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

摘要

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 (3) over barm 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 vertical bar Co26.1Na21(H3O)(7.1)(H2O)(14.2)vertical bar[Si112Al80O384]-FAU (a = 24.7892(2) angstrom) and vertical bar Co29.3Na6.2(H3O)(5.9)(H2O)(5.9)vertical bar[Si121Al71O384]-FAU (a = 24.7346(2) angstrom), 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.