Synthesis of high-silica AEI zeolites with enhanced thermal stability by hydrothermal conversion of FAU zeolites, and their activity in the selective catalytic reduction of NO_x with NH₃

Abstract

High-silica AEI zeolites with Si/Al ratios of 13-20 were synthesized by FAU interzeolite conversion, in which tetraethylphosphonium (TEP) cations as a structure-directing agent (SDA) and NaF or NH 4 F as a fluoride source were added to the starting gels. During the thermal treatment of the AEI zeolites, TEP cations in the zeolitic pores decomposed to yield the P-modified AEI zeolites with various P/Al ratios. The thermal stability of the P-modified AEI zeolite was higher than that of the non-modified AEI zeolite synthesized using the N,N-diethyl-2,6-dimethylpiperidinium cation as an SDA. The framework structure of the Pmodified AEI zeolite was maintained after calcination at 1000 C for 1 h, indicating an enhanced thermal stability by phosphorus modification. The catalytic performance of Cu-loaded AEI zeolites with different P/Al ratios in the selective catalytic reduction (SCR) of NO x with NH 3 was also investigated. The NO conversion was found to increase with decreasing P/Al ratio. No decrease in the NO conversion was observed after hydrothermal treatment at 900 C for 4 h, indicating the high potential of the P-modified AEI zeolite for NH 3 -SCR of NO x .

Building Zeolites from Precrystallized Units: Nanoscale Architecture

“…have reported the interzeolite transformation of two zeolites with large cavity sizes,E RI and AFX, by using abulky polycyclictemplate (Figure 15). [77] The sizes of the bulky polycyclic template (11.9 4.9 )f itted perfectly with that of the very large cavities (13 ), thus proving the excellent structure-directing role for stabilizing the ERI and AFX cavities.T he introduction of cationic copper and iron species within these ERI and AFX results in very active catalysts for the SCR of NOx with similar NO conversion profiles as well-stablished commercial metalcontaining SSZ-13 catalysts.…”

“…[11] Researchers from ITQ have proven that introducing Ge in the synthesis gel can lead to the formation of aseries of new zeolite structures with lower framework densities (FDs) and larger pore dimensions. [13] In general, well-formed zeolite precursors are described to decompose into small fragments containing characteristic SBUsi nt he synthesis gel when treated hydrothermally,t hus favoring the rearrangement and crystallization of other structures sharing similar SBUs. [13] In general, well-formed zeolite precursors are described to decompose into small fragments containing characteristic SBUsi nt he synthesis gel when treated hydrothermally,t hus favoring the rearrangement and crystallization of other structures sharing similar SBUs.…”

“…[12] Beyond the use of single inorganic atoms and organic molecules to design new or improved zeolite structures,t he use of zeolites as as ource of Si and Al to synthesize other zeolites has recently gained attention in the literature. [13] In general, well-formed zeolite precursors are described to decompose into small fragments containing characteristic SBUsi nt he synthesis gel when treated hydrothermally,t hus favoring the rearrangement and crystallization of other structures sharing similar SBUs. [14] Researchers have succeeded in the hydrothermal transformation of some crystalline zeolites (in this case,F AU)i nto many other structures (such as CHA, LEV,a nd AEI) by combining the use of the precrystallized zeolites and different OSDAm olecules.…”

Organic‐Free Interzeolite Transformation in the Absence of Common Building Units

“…This approach has been demonstrated for a range of metastable zeolites, such as faujasite (FAU) and beta (*BEA) . For instance, Sano and co‐workers synthesized high‐silica AEI zeolites by interzeolite transformation of FAU parent crystals . Corma and co‐workers employed a similar strategy to prepare high‐silica chabasite (CHA), which could not be obtained using traditional silica and alumina sources .…”

“…[14] For instance, Sano and co-workers synthesized high-silica AEI zeolites by interzeolite transformationo fF AU parent crystals. [15] Corma and co-workerse mployed as imilars trategy to prepare highsilica chabasite (CHA), whichc ould not be obtained using traditional silica and alumina sources. [16] Both of thesee xamples highlight the advantage of using interzeolite transformationt o overcome the limitations of conventional protocols for achieving high Si/Al ratios;h owever,t his approachh as also proven to be an effective route to accelerate the rate of crystallization and improve product yields.…”