Alkali Treatment of Commercial Silicoaluminophosphate Molecular Sieves (SAPO_-34) Enhances the Water Adsorption and Desorption Properties

Abstract

Commercial silicoaluminophosphate molecular sieves ( SAPO-34 ) received alkali treatment with either NaOH (0.2, 0.01, 0.005, or 0.001 M) or NH 4 OH (0.005 M). Treatment with NaOH (0.005 M) increased the water adsorption initial rate of SAPO-34 by 1.4-fold. The alkali treatment introduced Na + adsorption sites into the SAPO-34 . The desorption ratio (adsorption at 30 °C and desorption at 100 °C ) was 88.2% higher than the original rate (84.3%). On the other hand, after alkali treatment of SAPO-34 using NH 4 OH (0.005 M), calcination resulted in the highest desorption ratio at 91.3%. When combined with calcination, alkali treatment with NH 4 OH introduced H + adsorption sites into SAPO-34 , H + adsorption sites feature low levels of interaction with water, which enhanced the desorption ratio, but decreased the initial adsorption rate. These results indicate that treating commercial SAPO-34 with 0.005 M NaOH enhances both the adsorption and desorption behaviors.