Structure and chemistry of cobalt in CoAPO-5 molecular sieve

Abstract

The single crystals of various cobalt contained tetraethylamine (TEA) CoAPO-5 molecular sieves were studied by X-ray diffraction. The structure was refined to give a final R value of 0.065–0.067. The Al—O and P—O bond lengths and Al—O—P angle of the AlPO₄-5 framework were distorted by incorporation of cobalt. The coordination environment of cobalt in CoAPO-5 was studied by EPR and IR spectroscopies. One oxygen signal was observed on the oxidized CoAPO-5 samples with g= 2.00. After NO was adsorbed on the sample, EPR spectra of oxidized and reduced CoAPO-5 showed eight hyperfine splittings due to the interaction between Co(I= 7/2) and N. The adsorption of NO probe molecules on reduced CoAPO-5 gave two strong bands at 1894 and 1814 cm^–1 while the oxidized CoAPO-5 gave a weak band at 1860 or 1845 cm^–1. The cobalt in oxidized CoAPO-5 was reduced by NO treatment and remained in the tetrahedral framework. There is an additional weaker acid site on oxidized CoAPO-5 in comparison with reduced CoAPO-5 detected by TPD of ammonia.