Paramagnetic cupric ions ion-exchanged into TAPO-5 and TAPO-11 molecular sieves

Titaniumaluminophosphate molecular sieves TAPO-5 and TAPO-11 have been hydrothermally synthesized. These materials were characterized using XRD, TGA, BET, ICP, diffuse reflectance UV-Vis and IR techniques. Especially, infrared and diffuse reflectance UV-Vis spectroscopic measurements were made in order to determine the evidence for framework substitution of Ti into AlPO₄ materials. The calcined TAPO-5 and TAPO-11 molecular sieves were ion- exchanged with cupric nitrate solution. The location and interactions of cupric ions ion-exchanged into H-TAPO-5 and H-TAPO-11 molecular sieves with water and ammonia have been studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. Similarity and difference in Cu(II) location and coordination were discussed in these two structures. There is a gradual transition upon dehydration of Cu-TAPO-5 from a Cu(II) species with ESR parameters g is parallel with = 2.401, A is parallel with = 155 x 10^-4 cm^-1, and g is perpendicular to = 2.08 to a Cu(II) species with g is parallel with = 2.348, A is parallel with = 167 x 10^-4 cm^-1 and g is perpendicular to = 2.07. A similar gradual transition upon dehydration of Cu-TAPO-11 was also observed from a Cu(II) species with ESR parameters g is parallel with = 2.375, A is parallel with = 151 x 10^-4 cm^-1 and g is perpendicular to = 2.08 to a Cu(II) species with g is parallel with = 2.333, A is parallel with = 170 x 10^-4 cm^-1 and = 2.07. In the hydrated state, Cu(II) ion directly coordinates to three water molecules in Cu-TAPO-5 while to two water molecules in Cu-TAPO-11. Upon dehydration treatments, Cu(II) is suggested to be located in hexagonal prism sites recessed from a main channel for both Cu-TAPO-5 and Cu-TAPO-11. Upon equilibration with ammonia, Cu(II) forms a complex containing four molecules of ammonia for both structures based on resolved nitrogen hyperfine interaction.