Zeolite Rho Loaded with Methylamines. I. Monomethylamine Loadings

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, Imm, 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 I3m, 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, I3m, 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,Imm, 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 I3m 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.