**2. Materials and Methods**

### *2.1. Synthesis and Characterisation of LTL-Type Zeolite Nanoparticles*

The Linde Type L (LTL) zeolite suspensions were prepared in the following manner. Firstly, solution A was prepared by dissolving 2.19 g of KOH (ACS reagent, ≥85%, pellets, Sigma-Aldrich, Saint-Quentin Fallavier, France) and 0.49 Al(OH)3 (reagent grade, Sigma-Aldrich) in 6.94 g of doubly distilled water at room temperature and stirred until the water was clear. Solution B was prepared by dissolving 1.09 g of KOH (ACS reagent, <sup>≥</sup>85%, pellets, Sigma-Aldrich) and 10 g of LUDOX® SM 30 colloidal silica (30 wt.% suspension in H2O, Sigma-Aldrich) in 3.47 g of doubly distilled water at room temperature and stirred until the water was clear. Afterwards, solution A was added dropwise into solution B under vigorous stirring at room temperature to achieve a non-opaque suspension, free of organic template, with the following molar composition: 5 K2O:10 SiO2:0.5 A12O3:200 H2O [12]. The as-prepared precursor mixture was aged at room temperature for 24 h prior to hydrothermal treatment at 170 ◦C for 18 h. Upon completing the crystallization process, the nanosized product was washed with doubly distilled water and recovered by multistep centrifugation (20,000 rpm, 40 min) until pH = 8. The final stabilized nanocrystal suspension had a concentration of approximately 1.5 wt.%.

Dynamic light scattering and X-ray diffraction measurements were carried out to determine the size of the nanoparticles and to confirm their crystalline structure, respectively. The agglomeration and average size of particles and the aggregates in the crystalline suspensions were determined using dynamic light scattering (DLS) performed with a Malvern Zetasizer Nano instrument (Malvern, UK), scattering angle of 173◦, laser wavelength of 632.8 nm and output power of 3 mW). X-ray diffraction measurements were operated on a PANalytical X'Pert Pro diffractometer (Almelo, The Netherlands) using the Cu Kα monochromatized radiation (α = 1.54059 Å). A detailed crystal morphology, particle size distribution and crystallinity of the LTL zeolite were examined by field-emission scanning electron microscope (FESEM) using a TESCAN Mira (Brno, Czech Republic) operating at an accelerating voltage 30 kV, and high-resolution transmission electron microscope (HRTEM) using a Tecnai G2 30 UT (LaB6, Hillsboro, OR, USA) operated at 300 kV with 0.17 nm point resolution equipped with an EDAX EDX detector (Mahwah, NJ, USA).
