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The COS hydrolysis reaction (COS + H 2 O = CO 2 + H 2 S) using c-Al 2 O 3 at 220°C is described and discussed. The stoichiometric reaction of COS in the absence of water proceeds and the extent of reaction is comparable to the moisture content of the alumina that can be removed during TGA. The reaction of COS and H 2 O is long lived at this temperature but the sulphur balance based on H 2 S is ca. 80%. It is found that elemental sulphur is deposited in the reactor and on the catalyst during this reaction. Reaction in the presence of H 2 increases the sulphur balance to 100% and no sulphur is deposited on the catalyst. The beneficial effect of hydrogen is demonstrated by mixing sulphur with c-Al 2 O 3 which on reaction with H 2 leads to the formation of COS and H 2 S. The addition of formic acid to the reactants leads to a reversible loss of activity, but detailed long term studies show that formic acid is not formed during the operation of the catalyst over a wide range of conditions.

The effect of doping alumina catalysts with zinc oxide is investigated for the COS hydrolysis reaction (COS + H 2 O=CO 2 + H 2 S) 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 H 2 S and H 2 O 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.