Effect of Thermal Treatments on the Properties of Nickel and Cobalt Activated-Charcoal-Supported Catalysts

Abstract

The effect of thermal pretreatment in N 2 up to 723 K and the activation treatments in H 2 and an inert atmosphere on the properties of Ni and Co activated-charcoal-supported catalysts were studied. Catalysts were characterized by means of N 2 adsorption at 77 K, H 2 chemisorption at room temperature, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The catalysts′ activity and selectivity for acetone hydrogenation to 2-propanol under unusual and severe conditions (473 K and high overall acetone conversion) were also measured. TGA and XRD evidence was found for the charcoal-support-promoted NiO and CoO reduction to the metallic states when the catalysts were subjected to an inert atmosphere at 723 K. The thermal activation treatments under H 2 or inert atmosphere above 723 K caused a loss of acetone hydrogenation activity (calculated on a metal load basis) for both the Ni and Co activated-charcoal-supported catalysts, with respect to that of the low-temperature (573 K) activation treatments. In a series of activated-charcoal-supported Ni catalysts, a large decrease in the H 2 chemisorption uptake was also found for a sample pretreated in N 2 at 723 K prior to H 2 reduction. These results were not due to nickel or cobalt sintering, as shown by XRD line broadening measurements. The catalytic activity loss was accompanied by a decrease (in the case of Ni) and an increase (in the case of Co) in the 2-propanol selectivity.