Selective catalytic oxidation over ordered nanoporous metallo-aluminophosphates

The aluminophosphate molecular sieves, known as AIPO4-n (also referred as APO-n or AIPO-n), where n denotes to a distinct structure type, are built of strictly alternating [AIO4] and [PO4] tetrahedral units with a general formula: (AlO2)x(PO2)x-yH2O. They form a new class of microporous crystalline materials comparable to the well-known zeolites [1-9]. Further, unlike most zeolites, the aluminophosphate molecular sieves are ordered with an Al/P ratio of unity. The first successful synthesis of aluminophosphate molecular sieve, henceforth designated as APO-n, was reported in 1982 by Wilson et al. [6, 7] and addition of silicon to the aluminophosphate molecular sieves resulting in the silicoaluminophosphates (SAPO-n) was reported in 1984 [8, 9]. Among the various structures of APO-n, some are zeolite analogs but there are also novel, unique, and neutral open-frame-work structures. Apart from their structural similarity, the crystal chemistry of aluminophosphates and zeolites differs considerably. For example, the aluminophosphate framework is neutral in contrast to the negatively charged aluminosilicates.