Method for the preparation of synthetic crystalline zeolite materials with enhanced pore volume

A method for the preparation of a synthetic crystalline zeolite material comprising micropores and mesopores, said method either increasing the micropore volume without generating an additional mesoporosity, or creating uniform mesoporosity while maintaining or increasing the microporosity of said synthetic crystalline, said synthetic crystalline zeolite material having a silicon to aluminum molar ratio Si/Al≥1 and, wherein said method comprises at least the following steps:

• 1o) a step of dissolving a solid NH4F in a solvent creating a NH4F solution, said NH4F solution has a pH of approximately 7;
• 1) a step of contacting the NH4F solution with a dry starting crystalline zeolite material at a temperature ranging from 0° C. to 100° C., said NH4F solution having a NH4F mass concentration of at least 15 wt % and said starting crystalline zeolite material being a zeolite material in which the micropore volume represents more than 70% of the total pore volume and having a silicon to aluminum molar ratio Si/Al≥1, wherein said step 1) is carried out at a temperature ranging from 0° C. to 60° C.;
• 2) a washing step;
• 3) a drying step at a temperature ranging from 25° C. to 120° C., for 1 h to 24 h, to recover said synthetic crystalline zeolite material,
• wherein the pH of the NH4F solution during the contacting step is approximately 8 or greater, and
• wherein the Si/Al molar ratio of the dry starting crystalline zeolite material does not vary as a result of said method by more than about 1 from said silicon to aluminum molar ratio Si/Al≥1 of said synthetic crystalline zeolite material.