*4.4. Catalyst Characterization*

The investigation of the phase composition of the catalysts was carried out by the Rigaku DX-2700 (Rigaku, Tokyo, Japan) diffractometer equipment with Cu-Kα (λ = 0.154 nm) as the radiation source. The scan started from 10 to 80◦ with a scanning rate of 0.06◦/s. The results of the specific surface area and pore size distribution of the catalysts were obtained by nitrogen adsorption and desorption experiments on V-SorbX800 (Jin Aipu, Beijing, China) equipment at −196 ◦C. The microstructure of the fresh catalysts was investigated by an FEI Tecnai G2 F20 (GCEMarket, Blackwood, NJ, America) Transmission electron microscopy (TEM) equipped with a HAADF detector. The TEM experiment was carried out in an accelerated voltage environment of 2000 volts. The X-ray photoelectron spectroscopy was obtained by the PHI 5000 (Ulvac-PHI, Inc., Kanagawa, Japan) spectrometer with Al Kα as the radiation. The obtained binding energy was calibrated with C1s (284.8 eV) as the internal reference standard. AutoChem2920 (Micromeritics Instrument Corp, Norcross, GA, USA) chemisorption analyzer was used to analyze the reduction performance of the fresh catalysts. Before the reduction process, 30 mg prepared catalyst was pretreated at 300 ◦C for 1 h in an N<sup>2</sup> atmosphere (30 mL/min) to remove oxygen.
