Kinetic study of the carbonyl sulphide synthesis from carbon dioxide and carbon disulphide on alumina catalysts

Abstract

The kinetics of the CO 2+CS2=2COS reaction over new and used alumina catalysts was studied at 523–623 K. The adsorption of the reaction components was measured at the temperature of the catalytic tests by volumetric and thermogravimetric methods. The number and energetics of the acidic and basic sites were investigated with a combined volumetric-microcalorimetric method using NH 3 and CO 2 as probe molecules. The equilibrium constants of the main reaction and several assumed side reactions have also been calculated. Closely zero order and first order behaviour were observed for CO 2 and CS 2, respectively. The loss of catalytic activity upon long term loading was roughly proportional to the loss of the surface basic sites whereas the number of the acidic centers moderately increased. On all catalysts, very likely by the removal of basic OH and 0 2-sites, carbon tetrachloride immediately caused an ultimate cession of the catalytic activity. As CS 2 also reacts with the surface OH groups, leading to H 2S and side products, under steady state conditions the rate-determining step is considered to be the reaction of strongly adsorbed CO 2 (presumably in a bidentate or a bridging carbonate form) with physisorbed or gas-phase CS 2. Efforts to regenerate the aged catalysts by treatments with oxygen at 573 K or by leaching with liquid phase CS 2 have failed.