Construction of Pd(II)-poly(4-vinylpyridine) multilayers on quartz substrate surface as heterogeneous catalyst for selective hydrogenation of aromatic conjugated alkenes

Palladium-mediated layer-by-layer (LBL) multilayers with poly(4-vinylpyridine) (PVP) as linker have been constructed on quartz substrate surface and characterized by using UV–Vis absorption spectra, attenuated total reflection infrared spectra, X-ray photoelectron spectra as well as scanning electron microscopy. The as-prepared Pd-PVP multilayers modified substrate was used as heterogeneous catalyst for selectively catalytic hydrogenation of aromatic conjugated alkenes at room temperature. Hydrogen gas was used as a reductant for the connectors of Pd(II) ions as well as hydrogen source for the hydrogenation reactions of alkenes. X-ray photoelectron spectra revealed that the connectors of Pd(II) ions could be reduced to Pd(0) atoms by hydrogen saturated aqueous solution. Yields of the hydrogenation reaction were closely related to the nature of aromatic conjugated alkenes. Because the Pd(0) atoms were encapsulated in the matrix of Pd-PVP multilayers and immobilized on the quartz surface, the present Pd-PVP heterogeneous catalysts had the advantages of high stability, good recyclability as well as the advantage of monitoring the catalytic reaction process through immersing in or withdrawing the modified substrate from the reaction solutions.