New Strategy for Chromium Substitution and Crystal Morphology ControlSynthesis and Characteristics of CrAPO-5

Additional component(s) introduced into the reaction gel allow for a stable framework substitution of Cr in significant amounts. Appropriate component(s) and metal compounds, especially those of Al, are primary factors determining the substitution. The products of the system {triethylamine−acetate ions−Cr3+ ions} have been characterized in more detail and compared with those from other synthesis procedures. The Cr heteroatoms are 4-fold bonded to the framework and their coordination is complemented by two ligands from the pores (water molecules in the calcined form) to give the favored octahedral-like coordination. The coordination can be changed reproducibly from 6 to 4 by heating the crystals over 550 K (dehydration) and vice versa by cooling (hydration). The framework Cr(III) cannot be oxidized and causes no framework charge. The reaction conditions, differing from those in the classical syntheses, enable the control of the crystal morphology. The crystals can be grown as flat hexagonal pellets of a perfect morphology with high crystallinity and sorption properties