6 research outputs found
Single-Atom-Based Vanadium Oxide Catalysts Supported on Metal–Organic Frameworks: Selective Alcohol Oxidation and Structure–Activity Relationship
We report the syntheses, structures,
and oxidation catalytic activities
of a single-atom-based vanadium oxide incorporated in two highly crystalline
MOFs, Hf-MOF-808 and Zr-NU-1000. These vanadium catalysts were introduced
by a postsynthetic metalation, and the resulting materials (Hf-MOF-808-V
and Zr-NU-1000-V) were thoroughly characterized through a combination
of analytic and spectroscopic techniques including single-crystal
X-ray crystallography. Their catalytic properties were investigated
using the oxidation of 4-methoxybenzyl alcohol under an oxygen atmosphere
as a model reaction. Crystallographic and variable-temperature spectroscopic
studies revealed that the incorporated vanadium in Hf-MOF-808-V changes
position with heat, which led to improved catalytic activity
Increased Electrical Conductivity in a Mesoporous Metal–Organic Framework Featuring Metallacarboranes Guests
NickelÂ(IV) bisÂ(dicarbollide) is incorporated
in a zirconium-based
metal–organic framework (MOF), NU-1000, to create an electrically
conductive MOF with mesoporosity. All the nickel bisÂ(dicarbollide)
units are located as guest molecules in the microporous channels of
NU-1000, which permits the further incorporation of other active species
in the remaining mesopores. For demonstration, manganese oxide is
installed on the nodes of the electrically conductive MOF. The electrochemically
addressable fraction and specific capacitance of the manganese oxide
in the conductive framework are more than 10 times higher than those
of the manganese oxide in the parent MOF
Increased Electrical Conductivity in a Mesoporous Metal–Organic Framework Featuring Metallacarboranes Guests
NickelÂ(IV) bisÂ(dicarbollide) is incorporated
in a zirconium-based
metal–organic framework (MOF), NU-1000, to create an electrically
conductive MOF with mesoporosity. All the nickel bisÂ(dicarbollide)
units are located as guest molecules in the microporous channels of
NU-1000, which permits the further incorporation of other active species
in the remaining mesopores. For demonstration, manganese oxide is
installed on the nodes of the electrically conductive MOF. The electrochemically
addressable fraction and specific capacitance of the manganese oxide
in the conductive framework are more than 10 times higher than those
of the manganese oxide in the parent MOF
Pushing the Limits on Metal–Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for <i>o</i>‑Xylene Isomerization and Disproportionation
Acid-catalyzed skeletal
C–C bond isomerizations are important
benchmark reactions for the petrochemical industries. Among those, <i>o</i>-xylene isomerization/disproportionation is a probe reaction
for strong Brønsted acid catalysis, and it is also sensitive
to the local acid site density and pore topology. Here, we report
on the use of phosphotungstic acid (PTA) encapsulated within NU-1000,
a Zr-based metal–organic framework (MOF), as a catalyst for <i>o</i>-xylene isomerization at 523 K. Extended X-ray absorption
fine structure (EXAFS), <sup>31</sup>P NMR, N<sub>2</sub> physisorption,
and X-ray diffraction (XRD) show that the catalyst is structurally
stable with time-on-stream and that WO<sub><i>x</i></sub> clusters are necessary for detectable rates, consistent with conventional
catalysts for the reaction. PTA and framework stability under these
aggressive conditions requires maximal loading of PTA within the NU-1000
framework; materials with lower PTA loading lost structural integrity
under the reaction conditions. Initial reaction rates over the NU-1000-supported
catalyst were comparable to a control WO<sub><i>x</i></sub>-ZrO<sub>2</sub>, but the NU-1000 composite material was unusually
active toward the transmethylation pathway that requires two adjacent
active sites in a confined pore, as created when PTA is confined in
NU-1000. This work shows the promise of metal–organic framework
topologies in giving access to unique reactivity, even for aggressive
reactions such as hydrocarbon isomerization
Improving the Efficiency of Mustard Gas Simulant Detoxification by Tuning the Singlet Oxygen Quantum Yield in Metal–Organic Frameworks and Their Corresponding Thin Films
The
photocatalytically driven partial oxidation of a mustard gas simulant,
2-chloroethyl ethyl sulfide (CEES), was studied using the perylene-based
metal–organic framework (MOF) UMCM-313 and compared to the
activities of the Zr-based MOFs: PCN-222/MOF-545 and NU-1000.
The rates of CEES oxidation positively correlated with the singlet
oxygen quantum yield of the MOF linkers, porphyrin (PCN-222/MOF-545)
< pyrene (NU-1000) < perylene (UMCM-313). Subsequently, thin
films of UMCM-313 and NU-1000 were solvothermally grown on a conductive
glass substrate to minimize catalyst loading and prevent light scattering
by suspended MOF particles. Using a conductive glass support, the
initial turnover frequencies of the MOFs in the photocatalytic reaction
improved by 10-fold
Atomistic Approach toward Selective Photocatalytic Oxidation of a Mustard-Gas Simulant: A Case Study with Heavy-Chalcogen-Containing PCN-57 Analogues
Here
we describe the synthesis of two Zr-based benzothiadiazole- and benzoselenadiazole-containing
metal–organic frameworks (MOFs) for the selective photocatalytic
oxidation of the mustard gas simulant, 2-chloroethyl ethyl sulfide
(CEES). The photophysical properties of the linkers and MOFs are characterized
by steady-state absorption and emission, time-resolved emission, and
ultrafast transient absorption spectroscopy. The benzoselenadiazole-containing
MOF shows superior catalytic activity compared to that containing
benzothiadiazole with a half-life of 3.5 min for CEES oxidation to
nontoxic 2-chloroethyl ethyl sulfoxide (CEESO). Transient absorption
spectroscopy performed on the benzoselenadiazole linker reveals the
presence of a triplet excited state, which decays with a lifetime
of 9.4 ÎĽs, resulting in the generation of singlet oxygen for
photocatalysis. This study demonstrates the effect of heavy chalcogen
substitution within a porous framework for the modulation of photocatalytic
activity