Metal loading effects on CO hydrogenation of [formula omitted] zeolite prepared by ion-exchange and carbonyl complex impregnation

Abstract

The ion-exchange (IE) and the carbonyl complex impregnation (CI) methods were employed to prepare cobalt clusters encaged in the pores of Y zeolite, and their catalytic behaviors for CO hydrogenation were compared. The reaction was performed with a differential reactor operating at atmospheric pressure, temperature of 230–270 °C, and H 2 CO ratio of 2. Some measurements of hydrogen consumption, electron paramagnetic and ferromagnetic resonance, and temperature-programmed desorption were employed to characterize the catalysts. The catalytic behaviors of CO hydrogenation over the IE and CI catalysts were significantly different from each other. The activity of the IE catalysts increased significantly with increasing cobalt loading and reduction temperature, while the activity of the CI catalysts was almost constant irrespective of cobalt loading and reduction temperature. The IE catalysts showed a Schulz-Flory-type hydrocarbon product distribution, but the preference for C 3 and C 4 hydrocarbons was observed in the CI catalysts. The olefin fraction for the IE catalysts decreased with increasing cobalt loading, while the CI catalysts showed constant value with cobalt loading. The fraction of isobutene in C 4 hydrocarbons was significantly higher in the IE catalysts than in the CI ones. The difference in activity and olefin selectivity between the two preparation methods was explained by the acidity modification in the ion-exchanged catalysts.