## 3 Discussion  
The results reported here demonstrate that palladium NPs confined in a polymeric network of HPS can catalyze the selective hydrogenation of alkynols C\({}_{5}\), C\({}_{10}\), and C\({}_{20}\). HPS supports with different porosity were synthesized and divided into two groups: (i) \"microporous\" (PS and OF3), with the share of micropores about 37% by volume and also numerous giguepores, as confirmed by _SEM_ study; and (ii) \"mesoporous\" (C7 and OF2), with the share of micropores about 15% by volume and the presence of mesopores with a mean diameter about 25 nm. HPS-based catalysts with low Pd loadings (0.11-0.17 wt.%) have been prepared via the wet-impregnation of the polymers with Pd acetate. It was shown that impregnation has a negligible effect on polymer porosity, although slight blockage of the micropores takes place. Moreover, by the example of Pd/OF2 and Pd/OF3, it was shown that during the impregnation procedure the palladium acetate was decomposed to PdO (BE is 337.5-337.6 eV, according to the XPS data). All the catalysts were reduced in situ under the reaction conditions and tested in hydrogenation of alkynols--MBY, MNY, and DHIP. In the hydrogenation of MBY, selectivity, with respect to MBE, was about 95% at complete substrate conversion, which is typical for HPS-based catalysts [22, 23]. The catalytic activity, characterized by the initial rate of MBY transformation related to Pd content, was remarkably high for two samples--Pd/OF2 and Pd/OF3: 25.4 mol\({}_{\text{sub}}\)/(mol\({}_{\text{pd}}\)*s) and 17.2 mol\({}_{\text{sub}}\)/(mol\({}_{\text{pd}}\)*s), respectively. For comparison, in the case of commercial Lindlar catalyst (2%-Pd/CaCO\({}_{3}\)) \(R_{0}\) = 3.3 mol\({}_{\text{sub}}\)/(mol\({}_{\text{pd}}\)*s) under the same reaction conditions (90 \({}^{\circ}\)C, toluene).In the case of MBY, the influence of HPS porosity on the catalytic performance seems to be negligible, and the most important factor is the small size of Pd NPs. However, formation in situ of small NPs depends on the support morphology. Thus, the giguepores in the OF3 structure may provide intensive NPs migration, resulting in aggregates and the diminished active surface of Pd. While comparing two samples (Pd/OF2 and Pd/OF3) in the hydrogenation of long-chain alkynols (MNY and DHIP), it was shown that Pd/OF2 having mesopores and tiny Pd NPs (about 1.5 nm) is highly active in the hydrogenation of MNY (C\({}_{10}\)alkynol), while for DHIP (C\({}_{20}\)alkynol) the steric hindrance results in a decrease in catalytic activity and, likely, blockage of pores by both substrate and products. The sample Pd/OF3 presents close values of catalytic activity (\(R_{0}\)) for MBY and MNY. It is noteworthy that Pd/OF3 reveals higher activity for DHIP in comparison with MNY, which could be due to the higher reactivity of triple bond of DHIP and its relatively low dipole moment that is responsible for high affinity to HPS. However, the existence of giguepores with intensive mass-transfer results in aggregation of Pd NPs that makes OF3 less suitable for support, in comparison with \"mesoporous\"OF2. Thus, the influence of the support porosity is two-fold: (i) for the stage of catalyst preparation and formation of Pd NPs, it controls the distribution of catalytically active phase, sizes of NPs, and their tendency to aggregate; (ii) during the catalytic reaction, support porosity influences the accessibility of active sites to the reactants, but this factor can be responsible for the observed activity only if Pd NPs are equal in size. The complexity of the catalytic systems and the multiplicity of the interrelated parameters do not allow to determine which is the crucial one (see Table S1), but the general trend is as follows: mesoporous polymeric materials with high swelling ability (i.e., OF2) allow for more even distribution of the catalytically active phase that provides excellent activity, and for such systems the length of the alkane chain matters (due to different induction effect, hydrophobicity, and diffusion limitations).