Physicochemical Properties of the Co₃O₄/Al₂O₃, Ag₂O/Al₂O₃ and Ag₂O-Co₃O₄/Al₂O₃ Systems and Their Catalytic Activities towards Acid-Base and Redox Reactions

Abstract

A Co 3 O 4 /Al 2 O 3 catalyst containing 0.20 mol% Co 3 O 4 and an Ag 2 O/Al 2 O 3 catalyst containing 0.2 mol% Ag 2 O were prepared using the impregnation method. Co 3 O 4 –Ag 2 O/Al 2 O 3 samples containing 0.2 mol% Co 3 O 4 and varying small molar percentages of Ag 2 O were also prepared. Portions from the catalysts thus obtained were calcined at 773, 973 and 1173 K. The textural properties of the catalysts were determined from the adsorption of N 2 at 77 K, while their structural properties were investigated using TG, DTA, XRD and TPR techniques. The surface acidities of the catalysts were determined via titration with n-butylamine in a non-aqueous medium. The conversion of propan-2-ol at 573 K was followed using the micro-catalytic pulse technique, whereas the decomposition of H 2 O 2 at 298–313 K was followed by determining the volume of oxygen released with time. Solid-solid interactions between the components of the systems resulted in the formation of Co 3 O 4 and CoAl 2 O 4 , their ratio depending on the chemical composition and heat-treatment temperature employed with Ag in its metallic form. The textural properties of the investigated catalysts also depended on the chemical composition and calcination temperature. The surface acidity of the catalysts is an important factor in determining their catalytic activity towards the conversion of propan-2-ol whereas the redox-reactive ion-pairs formed between Ag and Co determine their activity towards H 2 O 2 decomposition.