Cu-based
catalysts possess prominent properties in the selective
hydrogenation of carbon-oxygen bonds but suffer from low stability
due to high-temperature sintering. Dandelion-like nanosized mesoporous
silica spheres (NMSSs) with short mesochannels can afford a nanoconfined
space restraining the metal from aggregating. Herein, we report an
air-assisted low-temperature carbonization of the surfactant template
strategy for fabricating N-doped carbon-coated NMSSs (NC@NMSSs) encapsulated
ultra-dispersed Cu cluster catalysts (Cu/NC@NMSSs). The as-obtained
catalysts have demonstrated excellent performances in the hydrogenation
of biomass-derived levulinic acid (LA) into γ-valerolactone
(GVL), achieving a GVL yield as high as 96% and commendable stability
in 100 h. The functional N species and CO groups on the NC
coating layer play a critical role in stabilizing and dispersing Cu
clusters. Theoretical calculations reveal that the pyrrolic and pyridinic
N sites can enrich LA reactants. Accordingly, the apparent activation
energy (E
a) is reduced by half and the
turnover frequency doubled compared to Cu/NMSS catalysts. Additionally,
the catalysts displayed high hydrogenation activities for a variety
of aldehydes, ketones, and nitroarenes. This work offers a convenient
strategy for constructing promising Cu-based catalysts in upgrading
biomass-derived compounds.
Hydrodearomatization attracts extensive interest for
removing polycyclic
aromatic hydrocarbons in diesel but still suffers from sluggish efficiency
due to the vulnerable sulfur resistance of noble metal catalysts and
inferior hydrogenation performance of traditional transition-metal
catalysts. Herein, we propose a low-temperature in situ carbonization
of the template strategy for constructing N-doped carbon interior-modified
MCM-41 (NC@MCM)-confined ultra-dispersed Ni nanocluster catalysts
(Ni/NC@MCM). The optimal hydrogenation catalyst Ni/NC300@MCM with ultrafine Ni nanoclusters (2.4 nm) exhibits 100% naphthalene
conversion and 100% decalin selectivity at 100 °C and atmospheric
pressure. Additionally, trans-decalin stereoselectivity up to 95%
is achieved compared with other catalysts. The N-doped carbon inside
mesochannels not only plays a critical role in stabilizing and dispersing
Ni species but also promotes H2 adsorption/activation and
enriches naphthalene molecules. Theoretical results reveal that the
pyridinic-N and pyrrolic-N species can boost the adsorption of naphthalene.
The dual confinement of active sites and reactants in this microenvironment
makes the outstanding trans-decalin stereoselectivity a reality. Moreover,
Ni/NC300@MCM shows distinguished activities in selective
hydrogenation of dibenzothiophene and quinoline, and the applicability
of the template carbonization method on HMS and MCM-48 is confirmed.
This work opens a unique avenue in promising metal nanocluster catalysts
for stereoselective hydrogenation.
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