The invention relates to a catalyst comprising an assembly of at least one wire that comprises, in % weight, between 60 and 90% iron, and between 10 and 25% chromium, at least one metal selected from the group formed by platinum, rhodium, palladium, ruthenium, iridium, gold and silver having been deposited on the assembly, the outside contour of the cross-section of the wire being included in a ring whose area is between a circle with a 90 .mu.m diameter and a circle with a 5 mm diameter, the length of the wire being at least equal to 20 cm, and the assembly being mechanically integral, the wire having been subjected to a prior depositing of aluminum, in a proportion going up to 10% by weight in relation to the weight of the wire, followed by a redrawing.A preferred assembly corresponds to a knitted structure (1) in the shape of a sock.