CATALYTIC PROPERTIES OF MANGANESE NODULES

The mineral composition, mineralogy and surface properties of manganes e nodules and their implications in the catalytic activity are describ ed. The high surface area (90-400m(2) nodules increases on calcination up to 400 degrees C due to partial dehydration and dehydroxylation. T he nodules show high catalytic activity for oxidation of CO, and reduc tion of NOx by H-2, CO or NH3. For oxidation of CO, the activity of no dules is more than that of Pt/Al2O3 at < 210 degrees C but less at hig her temperatures. A complete conversion of NOx by H-2 or CO with nodul es is achieved at 300 degrees C. The nodules show greater resistance t owards H2S poisoning than Pt/Al2O3. The nodules have been found to be good catalysts for demetallation and desulphurisation of topped petrol eum crude in the presence of H-2. About 55% of Ni and V present in pet roleum crude can be recovered by nodules in trickle bed reactor operat or at 110 bar, 433 degrees C and 0.5 h(-1) LHSV. Under drastic industr ial operating conditions, when the classical industrial catalysts (Co- Mo/Al2O3) are too rapidly poisoned, the use of nodules can be consider ed. The surface area of nodules after demetallation and desulphurisati on is, however, reduced significantly due to choking of pores and part ial conversion of metal oxides to sulphides. The thermal resistance as well as catalytic activity of the nodules is increased when the nodul es admired with lanthanide (as hydroxides or oxides) is calcined at 90 0 degrees C for 5-10h. This is due to the formation of perovskite type mixed oxides.