Single crystal structure of fully dehydrated partially Co-exchanged zeolite X:Comparison with partially dehydrated partially Co-exchanged zeolites X

摘要

The crystal structure of the fully dehydrated Co,Na-X zeolite(Na_(16)Co_(38)Al_(92)92Si_(100)O_(384))is investigated and compared to that of three partially hydrated zeolites.In the fully dehydrated crystal,cobalt ions almost entirely occupy Site I,and partially Site II while the residual sodium cations partly occupy Site II and Site III.The dehydration induces a migration of Co~(2+)cations from Site I'to Site I and severely affects the structure,the structural strain being released by changes of framework valence angles or,to a less extent,by distortions of TO4 tetrahedra.Comparison with dehydrated M-X zeolite structures(M=Ba,Na,Ca,Tl,Li)confirms the relation between the size of the charge compensating cation and the stresses on the skeleton that are mainly explained by cation-oxygen electrostatic interactions.