Catalytic properties of manganese nodules

Abstract

The mineral composition, mineralogy and surface properties of manganese nodules and their implications in the catalytic activity are described. The high surface area (90-400m(2) nodules increases on calcination up to 400 degrees C due to partial dehydration and dehydroxylation. The nodules show high catalytic activity for oxidation of CO, and reduction of NOx by H-2, CO or NH3. For oxidation of CO, the activity of nodules is more than that of Pt/Al2O3 at < 210 degrees C but less at higher temperatures. A complete conversion of NOx by H-2 or CO with nodules is achieved at 300 degrees C. The nodules show greater resistance towards H2S poisoning than Pt/Al2O3. The nodules have been found to be good catalysts for demetallation and desulphurisation of topped petroleum crude in the presence of H-2. About 55% of Ni and V present in petroleum crude can be recovered by nodules in trickle bed reactor operator at 110 bar, 433 degrees C and 0.5 h(-1) LHSV. Under drastic industrial operating conditions, when the classical industrial catalysts (Co-Mo/Al2O3) are too rapidly poisoned, the use of nodules can be considered. The surface area of nodules after demetallation and desulphurisation is, however, reduced significantly due to choking of pores and partial conversion of metal oxides to sulphides. The thermal resistance as well as catalytic activity of the nodules is increased when the nodules admired with lanthanide (as hydroxides or oxides) is calcined at 900 degrees C for 5-10h. This is due to the formation of perovskite type mixed oxides.