NOVELTY - A plate (10a), to be integrated in a plate stack of a heat exchanger system, has several channels (38) distributed in rows (40). Each row has opposite side walls (42) spaced along a first direction (44), such that two successive side walls define one of the channels, the rows being opposite and spaced along a second direction (46) perpendicular to the first. The fluid circulation zone (20) of the plate incorporates the channels, a catalytic coating being present in the channels only.    USE - The plates are useful in micro-heat exchangers, also serving as micro-reactors for carrying out catalytic chemical reactions. The plates are especially used in the claimed heat exchangers, steam reforming systems and fuels cells. Other possible applications include water or carbon dioxide reforming of hydrocarbons, catalytic dehydrogenation of cycloalkenes (e.g. conversion of methyl-cyclohexane to toluene) and catalytic combustions for vaporizing liquids (e.g. water), generating electric current (e.g. using Peltier or thermoionic effects), reheating fluids (e.g. in portable mini-reheater) or cooling.    ADVANTAGE - The selective distribution of catalyst in channel elements in spaced rows provides a highly even surface temperature in the plate, with no hot and cold spots. The plates provide heat exchangers having a high ratio of exchange surface to volume.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for    (1) a heat exchanger system, comprising a stack of plates alternately (in the direction of the stack) forming first and second fluid circulation zones, the first zone being at least partially coated with catalyst, where at least one of the plates is a plate (10a) as described above, forming at least part of one of the first circulation zones;    (2) a steam reforming system having a heat exchanger system as above, the reforming system being such that an exothermic catalytic reaction occurs in each first fluid circulation zone and a hydrogen generating endothermic steam reforming reaction occurs in each second fluid circulation zone; and    (3) a fuel cell installation, comprising a fuel cell and a steam reforming system as above.    DESCRIPTION OF DRAWING(S) - The figures show a detailed perspective view of a plate forming an integral part of a steam reforming system; and a plan view of the plate.    Burner plate (10a)    Stacking direction (12)    Fluid circulation zone (20)    Fluid inlet (24)    Main fluid distributor (26)    Secondary fluid distributor (28)    Secondary fluid collector (32)    Main fluid collector (34)    Channels (38)    Rows (40)    Side walls (42)    First direction (44)    Second direction (46)    Face of plate (48)    Wall element (50)    Side face (52)