The interaction of alkaline earth cations with metal-oxygen cluster compounds and the implications for their use as heterogeneous catalysts

The magnesium, calcium, strontium and barium salts of 12-tungstophosphoric and 12-molybdophosphoric acids have been prepared. Evidence of the presence of the Keggin anion (primary structure) was obtained from infrared spectroscopic measurements but powder X-ray diffraction and differential thermal analysis measurements indicated that changes to the secondary structure had occurred. BET surface areas were small for all of the materials studied and no dependence on the cation radius was observed. A crystallographic investigation demonstrated that divalent cations were not incorporated into the lattice suggesting that materials believed to be divalent 12-heteropoly salts are mixtures of the parent acid and a divalent cation salt.