Computational studies in the AlPO4-34 system

The lattice energies of the as-synthesized fluoride-containing chabazite-li ke 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 substituti on in the AlPO4-34F. The calculations show that the transition metal ions i n MeAPO-34F should preferentially occupy octahedral Al3+ sites, and kinetic reasons are suggested as an explanation for the actual preference of tetra hedral sites. The lattice energies have also been calculated for the calcin ed 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 AlP O4-34h, which is consistent with the fact that AlPO4-34 can only be prepare d starting from AlPO4-34F.