Synthesis of a catalyst comprising a high-purity nu-86 zeolite and iron for the converson of nox and n2o

A process for preparing a catalyst comprising a zeolite of Nu-86 structural type and on iron, said process comprising at least the following steps:

• i) mixing, in aqueous medium, of at least one source of silicon (Si) in SiO2 oxide form, at least one source of aluminum (Al) in Al2O3 oxide form, a nitrogen-containing organic compound R, R being octamethonium bromide (OctBr2), at least two sodium sources, one of these being sodium bromide (NaBr), the reaction mixture having the following molar composition:
• SiO2/Al2O3 of between 8 and 20,
• H2O/SiO2 of between 15 and 60,
• R/SiO2 of between 0.05 and 0.35,
• Na2O/SiO2 of between 0.05 and 0.3,
• NaBr/SiO2 of between 0.01 and 0.1, limits included,
• step i) being conducted for a duration of between 5 and 15 minutes until a homogeneous mixture referred to as precursor gel is obtained;
• ii) maturation of the precursor gel obtained at said step i) at a temperature of between 2° and 100° C., with or without stirring, for a duration of between 10 minutes and 48 hours, preferably between 18 and 24 hours;
• iii) hydrothermal treatment of said precursor gel obtained at step ii) at a temperature of between 120° C. and 220° C., preferably between 14° and 195° C., for a duration of between 12 hours and 35 days, preferably between 12 hours and 33 days, until said Nu-86 zeolite forms;
• iv) at least one ion exchange, comprising bringing said zeolite obtained at the preceding step into contact with a solution comprising at least one species capable of releasing iron, in solution in reactive form with stirring at a temperature between 2° and 95° C., preferably between 40 and 90° C., for a duration of between 1 hour and 2 days;
• v) heat treatment by drying of the Nu-86 zeolite obtained on conclusion of the preceding step at a temperature of between 2° and 150° C. for a duration of between 2 and 24 hours followed by at least one calcination under a stream of air at a temperature of between 40° and 700° C. for a duration of between 2 and 20 hours.