NOVELTY - A reactor for catalytic reactions with strong heat change in a process fluid, e.g. synthesis, hydrogenation or oxidation, has channels for process fluid and heat exchange medium between plates with catalyst coating towards process fluid.    USE - The reactor is used for carrying out an endothermic or exothermic reaction, preferably synthesis of methanol or higher alcohols, hydrogenation of hydrocarbons, especially selective hydrogenation of acetylene to ethylene or non-selective hydrogenation of ethylene to ethane, methanization or methane synthesis, carbon monoxide conversion, the Fischer-Tropsch synthesis, epoxidation, ethylene oxide synthesis, the Claus reaction, direct oxidation of hydrogen sulfide to sulfur, oxidation of sulfur dioxide to sulfur trioxide or ammonia synthesis (all claimed).    ADVANTAGE - Existing adiabatic reactors (mainly tube aggregate reactors) have numerous components or are costly. An existing reactor, with bent plates forming channels with reaction medium containing catalyst sandwiched between channels with heat exchange medium, develops a temperature profile and also requires a pressure-tight outer container. As only the average temperature can be controlled, optimum conversion and selectivity cannot be attained and local over-heating can occur. The present reactor avoids these drawbacks. No significant temperature profile can develop, as heat is supplied or removed by the shortest path. As the side sections can form mantle sections, forming a pressure-tight square block with the plates and collectors, the reactor can be operated at pressures of over 25 bar.    DETAILED DESCRIPTION - In a reactor for catalytic reactions with strong heat change in a process fluid, with spaced parallel plates forming flat channels between their opposite faces, in which the process fluid is passed through channels containing a solid catalyst and a heat exchange medium in indirect thermal contact with the process fluid is passed through other channels, the plates are smooth, grooved or ribbed and the surfaces facing the process fluid are (partly) coated with the catalyst.    DESCRIPTION OF DRAWING(S) - The drawing shows a 3-dimensional view of a reactor as used in the example.    Spaced parallel plates (1)    Channels for process fluid (2)    Channels for cooling medium (3)    Boundary plates (4)    Webs between plates and/or fins and plates (5)    Catalyst (6)    Reactor (7)    Stream containing acetylene (8)    Stream containing ethylene (9)    Liquid butane stream (10)    Gas stream (11)