## 2 Materials and Methods
### Material Characterization Techniques  
The phase purity and crystallinity of the samples were examined by X-ray powder diffraction (XRPD). XRPD data were collected using the Bruker D8 Advance Da Vinci powder diffractometer, which operates in Bragg-Brentano geometry and is equipped with a Cu-anode X-ray tube, a Ni-filter to suppress CuK\(\beta\) component, and a LynxEye XE silicon strip detector set to discriminate CuK\(\alpha_{1,2}\) radiation. The sample was mounted on a PMMA (polymethyl methacrylate) holder with pseudo-lateral loading, and a knife, perpendicular to the sample, was placed at a suitable distance from the sample surface to reduce the air-induced scattering. The samples were scanned in a continuous mode from 5 to 90\({}^{\circ}\) 20 with a step size of 0.02\({}^{\circ}\) 20 and a counting time of 2 s per step. Qualitative phase identification was conducted using the EVA software v.7.1 (Bruker), and the XRPD patterns obtained were refined using the Rietveld method (TOPAS v.7.0, Bruker and GSAS software in EXPGUI graphical interface), starting from the structural model reported by [PERSON] et al. (2018) for the same 13X used in this work [27]. The thermal behaviors of the samples were analyzed by thermogravimetric (TG) and differential thermal (DTA) analyses. TG analysis was carried out on both the unloaded and loaded powder samples under constant and controlled synthetic air-flow conditions using an STA 409 PC LUXX(r)--Netzch instrument (Geratebau, Germany). The heating rate was set at 10 \({}^{\circ}\)C/min, with the temperature ranging from room conditions (RT) to 1200 \({}^{\circ}\)C. Approximately 30 mg of sample was used for each test. Alumina (Al2O3) was used as the control and standard. Scanning electron microscopy (SEM) analyses were performed at the MEMA Center of the University of Florence (Italy). The samples were prepared by placing an aliquot of powder on double-sided conductive carbon tape on aluminum stubs. A carbon coating was applied to the top of the supports to ensure electrical conductivity. The choice of the carbon layer was made with the intention of providing preferential access to the microchemical information. Conversely, high-magnification morphological investigations (magnification: \(>\) 6000\(\times\)) were affected by a certain amount of noise. The samples were examined with a ZEISS EVO MA15 SEM equipped with an Oxford INCA 250 energy-dispersive X-ray (EDS) spectrometer for microanalysis. The operating accelerating voltage was maintained at 20 kV. The EDS peak quantification was automatically performed by Gaussian fitting of the peak profile, considering corrections for atomic number, absorption, and fluorescence (ZAF). Although the EDS microchemical information was semi-quantitative in nature, the spectral response was calibrated with respect to a metallic Co reference sample analyzed under the same conditions. All samples were subjected to at least 6 different microanalyses: 3 different raster analyses were conducted at 500\(\times\) magnification over the whole analytical field, while 3 different point analyses were performed at three points of a further analytical field at a magnification of 4000\(\times\). For all fields, high-resolution morphological micrographs were obtained using either secondary electrons (SEs) or backscattered electrons (BSEs) or both. X-ray photoelectron spectroscopy (XPS) measurements were conducted using a Kratos AXIS Ultra\({}^{\text{DLD}}\) instrument (Kratos Analytical, Manchester, UK) equipped with a hemispherical analyzer and a monochromatic Al K\(\alpha\) X-ray source (1486.6 eV) in spectroscopy mode. For the measurements, the powders were deposited on carbon tape and placed on a silicon support. Samples were analyzed at a 0\({}^{\circ}\) take-off angle between the sample surface normal and the analyzer axis, corresponding to a sampling depth of approximately 10 nm. A survey spectrum (binding energy range: \(-\)5 to 1350 eV) was acquired for each sample to identify surface elements.