Incorporation of Ti(III) into the AlPO4-5 framework by direct synthesis

Abstract

This work focuses on the synthesis and characterization of a conceptually innovative series of TAPO materials, particularly centered in the AFI-structured TAPO-5. Unlike the conventional TAPOs, the so-called Ti(III)APO-5 are prepared by using Ti(III) sources. This strategy aims to avoid the presence of both Ti-O-Al and Ti-O-Ti bonds in TAPOs, undesired for catalytic purposes. The thermodynamic stability of this oxidation state of Ti in water and in the presence of air is low, but the preparation of the gel and the filling of the autoclaves under N 2 atmosphere allowed Ti to maintain its 3+ oxidation state in a considerable proportion in the hydrothermally-crystallized solids. The materials were characterized by powder XRD, ICP chemical analysis, SEM, DR-UV-visible spectroscopy, TGA and 31 P and 27 Al MAS NMR. DR-UV-visible spectroscopy certified the presence of Ti(III) in both tetrahedral and octahedral environments in the as-made samples before being exposed to air, whereas 31 P MAS NMR

Atomic Observations of Microporous Materials Highly Unstable under the Electron Beam: The Cases of Ti‐Doped AlPO4‐5 and Zn–MOF‐74

“…would fall within the experimental error of the electron microscope. Despite the experimental impossibility of assuring the existence of structural deformation, the incorporation of Ti into the P and Al sites would be in good agreement with the conclusion reached by combining indirect characterization techniques in these TAPO materials prepared with Ti III sources as well as their redox catalytic behavior . In Figure b the simulated structure is presented, in which Ti replaced all P atoms, using a crystal thickness of 10 nm.…”

“…The original structure of AlPO 4 ‐5 alternates Al and P units as shown in Figure a in which the Al atoms appears in gray, P in blue, and O in red. It has been reported the isomorphic substitution of P by Ti; P and Al by 2 Ti, and Al by Ti . According to the latest results achieved by X‐ray absorption and emission spectroscopies, if Ti atoms would preferentially occupy the P positions it would result in a large framework deformation as a result of their difference in ionic radii, as Ti−O bonds would increase 0.33 Å.…”

“…Ti III AlPO‐5 material was prepared as described elsewhere . Both the preparation of the gel and the subsequent autoclave sealing were performed under N 2 atmosphere, in a glove bag.…”

Ti(III)APO-5 materials as selective catalysts for the allylic oxidation of cyclohexene: Effect of Ti source and Ti content

“…Recently, we have presented some innovative strategies in TAPO-5 synthesis [25,26], which take advantage of the higher versatility of AlPO 4 frameworks compared to zeolite ones to incorporate heteroatom ions with different charges. Such versatility would, in principle, allow to change the Ti environment within the aluminophosphate framework by means of its incorporation as Ti(III).…”

The state of iron sites in the calcined FeAlPO4-5 and its tuning to the property of microporous AlPO4-5 molecular sieve

“…However, the acidity, adsorption capacity and reactivity of AlPO 4 -5 is still restricted by its neutral framework which leads to the inadequate of active sites [18], and the traditional way to overcome this disadvantage is to introduce doping metals to AlPO 4 -5 [19][20][21][22]. Considering the oxides of Fe are also Lewis acids, the property of AlPO 4 -5 molecular sieves would be tuned after the introduction of Fe, which may also be beneficial to the adsorption and removal of sulfur compound such as thiophene.…”