Catalytic Decomposition of HO on CoO Doped with AgO or ZnO

The effects of doping Co 3 O 4 with Ag 2 O (0.40–3.00 mol%) or ZnO (0.75–6.00 mol%) on the surface and catalytic properties of the solid were investigated via nitrogen adsorption at −196°C and the decomposition of H 2 O 2 at 30–50°C. Pure and doped samples were prepared by the thermal decomposition in air at 500–900°C of pure cobalt carbonate and carbonate samples treated with different proportions of silver or zinc nitrates. The results showed that Ag 2 O doping followed by precalcination at 500–900°C resulted in a significant decrease (ca. 25%) in the BET surface areas of the treated Co 3 O 4 samples. Treatment of Co 3 O 4 with ZnO followed by precalcination over the same temperature range effected a corresponding increase in the specific surface areas (ca. 28%). The addition of Ag 2 O to Co 3 O 4 effected a record increase in the corresponding catalytic activity towards the decomposition of H 2 O 2 . Thus, the maximum increase noted in the catalytic rate constant (k) measured at 30°C over Co 3 O 4 doped with 3.00 mol% Ag 2 O exhibited a 36-fold, 26-fold and 3.5-fold increase for catalysts precalcined at 500°C, 700°C and 900°C, respectively. Treatment of Co 3 O 4 with ZnO also effected an increase in the catalytic activity of the resulting solid. Thus, treatment of Co 3 O 4 with 6.00 mol% ZnO followed by precalcination at 500°C, 700°C and 900°C effected an increase of 109%, 28% and 36%, respectively, in the catalytic activity expressed in terms of the reaction rate constant measured at 30°C. The doping process did not modify the activation energy of the catalyzed reaction but increased the concentration of catalytically active constituents considerably without changing their energetic nature. Doping with Ag 2 O or ZnO led to an increase in the concentration of Co 3+ –Co 2+ ion pairs in the system and also generated corresponding Ag + –Co 2+ and Zn 2+ –Co 3+ ion pairs, thereby increasing the number of active constituents involved in the catalytic decomposition studied

The Effects of LiO Doping on the Surface and Catalytic Properties of CuO/AlO Solids

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 −196°C, the decomposition of H 2 O 2 at 20–40°C and the oxidation of CO by O 2 at 175°C. The pure solids were prepared by wet impregnation of finely powdered solid Al(OH) 3 which had been precalcined at 400°C; the resulting material was then dried and calcined at 500°C 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 175°C. 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

Surface and Catalytic Properties of the CuO/AlO System as Influenced by Doping with CeO or ZrO and by γ-Irradiation

The effects of doping the CuO/Al 2 O 3 system with CeO 2 or ZrO 2 , or alternatively treatment with γ-irradiation, on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C, the decomposition of H 2 O 2 at 20–40°C and the oxidation of CO by O 2 at 175°C. 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 400°C, followed by drying the resulting product and subjecting the same to calcination at 500°C. The doped solids were prepared by treating Al(OH) 3 precalcined at 400°C 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. γ-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 γ-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

Effect of Al 2

Pure and doped Co 3 O 4 samples were prepared by thermal decomposition at 500–1000°C of pure basic cobalt carbonate and of the basic carbonate treated with aluminium nitrate and ammonium molybdate. The amounts of dopants added were varied within the range 0.75–6 mol% Al 2 O 3 , and 0.025–6 mol% MoO 3 . The influence of this treatment on the specific surface areas and catalytic activities of the Co 3 O 4 solids was investigated using nitrogen adsorption at −196°C and studies of the decomposition of H 2 O 2 at 30–50°C. The results obtained revealed that doping of cobaltic oxide solids with either Al 2 O 3 or MoO 3 , followed by calcination at 500°C and 700°C, resulted in a progressive increase in the BET surface areas. This increase was, however, more pronounced in the case of MoO 3 doping. Calcination of the doped solids at 900°C led to an increase in the BET surface areas of the Al 2 O 3 -treated solids and to a small decrease in the specific surface areas of the MoO 3 -doped samples. Calcination of the variously doped solids at 500–900°C brought about a decrease in their catalytic activity to an extent proportional to the amount of dopant added. Thus, treatment of Co 3 O 4 solids with 6 mol% Al 2 O 3 followed by calcination at 500°C, 700°C and 900°C effected a decrease of 36.9, 42.8 and 67.5% in their activities (expressed as reaction rate constant per unit area) measured at 30°C. The decrease in the catalytic activity of Co 3 O 4 solids due to MoO 3 doping was greater than that effected by Al 2 O 3 doping. The doping process did not change the mechanism of the catalytic reaction but effectively decreased the concentration of CO 3+ –CO 2+ ion pairs acting as the active sites involved in the catalytic process