The kinetics of H2S decomposition over precipitated cobalt sulphide catalyst

Cobalt sulphide catalyst prepared via a new method involving the precipitation reaction between cobaltous acetate and ammonium sulphide solutions has been shown to be favourably active for the catalytic decomposition of H2S when compared with data for other transition metal sulphides. The BET surface area of this unsupported catalyst is about an order of magnitude higher than cobalt sulphide formed by direct sulphidation of cobalt oxide with H2S gas. XRD, SEM and TEM analyses were used to obtain bulk composition and morphological characteristics. Catalyst 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 using about 11 feed compositions showed that below 40% H2S/Ar the reaction was essentially 1st order with respect to H2S partial pressure. Beyond this point, rate remained invariant with feed composition. A mechanism 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 temperatures also paralleled the behaviour seen for H2S decomposition. Activation energy for H2S decomposition and H-2 production rates were estimated as 111 kJ mol(-1) and 88 kJ mol(-1) respectively.