Magnetic HMS silica as a Support to Immobilization of Catalysts Based on Cationic Manganese Porphyrins

• Published in: ChemistrySelect (Weinheim) Vol. 2; no. 13; pp. 3703 - 3715
• Main Authors: Ucoski, Geani Maria, Pinto, Victor Hugo Araújo, DeFreitas‐Silva, Gilson, Rebouças, Júlio Santos, Mazzaro, Irineu, Nunes, Fábio Souza, Nakagaki, Shirley
• Format: Journal Article
• Language: English
• Published: 02-05-2017
• Subjects: HMS microporous silica; Immobilization; Magnetite; Oxidation Catalysis; Porphyrin
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.201700501

The immobilization of cationic manganese porphyrins (MnP) over the surface of a magnetic hexagonal HMS silica (HMS‐Mag) produced a solid with high surface area and relatively homogeneous pores. Given the presence of the magnetite, the catalysts are easily recovered and reused without loss of mass. The MnP immobilization explored the strong interaction between the positive charges of the cationic MnP and the deprotonated Si‐OH groups on the surface of HMS‐Mag. Soret bands on the UV‐Vis spectra of the MnP‐loaded HMS‐Mag confirmed the presence of MnP on the prepared solids. The catalytic efficiency, robustness, and reusability of the prepared solids were investigated on cis‐cyclooctene and cyclohexane oxidations. The solids showed similar or higher catalytic efficiency than the corresponding MnP under homogeneous catalysis, with selectivity for cyclohexanol in cyclohexane oxidation. Additionally, the solid catalysts showed high resistance against deactivation, confirming the reusability capacity in at least five cycles of cyclooctene oxidation.
In this work different cationic Mn porphyrin were immobilized in magnetic HMS silica (HMS‐Mag) via electrostatic attraction between the positive charges of the MnP and the negative charges from the deprotonated SiOH groups present in the support. The resulting solids showed alcohol selectivity when used in the cyclohexane oxidation and reusability capacity in at least five cycles of cyclooctene oxidation. Solids were easy recovered using a magnet, without any loss of mass.