The dependence of Co2+-exchange into zeolite FAU on its Si/Al ratio

Abstract

Three single crystals of fully dehydrated, largely Co2+-exchanged zeolites X and Y were prepared by the exchange of Na80-X (|Na80|[Si112Al80O384]-FAU, Si/Al = 1.40), Na75-Y (|Na75|[Si117Al75O384]-FAU, Si/Al = 1.56), and Na71-Y (|Na71|[Si121Al71O384]-FAU, Si/Al = 1.70) with aqueous streams 0.05 M in Co(NO3)2, pH = 5.1, at 294 K for 3 days. This was followed by vacuum dehydration at 673 K. Their crystal structures were determined by synchrotron X-ray diffraction techniques in the cubic space group Fd $$\overline{3}$$ m at 100(1) K. In all three crystals Co2+ ions occupy the 6-ring sites I, I’, and II; Na+ ions occupy sites II’ and II. The number of Co2+ ions exchanging into the zeolite was about 30 per unit cell for all three crystals. The number of residual Na+ ions, however, decreased sharply as Si/Al ratio increased, and the number of H+ ions co-exchanging into the zeolite decreased nearly to zero. Some dealumination of the zeolite framework was seen in the first crystal (initial Si/Al = 1.40).