Isolated redox centers within microporous environments.  1.  Cobalt-containing aluminophosphate molecular sieve five

Montes, Consuelo; Davis, Mark E.; Murray, Brendan D.; Narayana, M.

doi:10.1021/j100379a049

Cited by 147 publications

(89 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The spectra for fresh, air-treated and H 2 -treated CoAPO-5 and CoAPO-18 resemble those previously reported for CoAPO-5 12,13 and CoAPO-18. 24,25 Low-energy spectral features have been assigned to Co 2+ , but their sensitivity to coordination symmetry remains unclear, because multiple complex electronic transitions are available in both tetrahedral and octahedral Co 2+ complexes.…”

Section: Chemical and Structural Changes Insupporting

confidence: 86%

“…All MeAPO-5 and MeAPO-18 samples showed X-ray diffraction patterns for the expected crystal structure. 12,13 Very weak diffraction lines for trace crystalline impurities were detected only in CoAPO-5; these appear at angles corresponding to the most intense lines for AlPO-18, indicating the presence of ∼1% AlPO-18 crystals in this sample.…”

Section: Synthesis and Characterization Of Meapo Samplesmentioning

confidence: 86%

See 1 more Smart Citation

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

et al. 2004

View full text Add to dashboard Cite

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.

show abstract

Section: Chemical and Structural Changes Insupporting

confidence: 86%

Section: Synthesis and Characterization Of Meapo Samplesmentioning

confidence: 86%

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

et al. 2004

View full text Add to dashboard Cite

show abstract

“…The increased weight loss of metal-containing AlPO-5s at higher temperatures clearly indicated that there existed strong interactions between the framework of MeAPO-5s and the template, which made TEA molecules strongly bonded in MeAPO-5s. Other authors [16][17][18] have also observed the similar experimental results for metal-containing aluminophosphate molecular sieves (Me = Co, Mn, V, etc.). This is usually taken as a proof that charge deficiency had been induced in the framework by isomorphous substitution of transition metals.…”

Section: Thermal Analysissupporting

confidence: 67%

Characterization of metal-containing molecular sieves and their catalytic properties in the selective oxidation of cyclohexane

Tian

Liu

et al. 2004

Catalysis Today

View full text Add to dashboard Cite

“…1 shows XRD patterns of as-synthesized AlPO 4 -5, calcined AlPO 4 -5 and 0.4 % Rh loaded AlPO 4 -5. The XRD patterns of these samples correspond well with that for reported AlPO 4 -5 structure and do not show any impurity [21][22][23][24][25][26]. Upon calcination, a little increase in intensities of XRD patterns were observed due to little increased particle size.…”

Section: Resultssupporting

confidence: 84%

Catalytic Activity of 0.4 % Rhodium Supported Microporous AlPO4-5 Catalyst for NO-CO-C3H6-O2 Reactions

Samed¹,

Machida²

2018

Asian J. Chem.

View full text Add to dashboard Cite

Temperature-programmed reactions of mixtures of NO, CO, C3H6 and O2 were investigated over rhodium supported on microporous AlPO4-5 catalyst. Same reactions were studied after treating the catalyst in a stream of H2 to evaluate the catalytic performance after reduction treatment. Microporous AlPO4-5 was synthesized hydrothermally using triethylamine as structure directing agent and then been used as a support for rhodium metal. A lower amount of rhodium (0.4 wt %) supported on microporous AlPO4-5 catalyst exhibited satisfactory light-off at temperature (T50 % = 300 ºC) with a steep rise in conversion efficiency after aging the catalyst at 900 ºC for 25 h in a stream of 10 % H2O/air. Outstanding result was observed after reduction treatment of the catalyst, where light-off shifted to a lower temperature 200 ºC maintaining steep rise in conversion efficiency. Rhodium nanoparticles were well dispersed on the high surface area microporous AlPO4-5 material, which is believed to be the key factor for exhibiting excellent catalytic activity both in the oxidizing as well as reducing environment. This newly developed rhodium supported microporous AlPO4-5 catalyst with minimum rhodium loading having excellent catalytic performance after reduction treatment, has the potential to serve as a new generation there-way catalyst.

show abstract

Isolated redox centers within microporous environments. 1. Cobalt-containing aluminophosphate molecular sieve five

Cited by 147 publications

References 0 publications

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

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

Characterization of metal-containing molecular sieves and their catalytic properties in the selective oxidation of cyclohexane

Catalytic Activity of 0.4 % Rhodium Supported Microporous AlPO4-5 Catalyst for NO-CO-C3H6-O2 Reactions

Contact Info

Product

Resources

About