2 research outputs found
Combined Electrocatalytic Oxidation and Reduction to Selectively Cleave β‑O‑4 Linkage of Lignin over Platinum Electrode in Organic Solvent: Secondary Treatment Opportunity for CELF Process
Valorization of lignin is gaining popularity due to its
ability
to make industrial processes more sustainable. However, the currently
prevalent catalytic technologies use large amounts of energy and harsh
reaction conditions. As a result, bonds between lignin precursors
are cleaved unselectively and the selectivity of aromatic products
is reduced. An electrocatalytic approach may allow improved control,
and few studies have assessed the electrocatalytic oxidation and reduction
of lignin in organic solvents. Organic solvents like tetrahydrofuran
(THF) are of interest for lignin electrocatalysis due to their use
in the cosolvent-enhanced lignocellulosic fractionation (CELF) process.
The CELF process has the ability to overcome biomass recalcitrance
by breaking β-O-4 aryl ether interunit linkages. Using electrocatalytic
conversion processes, additional β-O-4, interunit linkages can
be broken down selectively. As a result, if these two processes are
integrated, a high amount of phenolic hydroxyl groups with low-content
aryl ether linkages will be produced, making the product suitable
for the development of biofuels and other chemicals. This study shows
that by using controlled electrocatalytic oxidation and reduction
in THF/aqueous acidic electrolytes in the ratio of 2:1, nonpolar β-O-4
linkages can be cleaved. This ratio was chosen to mimic the electrolyte
composition environment of the CELF pretreatment. The results from
both attenuated total reflection-infrared spectroscopy (ATR-IR) and
NMR characterization are consistent and show that β-O-4 interlinkage
bonds were broken. Quantitative calculations from NMR show that during
controlled oxidative potential holds (constant potential oxidation),
the presence of aromatic structural components of the lignin polymer
increased by 28.67% and aliphatic structural components decreased
by 32.73%. On the other hand, during controlled reductive potential
holds (constant potential reduction), the presence of aromatic structural
compounds decreased by 33.50% and aliphatic structural compounds decreased
by 78.43%. These results indicate that electrooxidation and electroreduction
may be used strategically to cleave interunit linkages. Thus, if electrochemical
degradation of lignin is used as a secondary treatment in conjunction
with the CELF process, it will greatly increase the possibility of
transforming lignin into value-added products
Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials
Electrolyte cations can have significant effects on the
kinetics
and selectivity of electrocatalytic reactions. We show an atypical
mechanism through which electrolyte cations can impact electrocatalyst
performancedirect incorporation of the cation into the oxide
electrocatalyst lattice. We investigate the transformations of copper
electrodes in alkaline electrochemistry through operando X-ray absorption
spectroscopy in KOH and BaÂ(OH)2 electrolytes. In KOH electrolytes,
both the near-edge structure and extended fine-structure agree with
previous studies; however, the X-ray absorption spectra vary greatly
in BaÂ(OH)2 electrolytes. Through a combination of electronic
structure modeling, near-edge simulation, and postreaction characterization,
we propose that Ba2+ cations are directly incorporated
into the lattice and form an ordered BaCuO2 phase at potentials
more oxidizing than 200 mV vs the normal hydrogen electrode (NHE).
BaCuO2 formation is followed by further oxidation to a
bulk Cu3+-like BaxCuyOz phase at 900 mV vs
NHE. Additionally, during reduction in BaÂ(OH)2 electrolyte,
we find both Cu–O bonds and Cu–Ba scattering persist
at potentials as low as −400 mV vs NHE. To our knowledge, this
is the first evidence for direct oxidative incorporation of an electrolyte
cation into the bulk lattice to form a mixed oxide electrode. The
oxidative incorporation of electrolyte cations to form mixed oxides
could open a new route for the in situ formation of active and selective
oxidation electrocatalysts