| The propylene hydrogenation activity, O(,2) chemisorption (at -78(DEGREES)C), and BET area of unsupported molybdenum sulfide prepared in-situ have been determined as a function of preparational variables and pretreatment. A prototype of an integrated microreactor system is used in the experiments.; The catalyst is prepared by in-situ decomposition of ammonium tetra-thiomolybdate (ATTM) in He. This initial catalyst is poorly crystalline and contains excess sulfur (S/Mo = 2.3 - 2.4). When it is subjected to temperature-programmed reduction (TPR) in pure H(,2), the H(,2)S evolution shows two peaks. The TPR data is analyzed to obtain information about the activation energy and catalyst morphology.; As the reduction temperature increases, excess sulfur is lost and the extent of sintering increases. The value of (ANGSTROM)('2)/O(,2) molecule chemisorbed decreases progressively with reduction temperature. The edge-plan rich catalyst adsorbs more O(,2) per unit area than the basal-plane rich catalyst after the same pretreatment.; The activity is measured by a pulse method since the reactant interacts with the catalyst in its initial (pretreated) state. A method to calculate the Langmuir-Hinshelwood parameters for propylene hydrogenation from pulsed microcatalytic reactors is developed. This method is based on a rectifying plot obtained from the variation of conversion with pulse volume.; There is a progressive increase in the specific hydrogenation rate constant (per unit area) and in the turnover number (based on O(,2) chemisorption sites), and a decrease in the activation energy for hydrogenation as sulfur is lost from the MoS(,2.3) during TPR. Catalysts that differ widely in edge/basal plane ratio show comparable values of the specific rate constant and activation energy.; The relation between O(,2) chemisorption and anion vacancies generated by desorption of H(,2)S is studied using the techniques of temperature-programmed desorption (TPD) and temperature-programmed surface reduction (TPSR). The TPD results indicate that a pair of adjacent anion vacancies is required to adsorb on O(,2) molecule.; Cobalt-promoted molybdenum sulfide is prepared as a chemical compound with Co/Mo = 1. Its TPR spectrum and O(,2) chemisorption are measured. |
