## 4 HPS-Based Catalysts for the Synthesis and Transformation of Platform Chemicals
### Hydrogenation of Furfural
The TEM data (Figure 10) show for the 3% Pd/HPS composite with the PdCl\({}_{2}\)(CH\({}_{3}\)CN)\({}_{2}\) precursor, a relatively narrow distribution of Pd nanoparticles with an average diameter of 5.4 \(\pm\) 1.2 nm (Figure 10a). When using the more hydrophobic precursor Pd(CH\({}_{3}\)COO)\({}_{2}\), a bimodal distribution of particles with average particle sizes of 3.7 \(\pm\) 1.0 nm and 13.8 \(\pm\) 5.4 nm is seen (Figure 10b). This observation is consistent with the literature, in that the behavior of metal species in HPS depends on the hydrophobic-hydrophilic balance. The obtained TEM data are also consistent with the BET results, and confirm Pd nanoparticles formation in mesopores rather than micropores. The results obtained from small-angle X-ray scattering (SAXS) showed that in the case of 3% Pd/HPS (PdCl\({}_{2}\)(CH\({}_{3}\)CN)\({}_{2}\)), Pd nanoparticles form a monomodal distribution with an average diameter of 7.5 nm. For the 3% Pd/HPS composite (Pd(CH\({}_{3}\)COO)\({}_{2}\)) (b), there are two fractions: a main fraction of small particles (\(\approx\)7 nm) and a small amount of larger particles (10-35 nm) (Figure 11). In general, these results are consistent with the TEM data. Figure 11: SAXS data for 3% Pd/HPS catalysts after their impregnation with masking liquids (**a**). Volume particle size distributions of Pd particles in the catalysts (**b**). Reprinted from ref. [177], Copyright 2019, with permission from Elsevier (Amsterdam, The Netherlands). Figure 10: TEM images of the 3% Pd/HPS (PdCl\({}_{2}\)(CH\({}_{3}\)CN)\({}_{2}\)) (**a**) and 3% Pd/HPS (Pd(CH\({}_{3}\)COO)\({}_{2}\)) (**b**). Reprinted from ref. [177], Copyright 2019, with permission from Elsevier (Amsterdam, The Netherlands). XPS data confirm the Pd\({}^{0}\) nature and oxide form of Pd nanoparticles using both precursors. The XPS spectrum of 3% Pd/HPS(PdCl\({}_{2}\)(CH\({}_{3}\)CN)\({}_{2}\)) is deconvoluted into two components: with Pd 3d\({}_{5/2}\) binding energies of 335.2 eV and 337.2 eV, which we assign to Pd\({}^{0}\) (32%) and Pd\({}^{2+}\) (68%), respectively (Figure 12). In the case of 3% Pd/HPS(Pd(CH\({}_{3}\)COO)\({}_{2}\)) Pd 3d spectrum is also deconvoluted into two components: with Pd 3d\({}_{5/2}\) binding energies of 335.2 eV (40%) and 336.7 eV (60%) which we also assign to Pd\({}^{0}\) and Pd\({}^{2+}\), respectively (Figure 12). The typical values of Pd 3d\({}_{5/2}\) binding energy for Pd\({}^{0}\) state is about 335.0-335.4 eV and the range of 336-337 eV corresponds to PdO. As the samples were kept on air before XPS study, some part of metal Pd is present in oxide form. The ratio of oxide form/metal form is higher in more disperse samples because small particles are more easily oxidized compared to larger particles. This value could be used to estimate of the ratio between small and large particles in series of such samples. Also, it could be concluded that the nature of Pd precursor in HPS matrix essentially does not influence the Pd oxidation state. A comparison of the catalytic activity of Pd-containing catalysts showed that a more dispersed sample (3% Pd/HPS (PdCl\({}_{2}\)(CH\({}_{3}\)CN)\({}_{2}\)) showed higher values of FF conversion and selectivity towards FA due to the presence of smaller particles catalytically active phase. After 200 min of the reaction, FA selectivity for both catalysts reached its maximum-87.4% for 3% Pd/HPS(PdCl\({}_{2}\)(CH\({}_{3}\)CN)\({}_{2}\)) and 83.8% for the 3% Pd/HPS (Pd(CH\({}_{3}\)COO)\({}_{2}\)) catalyst at FF conversion of 55.6% and 36.3%, respectively). Considering good catalytic properties of Pd-Cu alloys in the hydrogenation of FF to FA [179] and the advantages of micro/mesoporous HPS supports in a number of hydrogenation reactions [70; 124], we developed new catalysts with Pd-Cu alloy nanoparticles in the pores of HPS and compared their properties with those of monometallic Pd nanoparticles [175].