## 3 Results
### Raman Spectroscopic Analysis  
Phase transformations of titanium oxide with increase of the calcination temperature were also analyzed by Raman spectroscopy. Figure 4 shows evolution of the Raman spectra of the Pt/Ti-PLA (Figure 4a) and Pt/Ti-P25 (Figure 4b) samples depending on the calcination temperature. The optical  
Figure 3: (**a,c,d**) High-resolution transmission electron microscopy (HRTEM) and (**b**) high-angle annular dark-field imaging scanning transmission electron microscopy (HAADF-STEM) images for Pt/Ti-P25-400 sample. The inset shows the size distribution of platinum particles.  
range 300-800 cm\({}^{-1}\) is usually used to detect phase transformations of titanium oxide [38]. In this range, the B\({}_{\rm 1g}\) (396 cm\({}^{-1}\)), A\({}_{\rm 1g}\) + B\({}_{\rm 1g}\) (396 cm\({}^{-1}\)) and E\({}_{\rm g}\) (637 cm\({}^{-1}\)) modes related to TiO\({}_{2}\) anatase and E\({}_{\rm g}\) (444 cm\({}^{-1}\)), A\({}_{\rm 1g}\) (609 cm\({}^{-1}\)) modes related to TiO\({}_{2}\) rutile are located. The Pt/Ti-P25 catalyst changes significantly even after calcination at 600 \({}^{\circ}\)C (Figure 4b), as evidenced by the appearance of the rutile modes. For the Pt/Ti-PLA-600 sample the bands related to the rutile phase can hardly be noticed. Calcination at 800 \({}^{\circ}\)C in the case of both catalysts leads to a sharp increase of the intensity of the modes related to TiO\({}_{2}\)-rutile. The wide and intense lines completely mask the possible presence of the B\({}_{\rm 1g}\), A\({}_{\rm 1g}\) + B\({}_{\rm 1g}\) and E\({}_{\rm g}\) modes of TiO\({}_{2}\)-anatase.  
The presence of the anatase phase can be determined by analyzing the band at 144 cm\({}^{-1}\) corresponding to the E\({}_{\rm g}\) mode of the TiO\({}_{2}\)-anatase. Figure 5 shows that, in the case of a sample based on the PLA support, a significant part of TiO\({}_{2}\) anatase phase is present even after calcination at 800 \({}^{\circ}\)C. For the catalyst based on the P-25 support, the anatase-to-rutile transition can be considered complete after calcination at 800 \({}^{\circ}\)C. These data are fully consistent with the XRD results. TiO\({}_{2}\)-PLA-based catalysts have higher thermal stability of the TiO\({}_{2}\)-anatase phase.  
Figure 4: Raman spectra in range 300–800 cm\({}^{-1}\) for (**a**) Pt/Ti-PLA and (**b**) Pt/Ti-P25 catalysts calcined at 400 \({}^{\circ}\)C (1), 600 \({}^{\circ}\)C (2) and 800 \({}^{\circ}\)C (3).  
Figure 5: Raman spectra in range 100–200 cm\({}^{-1}\) for (**a**) Pt/Ti-PLA and (**b**) Pt/Ti-P25 catalysts, calcined at 400 \({}^{\circ}\)C (1), 600 \({}^{\circ}\)C (2) and 800 \({}^{\circ}\)C (3).  
The small shift of the position and the change of the E\({}_{\text{g}}\) peak width can be related to a change in the crystallite size of TiO\({}_{2}\) anatase nanoparticles [38]. A lower frequency corresponds to an increase in the crystallite size. However, in the case of a series of Pt/Ti-PLA samples, a multidirectional shift in the line position is observed. This is in poor agreement with the XRD data and could be traced back to simultaneous growth of anatase crystallites and transformation of small brookite particles into anatase.