Catalytic chemical reactor comprising a catalytic bed and a gas-permeable wall facing the catalytic bed, characterized in that: said gas-permeable wall is an assembly of a plurality of panels and each of said panels extends over an angular sector of said permeable wall and comprises first wall sectors which bear against a supporting wall (2, 4) adjacent to the gas permeable wall, and second wall sectors which are spaced from said supporting wall, the first sectors and the second sectors alternating with each other along the circumferential extension of the permeable wall; wherein said supporting wall (2, 4) is cylindrical or substantially cylindrical, wherein said second wall sectors comprise passages for a gas; the reactor further comprising local securing means of said gas-permeable wall to said supporting wall, said securing means comprising: a plurality of supports firmly fixed to the supporting wall and passing through respective openings of the first sectors of the gas-permeable wall; a respective plurality of locking elements which can be associated with said supports, the panels of the gas-permeable wall being clamped between said supporting wall and said locking elements; wherein said panels, being fixed together and secured to the supporting wall, form a single wall element which delimits the catalytic bed; and wherein said gas-permeable wall operates as a gas distributor or collector with respect to the catalytic bed. said gas-permeable wall is an assembly of a plurality of panels and each of said panels extends over an angular sector of said permeable wall and comprises first wall sectors which bear against a supporting wall (2, 4) adjacent to the gas permeable wall, and second wall sectors which are spaced from said supporting wall, the first sectors and the second sectors alternating with each other along the circumferential extension of the permeable wall; wherein said supporting wall (2, 4) is cylindrical or substantially cylindrical, wherein said second wall sectors comprise passages for a gas; the reactor further comprising local securing means of said gas-permeable wall to said supporting wall, said securing means comprising: a plurality of supports firmly fixed to the supporting wall and passing through respective openings of the first sectors of the gas-permeable wall; a respective plurality of locking elements which can be associated with said supports, the panels of the gas-permeable wall being clamped between said supporting wall and said locking elements; wherein said panels, being fixed together and secured to the supporting wall, form a single wall element which delimits the catalytic bed; and wherein said gas-permeable wall operates as a gas distributor or collector with respect to the catalytic bed. a plurality of supports firmly fixed to the supporting wall and passing through respective openings of the first sectors of the gas-permeable wall; a respective plurality of locking elements which can be associated with said supports, the panels of the gas-permeable wall being clamped between said supporting wall and said locking elements; wherein said panels, being fixed together and secured to the supporting wall, form a single wall element which delimits the catalytic bed; and wherein said gas-permeable wall operates as a gas distributor or collector with respect to the catalytic bed.