*2.3. Analytical Methods*

The crystalline structure of the catalyst, support, and active phase was evaluated by X-Ray Powder Diffraction (XRD) using a PANalytical Model Empyrean X-ray diffractometer with CuKα 2θ radiation (λ = 1.5418 Å) at 40 kV and 30 mA, angle ranging between 10◦ and 90◦, at step size of 0.02◦ and countdown time of 50 s per run. The catalyst surface morphology and structure were analyzed by SEM/EDX using Hitachi TM 3000 and Swifted 3000 equipment.

The textural properties of catalysts were investigated by specific surface area analysis using Quantachrome NOVA 2200e. For performing the analysis, a sample of 0.2 g was added to a glass cell and heated at 200 ◦C for 2 h under vacuum in order to remove impurities adsorbed on the catalyst surface. Specific surface area and pore volume were calculated by the Brunauer–Emmett–Teller (BET) the Barrett–Joyner–Halenda (BJH) methods, respectively.

The catalyst surface acidity was determined by acid-base titrations. In this analysis, 0.1 g of catalyst was suspended in 20 mL of 0.1 M NaOH. The suspension was stirred for 3 h at room temperature and then titrated with 0.1 M HCl in the presence of phenolphthalein. The catalyst surface acidity was expressed in mmol <sup>H</sup>+/g catalyst. The active phase thermal stability was evaluated by thermogravimetry (TGA) and derivative thermogravimetry (DTG) analysis using a Shimadzu TGA 50 equipment with 50 mL/min of nitrogen flow, heating rate of 10 ◦C/min in a temperature range of 30 to 1000 ◦C.

Glucose concentration was determined by high performance liquid chromatography (HPLC) using an Agilent Technologies 1260 Infinity chromatograph equipped with an isocratic pump, a refractive index detector and a Bio-Rad Aminex HPX-87H column (300 × 7.8 mm). Operational conditions were temperature of 45 ◦C, 0.005 mol/L using sulfuric acid as eluent at a flow rate of 0.6 mL/min and sample volume of 0.02 mL. HMF concentration was also determined by HPLC, but using a UV detector (at 276 nm), a Waters Spherisorb C18 5 μm column (100 × 4.6 mm) at room temperature, 1:8 *v*/*v* acetonitrile-to-water ratio using 1% of acetic acid as eluent, flow rate of 0.8 mL/min, and sample

volume of 0.02 mL. Glucose conversion (XGlu) and HMF yield (YHMF) were calculated according to Equations (1) and (2).

$$X\_{\rm Glu}(\%) = \frac{[\rmGlucose]\_{initial} - [\rmGlucose]\_{final}}{[\rmGlucose]\_{initial}} \cdot 100,\tag{1}$$

$$\Upsilon\_{HMF}(\text{\textquotedblleft}\_{0}) = \frac{[HMF]\_{\text{produced}}}{[Glucose]\_{initial}} \cdot 100.\tag{2}$$
