## 4 Discussion  
The laser ablation of the Ti target in liquid followed by calcination of the resulted dispersion produces a mixture of rutile, anatase and brookite TiO\({}_{2}\) phases. According to XRD data, the anatase and rutile particles are smaller than the one of brookite. A large amount of intercristalline boundaries \"rutile-anatase\" and \"brookite-anatase\" could be a key factor for the enhanced thermal stability of TiO\({}_{2}\)-anatase particles. The anatase phase could be observed even after calcination at 800 \({}^{\circ}\)C. It could be seen from TEM data that platinum deposition is not uniform and preferentially takes place on the intercristalline boundaries or the surface of the anatase particles. Thus, microheterogeneity of TiO  
Figure 11: NH\({}_{3}\) conversion curves for the first catalytic cycle for the (**a**) Pt/Ti-PLA and (**b**) Pt/Ti-P25 catalysts calcined at 400\({}^{\circ}\)C and 600\({}^{\circ}\)C.  
produced by PLA can be responsible for the increase in the thermal stability of TiO\({}_{2}\) support as well as stabilization of the small Pt particles. According to the XPS data, platinum in the catalysts calcined at 400 \({}^{\circ}\)C is in the ionic form, regardless of the type of the TiO\({}_{2}\) support. Metal clusters or metallic Pt nanoparticles are not observed. The highly oxidized forms of platinum in the catalysts have different binding energies: 73.7 eV for Pt/Ti-PLA-400 and 74.9 eV for Pt/Ti-P25-400. A significant difference in the binding energy -1.2 eV can be explained by different sizes of Pt particles and different degrees of interaction with the support. Highly dispersed platinum particles of less than 1 nm size are present on the surface of the commercial TiO\({}_{2}\)-P25 support, while the TiO\({}_{2}\)-PLA support stabilizes particles larger than 1 nm. Probably due to the small size of platinum particles on the surface of the TiO\({}_{2}\) - P25 support, the Pt particles are completely oxidized to Pt\({}^{4+}\) species [22]. For larger particles on the PLA support a partial reduction of Pt ions might be proposed. In this case, splitting of the Pt4f line into the two doublets from Pt\({}^{2+}\) and Pt\({}^{4+}\) forms would be expected. However, in the Pt4f spectra of the Pt/Ti-PLA-400 sample we observed only one doublet from PtO\({}_{x}\) species. The E\({}_{b}\) (Pt4f\({}_{7/2}\)) = 73.7 eV, determined from the Pt4f spectra for this state, is the intermediate value between the one typical for Pt\({}^{2+}\) and Pt\({}^{4+}\) ions. In the literature, this state was even described as a Pt\({}^{3+}\) state [43]. At the same time Pt\({}_{3}\)O\({}_{4}\) is described as a mixed oxide with defined Pt\({}^{4+}\) and Pt\({}^{2+}\) sites in the structure [44]. Thus we tentatively associate the Pt state in the Pt/Ti-PLA-400 sample with slightly reduced PtO\({}_{2}\) particles. Species with E\({}_{b}\) (Pt4f\({}_{7/2}\)) = 70.6-70.9 eV observed after catalyst calcination at T = 600 and 800 \({}^{\circ}\)C species (Figure 8) can be attributed to highly dispersed metallic platinum particles with a negative charge (Pt\({}^{8-}\)) due to electronic interaction with TiO\({}_{2}\). In this case, Pt4f binding energy is affected by photoemission relaxation effects [45; 46]. According to literature data [47; 48], for small Pt particles (less than 1 nm) the shifts of Pt4f\({}_{7/2}\) line relative to the E\({}_{b}\) value of bulk Pt can reach 0.6 eV. Taking the value of E\({}_{b}\) (Pt4f\({}_{7/2}\)) for the bulk metal as 71.1 eV [49], the obtained experimental values of 70.6-70.9 eV correspond to \(-0.5\div-0.2\) eV shifts. The slightly lower values of E\({}_{b}\) (Pt4f\({}_{7/2}\))= 70.6-70.7 eV and, accordingly, the larger shifts of the Pt4f doublet towards lower E\({}_{b}\) observed for Pt/Ti-P25 catalysts can point to the presence of smaller Pt particles in these catalysts. This is also in a good agreement with the HRTEM data.