Increasing the stability of the Ge-containing extra-large pore ITQ-33 zeolite by post-synthetic acid treatments

Extra-large pore ITQ-33 zeolite (ITT, 18 x 10 x 10-rings) is a very promising catalyst for the catalytic cracking of gasoil but, unfortunately, this material shows a limited hydrothermal stability due to the large germanium content present in the ITQ-33 structure. Taking this into account, the Ge-containing ITQ-33 has been post synthetically modified using different acid procedures with the aim of studying the effect of these treatments on the overall hydrothermal stability of this extra-large pore zeolite. In this sense, the as-prepared ITQ-33 has been treated with different HCl solutions in ethanol (from 0.1 to 1 M), containing also tetraethylorthosilicate (TEOS) as silicon precursor, at different temperatures (150-175 degrees C). From the different acid treatments, it is observed that treating ITQ-33 with a TEOS-containing 1 M HCl solution in ethanol at 150 degrees C for 24 h, allows increasing the Si/Ge ratio from 2 to 3.2, mostly preserving the crystalline structure. If this acid-treatment is repeated three consecutive times, the Si/Ge can be increased up to 7.5, resulting in a highly stable extra-large pore zeolite. This post-synthetically modified ITQ-33 zeolite has been characterized by different techniques, including PXRD, FESEM, N-2 and Ar adsorption, ICP and Al-27 MAS NMR to unravel its physico-chemical properties. Finally, the catalytic behavior of the treated ITQ-33 zeolite has been tested for the catalytic cracking of gasoil, confirming in this way a remarkably higher hydrothermal stability when compared to the as-prepared Ge-rich ITQ-33, permitting its regeneration for successive catalytic cycles.