## 3 Materials and Methods
### Characterization of the Catalysts  
X-ray fluorescence (XRF) analyses were made under vacuum on a Shimadzu EDX-720 (Tokyo, Japan) equipped with a rhodium tube as the X-ray source. X-ray diffraction (XRD) patterns were obtained on a Rigaku Ultima IV diffractometer (Tokyo, Japan) with CuK\(\alpha\) radiation (\(\lambda\) = 0.15409 nm) at 1\({}^{\circ}\) min\({}^{-1}\), 20 range between 2 and 80\({}^{\circ}\), and a step of 0.01\({}^{\circ}\). For peak deconvolution, Gaussian functions were fitted with an exponential decay baseline using the Peak Analyzer tool in OriginPro 2019. The calculation of the cell lattice parameter (\(a\)) was made using crystallographic knowledge of hexagonal crystal lattices and Bragg's law [95] according to Equations (1) and (2):  
\[a=(2/3^{1/2})d_{100} \tag{1}\]  
\[d_{100}=2d_{200} \tag{2}\]  
where \(d_{100}\) and \(d_{200}\) are interplanar spaces of the 100 and 200 reflections, respectively. Fourier transform infrared spectroscopy (FTIR) spectra were obtained on a Varian 640-IR (Palo Alto, CA, USA) using a 4 cm\({}^{-1}\) resolution, 32 scans, and 1 wt.% of sample in KBr pellets. The Raman spectroscopy measurements were performed on an In-Via\({}^{\mathrm{TM}}\) Raman system from Renishaw (Wotton-under-Edge, Glos., England) equipped with a thermoelectric cooled CCD detector and a 1200 lines/groove diffraction grating. A Leica microscope (Wetzlar, Germany) with a 50\(\times\) objective lens was used to focus the radiation of the excitation laser on the sample and to collect the scattered photons. The wavenumbers were calibrated using the Raman phonon of a silicon wafer at 520.5 cm\({}^{-1}\). Each spectrum was the accumulation of 10 scans with a 20 s integration time at 632.8 nm (HeNe laser). All Raman spectra were recorded at a laser power of 20 mW and the nominal spectra resolution was 6 cm\({}^{-1}\). A 1 mm optical path quartz cuvette was used to perform Raman measurements of the solutions. All Raman measurements were performed at room temperature. Diffuse reflectance UV-Vis spectroscopy (UV-Vis-DRS) spectra were obtained on a Varian Cary 5000 UV-Vis-NIR spectrophotometer (Palo Alto, CA, USA) equipped with a Harrick diffuse reflectance accessory and using BaSO4 as a background standard. The optical band gap was calculated using the Davis-Mott method [96], in which a plot is done according to Equation (3). After obtaining the Davis-Mott plot, an extrapolation to zero of the linear portion where the curvature of the graph first changes gives the optical band gap value:  
\[[\alpha hv]^{1/n}=A(E_{g}-hv) \tag{3}\]  
where \(\alpha\) is the absorption coefficient, replaced in this work by the Kubelka-Munk function, \(F(R)\); \(E_{g}\) is the optical band gap; \(hv\) is energy; \(A\) is a proportionality constant; and \(1/n\) is a coefficient dependent on the type of transition responsible for the absorption edge observed. Nuclear magnetic resonance (NMR) experiments were conducted in the solid state at 14 T with a Bruker AscendTM 600 (Kontich, AN, Belgium) equipped with a 4 mm magic-angle spinning (MAS) probe and zirconia rotors. \({}^{29}\)Si MAS-NMR spectra (119.237 MHz) were obtained with spinning rate at 10 kHz, pulse length of 4.25 us (\(\pi\)/2), 512 scans, and a recycle delay of 20 s. The spectra were referenced to TMS (\(\delta\) = 0.0 ppm). The molar percentage of silanol groups (Si molar%) was calculated using Equation (4) [97]:  
\[\text{Si molar\%}=[(2Q^{2}+Q^{3})/(Q^{2}+Q^{3}+Q^{4})]100 \tag{4}\]  
where \(Q^{2}\), \(Q^{3}\), and \(Q^{4}\) correspond to the relative proportions in the percentage of geminal silanols, terminal silanols, and siloxane groups, respectively. Peak areas were obtained after deconvolution by fitting the signals to Voigt peaks in the range between \(-110\) and \(-90\) ppm.