The Catalyst Review September 2019 - 15

EXPERIMENTAL
The FLPs containing fewer oxygen vacancies (VO
monomer and dimer) are less stable under vacuum,
but they can be dynamically formed at reaction
conditions such as thermal fluctuation at high
temperatures and reactant-adsorption. (2) The
dissociative activation of methane can be readily
achieved at solid FLPs with the activation energy
being as low as 0.74 eV on FLP-2VO and 0.63 eV on
FLP-3VO. The superb activity of FLPs for methane
activation is attributed to the stronger interaction
with methane via the local electric field of Lewis
pairs and the increased electron transfer from FLPbase sites to the antibonding orbital of C−H bond of
methane. (3) The nonoxidative coupling of methane
into ethane and ethylene is revealed to be feasible
at CeO2(110)-based FLPs. The critical C−C coupling
of methyl groups at FLP sites has a reaction barrier
of 1.1 eV, much lower than that of previously
reported methyl group desorption and gas-phase
C−C coupling. Although the formation of hydrogen
to regenerate FLPs seems to be difficult, it can be
overcome at high temperatures.

Figure 1. (a) Root-mean-square deviation of atom positions of CeO2(110)-3VO surface in AIMD
simulations at 300 and 700 K. Time evolution of Cartesian coordinates (z) of selected O atoms
(colored in magenta, blue, and cyan) neighboring to VOs on CeO2(110)-3VO at both (a) 300 K
and (b) 700 K. The dashed line at z = 8.2 Å is the reference coordinate. The structures in the
upper panels in (b) and (c) correspond to the states labeled as green dots in the corresponding
time evolution curves. The green circles marked within the structures denote the positions of
the intact VOs

Figure 2. Nonoxidative coupling of methane to ethane on CeO2(110) surfaces. (a) Potential
energy diagram of the reactions at FLP-2VO sites (blue curve) and FLP-3VO sites (green
curve). The zero energy reference corresponds for the sum of energies of CH4(g), and the
corresponding clean CeO2(110) surfaces. (b,c) Geometric structures of transition states in
dissociation of the second methane, formation of ethane and hydrogen.

These results provide insights into the formation of
solid FLPs on CeO2 surfaces and methane activation
at FLP sites. More importantly, this study uncovers
a possible strategy for nonoxidative coupling of
methane into valuable hydrocarbons on FLPscontained oxide catalyst and may provide guidance
for experimental design of FLP catalysts. Source:
Huang ZQ, Zhang T, Chang CR, et al. (2019). ACS
Catal., 9: 5523−5536.
Efficient Electrocatalytic CO2 Reduction Driven by Ionic Liquid Buffer-Like Solutions...
Rising levels of atmospheric CO2 are driving
Figure 1. Examples of ILs used as electrolytes for CO2 reduction.
the development of new methods for
its capture and utilization. One approach
that has generated considerable attention
involves electroreduction using reusable
electricity. Metals such as Ag and Au can
electrocatalyze the reduction of CO2 to CO
in aqueous media, but relatively high reduction overpotentials and low selectivities are often observed. Moreover, CO2 electroreduction in aqueous media is complicated by competitive co-electrogeneration of H2, which reduces the faradaic efficiency for CO
production, The use of ionic liquids (Figure 1), on the other hand, results in a dramatic reduction of the CO2-reduction overpotential
in aqueous electrolytes.
Herein, the authors show that the use of basic ILs capable of forming buffer-like solutions in aqueous media allows electro-chemical
reduction of CO2 at remarkably low overpotentials with high selectivity and faradaic efficiency for CO production. Specifically, they
demonstrated that mixtures of [BMMIm][OAc], DMSO, and water can dissolve up to 43 mol% CO2 (27 mol% through formation of
bicarbonate and 16 mol% through solvated CO2) at atmospheric pressure. The resulting solution supports selective electroreduction
of CO2 to CO at Au electrodes at potentials as low as -1.40 V vs. Ag/AgCl. At -1.80 V vs. Ag/AgCl, faradaic efficiencies for CO
formation above 98% are observed. Addition of large amounts of water to the electrolyte favors the formation of free bicarbonate,
which reduces the energy required for the electro-chemical reduction of CO2, but this is accompanied by the co-electrogeneration of
H2, yielding syngas that can be used for the formation of liquid fuel through follow-on processing.
The Catalyst Review

September 2019

The Catalyst Review September 2019

Table of Contents for the Digital Edition of The Catalyst Review September 2019