Wet air oxidation with tubular ceramic membranes modified with polyelectrolyte/Pt nanoparticle films

Gas–liquid reactions with membrane-supported catalysts often use the interfacial contactor configuration in which the reaction occurs at the gas–liquid-catalyst interface within the membrane. Thus, control over the catalyst location in the membrane is crucial for making efficient use of expensive materials such as noble metal nanoparticles. Layer-by-layer (LBL) adsorption of polyelectrolyte/metal nanoparticle films in tubular ceramic membranes allows deposition of the catalytic nanoparticles only near the interior of the tube, where the gas–liquid interface is typically located. In wet air oxidation of formic acid, tubular membranes modified by LBL deposition of polyelectrolyte/Pt nanoparticle films show 2 to 3 times higher specific activities than similar membranes modified by traditional methods such as anionic impregnation/reduction and evaporation/recrystallization/reduction. In acetic acid and phenol oxidations, the LBL method gives order of magnitude increases in specific activity relative to the traditional membrane modification methods. The enhanced activity with LBL-modified membranes is likely due to the controlled deposition of the Pt in the catalytic inner layer of the tubes, as only the LBL method gives tubular membranes that show higher activity than pulverized membranes in stirred tank reactors.