A noble-metal-free
Co-based catalyst, derived from pyrolysis of
natural vitamin B12 on activated carbon, is developed for
the first time for one-pot oxidative cleavage of lignin linkages to
phenols and aromatic esters with molecular oxygen as the oxidant under
mild reaction conditions. High yields of phenol were obtained, and
no oxidative coupling of phenol was produced based on the present
cobalt catalyst. Compared to the previous report, the present catalyst
can achieve the oxidative cleavage of β-O-4 ketones even at
room temperature using a dioxygen balloon. The heterogeneous catalyst
shows robust recyclability and can be conveniently recovered and reused
up to eight times without an appreciable loss of catalytic activity.
Moreover, this catalyst system can realize the bond cleavage of organosolv
lignin. The evidence of depolymerization was given by two-dimensional
heteronuclear single quantum coherence NMR and gel permeation chromatography.
Characterization of the catalyst by inductively coupled plasma, N2 adsorption–desorption, Raman spectroscopy, scanning
electron microscopy, transmission electron microscopy (TEM), high-resolution
TEM, high-angle angular dark-field scanning TEM, energy-dispersive
X-ray spectroscopy, X-ray photoelectron spectroscopy, and control
experiments provide a fundamental understanding of the catalytic materials
and the reaction pathway. Co3O4 in situ supported
on a N-doped carbon matrix by the way of high-temperature pyrolysis
might be a catalytically active species. Two reaction intermediates
are detected and confirmed by gas chromatograph–mass spectrometry.