Revealing substrate−molecule vibronic coupling enhancement, especially photoinduced charge transfer (CT) process, is hugely important for understanding Surface-enhanced Raman spectroscopy (SERS) enhancement mechanism. In this work, oxygen atoms were extracted from...
Selective breaking of β-O-4 bonds is a challenge
for lignin
depolymerization. Herein, boron (B) was utilized to construct superficial
MoO and subsurface Al(IV)–O–BO2 interfacial
sites of Mo/sepiolite (SEP), which acted as Lewis acid sites to promote
β-O-4 bond cleavage of lignin. Characterizations and density
functional theory (DFT) calculations showed that B could interact
with the quadridentate Al(IV) atoms of SEP to generate Al(IV)–O–BO2 and did not affect the incipient MoO of Mo/SEP. The
experimental results demonstrated that the B content altered the catalytic
performance of Mo/SEP, and B–Mo/SEP achieved 99.3% lignin liquefaction
and the highest selectivity of phenol (48.5%) and ethoxyphenol (27.4%)
monomers. Combined with DFT simulation, the results confirmed that
the antibonding orbital of MoO accepted electrons of alcohol
oxygen, while the B bonding orbital in Al(IV)–O–B–O2 received electrons of benzyl oxygen, promoting the formation
of C+ intermediates. Simultaneously, oxygen vacancies in
SEP activated the ethanol medium to facilitate enol intermediate hydrogenation
for phenolic compounds.
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