Control of Na-EMT Zeolite Synthesis by Organic Additives

Organic additives were used to control the formation of EMT-type zeolite in a sodium-rich initial system. Triethanolamine was employed as a nucleation suppression agent able to complex the aluminum during the synthesis of the EMT-type zeolite. The commonly used tetramethylammonium (TMA) chloride and tetraethylammonium (TEA) chloride as structure directing agents in zeolite synthesis were also employed in this study. The triethanolamine has the most pronounced effect on the crystal growth process of the EMT-type zeolite. The use of triethanolamine resulted in the formation of large crystals (100 nm) with the framework composition different from the counterpart obtained in the organic-free system. Therefore, the function of triethanolamine is attributed to the immobilization of Al in the initial gel and thus partial suppression of zeolite nucleation. The immobilization of a part of Al resulted in the EMT zeolite crystals with a higher Si/Al ratio (1.4). In contrast, the TMA and TEA organic additives have a limited impact on the physicochemical properties of the EMT crystals, the latter being a consequence of large presence of Na in the system. The bulky TMA and TEA ions prevent the aluminosilicate precursor species from agglomeration and formation of dense gels and thus resulting in the crystallization of nanosized EMT zeolite crystals (10–20 nm)

Nucleation and Crystal Growth Features of EMT-Type Zeolite Synthesized from an Organic-Template-Free System

The process of formation of ultrasmall EMT-type zeolite from organic-template-free homogeneous suspensions is presented. The formation of transparent uniform suspension utilizing sodium aluminate, sodium silicate, and sodium hydroxide under controlled mixing is found to be of primary importance to control the nucleation and growth process of EMT-type crystals. The investigation of zeolite intermediates reveals the formation of uniformly sized gel particles (5–10 nm in size). The mean hydrodynamic diameter of the crystalline EMT-type zeolite corresponds to the size of the amorphous particles formed after preparation of the clear precursor suspension. Controlled formation of uniform precursor particles predetermines, to great extent, the following nucleation and growth steps and, thus, the characteristics of the ultimate product. The amorphous particles are transformed to single EMT-type crystals 6–15 nm in size at 303 K within 36 h. Small changes in the initial composition or the preparation procedure lead to the formation of other sodalite-cage-containing zeolites. Thus, it is of critical importance to control the nucleation kinetics in order to obtain the EMT-type material as pure phase. Besides the EMT zeolite, the crystallization fields of other zeolites upon low-temperature synthesis conditions are studied. The careful control of gel chemistry, combined with slow nucleation kinetics at low temperature, can provide access to important nanoscale zeolites while avoiding the use of expensive organic templates

Synthesis and Catalytic Behavior of Ferrierite Zeolite Nanoneedles

The proton form of nanosized, needlelike ferrierite zeolite, which was synthesized using choline and Na⁺ cations as structure-directing agents, was found to be much more efficient for the skeletal isomerization of 1-butene to isobutene than the corresponding cation form of conventional, submicrometric ferrierite with a platelike shape, mainly because of the considerably lower density of strong acid sites, but as well as a result of the higher density of 10-ring pore mouths

High-Visible-Light Photoactivity of Plasma-Promoted Vanadium Clusters on Nanozeolites for Partial Photooxidation of Methanol

Cold VCl₃–plasma is employed for the preparation of highly dispersed vanadium oxide clusters on nanosized zeolite. Different types of zeolites, such as EMT, FAU (z.X), and Beta, are used. The activity of the prepared catalysts is studied in the selective photooxidation of methanol under polychromatic visible and UV irradiations. The physicochemical properties and catalytic performance of plasma-treated zeolite Beta (P-V₂O₅@Beta) catalyst is compared with zeolite Beta (V₂O₅@Beta) and amorphous silica (V₂O₅@SiO₂) impregnated vanadium oxide catalysts. Pure V₂O₅ is used as a reference material. The set of catalytic data shows that plasma-prepared zeolite Beta based catalyst displays the highest activity. Complementary characterization techniques including XRD, N₂-sorption, FTIR, ionic exchange, pyridine adsorption, Raman, NMR, TPR, and EDX-TEM are used to study the impact of the preparation approach on the physicochemical properties and catalytic performance of photocatalysts

Recrystallization on Alkaline Treated Zeolites in the Presence of Pore-Directing Agents

In previous works aiming at understanding the mesoporous network after alkaline treatment in the presence of organic additives, conventional bulk characterization techniques led to the conclusion that the dissolved zeolite does not undergo any kind of recrystallization [Verboekend, D., Cryst. Growth. Des. 2013, 13, 5025−5035]. Here for the first time, we demonstrate using the data obtained from ¹H and ¹²⁹Xe NMR spectroscopy that such recrystallization does occur, which leads to the formation of a very thin coating of the mesopore walls. This demonstration is done on a beta (BEA) zeolite treated in the presence of TPA⁺ in an alkaline solution. The formation of a small amount of nanosized crystals or embryonic phases of silicalite-1 (MFI) zeolite is evidenced, as well as their homogeneous dispersion on the mesoporous surface of the beta zeolite. We think that these results may explain why a homogeneous mesopore size distribution is obtained, when organic pore-directing agents are used in the zeolite hierarchization process performed in an alkaline medium

Opening the Cages of Faujasite-Type Zeolite

Zeolites are widely used in industrial processes, mostly as catalysts or adsorbents. Increasing their micropore volume could further improve their already exceptional catalytic and separation performances. We report a tunable extraction of zeolite framework cations (Si, Al) on a faujasite-type zeolite, the archetype of molecular sieves with cages and the most widely used as a catalyst and sorbent; this results in ca. 10% higher micropore volume with limited impact on its thermal stability. This increased micropore volume results from the opening of some of the small (sodalite) cages, otherwise inaccessible to most molecules. As more active sites become accessible, the catalytic performances for these modified zeolites are substantially improved. The method, based on etching with NH₄F, is also applicable to other cage-containing microporous molecular sieves, where some of the most industrially relevant zeolites are found

Opening the Cages of Faujasite-Type Zeolite

Zeolites are widely used in industrial processes, mostly as catalysts or adsorbents. Increasing their micropore volume could further improve their already exceptional catalytic and separation performances. We report a tunable extraction of zeolite framework cations (Si, Al) on a faujasite-type zeolite, the archetype of molecular sieves with cages and the most widely used as a catalyst and sorbent; this results in ca. 10% higher micropore volume with limited impact on its thermal stability. This increased micropore volume results from the opening of some of the small (sodalite) cages, otherwise inaccessible to most molecules. As more active sites become accessible, the catalytic performances for these modified zeolites are substantially improved. The method, based on etching with NH₄F, is also applicable to other cage-containing microporous molecular sieves, where some of the most industrially relevant zeolites are found

Insight in the Alginate Pd-IonogelsApplication to the Tsuji–Trost Reaction

A new class of catalytic ionogels based on the entrapment of an ionic liquid phase within a sodium alginate matrix was applied to the Pd-catalyzed allylic substitution reaction. High activity and promising recyclability were obtained in C–N bond formation. Scanning electron microscopy, scanning transmission electron microscopy, and solid-state NMR studies provided a better insight into the catalytic behavior, and the stability of the catalytic ionogels was studied through a recycling process