Ambient Temperature Hydrolysis of Carbonyl Sulfide Using γ-Alumina Catalysts: Effect of Calcination Temperature and Alkali Doping

The hydrolysis of COS using γ-alumina as catalyst at 20 °C is described and discussed. In particular, the effect of calcination on the catalyst activity is investigated. Catalysts calcined at 100 and 500 °C are found to give the highest catalyst activities, in terms of both specific (mol COS converted/g catalyst/h) and intrinsic (mol COS converted/m2 catalyst/h) activity. Calcination at other temperatures leads to diminished catalyst activity. The effects are discussed in terms of the known surface chemistry of γ-alumina involving physisorbed water, surface dehydroxylation and defect formation. The addition of alkali additives (Li+, Na+, K+, Cs+, Mg2+, Ca2+, Ba2+, Si2+) is also reported. Only K+ and Cs+ give a sustained enhancement in catalyst activity, whereas all the other additives act as catalyst poisons for the steady-state performance measured following 5 h time-on-stream. Interestingly, addition of Na+ and Mg2+ leads to a very high initial activity (>95% COS conversion) but the effect is very short-lived and, after 5 h time-on-stream, a much lower steady-state activity (∼15-30% COS conversion) is observed.