The present invention relates to a reactor R with apparatus D, the latter comprising a gas- and/or liquid-permeable tray B, in the edge region of which there is disposed a lateral boundary W which fully encloses the tray B and forms a volume V comprising catalytic and/or noncatalytic shaped bodies (F), wherein there is at least one braid made of precious metal and/or base metal on the upstream side opposite the tray B, and the catalytic and/or noncatalytic shaped bodies (F) are selected from (i) shaped bodies (F1) in the form of straight prisms, the footprint of which is selected from triangle, rectangle, hexagon or fragments of these polygons, and (ii) a combination of the shaped bodies (F1) with shaped bodies (F2) that are smaller than the shaped bodies (F1), wherein groups of m to n shaped bodies (F1), m and n being an integer from 3 to 30 with n>m, are framed in a metal cassette open in the upstream direction and closed in the downstream direction by a gas-permeable tray, in a virtually seamless manner with side face to side face and with their longitudinal axis aligned in vertical direction, virtually completely covering the cross section of the tray, to form modules (M), and the modules (M), optionally with cooperation of a joint filler material, with vertical alignment of the longitudinal axis of the shaped bodies (F1), are joined to one another virtually seamlessly in a mosaic-like manner.