3.2.2. Catalyst Characterization

Powder X-ray di ffraction (XRD) was performed on a Rigaku Smartlab SE X-ray di ffractometer with a Cu-k α radiation source at a tube voltage of 40 kV and a tube current of 25 mA. Di ffraction patterns were recorded between 5◦ and 60◦. FI-IR spectroscopy was measured on a Nicolet 380 spectrometer over a range of 4000 cm<sup>−</sup>1–400 cm<sup>−</sup><sup>1</sup> at a resolution of 4 cm<sup>−</sup>1. N2 adsorption–desorption isotherms were collected by a Gemini VII analyzer. Prior to the tests, about 100 mg samples were degassed at 250 ◦C for 4 hours. Then, the sample completing the pretreatment was subjected to a nitrogen adsorption–desorption isotherm test at a liquid nitrogen temperature (77 K). DR UV-Vis was performed on a TU-1901 spectrophotometer in the wavelength range from 800 to 190 nm. The induced coupled plasma-atomic emission spectroscopy (ICP-AES) was carried out using a 1000-type spectroscopy. The sample of the catalyst is completely dissolved by 40% HF, and the sample was made up to 50 mL with water after HF removal by electric heating plate. The metal content in the catalyst is quantitatively detected. The loading e fficiency (*e*) of Ni on TS-1 was calculated based on the actual loading of Ni element measured and the amount of Ni in the impregnating solution. TGA measurements were rendered on a DTG60A thermogravimetric analyzer from room temperature to 800 ◦C at the rate of 10 ◦C/min. The weight loss rate was the ratio of weight loss mass of catalyst to original mass of catalyst. The X-ray photoelectron spectroscopy was collected by A ESCALAB250 spectroscopy. Scanning electron microscopy (SEM) was performed on a JSM-6700F cold field high-resolution emission scanning electron microscope.

### 3.2.3. Point of Zero Charge (PZC) of Catalyst

The point of zero charge of catalyst (pHPZC) was determined by the salt titration method: 0.4 mol/L NaNO3 solution was prepared. We took 20 mL NaNO3 solution and adjusted the pH to 2, 3, 4, 5, 6, 7, and 8 with NaOH or H2SO4. Then, 0.2 g catalyst was added to shake for 0.5 h until the pH was stabilized, and the pH change value ( pH) before and after the addition of catalyst was calculated. The initial pH was horizontal coordinate and pH was vertical coordinate. When the ordinate is zero, the pH value is PZC.
