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 s alts. The materials obtained contained the elements Al:P:V=100:X:Y, wh ere 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 neutra l at high addition (20%) of those heteroatoms. The activation energies , calculated according to the Coats-Redfern procedure, were found to i ncrease on adding 5% of P or V and then to drop at higher addition. Th e 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 alumi na 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 it s original values. The maximum of the surface area appears in samples where the NH4NO3 decomposition follows almost equal endothermic and ex othermic routes. (C) 1997 Elsevier Science B.V.