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Abstract

Samples of two differently prepared zeolite rho loaded with different amounts of monomethylamine (MMA) were studied in their hydrated and dehydrated forms by X-ray and neutron diffraction. Both zeolites are partially dealuminated, as indicated by nonframework alumina, which is assumed to be Al₂O₃ or AlOOH. Series I was prepared from dry-calcined NH₄-rho at 873 K, series II from steam-calcined NH₄-rho at 773 K. The samples were loaded with different amounts of deuterated MMA, Rietveld refinements yielded the following results for series I (dry): (1) H_3.8(H-MMA)₅Cs_0.2Al₉Si₃₉O₂.Al₂O₃.28H₂O, X-ray data collection at room temperature, Im3̅m, a = 14.9991 (2) Å, R_wp = 0.095; (2) composition as in (1), anhydrous and deuterated, neutron data collected at 5 K, disproportionation into two phases in I4̄3m, with a = 14.8410 (7) and 14.5273 (11) Å, R_wp = 0.038; (3) (H-MMA)_8.8Cs_0.2Al₉Si₃₉O₉₆.Al₂O₃.25H₂O, X-ray data collection at room temperature, I4̄3m, a = 14.9771 (2) Å, R_wp = 0.090. Series II (steam): (4) H_0.3(H-MMA)₅Cs_0.7Al₆Si₄₂O₉₆.2.5Al₂O₃.23H₂O, X-ray data collected at room temperature, Im3̅m, a = 15.0323 (2) Å, R_wp = 0.124; (5) composition as in (4), anhydrous and deuterated, neutron data collected at 5 K, disproportionation into two phases in I4̄3m with a = 14.9151 (2) and 14.6475(8) Å, R_wp = 0.031. In the hydrated samples MMA resides on the center axis in the α-cage with the N atoms pointing to the single eight-ring; upon dehydration it migrates into the double eight-rings.