NH3 Sorption Isotherms in ALPO-11 and Its Si, Co, and Mn Analogues

Abstract

Equilibrium sorption capacities of different probe molecules such as water, n-hexane, cyclohexane, and ammonia were used as a tool for the characterization of ALPO-11 and protonic forms of SAPO-11, CoAPO-11, and MnAPO-11. Sorption uptake at P/P0 = 0.8 and 298 K, 2 h for water, n-hexane, and cyclohexane was found to be affected by incorporating Si, Co, and Mn in ALPO-11. Generation of Bronsted acidity is expected to increase the hydrophilicity; Si, Co, and Mn analogues have exhibited such trends depending upon the extent of substitution and characteristics of the substituted cation. The amount of ammonia retained irreversibly (on account of chemisorption) during sorption measurements was found to be correlated with the intrinsic acidity possessed by ALPO-11 and its analogues. Isotherms of ammonia sorption in ALPO-11, SAPO-11, CoAPO-11, and MnAPO-11 in the temperature range 333−483 K up to 500 Torr have been measured. The NH3 sorption capacity was also found to decrease in the order ALPO-11 > SAPO-11 > CoAP...