Optimized Synthesis of ZSM‐11 Catalysts using 1,8‐Diaminooctane as a Structure‐Directing Agent

Abstract

Developing new zeolite catalysts for (petro)chemical applications is nontrivial owing to challenges that include the identification of commercially-viable syntheses. The vast majority of syntheses require the use of an organic structure-directing agent (OSDA), which has economic and environmental shortcomings. In the search for alternative zeolites to common industrial catalysts, such as ZSM-5 (MFI), a promising candidate is ZSM-11 (MEL), a close structural analogue of MFI. ZSM-11 is comprised of 3-dimensional straight channels that have less diffusion limitations than MFI. Side-by-side comparisons of ZSM-11 and ZSM-5 catalysts reveal the former exhibits significantly longer time-on-stream lifetime in many reactions; however, there are several difficulties associated with the preparation of ZSM-11, which include the ability to identify inexpensive OSDAs that produce small crystals in high yield. Here, we examine ZSM-11 synthesis using 1,8-diaminooctane (DAO), which produces ZSM-11 crystals with sizes of ca. 300 nm. We demonstrate that the use of MEL seeds allows for an order of magnitude reduction in the quantity of DAO without sacrificing crystal purity or yield (>80 %). Catalytic tests using methanol to hydrocarbons as a representative reaction show that H-ZSM-11 lifetime and selectivity are similar for samples prepared with and without seeds. Collectively our findings highlight an efficient method to produce ZSM-11 as a potential alternative to ZSM-5 for catalytic applications.

Insight into the Formation of Nanostructured MFI Sheets and MEL Needles Driven by Molecular Recognition

“…This might be beneficial for the formation of the MEL zeolite because the MEL2 intersection is characterized by a large distance between the pore axes at the intersection and the flexible C 22 tail could thus provide stabilization via dispersion interactions with the siliceous framework. Yet, despite the propyl-based SDA being incorporated in the MEL zeolite, we see a substantial morphological difference between the commonly synthesized MEL zeolite cystals − and the MEL nanoneedles in our previous work . So, although an amount of the propyl-based SDA is incorporated in the growing crystal, the SDA is still likely to act as an a - and b -direction growth retardant and, especially, induces the formation of distinct needles and large mesoporous voids.…”

Organic Mesopore Generating Agents (OMeGAs) for Hierarchical Zeolites: Combining Functions on Multiple Scales

“…Since the first report on the use of OSDA to assist synthesis of zeolites by Barrer and Denny in 1961, OSDA molecules have been widely used in crystallization of porous zeolites, especially during the synthesis of high silica zeolites. These organic structure directing agents are typically in the form of tetraalkylammonium (TAA) cations, or their analogue molecules such as those with phosphonium‐derived organic cations, and to a lesser extent, some amines . The two most successful acidic zeolites of ZSM‐5 and beta, currently widely used in the industry, are synthesized by Mobil researchers in the 1960s utilizing OSDAs of tetrapropylammonium and tetraethylammonium cations respectively.…”

“…These organic structure directing agents are typically in the form of tetraalkylammonium (TAA) cations, [5] or their analogue molecules such as those with phosphonium-derived organic cations, [10] and to a lesser extent, some amines. [11] The two most successful acidic zeolites of ZSM-5 and beta, currently widely used in the industry, are synthesized by Mobil researchers [12] in the 1960s utilizing OSDAs of tetrapropylammonium and tetraethylammonium cations respectively. Compared to inorganic structure directing agents such as alkali cations of Na + or K + , organic OSDA molecules are larger in size with more delocalized positive charge, so less balancing negative charge, i. e., less T III elements, is required in the zeolite framework.…”

Robert A. Welch Award in Chemistry: A. Bax / Norman Hackerman Award in Chemical Research: J. D. Rimer / University Cup: X. C. Le

“…Rimer beschäftigt sich mit Kristall‐Engineering und der rationalen Entwicklung von Materialien für bestimmte Anwendungen, etwa bei der Synthese von mikroporösen Katalysatoren oder von Therapeutika, die pathologische Kristallisationsprozesse verhindern. Er beschrieb in ChemPhysChem eine optimierte Synthese für Zeolithkatalysatoren und in der Angewandten Chemie die Herstellung extrem kleiner Zeolith‐L‐Kristalle …”