Infiltration and immobilization of catalyst particles into the confined space of microstructured reactors via layer-by-layer self-assembly

Layer-by-layer (LbL) self-assembly was explored as a new coating method for assembling, infiltrating, and immobilizing catalyst particles in the confined space of microstructured reactors. One layer of negatively charged ∼3 μm Pd/Na-Al(Si)O catalyst particles was electrostatically deposited on Si, SiC, and stainless steel substrates. The substrates were made to be positively charged by applying a ∼20 nm-thick polyelectrolyte multilayer (PEM). The PEM and particle deposition steps were repeated to build a four-layer catalyst particle assembly. Surface coverage, microstructural morphology, and uniformity of the four-layer catalyst particle assembly prepared on the flat Si surface and on the skeleton surface inside the cellular SiC structure with ∼400 μm interconnected cells were similar, demonstrating the non-line-of-sight infiltration attribute of the LbL self-assembly technique. The four-layer assembly deposited on the inner wall of the stainless capillary tube with a 780 μm inner diameter was mechanically stable under a water flow rate up to 10 ml/min over a pH range of 3-11. Scotch tape peeling evaluation suggested that failure locations during peeling were mostly within the catalyst particle assembly, but near the assembly-PEM interface region. The study of catalyst performance in the hydrogenation of acetylene showed that activity and selectivity of the catalyst particles were not affected by the LbL self-assembly procedures.