Modular reactor panel (1) for catalytic processes, comprising a feed header (5), a product header (7) and adjacent channels (3), each channel (3) having a length, running from an entrance end to an exit end, and wherein the entrance ends are directly connected to and open into the feed header (5) and the exit ends are directly connected to and open into the product header (7) and wherein the feed header (5) has at least one connection (9) to a feed line (51) and the product header (7) has at least one connection to a product line (55) and wherein part (21) of at least one of the feed header (5) and the product header (7) is detachable giving access to the channel ends and reactor comprising a housing (47) containing one or more of said reactor panels (1, 29), the reactor further comprising a feed line (51) and a product line (55), the panels (29) being connected to the feed line (51) and to product line (55).