Langmuir p. 14408 - 14418 (2011)
Update date:2022-08-28
Topics:
Biradar, Ankush V.
Biradar, Archana A.
Asefa, Tewodros
We report the synthesis, characterization, and catalytic properties of novel monodisperse SiO2@Pd-PAMAM core-shell microspheres containing SiO2 microsphere cores and PAMAM dendrimer-encapsulated Pd nanoparticle (Pd-PAMAM) shells. First, SiO2 microspheres, which were prepared by the Stoeber method, were functionalized with vinyl groups by grafting their surfaces with vinyltriethoxysilane (VTS). The vinyl groups were then converted into epoxides by using m-chloroperoxybenzoic acid. Upon treatment with amine-terminated G4 poly(amidoamine) (PAMAM) dendrimers, the SiO 2-supported epoxides underwent ring-opening and gave SiO 2@PAMAM core-shell microspheres. Pd nanoparticles within the cores of the SiO2-supported PAMAM dendrimers were synthesized by letting Pd(II) ions complex with the amine groups in the cores of the dendrimers and then reducing them into Pd(0) with NaBH4. This produced the SiO 2@Pd-PAMAM core-shell microspheres. The presence of the different functional groups on the materials was monitored by following the changes in FTIR spectra, elemental analyses, and weight losses on thermogravimetric traces. Transmission electron microscopy (TEM) images showed the presence of Pd nanoparticles with average size of 1.56 ± 0.67 nm on the surface of the monodisperse SiO2@Pd-PAMAM core-shell microspheres. The SiO 2@Pd-PAMAM core-shell microspheres were successfully used as an easily recyclable catalyst for hydrogenation of various olefins, alkynes, keto, and nitro groups, giving ~100% conversion and high turnover numbers (TONs) under 10 bar H2 pressure, at room temperature and in times ranging from 10 min to 3 h. In addition, the SiO2@Pd-PAMAM core-shell microspheres were proven to be recyclable catalysts up to five times with barely any leaching of palladium into the reaction mixture.
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