Zeolite Nanocrystals (MOR, EU-1, and ZSM-12) Synthesized Using a Versatile Diquaternary Ammonium Template as Robust Catalysts

Abstract

Nanocrystals of zeolites with shortened diffusional pathways compared to bulk counterparts are attractive catalysts, but their direct synthesis often remains challenging and expensive. Here, we describe the utility of p-phenylenedimethylene−bis(trimethylammonium) dichloride, an organic diquaternary ammonium compound that can be easily prepared, as an effective organic structuredirecting agent (OSDA) for obtaining several zeolites composed of agglomerated nanocrystals. By modifying the gel composition (NaOH/ Si and Si/Al ratios) and crystallization time, synthesis can be tuned to obtain mordenite, EU-1, and ZSM-12 zeolites. 13 C NMR spectra of the occluded OSDA reveal subtle differences in host−guest interactions between the OSDA and the respective zeolites, which derives from the flexibility of the OSDA. The relatively strong interaction between the OSDA and inorganic aluminosilicate precursor species during the induction period explains how small zeolite nanocrystals are obtained. Nanosized EU-1 and ZSM-12 significantly outperform their corresponding bulk counterparts as acid catalysts in the methanol-to-hydrocarbons reaction and the alkylation of benzene with benzyl alcohol, respectively.

The effect of Si/Al ratio of ZSM-12 zeolite on its morphology, acidity and crystal size for the catalytic performance in the HTO process

“…In the Z120 sample, were observed ZSM-12 peaks and the main peaks of the ZSM-5 zeolite structure (including five diffraction peaks at 2 θ = 7.96, 8.86, 23.08, 23.98, 24.52°). 23–25 Also, the peak related to cristobalite was identified in the structure. To determine the amount of each of the existing phases, using Rietveld refinement with MAUD software and the experimental X-ray diffraction pattern of the synthesized sample was simulated by MAUD.…”

Nanoplatelet Mordenite Zeolite with a Controlled Aspect Ratio: Implications for the Alkylation of Benzene with Benzyl Alcohol

“…The solid product collected at 336 h showed a typical XRD pattern of MOR zeolite (PDF: 49-0924) without any impurity phase (Figure 1a). 33 SEM images (Figure 1b,c) demonstrated the well-defined platelet-like morphology of MOR zeolite, which was dramatically changed compared to that of MOR zeolites synthesized with TEAOH or HMI as a single OSDA (Figure S3). 32 This phenomenon highlighted the importance of the cooperative effect of dual OSDAs in altering the morphology of the MOR zeolite.…”

Synthesis of Dendritic ZSM-5 Zeolite through Micellar Templating Controlled by the Amphiphilic Organosilane Chain Length

“…Several strategies have been proposed for overcoming steric and diffusional constraints in zeolites. The reduction of the zeolite crystal size (nanozeolites) is one of the most widely studied alternatives. − Likewise, another interesting strategy consists of the introduction of a secondary porosity that may lie in the supermicro-, meso-, and macropore ranges (hierarchical zeolites), which has arisen a huge amount of interest during the past 15 years. − In comparison with conventional microporous zeolites, hierarchical ones have shown a number of relevant advantages derived from their enhanced accessibility. Thus, the presence of a large share of mesopore surface area, which may represent up to 50% of the overall surface area, has made possible their use as efficient catalysts in a large variety of chemical transformations involving bulky reactants or products, unable to enter or leave the zeolite micropores .…”