Process for preparing a solid comprising the stages of: a) mixing a set comprising at least two Cu 2 2 CO 3 powders with different particle sizes and at least one binder, wherein: - said set comprises from 0.1% to 99.9% by weight of a first malachite powder, the D 50 of which is between 1 and 15 μm, and from 99.9% to 0.1% by weight of a second malachite powder, the D 50 of which is between 25 and 100 μm, the percentage by weight being expressed with respect to the total weight of the malachite powders, - the weighted medium diameter (Dm) of said set is between 10 and 45 μm, said weighted medium diameter being calculated by the formula: Dm = ∑ 1 n x n Pn × D 50 Pn with: x n (Pn) being the fraction by weight of the malachite powder Pn in said assembly, D 50 (Pn) being the D 50 of the malachite powder Pn of said set; b) bringing the mixture of stage a) into contact with an aqueous solution and kneading the paste obtained; c) extruding the paste kneaded in stage b) at a pressure of between 3 and 25 MPa; d) calcining the extrudates at a temperature of between 140°C and 500°C and for a period of time of between 10 min and 6 hours, under a gas stream comprising oxygen; wherein the prepared solid comprises from 50% to 99% by weight, equivalent by mass, of CuO and from 1% to 50% by weight of binder, the percentages by mass being measured after loss on ignition and decomposition of the precursors at 550°C over 2 h at 550°C over 2 h. a) mixing a set comprising at least two Cu 2 2 CO 3 powders with different particle sizes and at least one binder, wherein: - said set comprises from 0.1% to 99.9% by weight of a first malachite powder, the D 50 of which is between 1 and 15 μm, and from 99.9% to 0.1% by weight of a second malachite powder, the D 50 of which is between 25 and 100 μm, the percentage by weight being expressed with respect to the total weight of the malachite powders, - the weighted medium diameter (Dm) of said set is between 10 and 45 μm, said weighted medium diameter being calculated by the formula: Dm = ∑ 1 n x n Pn × D 50 Pn with: x n (Pn) being the fraction by weight of the malachite powder Pn in said assembly, D 50 (Pn) being the D 50 of the malachite powder Pn of said set; - said set comprises from 0.1% to 99.9% by weight of a first malachite powder, the D 50 of which is between 1 and 15 μm, and from 99.9% to 0.1% by weight of a second malachite powder, the D 50 of which is between 25 and 100 μm, the percentage by weight being expressed with respect to the total weight of the malachite powders, - the weighted medium diameter (Dm) of said set is between 10 and 45 μm, said weighted medium diameter being calculated by the formula: Dm = ∑ 1 n x n Pn × D 50 Pn with: x n (Pn) being the fraction by weight of the malachite powder Pn in said assembly, D 50 (Pn) being the D 50 of the malachite powder Pn of said set; x n (Pn) being the fraction by weight of the malachite powder Pn in said assembly, D 50 (Pn) being the D 50 of the malachite powder Pn of said set; b) bringing the mixture of stage a) into contact with an aqueous solution and kneading the paste obtained; c) extruding the paste kneaded in stage b) at a pressure of between 3 and 25 MPa; d) calcining the extrudates at a temperature of between 140°C and 500°C and for a period of time of between 10 min and 6 hours, under a gas stream comprising oxygen;