Catalytic cracking deposition of methyldiethoxysilane for modification of zeolitic pores in MFI/α-Al₂O₃ zeolite membrane with H⁺ ion exchange pretreatment

Catalytic cracking deposition (CCD) of methyldiethoxysilane (MDES) can be used to tune the zeolitic pores over MFI zeolite membranes for H ₂/CO₂ separation. CCD of MDES over MFI zeolite was investigated to reveal the catalytic cracking behavior of silane. The cracking products were found to be strongly influenced by cracking temperature and acid sites. The increases of temperature and acid sites were beneficial to CCD of MDES in the zeolitic pores, which could effectively reduce the pore size of zeolite. H⁺ ion exchange on MFI zeolite membranes has been adopted to increase acid sites in the membrane layer. The membranes were further modified by on-stream CCD of MDES to improve H₂ selectivity. The achieved H₂ selectivity over ion-exchanged membranes was much higher than that for MFI zeolite membranes without ion exchange. Typically, an ion-exchanged membrane after CCD modification possessed an H₂/CO₂ separation factor of 42.6 and H₂ permeance of 2.82 × 10 ^-7 mol/m²·s·Pa at 500 C.