A CoAPO-34 derived from a triclinic precursor prepared in the presence of HF

Abstract

The fluoride route of synthesis of AIPO,-34 is also successful in the preparation of its cobalt modified product (CoAPO-34). The triclinic precursor of CoAPO-34 has been synthesized in the presence of HF and piperidine. Although two different Al sites are available for cobalt(ll) substitution (i.e., tetrahedral and octahedral sites), cobalt(ll) substitutes exclusively the tetrahedral aluminum. Calcination of the as-synthesized material results in oxidation of Cofll). This is evident from the electron absorption, electron paramagnetic resonance, and infrared measurements. The calcined product exhibits a particular sensitivity to humidity: upon hydration, the chabazite struc ture transforms to a new one. However, the hydration is a reversible process: thermal evacuation of the hydrated sample causes a complete return to the chabazite material. In comparison with the CoAPO-34 obtained in a nonfluoride medium, the CoAPO-34 prepared in this work exhibits a higher thermal stability.