Microwave assisted oxidation of a lignin model phenolic monomer using Co(salen)/SBA-15

The microwave assisted oxidative degradation of a lignin model phenolic monomer (1-(4-hydroxy-3-methoxyphenoxy)-ethanol, apocynol) catalysed by Co(salen)/SBA-15 is reported. The catalyst was prepared by immobilizing [N,N'-bis(salicylidene)ethane-1,2-diaminato]Cobalt(II), Co(salen) complex on to the periodic mesopore channels of siliceous SBA-15. Powder X-ray diffraction data revealed that the host retains its hexagonal mesoporous structure after immobilization. Upon immobilization, the surface area and pore size of SBA-15 was considerably decreased indicating the intrapore confinement of the complex. A blue shift (about 30 nm) observed in the DRUV-vis spectra of the immobilized complex as compared to the free complex revealed that the Co(salen) is anchored onto the inner surface, presumably through silanol groups. Cobalt content in the final catalyst was found to be 16 mu mol g(-1). The activity of the Co(salen)/SBA-15 was investigated in the oxidation of apocynol in the presence of hydrogen peroxide as oxidant. Complete degradation of apocynol was obtained after 40 min of reaction under microwave irradiation, compared to a poor 57% degradation after 24 h under conventional heating. (C) 2008 Elsevier B.V. All rights reserved.