Hydrothermal synthesis of co-rich CoAPO-5 molecular sieves

A series of CoAPO-5 materials have been hydrothermally synthesized to maximize the degree of isomorphous substitution of Co2+ ions in the AFI framework. The as-synthesized as well as the calcined CoAPO-5 materials have been characterized with XRD, SEM, ICP, DRS (diffuse reflectance spectroscopy) and FT-IR techniques. Optimum conditions for the synthesis of Co-rich CoAPO-5 molecular sieves have been obtained by evaluating the influence of the amount and type of cobalt source, the type of aluminium source, the type of template molecule, the [template]:[P2O5] ratio and the amount of different monovalent cations on the isomorphous substitution of Co2+ in the lattice. It will be shown that highly-crystalline hexagonal CoAPO-5 crystals with a substitution degree of 12% can be obtained from a CsCl . Co(CH3COO)(2). 4H(2)O . pseudo-gamma -AlO(OH).H3PO4. (C2H5)(3)N .H2O gel (with [(C2H5)(3)N]:[P2O5] and [CsCl]:[Co(CH3COO)(2)] ratios of respectively 1.0 and 0.5) autoclaved for 41 h at 190 degreesC. In addition, the effect of monovalent cations on the redox properties of Co2+ in CoAPO-5 molecular sieves will be discussed. The degree of oxidation of framework Co2+ to Co3+ is always relatively low and increases in the order Li+<K(+)approximate to Rb(+)approximate to Cs+< NH(4)(+)approximate to Na+. Thus, the addition of Li+ results in a stabilization of Co2+ in the framework of CoAPO-5 molecular sieves upon calcination.