Abstract: The invention relates to the use of manganese nodules or deep-sea ores containing manganese of more recent or older crustal layers as catalysts or for the manufacture of catalysts for the reduction of NO.sub.x components in exhaust gases or for the oxidation of NO.sub.x components and SO.sub.2 particles in exhaust gases.With the use of such catalysts, it becomes possible to reduce the NO.sub.x components in exhaust gases by using reduction agents such as NH.sub.3 at relatively low temperatures, for example, 250.degree. C. It is also possible to perform an oxidation reaction first in exhaust gases with the use of such catalysts, for example, with excess oxygen from NO to NO.sub.2.

Abstract: A process for the preparation of pentavalent vanadium compounds from acid extracts obtained by regenerating spent catalysts which contain vanadium, this process comprising the successive steps of (1) oxidizing extracts containing tri- and tetravalent vanadium with an oxygen-containing gas at a pH of at least 0.7 to 1.4 p.sub.o and at most 2.3-1.4 p.sub.o to form a solution of tetravalent vanadium compounds, and (2) continuing the oxidation at a pH lying in the range of from 3.2-1.4 p.sub.o to 2.3-1.4 p.sub.o to form concentrates of pentavalent vanadium having a partial oxygen pressure, 0.05 MPa.