## 2 Results
In our previous study, using commercial HPS with predominant microporosity and impregnated by Pd acetate, we found that irrespective of palladium loading in a relatively wide range (0.5-2.0 wt.%) and reduction method, NPs were evenly distributed and had diameters of 2-5 nm [22; 23]. It is noteworthy that PS and OF3 also had gigue pores, which cannot be measured by the low-temperature nitrogen physisorption but were clearly identified in the SEM images (Figure 7). Such huge pores, which are visible not only on the outer surface of the initial polymer granules (Figure 7a) but also in their internal structure (Figure 7b,c), facilitate mass transport of metal precursor. Thus, a lot of Pd aggregates can be found closer to the outer surface of the catalysts taken after hydrogenation experiments. Obviously, there is no direct correlation between the observed sizes of Pd NPs and the catalytic activity of HPS-based samples in the reaction of MBY hydrogenation, since the NPs formation and possible aggregation occurred during preliminarily liquid-phase reduction and also in situ. It is known [29] that for relatively big particles (about 6-13 nm) the rate of MBY hydrogenation is almost independent of the particle sizes. In the absence of aggregation, smaller Pd NPs, with sizes less than 2 nm, usually possesses lower activity in hydrogenation reactions of unsaturated compounds [30]. However, small NPs are proven to have higher selectivity [31; 32]. As can be seen (Figure 5b), Pd/OF2 revealed the highest selectivity (about 98% until 80% conversion of MBY) among all the samples. The highest  
Figure 6: S/TEM images of catalysts taken after the reaction of MBY hydrogenation: (**a**) Pd/C7 (scale 100 nm), (**b**) Pd/C7 (scale 20 nm), (**c**) Pd/PS (scale 100 nm), (**d**) Pd/OF3 (scale 100 nm), (**e**) Pd/OF2 (scale 100 nm), and (**f**) HAADF STEM of Pd/OF2 (scale 10 nm). activity of Pd/OF2 (Table 1, #3) can be attributed to the absence of Pd NPs aggregates, while the activity of all other samples suffers from noticeable aggregation of palladium NPs during the reaction. Catalyst Pd/OF3 was studied by the method of low-temperature nitrogen physisorption, after the reaction of MBY hydrogenation (Figure 8). It was found that BET SSA slightly increased after the reaction from 710 \(\pm\) 14 m2/g up to 750 \(\pm\) 15 m2/g. This increase in SSA was accompanied by decrease in micropore volume from 0.19 mL/g to 0.12 mL/g(that comprised nearly 13% of the total pore volume). The observed changes in porosity are likely due to the nucleation of Pd NPs followed by redistribution and agglomeration during the reaction. Samples Pd/OF2 and Pd/OF3 were characterized by the _XPS_ method. It was shown that in both initial catalysts, Pd acetate on the surface was transformed to PdO(binding energy (BE) of Pd 3d\({}_{5/2}\) was equal to 335.7-335.6 eV [33]) during the catalysts' impregnation and subsequent storage. It is noteworthy that Pd content on the surface was very low (0.03-0.05 at.%),which did not allow reliable quantitative estimation. After the MBY hydrogenation, Pd content on the surface (in at.%) remained nearly the same; the results of _XFA_ additionally revealed that no Pd loss occurred during the reaction in toluene medium. It is interesting that the BE of Pd 3d\({}_{5/2}\) was 337.1 eV in both used samples, which is lower compared to the initial catalysts and may indicate the formation of larger NPs of PdO  
Figure 8: Comparison of adsorption–desorption isotherms (**a**) and pore-volume distributions (**b**) for Pd/OF3: initial and taken after the MBY hydrogenation. Figure 7: _SEM_ images of PS and OF3: (**a**) initial PS granule (scale 500 \(\upmu\)m), (**b**) crushed PS (scale 10 \(\upmu\)m), and (**c**) crushed OF3 (scale 10 \(\upmu\)m). (note that after the reaction the samples were filtrated, dried, and stored under air, which resulted in the oxidation of Pd NPs).