Thermochemical effects in the development of mesoporous alumino-phosphoro-vanadates from ammonium nitrate precursors

Mesoporous alumino-phosphoro-vanadate solids were prepared by heating precipitates of the corresponding metals containing ammonium nitrate salts. The materials obtained contained the elements Al:P:V=100:X:Y, where X, Y=O, 5, 10, 20 (16 samples overall). Thermogravimetric analysis showed that the addition of P or V in the solids influences the endo- and exothermicity of the NH4NO3 decomposition, driving the net result from highly endothermal at no addition of P and/or V to almost neutral at high addition (20%) of those heteroatoms. The activation energies, calculated according to the Coats-Redfern procedure, were found to increase on adding 5% of P or V and then to drop at higher addition. The order of the decomposition reaction drops from approximate to 0.5 to 0 at 20% of P and/or V heteroatoms. The materials obtained had a high surface area (BET) which increases from 200 m(2) g(-1) for pure alumina to almost 400 m(2) g(-1) on addition of 5-10% of P and/or V, while further addition of those heteroatoms decreases the surface area to its original values. The maximum of the surface area appears in samples where the NH4NO3 decomposition follows almost equal endothermic and exothermic routes. (C) 1997 Elsevier Science B.V.