Parallel Array of Pt/Polyoxometalates Composite Nanotubes with Stepwise Inside Diameter Control and Its Application in Catalysis

A nanotubular catalytic reactor composed of an parallel array of Pt-loaded polyoxometalates/polyelectrolyte nanotubes is presented. Pt/POM composite nanotubes with precisely controlled wall thickness as well as tube inside diameters are prepared by a layer by layer method. Negative-charged polyoxometalates (POMs) and positive-charged polyelectrolytes were alternatively coated onto the inside walls of the porous polycarbonate template. The wall thicknesses as well as the inside diameters of the tubes are precisely controlled by the number of coating bilayers, with a stepwise tailoring at 2.2 nm per step and up to at least 40 steps. Scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, UV, fluorescence spectroscopy, and solid-state NMR characterization of the POM/polyelectrolyte tubes were carried out. The Pt/POM nanotubular reactor with smaller inside diameters shows higher catalytic activities for cyclohexene hydrogenation, indicating promising potential in designing reactors with specific sizes for specific reactions.