Understanding the Anion‐Templated, OSDA‐Free, Interzeolite Conversion Synthesis of High Silica Zeolite ZK‐5**

Abstract

High silica zeolite ZK-5 (framework Si/Al = 4.8) has been prepared by interzeolite conversion from ultrastable zeolite Y via a co-templating route using alkali metal cations and nitrate anions but without organic structure directing agents. The mechanism, which involves zeolite frameworkalkali metal cation -nitrate anion ordering, has been established by a combination of chemical and thermal analyses, Raman spectroscopy, computational modelling, and X-ray powder diffraction. Ammonium exchange gives ZK-5 with occluded ammonium nitrate and subsequent heating gives microporous zeolite ZK-5.

Structural Aspects Affecting Phase Selection in Inorganic Zeolite Synthesis

“… 50 Feasibility of this concept has very recently been demonstrated in the inorganic synthesis of KFI-type zeolite with unusually high silica content, by inclusion of K + –NO 3 – pairs. 59 The framework Si/Al ratio was 4.8, cation occupancy was found to be 100%, and the material remained stable after extraction of the excess ions. An earlier study 60 describing the synthesis of high silica KFI (Si/Al = 5.2–5.8) also required the use of high concentrations of KNO 3 in the synthesis batch as a source of potassium to obtain the desired product.…”

“…These ion pairs can be removed post-synthesis, simply by making the crystals to come into contact with water . Feasibility of this concept has very recently been demonstrated in the inorganic synthesis of KFI-type zeolite with unusually high silica content, by inclusion of K + –NO 3 – pairs . The framework Si/Al ratio was 4.8, cation occupancy was found to be 100%, and the material remained stable after extraction of the excess ions.…”

Acidic properties of Al-rich ZSM-5 crystallized in strongly acidic fluoride medium

“…26 Inter-zeolite transformations (IZT), employing industrial zeolites as silica-alumina sources to generate another target zeolite, has recently drawn much attention. [27][28][29][30][31] The zeolite crystallization by IZT is faster and yields high. [32][33][34] The method can also provide pathways to synthesize zeolites with specific frameworks and compositions that are not possible with conventional silica and alumina sources.…”

Synthesis of ZSM-22 with Enhanced Acidity Using Alcoholamine as a Structure-Directing Agent to Promote the Hydroisomerization of n-Heptane

“…On the other hand, OSDAs play a pivotal role in the hitherto synthesis of zeolites, which directly determines the morphologies, topologies, and acidities of the final products . Molecules such as quaternary ammonium salts, , ethers, , alcohols, , amines, , polymers, and even inorganic cations , are among the frequently used OSDAs, considering their intense interactions with the zeolite frameworks. , Commensurate sizes with zeolite channels and proper interactions with zeolite frameworks are critical factors of OSDAs that govern their structure-directing effect and further decide the physiochemical properties of the obtained materials . As unveiled by recent studies, the usage of OSDAs can also achieve the precise regulation of the acidity locations and the hydrothermal stabilities, which could significantly improve the catalytic performances.…”