A COAPO-34 DERIVED FROM A TRICLINIC PRECURSOR PREPARED IN THE PRESENCE OF HF

The fluoride route of synthesis of AlPO4-34 is also successful in the preparation of its cobalt-modified product (CoAPO-34). The triclinic p recursor of CoAPO-34 has been synthesized in the ct 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 a s-synthesized material results in oxidation of Co(ll). This is evident from the electron absorption, electron paramagnetic resonance, and in frared measurements. The calcined product exhibits a particular sensit ivity to humidity: upon hydration, the chabazite structure transforms to a new one. However, the hydration is a reversible process: thermal evacuation of the hydrated sample causes a complete return to the chab azite material. In comparison with the CoAPO-34 obtained in a nonfluor ide medium, the CoAPO-34 prepared in this work exhibits a higher therm al stability. (C) Elsevier Science Inc. 1997.