## 1 Introduction
Our research group gained over the years an appreciable experience in the use of cross-linked organic polymers [22; 23; 24; 25] (hereafter referred to as resins) as supports for heterogeneous metal catalysts. Resins are much less popular catalytic supports in comparison with inorganic materials, in view of  
Figure 1: Reaction scheme for the DS of H\({}_{2}\)O\({}_{2}\) from its elements with standard reaction enthalpy data (25 \({}^{\circ}\)C). their lower thermal and mechanical stability. However, when reaction conditions are mild, as it is the case of DS, resins can easily withstand them and be successfully employed. Resins are available in very different chemical structures and textures and can be conveniently tailor-made by a \"molecular engineering\" approach [26]. Moreover, catalytic reactions can occur in their interior and the micro-environment of the polymer framework can positively affect the outcome [27; 28]. The use of an ion-exchange resin as support in the DS was first reported by [PERSON] and co-workers in 2004 [7]. They employed Lewatit K2641, a sulfonated co-poly-(styrene-divinylbenzene) (S-pSDVB), in which palladium was introduced as divalent cations and used without any reduction. Shortly after one of us co-authored a report [29] describing the DS promoted by palladium and palladium-gold catalysts supported by Lewatit K2621 (a S-pSDVB resin similar to K2641) [30] and an acrylic resins, either sulfonated or functionalized with alkylsulfide groups [29]. Since then our group contributed to a number of other papers illustrating the performance of palladium, palladium-platinum and palladium-gold catalysts in the DS with and without halide ions as promoters [31; 32; 33; 34; 35; 36; 37]. Among crosslinked resins \"solvothermal\" poly-divinylbenzene [38] recently emerged as the first representative of a new class of porous polymers, including also acrylic resins [39]. It has permanent mesopores with diameters up to several tens of nm, relatively high pore volumes (up to almost 2 cm\({}^{3}\cdot\)g\({}^{-1}\)) and practically no permanent micropores. In spite of this, its specific surface area can be as high as 400 m\({}^{2}\cdot\)g\({}^{-1}\). This is one order of magnitude higher than in macroreticular S-pSDVB conventional resins. In addition to this it absorbs a volume of liquids much higher than its pore volume, which further increase its specific surface area to almost 1000 m\({}^{2}\cdot\)g\({}^{-1}\)[40]. These features apparently arise from the high nominal cross-linking degree and the high dilution of the monomer in the polymerization mixture [41], which favors the chain growth with respect to cross-linking and the switch from macroretiosynesis as the mechanism of phase separation [42]. As the result the pore system of this kind of pDVB, which will be hereafter referred to as mesoporous (\(\mu\)-pDVB), can be described as interconnected cavities crossing a continuous polymer framework rather than void spaces between partially aggregated polymer lumps (Figure 2), as in conventional macroreticular resins [39; 40; 42]. Figure 2: Sketch of the chemical structure (top) and of the pore morphology (bottom) of a typical macroreticular pSDVB resin (**a**; x = 15, y = 85) and of \(\mu\)-pDVB (**b**; x = 85, y = 15). Ethylstyrene from technical grade divinylbenzene usually employed in polymerization is the source of the ethylbenzene moieties, which can be also present in low amount in pSDVB (omitted for simplicity). Interestingly, \(\mu\)-pDVB can be sulfonated with retention of its morphology to give a very useful ion-exchange resin (\(\mu\)S-pDVB) with pore features comparable to those of \(\mu\)-pDVB [40; 43]. Sulfonated ion-exchangers have been the kind of resins most commonly employed as supports for DS so far, which makes \(\mu\)S-pDVB an interesting candidate as a catalytic support for this reaction. Its very open porous system should allow a fast diffusion of reagents, intermediate, and products, which could be particularly relevant to the control of the selectivity.