## 1 Introduction  
A major research topic in the field of adsorption systems for solar thermal energy storage, air-conditioning and dehumidification processes involves the development of new or modified adsorbent materials with enhanced adsorption and thermo-physical properties, low cost, high stability, and low regeneration temperature [1; 2; 3; 4; 5]. Possible adsorbent classes are zeolites, silica gels, activated carbons, metal organic frameworks (MOFs), and composite adsorbents made of a sorbent matrix embedding a hygroscopic salt [6]. Among them, silico-aluminophosphate zeotype materials (SAPO, ALPO) are very attractive due to the low regeneration temperature (<100 \({}^{\circ}\)C) and optimal shape of the water adsorption equilibrium curve [7; 8; 9]. In closed systems research on components optimization is mainly focused on the integration between heat exchanger and adsorbent material, to create the so called adsorber [10]. Two different approaches are currently under investigation: embedding a granular adsorbent in the heat exchanger [11]; coating the heat exchanger with the adsorbent material either using a binder [12] or by direct synthesis of the zeolite over the metallic surface of the heat exchanger [13]. The first approach allows good heat transfer efficiency without significantly affecting the vapor diffusion through the adsorber if a proper grain size and dispersion is selected [14]. The second approach is based on the reduction of the contact resistance between the heat exchanger and a thin adsorbent coating (generally 0.05-0.2 mm), thus enhancing the heat transfer efficiency. However, a sufficiently high amount of adsorbent must be deposited over the heat exchanger, to avoid reduction of the achievable power density [15]. Similarly, in open systems the adsorption and desorption process is typically achieved through a honeycomb matrix impregnated with a desiccant material [16; 17] or through a packed bed made of spherical beads of a sorption material [18]. In the first case, a high heat and mass exchange area between the air stream and the desiccant matrix is obtained and air pressure drop is low. Anyway, the manufacturing process of the honeycomb structure is quite complex and it requires the use of support materials (such as paper or glass fiber) and appropriate binders that partially limit the net sorption capacity of the desiccant. In the second case, packed bed can be easily realized by using beads of pure materials, without any need of binders. On the other side, this approach leads to a device with high water mass transfer resistance within desiccant beads and high air pressure drop, limiting the application of the system. Optimization of adsorber/desorber configuration in both open and closed systems is still an open issue, which heavily depends on the final application of the adsorption system [19]. Recently, an innovative silicone-zeolite foaming process has been developed in order to enhance the power density of the zeolite heat and mass exchanger in closed-cycle adsorption heat pumps and chillers [20; 21]. Indeed, foamed materials, due to their intrinsic high surface area per unit mass, could allow to obtain a large amount of zeolite coating per unit of volume, and at the same time the foam porosity could act as a preferential pathway for the vapor diffusion. This approach allows improving the amount of active material embedded into the adsorbent heat exchanger and can be suitable for both open and closed systems. In a previous preliminary work, several samples of SAPO34 foams have been prepared and water adsorption isotherms have been measured by a gravimetric adsorption apparatus, demonstrating that they can adsorb a significant amount of water (up to 30 wt.%) under typical operating conditions of open-cycle adsorption systems [22]. Moreover, the tested foams exhibited sufficiently fast water sorption rate, as the silicone does not significantly reduce the transient adsorption capacity of pure zeolite.