Surface-selective infiltration of thin-film catalyst into microchannel reactors

A thin-film Pt/Al₂O₃ catalyst was synthesized by a sol-gel synthesis method with hydrogen hexachloroplatinate hydrate and aluminum isopropoxide as precursors in a water-based solvent. The catalyst contained ∼5 nm Pt particles dispersed on Al₂O₃ support, which was mostly amorphous with a specific surface area of 400-450 m²/g and a pore size distribution in the range of 2-8 nm. For uniform infiltration of the solgel catalyst precursor into the microchannel of Si-based reactors, a hydrophobic film was applied to the top surface of the reactors while reactive ion etched microchannel surface of the reactors remained hydrophilic. Under these surface conditions, the catalyst precursor infiltrated selectively into the microchannel without spilling over to the reactor surface. In comparison to other infiltration methods, this surface-selective approach provided an effective means of precisely controlling the amount of catalyst loaded into the reactors and keeping the reactor surface clean for subsequent sealing via anodic bonding. However, as delamination occurred preferentially at the sharp corners of the microchannel, the thickness of the catalyst layer that could be practically incorporated into the reactors was limited to ∼3 μm.