Catalytic transfer hydrogenation
(CTH) of α,β-unsaturated
aldehydes using single metal atom catalysts supported on nitrogen-incorporated
graphene sheet (M–N
x
-Gr) materials
has attracted increasing attention recently, yet the reaction mechanism
remains to be explored. Compared to the Ni–N4-Gr
model in which the dissociation of isopropanol is highly unfavorable
as a result of steric hindrance and inertness of the Ni–N4 site embedded in graphene, the Ni–N3 site
in Ni–N3-Gr is more active and facilitates the formation
of *H with isopropanol as the H donor, where the dissociation of H
from isopropanol with an energy barrier of 0.83 eV is the rate-determining
step. An alternative reaction path starts from the coadsorption of
isopropanol and furfural molecules at the Ni–N3 site,
followed by a direct hydrogen transfer between the two molecules;
however, the rate-determining step has a much higher energy barrier
of 1.32 eV. Our calculations suggest that the hydrogenation of the
aldehyde group is kinetically more favorable than the CC hydrogenation,
revealing the high chemoselectivity of furfural to furfuryl alcohol.
Our investigations reveal that the CTH mechanism using the Ni–N3-Gr catalyst is different from that on traditional metal oxides,
where the former has only one single active site, while two active
sites are required for the latter. The proposed reaction mechanism
of CTH for furfural in this study should be helpful to guide the design
of single metal atom catalysts with appropriate N coordination for
application in chemoselective hydrogenation reactions.
The exploration of reticular chemistry pertaining to
rod-packing
metal–organic frameworks and the development of solid adsorbents
for multitask hydrocarbon separations are two active topics of current
research. In this study, an In-organic coordination framework compound
denoted ZJNU-121 was assembled from a custom-designed
bithiophene-functionalized tetracarboxylate ligand. The title compound
not only exhibited a rare two-way rod-packing pattern but also displayed
the impressive capability of capturing C2 hydrocarbons
from CH4 and CO2 to achieve C2/C1 and C2/CO2 separations. Under ambient
conditions, the ideal adsorbed solution theory-predicted adsorption
selectivities for equimolar mixtures fall in the range of 8.4–13.8
(C2H
n
/CH4) and 2.3–3.4
(C2H
n
/CO2). Such
separation potentials were also ascertained by the column breakthrough
experiments. Furthermore, the in-depth theoretical insight unveiled
the crucial role of active sites such as thiophene sulfur, carboxylate
oxygen, and the bridging μ2-OH group in capturing
C2 hydrocarbons in preference to CO2 and CH4. Additionally, the structural integrity of ZJNU-121 can be retained in aqueous solutions with pH values varying from
3 to 11 for 24 h at ambient temperature, as verified by the preservation
of PXRD patterns, textural characteristics, and static/dynamic adsorption
behaviors. This research not only enriched the architectural diversity
of rod MOFs but also reported a robust adsorbent with good application
prospects for diversified hydrocarbon separations.
Designing all-solid heterogeneous catalysts with frustrated Lewis pairs (FLPs) has aroused great attentions recently because of its appealing low dissociation energy for H2 molecule and thus a promotion of hydrogenation reaction is expected. The sterically encumbered Lewis acid (metal site) and base (nitrogen site) in the cavity of single transition metal atom doped M/C2N sheet makes it potential candidate with FLP, while a comprehensive understanding of its intrinsic property and reactivity is still required. Calculations show that the complete dissociation of H2 molecule into two H* at the N sites requires two steps, i.e., heterolytic cleavage of H2 molecule and the transfer of H* from metal site to N site, which are highly related to the acidity of the metal site. The Ni/C2N and Pd/C2N, which outperform over the other 8 transition metal atom (M) anchored M/C2N candidates, possess low energy barriers for the complete dissociation of H2 molecule, with values of only 0.30 and 0.20 eV, respectively. Furthermore, both Ni/C2N and Pd/C2N catalysts can achieve semi-hydrogenation of C2H2 into C2H4, with overall barriers of 0.81 and 0.75 eV, respectively, lower than many reported catalysts. It is speculated that M/C2N catalysts with intrinsic FLPs may also find applications in other important hydrogenation reaction.
Improving the reaction selectivity and activity for challenging substrates such as nitroaromatics bearing two reducible functional groups is important in industry yet remains a great challenge using traditional metal nanoparticle...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.