THE KINETICS OF H2S DECOMPOSITION OVER PRECIPITATED COBALT SULFIDE CATALYST

Cobalt sulphide catalyst prepared via a new method involving the preci pitation reaction between cobaltous acetate and ammonium sulphide solu tions has been shown to be favourably active for the catalytic decompo sition of H2S when compared with data for other transition metal sulph ides. The BET surface area of this unsupported catalyst is about an or der of magnitude higher than cobalt sulphide formed by direct sulphida tion of cobalt oxide with H2S gas. XRD, SEM and TEM analyses were used to obtain bulk composition and morphological characteristics. Catalys t specimen calcined at 823 K showed the best activity. The kinetics of the decomposition reaction has been studied over this new preparation . Experiments conducted at atmospheric pressure between 933-983 K usin g about 11 feed compositions showed that below 40% H2S/Ar the reaction was essentially 1st order with respect to H2S partial pressure. Beyon d this point, rate remained invariant with feed composition. A mechani sm involving catalysis via co-ordinative unsaturation sites on the CoS was proposed and kinetic model based on the cleavage of the surface H -S bond as the rate-determining step appeared to be the most adequate representation of the rate data. Hydrogen production rates at all temp eratures also paralleled the behaviour seen for H2S decomposition. Act ivation energy for H2S decomposition and H-2 production rates were est imated as 111 kJ mol(-1) and 88 kJ mol(-1) respectively.