The
development of an economic and sustainable catalytic system
was crucial for lignin-based biorefinery. Herein, we reported a low-cost
Cu/CuMgAlO
x
catalyst with promising activity
toward lignin hydrodeoxygenation (HDO) through a H2-free
method. Supercritical methanol was used as the hydrogen donor, solvent,
and reactant simultaneously. Guaiacol was employed as a representative
lignin model compound to reveal the HDO mechanism of lignin derivatives.
HDOs of guaiacol performed at 250, 275, 300, and 350 °C with
durations ranging from 15 to 120 min indicated a high HDO efficiency
of the catalytic system. The obtained liquid products were categorized
to oxygen-containing unsaturated products (OUPs), oxygen-containing
saturated products (OSPs), and cycloalkanes. A kinetic model based
on a simplified reaction process containing the three following conversion
steps was established: guaiacol transformed to OUPs through the initial
HDO, then hydrogenated to OSPs (medium HDO), and eventually turned
to cycloalkanes by the deep HDO. The deep HDO was the rate-determining
step, and the apparent activation energies of the three steps were
all lower than those in the literature. Phenol, 1,2-cyclohexanediol,
anisole, and veratrole were the major intermediates, the HDOs of which
were programed for pathway verification. Remarkably, catechol (the
culprit of condensation) was not produced in this system. Overall,
a detailed reaction network of guaiacol HDO was established, and the
veil of Cu/CuMgAlO
x
-catalyzed lignin-derivatives
HDO in supercritical methanol was revealed. This work paved the way
for the application of Cu/CuMgAlO
x
catalyst
in lignin-derivatives upgrading.
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