Abstract:A large-pore iron-substituted aluminophosphate molecular sieve of structure type AlPO4-36 was synthesized. Pure and highly crystalline FAPO-36 crystallized hydrothermally from
a gel with a molar composition of 0.2:0.9:1:2:50 FeO:Al2O3:P2O5:Pr3N:H2O at 125°C after 7
days. The effects of the crystallization time and temperature on the crystallinity and phase
purity were examined. FAPO-36 is thermally stable up to 900 °C in air. Elemental analysis
and thermogravimetry indicate isomorphous aluminum substitution by… Show more
“…Detailed Mössbauer results on the Fe-VSB-5 will be published elsewhere . The oxidation of Fe 2+ to Fe 3+ in the synthesis of a porous material has also been reported in FAPO-5, FAPO-34, and FAPO-36. ,, The mean radius ( R Fe = ∼0.652 Å) corresponding to the occupancy (95% Fe 3+ and 5% Fe 2+ ) is then in agreement with the observed decrease of UC volume ( R Ni 2+ = 0.69 Å). 6 Mössbauer spectra (black) of Fe-VSB-5 (sample D) at 77 K fitted with three quadrupolar doublets.…”
The transition-metal-incorporated nickel phosphate molecular sieves (TMI-VSB-5) have been hydrothermally synthesized at 453 K in weak basic conditions under microwave irradiation. By means of X-ray diffraction, inductively coupled plasma (ICP), ultraviolet-visible (UV-vis) diffuse reflectance, and Mössbauer spectroscopies, successful isomorphous (at least partial) substitution of transition-metal ions in the VSB-5 framework has been verified. Characterization results show that the framework structure of nanoporous VSB-5 can accommodate a substantial level of isomorphous substitution of transition-metal ions up to about 10, 5, and 3 atom % for Fe, Mn, and V, respectively, in both octahedral nickel sites (Mn and Fe) and tetrahedral phosphorus sites (V). The isomorphous substitution including the replacement mechanism was studied by not only the change of unit cell parameters but also spectroscopic analysis. The unit cell parameters of TMI-VSB-5 including a unit cell volume and a-axis length relied on the ionic radii difference between the incorporated ion and the original framework ions such as Ni or P (RTMI - RNi or RTMI - RP).
“…Detailed Mössbauer results on the Fe-VSB-5 will be published elsewhere . The oxidation of Fe 2+ to Fe 3+ in the synthesis of a porous material has also been reported in FAPO-5, FAPO-34, and FAPO-36. ,, The mean radius ( R Fe = ∼0.652 Å) corresponding to the occupancy (95% Fe 3+ and 5% Fe 2+ ) is then in agreement with the observed decrease of UC volume ( R Ni 2+ = 0.69 Å). 6 Mössbauer spectra (black) of Fe-VSB-5 (sample D) at 77 K fitted with three quadrupolar doublets.…”
The transition-metal-incorporated nickel phosphate molecular sieves (TMI-VSB-5) have been hydrothermally synthesized at 453 K in weak basic conditions under microwave irradiation. By means of X-ray diffraction, inductively coupled plasma (ICP), ultraviolet-visible (UV-vis) diffuse reflectance, and Mössbauer spectroscopies, successful isomorphous (at least partial) substitution of transition-metal ions in the VSB-5 framework has been verified. Characterization results show that the framework structure of nanoporous VSB-5 can accommodate a substantial level of isomorphous substitution of transition-metal ions up to about 10, 5, and 3 atom % for Fe, Mn, and V, respectively, in both octahedral nickel sites (Mn and Fe) and tetrahedral phosphorus sites (V). The isomorphous substitution including the replacement mechanism was studied by not only the change of unit cell parameters but also spectroscopic analysis. The unit cell parameters of TMI-VSB-5 including a unit cell volume and a-axis length relied on the ionic radii difference between the incorporated ion and the original framework ions such as Ni or P (RTMI - RNi or RTMI - RP).
“…MeAlPO 4 -34 materials have chabazite topology with 8-membered pore openings of the diameter 0.38 nm and thus belong to so-called small-pore microporous materials. The FeAlPO 4 -36 zeotype was prepared hydrothermally as described in ref . The material exhibits a one-dimensional system of channels formed by elliptical 12-membered rings with dimensions of 0.74 nm × 0.65 nm.…”
The incorporation of moderate amounts of Ni(II), Co(II), Fe(II/III), and Mn(II/III) into aluminophosphate zeotype AlPO4-34 and Fe(II/III) into aluminophosphate zeotype AlPO4-36 was studied by broadline 31P NMR. The technique provided direct evidence on isomorphous substitution of framework aluminum by transition metals and allowed us to determine the extent of the substitution. 31P NMR proved to be complementary to other spectroscopic techniques such as X-ray absorption spectroscopy (XAS), Mössbauer, electron paramagnetic resonance (EPR), and electron nuclear double resonance (ENDOR) spectroscopies. The position of the NMR signal belonging to phosphorus in the P(OAl)3(OMe) environment depended mostly on the magnitude of the hyperfine interaction between a phosphorus nucleus and an unpaired electron, which was delocalized from the transition metal atom Me by covalent bonding. The width of the NMR signal was dominated by dipolar coupling among phosphorus nuclei and nearest paramagnetic centers. In addition, broadline NMR of ethylenediamine-templated manganese phosphate (C2H10N2)[Mn2(HPO4)3(H2O)], which was used as a model compound, showed that on the basis of line positions and line widths different 31P signals could easily be assigned to different phosphorus crystallographic sites. The technique could thus be applied to extract valuable structural information about metal phosphates as well.
“…Recently, we have successfully used it for the analysis of FeAPO materials. 33 We applied the carbon monoxide adsorption to assess the presence of Brønsted or Lewis sites on the MnS-1 material and to compare these sites with those observed on the reference ZSM-5 sample (Figure 12):…”
Manganese-containing silicalite-1 (MnS-1) was synthesized hydrothermally in the presence of the structure-directing agent (template) tetraethylammonium hydroxide (TEAOH) for the first time. The highly crystalline MnS-1 crystallized from a gel with a molar composition of 2:1:1:50:25:935 Na 2 O:K 2 O:MnO:SiO 2 :TEAOH:H 2 O at 175 °C after 3 days. The product was thermally stable up to 700 °C in air. The template-free MnS-1 was prepared by calcination at 550 °C in an oxygen flow. The incorporation of manganese into the framework sites of silicalite-1 was suggested by elemental, thermogravimetric, and cation exchange analyses. The X-ray absorption spectroscopic methods XANES and EXAFS confirmed the incorporation of Mn 3+ into a silicalite-1 framework. FT-IR spectroscopic studies of CO adsorption at 100 K on the MnS-1 revealed the Lewis acidity of the sample and the presence of both Mn 3+ and Mn 2+ cations in the structure.
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