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Palladium catalysts supported by a mesoporous form of sulfonated poly-divinylbenzene, Pd/&#181;S-pDVB10 (1%, <i>w</i>/<i>w</i>) and Pd/&#181;S-pDVB35 (3.6% <i>w</i>/<i>w</i>), were applied to the direct synthesis of hydrogen peroxide from dihydrogen and dioxygen. The reaction was carried for 4 h out in a semibatch reactor with continuous feed of the gas mixture (H₂/O₂ = 1/24, <i>v</i>/<i>v</i>; total flow rate 25 mL&#183;min^&#8722;1), at 25 &#176;C and 101 kPa. The catalytic performances were compared with those of a commercial egg-shell Pd/C catalyst (1%, <i>w</i>/<i>w</i>) and of a palladium catalyst supported by a macroreticular sulfonated ion-exchange resin, Pd/mS-pSDVB10 (1%, <i>w</i>/<i>w</i>). Pd/&#181;S-pDVB10 and Pd/C showed the highest specific activity (H₂ consumption rate of about 75&#8315;80 h^&#8722;1), but the resin supported catalyst was much more selective (ca 50% with no promoters). The nanoparticles (NP) size was somewhat larger in Pd/&#181;S-pDVB10, showing that either the reaction was structure insensitive or diffusion limited to some extent over Pd/C, in which the support is microporous. The open pore structure of Pd/&#181;S-pDVB10, possibly ensuring the fast removal of H₂O₂ from the catalyst, could also be the cause of the relatively high selectivity of this catalyst. In summary, Pd/&#181;S-pDVB10 was the most productive catalyst, forming ca 375 mol_H₂O₂&#183;kg_Pd^&#8722;1&#183;h^&#8722;1, also because it retained a constant selectivity, while the other ones underwent a more or less pronounced loss of selectivity after 80&#8315;90 min. Ageing experiments showed that for a palladium catalyst supported on sulfonated mesoporous poly-divinylbenzene storage under oxidative conditions implied some deactivation, but a lower drop in the selectivity; regeneration upon a reductive treatment or storage under strictly anaerobic conditions (dry-box) lead to an increase of the activity but to both a lower initial selectivity and a higher drop of selectivity with time.