Reactor with a catalytic bed

A catalytic reactor, comprising:

• a catalytic bed suitable for a chemical reaction of conversion of a gaseous charge into a gaseous product, said catalytic bed having an annular-cylindrical geometry, said catalytic bed including at least one collector made with a gas-permeable cylindrical wall;
• and
• an outer collector and an inner collector;
• wherein said at least one collector includes at least one annular layer of a first granular material that includes a catalyst adapted to catalyse said reaction of conversion, and at least one annular layer of a second granular material;
• wherein the second granular material is coarser than the first granular material, the second granular material having a larger particle size than the first granular material;
• wherein said at least one collector includes an outlet collector and said layer of second granular material is adjacent to and in contact with said outlet collector, so that said layer of first granular material is separated from the collector by the layer of second granular material;
• wherein said outer collector and said inner collector are cylindrical, coaxial, and gas-permeable;
• wherein said outer collector and said inner collector include two annular layers of said second granular material;
• wherein a first layer of said second granular material is in contact with the outer collector and a second layer of said second granular material is in contact with the inner collector;
• wherein the layer of the first granular material is a central layer located between said first layer and said second layer of the second granular material.