## 2 Results and Discussion
### Catalytic Runs: Fresh Catalysts
In fact, the initial rate values of H\({}_{2}\) consumption, hence of conversions, are strictly comparable to the final ones as expected for catalysts working under steady state conditions. Pd/mS-pSDVB10 turns out to be the least active catalysts by a great deal even when the specific rates are compared. In spite of this, the least productive one is Pd/C, because it produces H\({}_{2}\)O\({}_{2}\) at the smallest rate. At the beginning of the reaction, Pd/mS-pSDVB10, Pd/uS-pDVB10, and Pd/uS-pDVB35 are therefore four to six times more selective than Pd/C (Table 3, #7). With Pd/uS-pDVB10 the selectivity in the first 80 min is a bit higher than 50% (at room temperature and with no promoters), with a conversion slightly above 30%. These data show that the cross-linked sulfonated resins were better supports than carbon for the palladium catalysts for the DS, at least under the mild pressure conditions employed in this  
Figure 5: Representative HAADF-STEM (**top**) and TEM (**bottom, left**) microphotographs of Pd/uS-pDVB10 and HR-TEM of a Pd NP with corresponding FFT pattern (**bottom, right**). work. This was especially true for \(\mu\)S-pDVB, which gave the most active and the most selective catalyst. This support was employed to prepare two catalysts, Pd/\(\mu\)S-pDVB35 and Pd/\(\mu\)S-pDVB10, with different metal loads (respectively 1.0% and 3.6%, \(w/w\)). \(R_{s,H_{2}}\) of Pd/\(\mu\)S-pDVB35 (ca 50 h\({}^{-1}\)) was always smaller Pd/\(\mu\)S-pDVB10 (75-80 h\({}^{-1}\)), which is compatible with a smaller proportion of active metal. Pd/\(\mu\)S-pDVB10 is particularly interesting in that it was the only catalyst stable from the point of view of both activity and selectivity. We speculate that this was the consequence of the very open pore structure of this resin, which allow at the same time a fast inwards diffusion of the reagents and a fast outwards diffusion of H\({}_{2}\)O\({}_{2}\). This circumstance likely limited the transformation of H\({}_{2}\)O\({}_{2}\) into water, provided that the palladium load is was not too high. In fact Pd/\(\mu\)S-pDVB35 is much less selective at relatively long time. The bottom part of Figure 4 shows that the actual selectivity to H\({}_{2}\)O\({}_{2}\) of Pd/\(\mu\)S-pDVB35 approached zero after about 90 min, when a very slight decrease of the concentration of H\({}_{2}\)O\({}_{2}\) started to be observed. In this case H\({}_{2}\)O\({}_{2}\) was transformed into water (hydrogenation + dismutation) slightly faster than it was formed, which could be caused by the transformation of the catalyst into a still active, not selective form or by the onset of some transport limitations. The build-up of the concentration of H\({}_{2}\)O\({}_{2}\) in the liquid could have increased the rate of the chemical reaction inside the catalyst and decreased the rate of its diffusion from the catalyst to the liquid phase, making them comparable. In this connection, the catalytic activities of Pd/\(\mu\)S-pDVB35 and Pd/\(\mu\)S-pDVB10 are in a slightly smaller ratio than the respective palladium loads (2.4 vs. 3.5), a hint that some mass transport limitations might be in operation with Pd/\(\mu\)S-pDVB35. As the result at the end of the catalytic run with Pd/\(\mu\)S-pDVB10 H\({}_{2}\)O\({}_{2}\) was more than twice concentrated (and its yield proportionally higher) in comparison with Pd/\(\mu\)S-pDVB35, showing that the increase of the palladium load was detrimental to the catalytic performance altogether. Pd/C and Pd/\(\mu\)S-pSDVB10 seemed also stable, but because of their low selectivity (Pd/C) or activity (Pd/\(\mu\)S-pSDVB10) the final yield of H\({}_{2}\)O\({}_{2}\) was so low that it was difficult to appreciate changes in the catalysts' performance, if any. For Pd/\(\mu\)S-pSDVB10, the possible confinement of palladium in the gel phase beneath the surface of the permanent pores could have made both its participation to the catalytic reaction and the removal of H\({}_{2}\)O\({}_{2}\) away from the active surface with adverse effects on the selectivity and, above all, the activity.