Tunable Porosity of Cross-Linked-Polyhedral Oligomeric Silsesquioxane Supports for Palladium-Catalyzed Aerobic Alcohol Oxidation in Water.
Polyhedral oligomeric silsesquioxane (POSS)-based materials, poly-POSS-Tn[n = 8 (1), 10 (2), 12 (3), and mix (4)], were prepared in high yields via free radical polymerization of corresponding pure forms of methacrylate-functionalized POSS monomers, MMA-POSS-Tn(n = 8, 10, 12), and the mixture form, MMA-POSS-Tmix. Powder X-ray diffraction (XRD) spectra and BET analysis indicate that 1-4 are amorphous materials with high surface areas (683-839 m2g-1). The surface areas and total pore volumes follow the trend: poly-POSS-T12> poly-POSS-T10> poly-POSS-Tmix> poly-POSS-T8. In addition, on the basis of Barrett-Joyner-Halenda (BJH) analysis, poly-POSS-T12contains the highest amount of mesopores. The Pd nanoparticles immobilized on poly-POSS-Tn[n = 8 (5), 10 (6), 12 (7), and mix (8)] are well dispersed with 4-6 wt % Pd content and similar average particle sizes of 6.2-6.5 nm, according to transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDX) and microwave plasma-atomic emission spectroscopy (MP-AES). At 90 °C, the stabilized Pd nanoparticles in 5-8 catalyzed aerobic oxidation of benzyl alcohol to benzaldehyde in 72-100% yields at 6 h using a mixture of a H2O/Pluronic (P123) solution. The PdNp@poly-POSS-T8catalyst (5) exhibited the lowest catalytic activity, as a result of its lowest surface areas, total pore volumes, and amounts of mesopores. With the catalyst 8, various benzyl alcohol derivatives were converted to the corresponding aldehydes in good to excellent yields. However, with alcoholic substrates featuring electron-withdrawing substituents, high conversions were achieved with 1 equiv of K2CO3additive and longer reaction times.
Preeyanuch
P
Sangtrirutnugul
Thanawat
T
Chaiprasert
Warodom
W
Hunsiri
Thanudkit
T
Jitjaroendee
National Nanotechnology Center, National Science and Technology Development Agency , Phaholyothin road, Patumthani 12120, Thailand.
Patsaya
P
Songkhum
National Nanotechnology Center, National Science and Technology Development Agency , Phaholyothin road, Patumthani 12120, Thailand.
Kritapas
K
Laohhasurayotin
Tanakorn
T
Osotchan
Vuthichai
http://orcid.org/0000-0002-1999-2463
V
Ervithayasuporn
alcohol oxidation; free-radical polymerization; palladium nanoparticle; polyhedral oligomeric silsesquioxane; porous materials