The present invention relates to a catalyst comprising a honeycomb (1) and a surrounding jacket, the honeycomb comprising a structure formed of a stack of metal sheets, of which at least part are profiled, and the honeycomb structure including several through-flow channels for gas. The free ends of the said metal sheets are distributed over a part (S1) of the honeycomb periphery unsymmetrically to the centre of the honeycomb so that part (F1) of the honeycomb's periphery is free from the free ends of the metal sheets. The said honeycomb is attached either directly or through an intermediate layer to the said jacket over an area (L1) comprising at least part of the said free ends.