Catalytic Decomposition of HO over a γ-Irradiated CuO–ZnO/AlO System

A CuO–ZnO/Al 2 O 3 , catalyst sample was prepared by wet impregnation methods using Al(OH) 3 , zinc and copper nitrate solutions followed by drying at 110°C and calcination at 600°C. The nominal molar composition of the resulting material was calculated to be 0.25CuO · 0.03ZnO/Al 2 O 3 Samples of this solid were exposed to varying dosages of γ-irradiation (20–160 Mrad) and the effect of such treatment on their surface characteristics and catalytic activity investigated using nitrogen adsorption studies at −196°C and studies of the decomposition of H 2 O 2 at 30–50°C. The results obtained indicate that doses of γ-rays up to 80 Mrad had no significant effect on the specific surface area. S BET , of the supported mixed oxide material although this quantity increased by 20% when the solid was exposed to γ-irradiation doses of 160 Mrad. In contrast, such treatment brought about a progressive decrease in the catalytic activity of the treated catalyst samples. Thus, the reaction rate constant (k) of the catalyzed reaction measured at 50°C diminished from 8 × 10 −2 min −1 to 0.3 × 10 −2 min −1 on exposure of the supported mixed oxide material to a dose of 160 Mrad. What was surprising was that the activation energy (δE) of the catalytic reaction decreased as a function of the dose employed whereas it should have been expected to increase in the light of the observed decrease in the catalytic activity. This apparent discrepancy was resolved by recalculating the values of ΔE taking into account any possible changes in the pre-exponential factor of the Arrhenius equation brought about by γ-irradiation. The observed decrease in the catalytic activity due to treatment with γ-rays was attributed, mainly, to the enhanced removal of Brönsted acid centres by the action of such irradiation

Adsorption of Iodine & Methylene Blue from Aqueous Solutions & Decolorizing Power of Carbons

509-51

Effect of LiO Doping on the Surface and Catalytic Properties of NiO Solid

The influence of Li 2 O treatment (0.19–0.75 mol%) on the surface and catalytic properties of NiO were investigated using nitrogen adsorption at −196°C and the catalytic decomposition of H 2 O 2 at 30–50°C. Pure and treated solid samples were subjected to thermal treatment at 300°C, 500°C and 700°C, respectively. The results obtained revealed that Li 2 O treatment of NiO solid brought about a measurable decrease (30–63%) in its BET surface area, S BET , and a decrease of 20–44% in its total pore volume, V p , especially for the solid samples calcined at 700°C. The observed decrease in the S BET value of NiO due to treatment with Li 2 O was attributed to transformation of some of the Ni 2+ ions into Ni 3+ ions with a subsequent contraction in the lattice and also to pore widening. The catalytic activities of all the doped catalyst samples investigated showed that their catalytic activity was smaller than that measured for the untreated samples. The catalytic activity, expressed as the reaction rate constant per unit surface area (k), was effectively decreased by the doping process. Although this process increased the number of Ni 3+ ions, it decreased the activity of the treated solids because of the formation of Li + –Ni 3+ ion pairs which could not readily exchange electrons with the reacting substrate (H 2 O 2 ). The formation of such ion pairs may take place at sites associated with the most active Ni 2+ ions. The doping process did not modify the mechanism of the catalytic reaction but decreased the concentration of active sites involved in the catalysis of H 2 O 2 decomposition without changing their energetic nature