Selective Ammoxidation of Propane on Vanadoaluminophosphate Catalysts

Vanadoaluminophosphate(VAPO) crystals having the AlPO-5 structure were synthesized by the rapid crystallization method, and their physical properties and catalytic performance in the ammoxidation of propane were compared with those of vanadosilicate(V-silicate) having the pentasil structure. It was shown that vanadium ions are incorporated more in the AlPO-5 crystal than in the silicate crystal. ESR signal of V⁴⁺ indicated that the vanadium ion was atomically dispersed in VAPO crystal and has the redox property to change its oxidation state between V⁴⁺ and V⁵⁺. Although the vanadium ion in the V-silicate was also atomically dispersed, ESR and UV-visible measurements suggested that V⁴⁺ state is more stable in VAPO than in V-silicate. In accordance with the difference between VAPO and V-silicate, VAPO was more active and selective than V-silicate for the ammoxidation of propane; the selectivity to acrylonitrile attained 33% for VAPO.