Effects of gamma-irradiation and Li2O-doping on surface and catalytic properties of unloaded Co3O4 solid

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.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Effects of Li₂O Doping on the Surface and Catalytic Properties of CuO/Al₂O₃ Solids

El-Shobaky

Radwan

Turky

et al. 2000

“…Mixed oxides are oxygen-containing combinations of two or more metallic ions in proportions which may vary, resulting in either the formation of solid solutions between the oxides or leading to the formation of mixed oxides which exhibit a strict stoichiometry between the individual constituents. A great deal of fundamental research has been undertaken on mixed oxides regarding their behaviour as heterogeneous catalysts (Reddy et al 1999;Choudhary et al 1995Choudhary et al , 1997Choudhary et al , 1998aMonzon et al 1999;Boaro et al 2000). The catalytic activity of mixed oxides is often quite different from that of simple oxides because of the relationship between this property and other special properties of mixed oxides (Viswanath and Wilson 2000;Liu et al 2000).…”

Section: Introductionmentioning

confidence: 99%

Surface and Catalytic Properties of the γ-Irradiated ZnO-Treated Co₃O₄/Al₂O₃ System

Doheim

El-Boohy

Mokhtar³

et al. 2001

Pure and ZnO-doped Co3O4/Al2O3 catalysts were subjected to γ-irradiation (0.2–1.6 MGy). These catalysts were employed for the conversion of ethanol and isopropanol at 250–400°C using micropulse techniques. The results obtained showed that ZnO treatment increased the activity and selectivity towards dehydrogenation of the alcohols studied. On the other hand, γ-irradiation resulted in a progressive decrease in activity which fell to a minimum value at 0.8 MGy and then increased back to the original (unirradiated) value on increasing the dose further. γ-Irradiation of ZnO-treated catalysts also led to a decrease in their catalytic activity. However, in this case, the extent of such a decrease as a function of the dose applied decreased as the amount of ZnO in the catalysts increased up to 2.63 wt%. This finding was observed when the catalyzed reaction was conducted at 250–350°C, but the reverse trend was exhibited when the reaction was conducted at 350–400°C.

“…Pure unloaded Co 3 O 4 solid exhibits high catalytic activity in oxidation-reduction reactions (ElShobaky et al 1980, 1998, Al-Noaimi et al 1994El-Shobaky and Turky 2000). However, *Author to whom all correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

Surface and Catalytic Properties of the Co₃O₄/MgO System Doped with Fe₂O₃

El-Shobaky

Shaheen

Mokhtar

2001

ABSTRACT:The surface and catalytic properties of pure and Fe 2 O 3 -doped Co 3 O 4 / MgO solids were investigated. The extent of loading was maintained at 38 wt% Co 3 O 4 and the amount of dopant varied between 1.2 wt% and 11.0 wt% Fe 2 O 3 . The pure and doped solids were prepared by calcination at 400-1000ºC of pure and ferric nitrate-treated magnesium carbonate impregnated with cobalt nitrate solution. The samples thus obtained were examined by TG, DTA and XRD methods, nitrogen adsorption studies at -196ºC and the catalysis of H 2 O 2 decomposition at 30-50ºC.The results revealed that Fe 2 O 3 treatment of the Co 3 O 4 /MgO system followed by calcination at 400ºC resulted in an increase in the particle size of the Co 3 O 4 and MgO phases, whilst the opposite effect was observed when the doped solids were calcined at 600ºC. Doping of the Co 3 O 4 /MgO system followed by calcination at 400ºC effected a measurable decrease in its BET surface area with the reverse effect being observed upon heating at 600ºC. An increase in the calcination temperature of pure Co 3 O 4 /MgO up to 800ºC brought about an abrupt decrease in the intensity of all the diffraction lines associated with the Co 3 O 4 phase. These disappeared completely upon heating the system at 900ºC or 1000ºC due to dissolution of the cobalt oxide in the MgO lattice to form a solid solution.