## 4 Discussion
Despite the common trend in the transition of ionic forms of platinum to metal with an increase in the calcination temperature of the catalysts, the resulting Pt4f spectra show some differences. For the Pt/Ti-PLA-600 catalyst only two forms of platinum can be observed: Pt\({}^{8-}\) (E\({}_{b}\) = 70.9 eV) and Pt\({}^{4+}\) (E\({}_{b}\) = 74.3 eV). At the same time, in the Pt/Ti-P25-600 catalyst three platinum forms are present: Pt\({}^{8-}\) (E\({}_{b}\) = 70.6 eV), Pt\({}^{2+}\) (E\({}_{b}\) = 72.3 eV) and Pt\({}^{4+}\) (E\({}_{b}\) = 74.5 eV). A highly oxidized form of platinum with E\({}_{b}\) = 73.7 eV is present in the TiO\({}_{2}\)-PLA-based catalyst even after calcination at 800 \({}^{\circ}\)C, demonstrating higher thermal stability than in the case of the Pt/Ti-P25 catalysts. The increased stability of the ionic forms of platinum might be associated with their localization at the boundaries of TiO\({}_{2}\) particles in the Pt/Ti-PLA catalyst. According to the XRD and HRTEM data, small particles of TiO\({}_{2}\)-anatase and TiO\({}_{2}\)-brookite cover the TiO\({}_{2}\)-rutile. In this case, oxidized platinum is in contact with anatase and brookite surfaces. According to XPS, platinum in the Pt/Ti-PLA-400 catalyst has lower binding energies indicating lower stoichiometry of oxygen in PtO\({}_{x}\) particles. The quantitative estimation of the Pt/O ratio obtained from TPR-H\({}_{2}\) data are in good agreement with the XPS data. Fitting of the hydrogen consumption curve for the Pt/Ti-P25-400 sample (Figure 9b, inset) shows that the areas of the individual consumption peaks are very similar. The XPS data give the ratio of the Pt\({}^{2+}\): Pt\({}^{4+}\) components as 2:1. Hence, the amount of hydrogen consumed by the PtO oxide should be similar to the one for the PtO\({}_{2}\) oxide in good agreement with the TPR-H\({}_{2}\) data. The two hydrogen consumption peaks observed for the Pt/Ti-P25-400 catalyst indicate two nonequivalent states of oxygen either as a part of one PtO\({}_{x}\) structure or as separate PtO\({}_{2}\) and PtO clusters. The low-temperature peak has a maximum at T = \(-2\)\({}^{\circ}\)C. This is a lower temperature value than was observed for the Pt/Ti-PLA-400 catalyst. It indicates higher reactivity of oxygen in the Pt/Ti-P25-400 catalyst. In addition, the total amount of consumed hydrogen is slightly higher for the Pt/Ti-P25-400 catalyst (150 umol/g versus 128 umol/g for Pt/Ti-PLA-400 catalyst) which gives the H\({}_{2}\)/Pt ratio of 1.46 and 1.28, respectively. A comparison of the H\({}_{2}\)O evolution curves shows that, in the case of the Pt/Ti-PLA-400 catalyst, the evolution occurs at temperatures above 120 \({}^{\circ}\)C as a single peak with a maximum at T = 180 \({}^{\circ}\)C. H\({}_{2}\)O evolution for the Pt/Ti-P25-400 catalyst occurs in two stages, one of which is described by a low-temperature peak with maximum at T\(\sim\) 60 \({}^{\circ}\)C. The appearance of a low-temperature peak indicates formation of the weakly-bonded reactive OH groups on the surface of the Pt/Ti-P25-400 catalyst. As a consequence, in the case of the Pt/Ti-P25-400 catalyst, the H\({}_{2}\)O evolution takes place along with the second hydrogen consumption peak. While for the Pt/Ti-PLA-400 catalyst the significant temperature difference (4-120 \({}^{\circ}\)C) between the consumption of H\({}_{2}\) and the evolution of water is observed due to formation of more strongly bound OH groups. For the Pt/Ti-PLA-400 catalyst the single peak in the TPR-H\({}_{2}\) (T\({}_{\text{max}}\)= 4 \({}^{\circ}\)C) has narrow width and high intensity. These facts indicate a high homogeneity of the reactive oxygen species. It can probably be associated with highly oxidized Pt with E\({}_{\text{b}}\) (Pt4f\({}_{7/2}\)) = 73.7 eV. The XPS spectra also show a platinum component with the binding energy E\({}_{\text{b}}\) (Pt4f\({}_{7/2}\)) = 71.7 eV (Figure 8a), designated as Pt\({}^{5+}\). This state is formed due to the strong interaction of Pt with the TiO\({}_{2}\) surface.