Development and use of an iron-based catalyst for implementing an oxidation-reduction process for substances to be reduced

Method for the implementation of an oxidation-reduction process by means of at least one lamellar double hydroxide (LDH) as catalyst or as precursor of said catalyst, with the same crystalline structure as that of said catalyst, said LDH containing a divalent cation M2+ partially or completely substituted with FeII, and a trivalent cation T3+ optionally substituted with FeIII, of the following general formula:

• [M2+(z)FeII(1−y−z)T3+tFeIII(y−t)O2H2]n+[(y/n)An−,mH2O]n−,
• in which:
• ¼<y<⅓, z<1−y and t<y, An− is an anion with charge n, n having the values 1, 2 or 3, m is an integer varying from 1 to 10,
• and the ratio x=(y−t)/(1−z−t) can vary from 0 to 1,
• said LDH being used in association with iron-reducing bacteria that are able to reduce FeIII to FeII and in the presence of organic matter, and can be deprotonated to give the following formula:
• [M2+(z)FeII(1−y−z−w)T3+tFeIII(y−t+w)O2H2−w]n+[(y/n)An−,mH2O]n−,
• in which:
• A, y, z, m and n are as above,
• and the ratio x=(y−t+w)/(1−z−t) can vary from 0 to 1, in order to reduce a substance S to a substance Sreduced, the redox potential of the pair Sreduced/S being greater than that of the pair FeII/FeIII at the crystallographic sites of the FeII, x varying essentially in the range from 0.33 to 0.66 after the start-up of the oxidation-reduction process, and without a substantial change in the crystalline structure of the aforesaid LDH.

Process permitting the reduction of a substance S to a substance Sreduced comprising:

• introducing a LDH, as catalyst or precursor of said catalyst with the same crystalline structure as that of said catalyst,
• said LDH containing a divalent cation M2+ partially or completely substituted with FeII, and a trivalent cation T3+ optionally substituted with FeIII, of the following general formula:
• [M2+(z)FeII(1−y−z)T3+tFeIII(y−t)O2H2]n+[(y/n)An−,mH2O]n−
• in which:
• ¼<y<⅓, z<1−y and t<y, An− is an anion with charge n, n having the values 1, 2 or 3, m is an integer varying from 1 to 10,
• and the ratio x=(y−t)/(1−z−t) varies from 0 to 1,
• said LDH being used in association with iron-reducing bacteria able to reduce FeIII to FeII and in the presence of organic matter,
• if x is greater than 0.66 at the initial moment, a start-up phase of the oxidation-reduction process corresponding to the reduction of FeIII to FeII within said LDH by said iron-reducing bacteria, leading to a change in x to a value less than or equal to 0.66, in order to obtain said LDH in the form of a catalyst, without a substantial change in the crystalline structure of said LDH,
• a phase of catalytic reduction of the substance S, added to the whole comprising the LDH, the bacteria and the organic matter, to a substance Sreduced by oxidation of the FeII to FeIII within said LDH coupled to a stage of catalytic oxidation of the organic matter by reduction of the FeIII to FeII, the redox potential of the pair Sreduced/S being greater than that of the pair FeII/FeIII at the crystallographic sites of the FeII.

Process permitting the reduction of a substance S to a substance Sreduced comprising:

• introducing a LDH, as catalyst precursor, said LDH containing a divalent cation M2+ partially or completely substituted with FeII, and a trivalent cation T3+ optionally substituted with FeIII, of the following general formula:
• [M2+(z)FeII(1−y−z)T3+tFeIII(y−t)O2H2]n+[(y/n)An−,mH2O]n−
• in which:
• ¼<y<⅓, z<1−y and t<y, An− is an anion with charge n, n having the values 1, 2 or 3, m is an integer varying from 1 to 10,
• and the ratio x=(y−t)/(1−z−t) can vary from 0 to 1, said LDH being used in association with iron-reducing bacteria able to reduce FeIII to FeII and in the presence of organic matter,
• if x is greater than 0.66 at the initial moment, a start-up phase of the oxidation-reduction process corresponding to the reduction of FeIII to FeII within said LDH by said iron-reducing bacteria, leading to a change in x to a value less than or equal to 0.66, in order to obtain said LDH in the form of a catalyst, without a substantial change in the crystalline structure of said LDH,
• a phase of catalytic reduction of the substance S, added to the whole comprising the LDH, the bacteria and the organic matter, to a substance Sreduced by oxidation of the FeII to FeIII within said LDH coupled to a stage of catalytic oxidation of the organic matter by reduction of the FeIII to FeII, the redox potential of the pair Sreduced/S being greater than that of the pair FeII/FeIII at the crystallographic sites of the FeII.

Product constituted by at least one LDH, said LDH containing a divalent cation M2+ partially or completely substituted with FeII, and a trivalent cation T3+ optionally substituted with FeIII, of the following general formula:

• [M2+(z)FeII(1−y−z)T3+tFeIII(y−t)O2H2]n+[(y/n)An−,mH2O]n−
• in which:
• ¼<y<⅓, z<1−y and t<y, An− is an anion with charge n, n having the values 1, 2 or 3, m is an integer varying from 1 to 10,
• and the ratio x=(y−t)/(1−z−t) can vary from 0 to 1, in crystalline form, the ratio of surface volume to specific volume being greater than 100, without a substantial change in the crystalline structure of said LDH.

Product constituted by at least one support coated with at least one LDH, said LDH containing a divalent cation M2+ partially or completely substituted with FeII, and a trivalent cation T3+ optionally substituted with FeIII, of the following general formula:

• [M2+(z)FeII(1−y−z)T3+tFeIII(y−t)O2H2]n+[(y/n)An−,mH2O]n−
• in which:
• ¼<y<⅓, z<1−y and t<y, An− is an anion with charge n, n having the values 1, 2 or 3, m is an integer varying from 1 to 10,
• and the ratio x=(y−t)/(1−z−t) can vary from 0 to 1, in crystalline form, the support being selected from sand, clay, polymer beads.

Kit comprising:

• at least one LDH, said LDH containing a divalent cation M2+ partially or completely substituted with FeII, and a trivalent cation T3+ optionally substituted with FeIII, of the following general formula:
• [M2+(z)FeII(1−y−z)T3+tFeIII(y−t)O2H2]n+[(y/n)An−,mH2O]n−
• in which:
• ¼<y<⅓, z<1−y and t<y, An− is an anion with charge n, n having the values 1, 2 or 3, m is an integer varying from 1 to 10,
• and the ratio x=(y−t)/(1−z−t) can vary from 0 to 1, in crystalline form,
• at least one support, selected from sand, clay, polymer beads,
• to be used simultaneously, separately or spread over time, intended for the implementation of a process for pollution control of a medium to be treated.