Positions of cations and molecules in zeolites with the mordenite-type framework X dehydrated calcium hydrogen mordenite

Abstract

Prolonged acid treatment of natural mordenite (2M Hc1, 90°C, 2 months) did not remove 1.4Ca atoms which persisted in site I of the final product after dehydration at 300°C. Electron microprobe analysis showed no detectable reduction of Al/Si ratio, but the cell parameters at room temperature ( a 18.058(3) b 20.297(3) c 7.484(2)Å) are lower than for the dehydrated-deammoniated variety, and the mean T-O distance is lower (1.606 vs. 1.617Å). The O-T-O and T-O-T angles are closer generally to those of dehydrated Ca-mordenite than to dehydrated-deammoniated mordenite. Population refinement produced no evidence in favor of vacant tetrahedral sites, but technical considerations cause complications. The present data would not be inconsistent with earlier suggestions that Al is replaced by Si in tetrahedral sites.