Synthesis of molecular sieves using ketal structure-directing agents and their degradation inside the pore space

Abstract

Molecular sieves are synthesized using degradable, ketal-containing structure-directing agents (SDA). Eight quaternary ammonium compounds that contain ketal groups are synthesized and used as degradable SDAs for the synthesis of ZSM-5, mordenite, ZSM-12 and VPI-8. The ketal-containing SDAs are degraded into smaller fragments by acidic hydrolysis while in the micropore space, and the degradation products observed by (13)C CP MAS NMR. This synthetic methodology is used to circumvent the need for SDA removal by calcination. The effects of organic content, hydrophilicity and pore connectivity of the synthesized molecular sieves on the ability to degrade the entrapped SDA are investigated. The SDAs are degraded more readily inside molecular sieves with more hydrophilic character and higher pore connectivity. This is likely due to better mass transfer of H(2)O and H(+) that are necessary for the hydrolysis of the SDA within the micropore space. (c) 2005 Elsevier Inc. All rights reserved.