This study focused on producing membranes for molecular sieving of gases by reducing the pore size of an already existing membrane structure. To do this, SiO2 was deposited inside the pores of a Vycor tube with initial pore diameter of 4 nm. The film deposition took place by a low pressure chemical vapor deposition (LPCVD) process where diethylsilane (DES) and nitrous oxide (N2O) were used as precursor gases. A counterflow reactant geometry was used where the precursor gases were flowed on both sides of the porous membrane. This deposition geometry gave higher selectivities and better mechanical stability. The flows of H2, He, N2, Ar, toluene, and dichloromethane (DCM) were monitored in-situ after each deposition. Selectivities on the order of 1000:1 were observed for H2 and He over N2. It was also shown that N2/toluene selectivities of 40:1 were also possible
