Synthesis of phosphorus-modified small-pore zeolites utilizing tetraalkyl phosphonium cations as both structure-directing and phosphorous modification agents

A rational strategy for the synthesis of phosphorus-modified small-pore zeolites by utilizing tetraalkyl phosphonium cations as both a structure-directing agent and a phosphorous modification agent was developed. Initially, we investigated the hydrothermal conversion of FAU zeolites as a starting silica/alumina source in the presence of tetraalkyl phosphonium cations with different structures. Various types of zeolites, including small-pore zeolites with 8-MR windows such as LEV, GIS, AEI, and CHA zeolites, were obtained. Next, we applied the dual-template method with a mixture of the N-containing organic structure-directing agent (OSDA) N,N,N-trimethyl-1-adamantammonium cation and the P-containing OSDA tetraethyl phosphonium cation to the synthesis of phosphorus-modified zeolites with small pores, especially CHA zeolites. Using this method, the proportion of P-containing OSDA/N-containing OSDA in as-synthesized CHA zeolites can be easily controlled. After the calcination of the as-synthesized zeolites, CHA zeolites with different degrees of phosphorus modification were easily obtained without significant pore occlusion or toxification of catalytically active sites. The phosphorus modified CHA zeolite had high thermal stability and retained its structure even after calcination at 1050 degrees C for 1 h. In addition, in the selective catalytic reduction of NOx with NH3, the Cu-loaded phosphorus-modified CHA zeolite exhibited NO conversion above 90%, even after hydrothermal treatment at 900 degrees C for 8 h, indicating extremely high hydrothermal stability. (C) 2015 Elsevier Inc. All rights reserved.