Epoxidation of propylene by hydrogen peroxide catalyzed by the silanol‐functionalized polyoxometalates‐supported ferrate: Electronic structure, bonding feature, and reaction mechanism
Abstract:Hydrogen peroxide (H2O2), as clean oxidant, has been disregarded due to its low efficiency and selectivity for the oxidation of olefins. In the present paper, the redox‐important ferrate anion (FeO42−) has been anchored to a silanol‐decorated polyoxometalates (POM) to form a single site‐supported Fe‐POM catalyst. Possible reaction mechanisms for the epoxidation of propylene with H2O2 catalyzed by the Fe‐POM catalyst have been investigated based on density functional theory with the M06L functional. The study o… Show more
“…The catalytic efficiency (CAT) of 1 -GO-GCE was calculated by the following formula where I p (POM, substrate) and I p (POM) are the anode peak currents of 1 -GO-GCE with and without the attendance of DA.…”
{P6Mo18} poly(oxometalate) (POM) clusters
have huge steric hindrance and limited active oxygen atoms, which
make them difficult to combine with metal–organic units to
form three-dimensional (3D) porous structures. Therefore, functionalization
of such POMs has always been a bottleneck that is difficult to break
through. In this study, {P6Mo18} POM was successfully
grafted on a lock-like metal–organic chain to generate a multiporous
coordination polymer, [{Na(H2O)(H2btb)}{Cu4
I(H2O)(pz)5Cl}{H2Sr⊂P6Mo2
VMo16
VIO73}]·3H2O (1) (pz
= pyrazine; btb = 1,4-bis(1,2,4-triazole) butane). Meanwhile, a zero-dimensional
(0-D) control compound with only btb ligands as counterions, (H4btb)[H4Sr⊂P6Mo2
VMo16
VIO73]·3H2O (2), was also obtained via a hydrothermal reaction.
Compound 1 represents the first basket-type 3D poly(oxometalate)
metal–organic framework (POMOF) assembly, which possesses interpenetrating
pores and complex topology. 1-GO-CPE displays improved
supercapacitor (SC) performance (the specific capacitance of 929.4
F g–1 at a current density of 3 A g–1 with 94.1% of cycle efficiency after 5000 cycles) compared with 2-GO-CPE and most reported POMOF electrode materials, which
may be due to the outstanding redox capability of basket-POM, introduction
of metal–organic chains, intersecting pores, and excellent
conductivity of graphene. An asymmetric SC device with 1-GO-CPE as the negative electrode exhibits an energy density of 29.7
Wh kg–1 with a power density of 3148.2 W kg–1 and long-lasting cycling life. In addition, 1-GO-GCE as an electrochemical sensor responds to dopamine
(DA) at a voltage of 0.40 V and shows lower detection limits (0.19
μM (signal-to-noise ratio (SNR) = 3)), higher selectivity, and
good reproducibility in the linear range of 0.56 μM to 0.24
mM. The ability to accurately detect the content of DA in biological
samples further proves the feasibility of the sensor in practical
applications.
“…The catalytic efficiency (CAT) of 1 -GO-GCE was calculated by the following formula where I p (POM, substrate) and I p (POM) are the anode peak currents of 1 -GO-GCE with and without the attendance of DA.…”
{P6Mo18} poly(oxometalate) (POM) clusters
have huge steric hindrance and limited active oxygen atoms, which
make them difficult to combine with metal–organic units to
form three-dimensional (3D) porous structures. Therefore, functionalization
of such POMs has always been a bottleneck that is difficult to break
through. In this study, {P6Mo18} POM was successfully
grafted on a lock-like metal–organic chain to generate a multiporous
coordination polymer, [{Na(H2O)(H2btb)}{Cu4
I(H2O)(pz)5Cl}{H2Sr⊂P6Mo2
VMo16
VIO73}]·3H2O (1) (pz
= pyrazine; btb = 1,4-bis(1,2,4-triazole) butane). Meanwhile, a zero-dimensional
(0-D) control compound with only btb ligands as counterions, (H4btb)[H4Sr⊂P6Mo2
VMo16
VIO73]·3H2O (2), was also obtained via a hydrothermal reaction.
Compound 1 represents the first basket-type 3D poly(oxometalate)
metal–organic framework (POMOF) assembly, which possesses interpenetrating
pores and complex topology. 1-GO-CPE displays improved
supercapacitor (SC) performance (the specific capacitance of 929.4
F g–1 at a current density of 3 A g–1 with 94.1% of cycle efficiency after 5000 cycles) compared with 2-GO-CPE and most reported POMOF electrode materials, which
may be due to the outstanding redox capability of basket-POM, introduction
of metal–organic chains, intersecting pores, and excellent
conductivity of graphene. An asymmetric SC device with 1-GO-CPE as the negative electrode exhibits an energy density of 29.7
Wh kg–1 with a power density of 3148.2 W kg–1 and long-lasting cycling life. In addition, 1-GO-GCE as an electrochemical sensor responds to dopamine
(DA) at a voltage of 0.40 V and shows lower detection limits (0.19
μM (signal-to-noise ratio (SNR) = 3)), higher selectivity, and
good reproducibility in the linear range of 0.56 μM to 0.24
mM. The ability to accurately detect the content of DA in biological
samples further proves the feasibility of the sensor in practical
applications.
“…On comparison of the IR spectra of 1 – 3 before and after electrocatalytic studies, the characteristic peak positions of the three samples are basically consistent with each other, which shows that polymers 1 – 3 have outstanding electrocatalytic stability. The catalytic efficiencies of 1 -GCE– 3 -GCE according to the formula of catalytic efficiency (CAT) were calculated, and the bar graph of the CAT% of 1 -GCE– 3 -GCE vs AA/H 2 O 2 concentration is shown in Figure d. The order of CAT of 1 -GCE– 3 -GCE for reduction of H 2 O 2 or oxidation of AA is 2 -GCE > 3 -GCE > 1 -GCE, indicating that the host–guest POMOF structure of 3 exhibits a more prominent catalytic effect.…”
Different metal−organic units were introduced into the {PMo 12 } polyoxometalate (POM) system to yield three porous coordination polymers with distinct characteristics, {Cu(pra) 2 } [{Cu-(pra) 2 } 3 {PMo 11 VI Mo V O 40 }] (1), [{Ag 5 (pz) 6 (H 2 O) 0.5 Cl}{PMo 11 VI Mo V O 40 }] (2), and [{Cu 3 (bpz) 5 (H 2 O)}{PMo 12 O 40 }](3) (pra = pyrazole; pz = pyrazine; bpz = benzopyrazine), via an in situ hydrothermal method. In comparison with the maternal Keggin cluster and most reported POM electrode materials, compounds 1−3 exhibit larger specific capacitances (672.2, 782.1, and 765.2 F g −1 at a current density of 2.4 A g −1 , respectively), superior cyclic stability (91.5%, 89.3%, and 87.8% of cycle efficiency after 5000 cycles, respectively), and boosted conductivity, which may be attributed to the introduction of metal−organic units. The result indicates that metal−organic units can effectively enhance the capacitance performance of POMs. This may be due to the fact that they provide additional redox centers, induce the formation of stable porous structures, and improve ion/electron transfer efficiency. Compounds 1−3 present excellent electrocatalytic activity in reducing peroxide (H 2 O 2 ) and oxidizing ascorbic acid (AA). In addition, compound 2 shows an outstanding sensing performance detection of AA and H 2 O 2 .
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