COS Hydrolysis Using Zinc-promoted Alumina Catalysts

The effect of doping alumina catalysts with zinc oxide is investigated for the COS hydrolysis reaction (COS + H₂O=CO₂ + H₂S) at 150 °C. The effect of the catalyst preparation method is described and discussed, and two methods are compared, namely: impregnation by incipient wetness of zinc nitrate followed by calcination to form the oxide and coprecipitation to form a hydroxide followed by calcination. The most effective zinc-promoted catalysts are prepared using the incipient wetness impregnation method. The promotional effect of zinc oxide on alumina is only observed on the basis of intrinsic activity and is not particularly significant at the initial time on stream, but becomes more marked with increased reaction time. The addition of the zinc oxide therefore decreases the deactivation and experiments using catalysts pretreated with H₂S and H₂O show that the alumina is deactivated by adsorption of these reactants. However, the effect is related to ZnO acting as a sulfur scavenger at 150 °C and we conclude that any promotional effect is likely to be relatively short lived.