Transition Metal Ions in Microporous Crystalline Aluminophosphates: Isomorphous Substitution

Abstract

Microporous crystalline metalloaluminophosphates (MeAPO‐n) represent an important group of molecular sieves because of their potential catalytic and adsorptive properties. Many transition metal ions are claimed to incorporate in the framework of these molecular sieves. Here, the concept of isomorphous substitution, and the different indirect and direct tools available to verify this substitution process for Co, Cr, V, Fe and Mn are reviewed taking the AlPO4‐5 structure as an example. In addition, it will be shown that transition metal ions can be used as a probe to follow the hydrothermal synthesis process of microporous aluminophosphates.

One-Step Cyclohexane Nitrosation to e-Caprolactam over Metal Substituted AlPO-5

“…In contrast, the values of d 100 and the lattice constant a of SAPO-5 were smaller than AlPO-5, which can be explained by that the Al-O bond (0.053 nm) is longer than the Si-O bond (0.042 nm). The d 100 values gave the sequence of ionic radii as P 5+ < Si 4+ < Al 3+ < Co 2+ < Mn 2+ < Cr 2+ and P 5+ < Si 4+ < Al 3+ < Co 3+ < Mn 3+ < Cr 3+ , which is in agreement with the ionic radii data shown in Table 2 [26]. The corresponding XRD peaks of the MeAlPOs are shifted to the left with respect to AlPO-5, which may be because the lattice constants increased with metal substitution of Al atoms in the aluminophosphate network.…”

Isomorphous Substitution of Transition-Metal Ions in the Nanoporous Nickel Phosphate VSB-5

“…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.

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Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

“…This allows the isomorphous substitution of Al 3+ and/or P 5+ by transition metal ions. This process is of considerable interest since it gives rise to materials with acid and/or redox sites and consequently leading to interesting catalytic properties [1][2][3][4][5]. In this respect, Co-, Cr-, Fe-, Mn-, Ti-and V-containing aluminophosphate molecular sieves have been extensively studied .…”