Characterization of MnAPO-5 for Ethane Oxydehydrogenation

Wu, Juinn-Yao; Chien, Shu‐Hua; Wan, Ben‐Zu

doi:10.1021/ie000291k

Cited by 15 publications

(18 citation statements)

References 37 publications

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“…The maximum absorption is observed at 41 700 30 Wu et al reported UV-visible spectra for MnAPO-5 treated in air at 823 K for 6 h but then exposed to ambient moisture, which leads to coordination by water and changes in the electronic spectrum of Mn centers. 7 Nevertheless, their spectra resemble those reported here for samples held within strictly controlled anhydrous environments. Their study reported two ligand-to-metal charge-transfer bands at 45 450 and 38 760 cm -1 and one d-d absorption band at 20 000 cm -1 .…”

Section: Chemical and Structural Changes Insupporting

confidence: 79%

“…Their study reported two ligand-to-metal charge-transfer bands at 45 450 and 38 760 cm -1 and one d-d absorption band at 20 000 cm -1 . 7 In contrast with air-treated MnAPO-18, UV-visible spectra for fresh and H 2 -treated MnAPO-18 resemble those for pure The results of chemical analysis of the effluent during H 2 -TPR were compared with the relative amounts of divalent and trivalent cations obtained from UV-visible spectra by carrying out H 2 -TPR experiments while continuously monitoring UVvisible spectra (e.g., MnAPO-5-1; Figure 7a). The d-d band for Mn 3+ (18 000 cm -1 ) was used as reference as the spectrum changed during TPR; using the band at 37 000 cm -1 led to identical results, because it decreased to the same extent during reduction and corresponds to the same species.…”

Section: Chemical and Structural Changes Inmentioning

confidence: 99%

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Structural and Functional Characterization of Redox Mn and Co Sites in AlPO Materials and Their Role in Alkane Oxidation Catalysis

et al. 2004

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The number of redox-active and inactive Mn and Co species in MeAPO-5 and MeAPO-18 (Me ) Mn, Co) was measured from H 2 consumption rates during H 2 temperature-programmed reduction (H 2 -TPR), and their structure and oxidation state were probed at identical conditions by UV-visible and X-ray absorption spectroscopies. H 2 consumption, loss of Me 3+ UV-visible features, and a decrease in X-ray absorption edge energy occurred concurrently and at similar rates, indicating excellent agreement between these techniques. No H 2 O or CO 2 were detected during treatment in H 2 or CO, respectively, indicating that reduction from Me 3+ to Me 2+ occurred by introduction of protons. These protons are fully removed by treatment in O 2 to 773 K, and O 2 -H 2 redox cycles involving reversible proton formation suggest that cations reside within AlPO framework positions, in which protons reside as charge balancing cations at Me 2+ -O-P bridges. H 2 consumption rates measured during H 2 -TPR could be accurately described by Arrhenius-type behavior, and H 2 /Me ratios showed that only a fraction of all Me cations undergo reversible redox cycles. This fraction was 0.86 for MnAPO-18 (atomic Mn/P ) 0.05); it decreased from 0.68 to 0.40 for MnAPO-5 as Mn/P ratios increased from 0.028 to 0.10. For CoAPO-18 with 0.028 Co/P and CoAPO-5 with 0.40 Co/P, the fractions of redox sites were 0.64 and 0.40, respectively. UV-visible spectra showed no detectable Me 3+ features after thermal treatment in H 2 . Thus, cations that do not undergo redox cycles remain as permanently divalent cations throughout O 2 -H 2 cycles. The redox-active fraction also decreased during repeated H 2 -O 2 redox cycles above 773 K, indicating that redox cations convert into permanently divalent sites. This conversion coincides with the evolution of H 2 O during H 2 treatments above 773 K. These findings together with the effects of Me/P ratio on the redox fraction are consistent with a mechanism in which OH groups at divalent framework cation sites recombine to form H 2 O and an oxygen vacancy. Cyclohexanol and cyclohexanone formation rates during liquid-phase cyclohexane oxidation with O 2 on MnAPO-5 samples increased linearly with the number of redox-active sites, suggesting that elementary steps of cyclohexane oxidation involve cycling between Me 2+ and Me 3+ , and require cation sites able to reversibly form charge balancing cationic species.

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Section: Chemical and Structural Changes Insupporting

confidence: 79%

Section: Chemical and Structural Changes Inmentioning

confidence: 99%

Structural and Functional Characterization of Redox Mn and Co Sites in AlPO Materials and Their Role in Alkane Oxidation Catalysis

et al. 2004

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“…The ESR signal at g = 2.007 is typical of superoxide anion radicals (O 2 − ). 22,23 After discharge, the intensity of this ESR peak decreased drastically, suggesting that O 2 − contributes to the formation of Li 2 O 2 or Li 2 O. Although we did not detect LiO 2 , Bruce et al reported that the initial product in an air electrode is LiO 2 from the Raman spectra.…”

Section: Resultscontrasting

confidence: 50%

“…ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.114.34 22. Downloaded on 2014-11-Ex-situ Raman spectroscopy of mesoporous β-MnO 2 /Pd/TAB (75/15/10) electrode before discharge and after discharge to 2.Charge-discharge curves of a lithium-air battery using mesoporous β-MnO 2 modified with Pd air electrode in dry air atmosphere between 4.0-2.0 V at a current density of 0.12 mA cm −2 .…”

mentioning

confidence: 99%

Mesoporous β-MnO2 Air Electrode Modified with Pd for Rechargeability in Lithium-Air Battery

Thapa

Hidaka

Hagiwara

et al. 2011

J. Electrochem. Soc.

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The electrochemical performance and electrode reactions using ordered mesoporous β-MnO 2 modified with Pd as a cathode catalyst for rechargeable Li-air batteries was reported. Well-ordered mesoporous β-MnO 2 was prepared using mesoporous silica KIT-6 as a template under hydrothermal synthesis of Mn(NO 3 ) 2 · H 2 O. The obtained mesoporous β-MnO 2 shows narrow pore size distribution of 1 nm. With the dispersion of small amounts of Pd to β-MnO 2 , mesoporous β-MnO 2 exhibited a high initial discharge capacity of 817 mAh/g -cat. with high reversible capacity. Charging potential is suppressed at 3.6 V vs. Li/Li + , which is highly effective for preventing the decomposition of organic electrolyte. The mesoporous β-MnO 2 /Pd electrode shows good rate capability and cycle stability. Ex-situ and in-situ XRD results suggested that the observed capacity comes primarily from the oxidation of Li + to Li 2 O 2 followed by Li 2 O after discharge to 2.0 V vs. Li/Li + . Electron spin resonance measurements suggest that the formation of superoxide anion radicals contributs to the oxidation of Li + and the radicals were recovered during charge. Ex-situ FTIR measurement suggested that no electrolyte decomposition was observed and no Li 2 CO 3 was formed during discharge when ethylene carbonate (EC)-diethyl carbonate (DEC) (3:7), which is highly stable for Li-air battery, was used as the electrolyte.The coming new energy economy must be based on a cheap and sustainable energy supply. Combined with sustainable resources such as wind and solar power, chemical energy storage using batteries can contribute to a potential solution. Currently, battery research and development is focused on energy storage and conversion with highenergy high-power density and reliable safety. 1-4 Metal-air batteries have attracted considerable attention because of their extremely large specific capacity. The reason for such a large specific capacity is that these cells consist of lithium metal as an anode and an air electrode for activation of oxygen in air; hence these metal-air batteries have a simple structure. Among the various metal-air battery systems, the lithium-air battery is the most attractive because it has the highest energy density per unit weight. The cell discharge reaction occurs between Li and oxygen to yield Li 2 O or Li 2 O 2 , with a theoretical discharge voltage of ca. 3.0 V and a theoretical specific energy density up to 5200 Wh/kg -Li . In practice, the storage of oxygen in the battery is unnecessary, because air can be directly used. Therefore, the theoretical specific energy (excluding oxygen) is 11.140 kWh/kg -Li , which is much higher than that of other advanced batteries and methanol direct fuel cells. Abraham and Jiang reported an Li-air battery using a nonaqueous electrolyte. 5 They suggested that lithium peroxide is a discharge product based on 2(Li + + e − ) + O 2 → Li 2 O 2 , which resulted in a theoretical voltage of 2.96 V. However, because of low oxygen solubility in a nonaqueous electrolyte, the reported power density ...

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“…The spectra show a strong and narrow signal with axial symmetry (g ⊥ = 1.987 and g || = 1.938; H PP = 44 G), which ascribed to Cr (V) [22]. For CrAPO-5 (D), a weak broad band at g = 2.028 was also detected, which coincides with the position of Mn (III) signal [23]. This spectral feature is in agreement with our EDX analysis result shown in Table 2 and Fig.…”

Section: Resultsmentioning

confidence: 81%