Preparation of crystal-like periodic mesoporous phenylene-silica derivatized with ferrocene and its use as a catalyst for the oxidation of styrene

abstract

The surface silanol groups in crystal-like mesoporous phenylene-silica have been derivatized with trimethylsilyl, benzyldimethylsilyl and dimethylsilyl(ferrocene) groups by performing a post-synthetic grafting reaction with the corresponding chlorosilane precursors. The success of the grafting procedure was demonstrated by transmission FT-IR spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and C-13 and Si-29 magic-angle spinning (MAS) NMR spectroscopy. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and N-2 adsorption data for the modified materials indicated preservation of the mesostructure as well as the molecular-scale periodicity in the pore walls. Ferrocene and the ferrocenyl-modified periodic mesoporous organosilica (PMO) were employed in the catalytic oxidation of styrene at 55 degrees C using either hydrogen peroxide or tert-butylhydroperoxide as an oxidant. The main reaction product was always benzaldehyde (BzCHO), and other products included styrene oxide, benzoic acid and 2-hydroxyacetophenone. Using a styrene : H2O2 molar ratio of 1 : 5, the highest BzCHO yields at 24 h were 65% (85% selectivity) for ferrocene (semibatch conditions involving stepwise addition of H2O2, 1 mol% Fe) and 34% (83% selectivity) for the modified PMO (batch conditions, 0.06 mol% Fe). The modified PMO could be recovered and reused, albeit with a drop in catalytic activity due to partial metal leaching during the first catalytic run.

keywords

MOLECULAR-SCALE PERIODICITY; BENZENE-SILICA; HETEROGENEOUS CATALYST; SELECTIVE OXIDATION; HYBRID MATERIAL; AQUEOUS-MEDIUM; ORGANIC GROUPS; CHANNEL WALLS; PORE WALLS; ORGANOSILICAS

subject category

Chemistry

authors

Gomes, AC; Ferreira, MJ; Bruno, SM; Bion, N; Ferreira, P; Valente, AA; Pillinger, M; Rocha, J; Goncalves, IS

Groups

G1 - Porous Materials and Nanosystems
G2 - Photonic, Electronic and Magnetic Materials
G4 - Renewable Materials and Circular Economy

Projects

Design of acid-functionalised periodic mesoporous organosilica catalysts for reactions with/in water (PTDC/QUI-QUI/113678/2009)

Centre for Research in Ceramics and Composite Materials - CICECO (LA0011: 2013-2014) (PEst-C/CTM/LA0011/2013)

RMNE-UA-National Network of Electron Microscopy (REDE/1509/RME/2005 )

acknowledgements

We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT), Fundo Europeu de Desenvolvimento Regional (FEDER), QREN-COMPETE (PTDC/QUI-QUI/113678/2009), the European Union, and the Associate Laboratory CICECO (PEst-C/CTM/LA0011/2013) for continued support and funding. The authors acknowledge the Portuguese network of electron microscopy, the RNME, FCT Project REDE/1509/RME/2005. The FCT and the European Union are acknowledged for a post-doctoral grant to S. M. B. (SFRH/BPD/46473/2008) cofunded by MCTES and the European Social Fund through the program POPH of QREN.