4 DISCUSSION
In this study, we demonstrate a chelation-anchored strategy for the
synthesis of Ni@N-C SAC with a Ni loading up to 7.8 wt%. In the
preparation of Ni@N-C SAC, Ni ions
are first well dispersed by chelating with precursor containing OH or
NH2 groups, and then a two-step pyrolysis process not
only restrains the growth of Ni particles but also introducing active N
species into C carrier to form atomically dispersed Ni sites by
providing N coordination site between the Ni and N species. The active
site of Ni@N-C is a Ni-N4 structure according to X-ray
absorption fine structure analysis and computational modeling. Compared
to Ni nano-cluster, the atomically dispersed Ni contributes to lower
adsorption energies of Ni on the carrier, lower H2dissociation energy and energy barriers of the transition states in the
hydrogenolysis process. Therefore,
Ni@N-C SAC exhibits high catalytic
activity in the hydrogenolysis of a lignin model compound and birch
lignin. The 2 D HSQC analysis of lignin and oily products reveals that
Ni@N-C SAC shows high activity not only in cleaving C-O bonds, but also
in cracking C-C bonds in lignin. This methodology opens up a facile
strategy for the design of Ni@N-C SAC catalyst featuring high Ni loading
and excellent catalytic activity in hydrogenolysis of both C-O and C-C
bonds in lignin, highlighting the application potential not only in
hydrocracking of large biomass molecules, but also in other catalytic
reactions.