## 2 Materials and Methods  
### Sample Preparation  
The composite zeolite/siloxane foam was obtained by mold foaming process. Details of compounds used for the synthesis are summarized in Table 1. As zeolite filler, a SAPO34, (AQSOA-FAM Z02, supplied by Mitsubishi Chemicals, Tokyo, Japan) with average size in the range of 4-8 um was used. The foaming matrix is constituted by two reactants (acquired by Gelest Inc., Morrisville, NY, USA) selected in order to have a dehydrogenase coupling reaction: a Methylhydrosiloxane--dimethylsiloxane copolymer, trimethylsiloxane terminated, PMHS (M.W. 1400-1800, viscosity 15-25 cSt), and a silanol terminated polydimethylsiloxane (PDMS--M.W. 110,000, viscosity 50,000 cSt). In order to activate the reaction between the two siloxane compounds, Tin(II) 2-ethylhexanoate (Sn(II)) (supplied by Sigma Aldrich, St. Louis, Missouri, NY, USA) was used as catalyst. Two different types of samples have been prepared in this study. In the first case the slurry has been introduced in an open mold, in order to guarantee an almost free expansion of the foam. In the second case, the slurry has been forced inside channels of a paperboard, in order to constrain the foam expansion in a similar way to what would happen in the construction of real components. As shown in Figure 1, the foamed composite sample preparation can be summarized in five main steps:  
1. Filler dispersion. Preliminarily SAPO34 zeolite powder was gradually dispersed under vigorous magnetic stirring in the polydimethylsiloxane (PDMS) compound for about 60 s. In order to obtain a homogenous dispersion of the filler and to reduce the solution viscosity, water and ethanol solvents were added to the mixture. 2. Composite slurry. Afterward, the polymethylhydrosiloxane (PMHS) compound was thoroughly added in the mixture obtained in point 1, always under vigorous magnetic stirring. The stirring was maintained for 60 s until a homogenous composite slurry is obtained. 3. Reaction activation. The catalyst (diluted in ethanol) is gently added in the composite slurry. A vigorous mixing was applied for about 20 s.
4. Molding. Immediately, the catalyst activated composite slurry was poured, by using a syringe tool: * Into a cylindrical open mold (diameter 25 mm). * Into the cavities of a corrugated cardboard (inner height and base of the cross section respectively equal to 5 mm and 10 mm, channel length equal to 5 cm). The samples rest open to air at room temperature for about 30 s, to stabilize the mixture in the free surface area of the mold. 5. Foaming. Finally, the foaming process was triggered putting the filled samples into an oven set at 60 \({}^{\circ}\)C for 24 h to allow the matrix curing. At the end of the curing process the obtained foams poured in a cylindrical mold were cut in order to get cubic samples with edge of about 20 mm. The foamed structure is obtained during the last point 5 of the process thanks to the dehydrogenase coupling reaction between hydroxyl terminated polydimethylsiloxane (PDMS) that react with hydride functional siloxane (PMHS) to produce foamed silicone materials, according to the following reaction:  
\[\equiv Si-OH+H-Si\equiv\rightarrow\equiv Si-O-Si\equiv+H_{2}\uparrow \tag{1}\]  
The reaction of siloxane compounds leads to a polymer network in a silicone rubber [23]. As reaction product gaseous hydrogen is formed, acting as blowing agent [24]. This process is indicated as chemical blowing process. Furthermore, a physical blowing phenomenon occurs during the crosslinking reaction, due to the evaporation of the solvent during the curing stage. The combination of chemical and physical blowing allows to obtain a microporous structure with good foaming ration and well-interconnected bubbles. Three different foam formulations were produced by varying the SAPO34 filler content in the range 20-60 wt.% of the PDMS-PMHS siloxane matrix. All produced formulations with details of compound amounts are summarized in Table 1. The samples were codified by means a prefix \"Z\" coupled to a number.