Structural comparison of partially dehydrated partially Co²⁺-exchanged zeolites X (FAU, Si/Al = 1.40) and Y (FAU, Si/Al = 1.70)

Abstract

The structures of partially dehydrated and partially Co²⁺-exchanged zeolites X (Si/Al = 1.40) and Y (Si/Al = 1.70) were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd $\overline{3}$ m and were refined to the final error indices R ₁/wR ₂ = 0.0773/0.2152 and 0.0683/0.2184, respectively. Their unit-cell formulas are |Co_26.1Na₂₁(H₃O)_7.1(H₂O)_14.2|[Si₁₁₂Al₈₀O₃₈₄]-FAU (a = 24.7892(2) Å) and |Co_29.3Na_6.2(H₃O)_5.9(H₂O)_5.9|[Si₁₂₁Al₇₁O₃₈₄]-FAU (a = 24.7346(2) Å), respectively. In the structure of Co²⁺-X, Co²⁺ ions occupy sites I′, II′, II, and III′; the Na⁺ ions are at sites I′ and II. In the structure of Co²⁺-Y, Co²⁺ ions occupy sites I′, II′, II, and III′; the Na⁺ ions are at site I′. Because of the low pH of the Co²⁺ exchange solution, some H₃O⁺ ions are observed in both structures. The number of Co²⁺ ions in zeolite was increased slightly as Si/Al ratio increased, and Na⁺ content and the unit cell constant of the framework were decreased.