2 O added was increased above this limit, falling to values which were smaller than those measured for the pure catalyst samples.The doping process did not modify the activation energy of the catalyzed H 2 O 2 reaction but modified the concentration of the catalytically active constituent present in the system.

ABSTRACT:The effects of doping the CuO/Al 2 O 3 system with CeO 2 or ZrO 2 , or alternatively treatment with g-irradiation, on its surface and catalytic properties were investigated using nitrogen adsorption at -196ºC, the decomposition of H 2 O 2 at 20-40ºC and the oxidation of CO by O 2 at 175ºC. The pure solids were prepared by wet impregnation with copper nitrate dissolved in the least amount of distilled water of finely powdered solid Al(OH) 3 precalcined at 400ºC, followed by drying the resulting product and subjecting the same to calcination at 500ºC. The doped solids were prepared by treating Al(OH) 3 precalcined at 400ºC with a known amount of dopant, i.e. cerium or zirconyl nitrate dissolved in the least amount of distilled water, prior to impregnation with the copper nitrate solution. The amount of copper oxide thus introduced was fixed at 13.5 wt% while the amounts of dopants were varied between 1 wt% and 10 wt% CeO 2 or ZrO 2 .The results obtained indicated that ZrO 2 doping increased the degree of dispersion of the CuO phase, while CeO 2 treatment had the reverse effect. Doping the CuO/Al 2 O 3 system with CeO 2 or ZrO 2 led to an increase of 15.4% or 8.1%, respectively, in its BET surface area. The catalytic activity of the system towards the decomposition of H 2 O 2 decreased on doping with ZrO 2 but increased when CeO 2 was used as a dopant. g-Irradiation (at 20-160 Mrad) of CuO/Al 2 O 3 solids resulted in a measurable and progressive decrease in their catalytic activity towards H 2 O 2 decomposition.In CO oxidation with O 2 , ZrO 2 treatment of the CuO/Al 2 O 3 solids brought about a progressive increase in their catalytic activity with the maximum value (a 31% increase) being observed in the presence of 3 wt% ZrO 2 but then decreasing with further increases in the amount of dopant present until the final value attained with 10 wt% ZrO 2 was smaller than that measured for the pure CuO/Al 2 O 3 catalyst sample. In contrast, the addition of the smallest amount of CeO 2 (1 wt%) led to an effective increase of 69% in the catalytic activity of the CuO/Al 2 O 3 system towards the O 2 oxidation of CO, which then decreased when further amounts of CeO 2 were added to the system although still exhibiting a catalytic activity greater than that of the undoped catalyst sample.Doping or g-irradiation of the CuO/Al 2 O 3 system had no influence on the activation energy for the decomposition of H 2 O 2 in the presence of the resulting solid catalysts although the concentrations of catalytically active sites present on the surfaces of the solids investigated were modified by such treatment.

Pure and doped Co3O4 samples were prepared by the thermal decomposition at 500–900°C of pure and lithium nitrate-treated basic cobalt carbonate. The amounts of dopant added were varied in the range 0.75–6 mol% Li2O. The effects of this treatment on the surface and catalytic properties of cobaltic oxide solid were investigated using nitrogen adsorption at −196°C and studies of the decomposition of H2O2 at 30–50°C. The results obtained revealed that Li2O doping of Co3O4 followed by heat treatment at 500°C and 600°C resulted in a progressive increase in the value of the specific surface area, SBET, to an extent proportional to the amount of dopant present. However, the increase was more pronounced in the case of solid samples calcined at 500°C. This increase in the specific surface areas has been attributed to the fixation of a portion of the dopant ions on the uppermost surface layers of the solid leading to outward growth of the surface lattice. The observed increase in SBET due to Li2O doping at 500°C might also result from a narrowing of the pores in the treated solid as a result of the doping process. Lithium oxide doping of cobaltic oxide followed by heat treatment at 700–900°C resulted in a significant decrease in the SBET, Vp and r̄ values. Pure and doped solids precalcined at 500°C and 600°C exhibited extremely high catalytic activities which were not much affected by doping with Li2O. On the other hand, doping followed by calcination at 700–900°C brought about a considerable and progressive increase in the catalytic activity of the treated solids. This treatment did not modify the activation energy of the catalysed reaction, i.e. doping of Co3O4 solid followed by heating at 700°C and 900°C did not alter the mechanism of the catalytic reaction but increased the concentration of catalytically active constituents taking part in the catalytic process without altering their energetic nature.

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