Computational Studies in the AlPO4-34 System

The lattice energies of the as-synthesized fluoride-containing chabazite-like aluminophosphate (AlPO₄-34F) and of the corresponding metal-substituted materials MeAPO-34F, Me = Mn(II), Co(II), Ni(II)] have been calculated in order to investigate the Al-site preference the transition metal substitution in the AlPO₄-34F. The calculations show that the transition metal ions in MeAPO-34F should preferentially occupy octahedral Al³⁺ sites, and kinetic reasons are suggested as an explanation for the actual preference of tetrahedral sites. The lattice energies have also been calculated for the calcined AlPO₄-34F material (AlPO₄-34) and the rehydrated-calcined product (AlPO₄-34h). The AlPO₄-34 is found to be less stable than either AlPO₄-34F or AlPO₄-34h, which is consistent with the fact that AlPO₄-34 can only be prepared starting from AlPO₄-34F.