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.