[M]-CAL-2: MeAPSO-34-like molecular sieves using a lamellar aluminophosphate as precursor

[M]-CAL-2 (M = Mn, Co and Fe) are metallosilicoaluminophosphates ([M]-APSO) with chabazite-related structure, which are part of the CAL molecular sieves family. They were prepared with a recently developed synthesis based on the use of layered AlPO precursor. The used procedure allowed to obtain high loadings of metal ions and to control the morphology of the crystals. The materials were characterized by structural techniques such as X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetry (TGA), and spectroscopic techniques such as UV-Vis and Fourier transformed Infrared (FTIR) with particular attention to the study of their redox functionalities. The results show that [M]-CAL-2 crystals presented rhombohedra morphology and the particles sizes are dependent of the metal concentration in the precursor gel, in addition these particles have a lamellar memory originated from the layered AlPO precursor. The FTIR, UV-Vis and elemental results supported the presence of transition metal ions on the framework of the synthesized materials and allowed to envisage the dependency of the metal and silicon concentrations on a Lowenstein-like ruled substitution mechanism. Finally, the reversible redox behavior of the materials was studied by in situ UV-Vis-NIR spectroscopy. This aspect together with the already shown acidity of CAL samples allowed confirming the acid and redox bifunctionality of the obtained molecular sieves, which can thus be proposed for catalytic applications.