*2.3. Characterization of Catalysts*

### 2.3.1. XRD and FT-IR Characterization

The crystal structure information of commercial TS-1, M-TS-1, and XNi-TS-1 were analyzed by the XRD (Figure 2A,B). All samples exhibited same diffraction peaks at 2θ = 7.8◦, 8.8◦, 23.2◦, 23.8◦, and 24.3◦, which represented that the MFI skeleton structure of TS-1 was not changed or destroyed after metal modification. There was no characteristic diffraction peak of metal oxides in the XRD patterns. It may be that parts of metal entered the framework of TS-1 and a small amount of metal oxides were well dispersed on the TS-1 surface by the ultrasonic impregnation synthesis method [24].

The stretching vibration of chemical bonds or functional groups in the TS-1 and M-TS-1 samples were detected by FT-IR spectroscopy (Figure 2C). The vibration peaks at 550 cm<sup>−</sup><sup>1</sup> and 1225 cm<sup>−</sup><sup>1</sup> were characteristic peaks of the molecular sieve with MFI topology; 450 cm<sup>−</sup><sup>1</sup> was the bending vibration peak of Si–O bond; 1110 cm<sup>−</sup><sup>1</sup> and 800 cm<sup>−</sup><sup>1</sup> absorption peaks corresponded to antisymmetric and symmetrical stretching vibration of internal silicon-oxygen tetrahedral units [25]; the characteristic peak of 960 cm<sup>−</sup><sup>1</sup> indicated the existence of the tetra-coordinated framework titanium. After the metals

modified TS-1, the characteristic peak of 960 cm<sup>−</sup><sup>1</sup> still existed obviously. However, the modification of metals made the infrared absorption band shift at around 966 cm<sup>−</sup>1. In the different metals used to modify the TS-1 catalyst, the metal with the greatest wave number migration is Ni, followed by Fe, Co, and Ce. With the addition of Cu, wave number migration is almost not realized. The local FT-IR spectrum of XNi-TS-1 is shown in Figure 2D. It can be seen that the introduction of Ni caused a deviation in the IR absorption bands around 965 cm–1 to lower wave numbers. The wave number of [Ti–O] bond vibration decreased from 965.37 cm<sup>−</sup><sup>1</sup> to 962.11 cm<sup>−</sup><sup>1</sup> as the dosage of Ni increased from 1 wt % to 5 wt %, which indicated that the introduction of Ni weakened the [Ti–O] bond. It may be related to the charge transfer of [Ti–O] in the tetrahedral [26]. In other words, the interactions between Ni and Ti decreased the strength of the titanium oxygen bond and increased the electrophilicity of the Ti center as the dosage of Ni in the TS-1 increased, which made a substantial contribution to the satisfactory conversion of MEK to MEKO.

**Figure 2.** (**A**) XRD patterns of M-TS-1, (**B**) XRD patterns of XNi-TS-1, (**C**) FI-IR spectra of M-TS-1, and (**D**) FI-IR spectra of XNi-TS-1.
