Interaction of acetonitrile with cobalt-containing aluminophosphates: An X-ray absorption investigation

XAFS data have been collected on reduced cobalt-containing aluminophosphate molecular sieves, both before and after sorption of the probe molecule, acetonitrile. Data are reported for CoAlPO-5, CoAlPO-18, CoAPSO-44, and cobalt-exchanged SAPO-18. Analysis of both the XANES and EXAFS reveals three different types of species: in the first the acetonitrile is coordinated linearly to the Co2+ in the framework (Bronsted acid) center; in the second, a nonlinear structure is suggested in which the nitrogen of the acetonitrile occupies an oxygen vacancy, thereby coordinating to Co2+ Lewis acid sites. In the third, two or more of the probe molecules coordinate to extraframework Co2+ ions. The results are consistent with the models proposed for Bronsted and Lewis acid centers in these systems in a previous EXAFS study.