The synthesis of chabazite with high solid yields is achieved by the rational combination of directing effects of a source of Si and Al coming from USY zeolites and the inexpensive tetraethylammonium.

The use of small pore zeolites with large cavities has been reported for relevant applications in catalysis or gas separation.[1] One of the most important applications of these materials as catalysts is the selective catalytic reduction (SCR) of nitrogen oxides (NO x ), where copper-containing zeolites with small pore sizes show excellent activities to remove these hazardous compounds produced during combustion in diesel engines. [1,2] Interestingly, these small-pore zeolites show higher hydrothermal stability compared to other zeolitic materials presenting larger pore sizes, such as Cu-ZSM-5 or Cu-Beta. [3] The particular stabilization of the Cu 2+ cations within the double 6-rings (D6Rs) present in some structures of these small pore zeolites, i.e. chabazite (CHA structure), has been claimed as a plausible reason for their higher hydrothermal stability.[4]Another zeolite with related structural properties to chabazite is SSZ-39 (AEI structure), which is an aluminosilicate with large cages connected by a three-directional small 8-ring (8-R) pore system, and also with D6R as secondary building units in its structure.[5]Recently, we have reported that Cu-exchanged SSZ-39 zeolite is an active and hydrothermally stable catalyst for the SCR of NO x with ammonia, showing even better catalytic performance than Cu-exchanged CHA.[6]The preferred synthesis procedure of SSZ-39 requires the use of simple alkylsubstituted cyclic quaternary ammonium cations as organic structure directing agents (OSDAs) in alkaline conditions. [7] These organic cations could be easily prepared from commercially-available pyridine precursors, [8] making attractive the use of these OSDAs for the synthesis of the SSZ-39 from an economic point of view. Unfortunately, this methodology can afford the preparation of the SSZ-39 in low solid yields (lower than 50%), since the final crystalline solids show much lower Si/Al ratios than the Si/Al ratios initially introduced in the synthesis gels, [6,7,8] indicating that most of the Si species remain in solution after the crystallization procedure. This fact limits the potential use of SSZ-39 in commercial applications.Recently, the synthesis of the high silica AEI zeolite with high solid yields (above 80%) has been reported using USY zeolite as silicon source and tetraethylphosphonium (TEP)cations as OSDA. [9] Although this achievement is highly relevant in terms of the optimization of the SSZ-39 synthesis, the use of P-based OSDAs still presents some 3 important drawbacks. On one hand, phosphine-derived organic molecules show important environmental and health hazards, and, on the other hand, the complete removal of the phosphorous-species entrapped within the zeolitic cavities is very difficult, especially within small pore zeolites, and their calcination process requires high temperatures and hydrogen atmospheres for the complete decomposition/elimination of these compounds.[9]It is worth mentioning that in the last years the use of pre-formed crystalline zeolitic precursors to synthesize different...

The synthesis of nanosized SSZ-39 zeolite has been achieved using a high silica FAU zeolite as the Si and Al source and tetraethylphosphonium (TEP) cations as OSDAs. The obtained SSZ-39 material shows a remarkably high catalyst lifetime compared to conventional SSZ-13 and SSZ-39 materials.

From theoretical calculations and a rational synthesis methodology, it has been possible to prepare nanocrystalline (60-80 nm) chabazite with an optimized framework Al distribution that has a positive impact on its catalytic properties. This is exemplified for the methanol-to-olefin (MTO) process. The nanosized material with the predicted Al distribution maximizes the formation of the required MTO hydrocarbon pool intermediates, while better precluding excessive diffusion pathways that favor the rapid catalyst deactivation by coke formation.

This study aimed to assess the capacity of saponite modified with n-hexadecyltrimethylammonium bromide (CTAB) and/or 3-aminopropyltriethoxysilane (APTS) to adsorb and remove caffeine from aqueous solutions. Powder X-ray diffraction (PXRD) revealed increased basal spacing in the modified saponites. Small-angle X-ray scattering (SAXS) confirmed the PXRD results; it also showed how the different clay layers were stacked and provided information on the swelling of natural saponite and of the saponites functionalized with CTAB and/or APTS. Thermal analyses, infrared spectroscopy, scanning electron microscopy, element chemical analysis, and textural analyses confirmed functionalization of the natural saponite. The maximum adsorption capacity at equilibrium was 80.54 mg/g, indicating that the saponite modified with 3-aminopropyltriethoxysilane constitutes an efficient and suitable caffeine adsorbent.

A key factor to improve the performance of metal−organic frameworks (MOFs) is the design and synthesis of hierarchical interconnected porosity at different length scales. The presence of secondary mesopore systems, in addition to the intrinsic framework micropores, avoids inherent mass-transfer constraints that occur in multiple examples of liquid phase chemical processes. Different strategies to introduce ordered void spaces in the MOF materials are reviewed here, based on either bottom-up or top-down approaches. A thorough discussion of the different bottom-up synthesis protocols, based on the interactions of the molecular building blocks with soft or hard templates, is followed by presenting synthesis concepts relating to multidimensional MOF transformations, interfacial and modulated synthesis. The holy grail of defect engineering MOF crystals with controlled porosity is tackled through several topdown approaches in the nanoscale regime. The resultant hierarchical MOFs with interconnected porosity represent the next generation of advanced catalysts and adsorbents, as is presented here by using a vast number of examples where the hierarchical porous structure is key to the MOF performance. A combination of tailor-made pore shape, size, and functionality leads to a synergistic effect between the MOF structures and functions, which offers an improvement on catalysis and adsorption while preserving their porosity, reactivity, and stability. The hierarchical MOFs presented in the different sections of this Review are compared with the purely microporous parent MOFs, used as benchmark in challenging applications where the performance is boosted in the case of hierarchical MOFs.

Cage-based small-pore catalysts for NH3-SCR prepared by combining bulky organic structure directing agents with modified zeolites as reagents.

The preparation of the iron‐containing SSZ‐39 zeolite is described for the first time through two different synthesis methods: post‐synthetic cation exchange and one‐pot synthesis. The nature and stability of the iron species within the different Fe‐SSZ‐39 materials have been studied through different characterization techniques, and their catalytic activity has been evaluated for the selective catalytic reduction (SCR) of NOx with ammonia. The directly synthetized Fe‐SSZ‐39 performs better for the SCR of NOx with ammonia than other related Fe‐zeolites, particularly at elevated reaction temperatures (above 450 °C), and presents improved hydrothermal stability when aged under severe conditions.