Energetic performances of pure silica STF and MTT-type zeolites under high pressure water intrusion

Experimental water intrusion-extrusion isotherms were performed at room temperature on two pure silica MTT- and STF-type hydrophobic zeolites (zeosils) with 1D channel and cage pore systems, respectively by applying or releasing a high hydraulic pressure. These zeosils were obtained by hydrothermal synthesis in fluoride medium and characterized by structural and physicochemical methods before and after water intrusion. The system "MTT-type zeosil-water" displays a spring behavior with an intrusion pressure of 176 MPa and a stored energy of 5.3 J g(-1). No influence of water intrusion on the structure of MTT-type zeosil was found. The "STF-type zeosil-water" system shows a combination of shock-absorber and bumper behavior in the first cycle with an intrusion pressure of 51 MPa. Nevertheless in the following cycles the system demonstrates a spring behavior with an intrusion pressure of 38 MPa. Such behavior can be explained by the formation of silanol groups under intrusion in some pores confirmed by NMR spectroscopy and TG data.