Continuous Flow Synthesis of ZSM-5 Zeolite on the Order of Seconds

Zeolites have typically been synthesized via hydrothermal treatment, a process designed to artificially mimic the geological formation conditions of natural zeolites. This synthesis route, typically carried out in batch reactors like autoclaves, takes a time so long (typically, on the order of days) that the crystallization of zeolites had long been believed to be very slow in nature. Long periods of hydrothermal treatment also cause a burden on both energy efficiency and operational costs. Recently, we have reported the ultrafast syntheses of a class of industrially important zeolites within several minutes.[1,2] Further shortening the crystallization time to the order of seconds would be a great challenge but can significantly benefit the mass product of zeolites as well as the fundamental understanding of the crystallization mechanism

Testing the limits of zeolite structural flexibility: ultrafast introduction of mesoporosity in zeolites

A mild alkaline treatment with the assistance of surfactants has proved to be an effective way to introduce uniform mesopores into zeolites, yielding hierarchical materials with superior catalytic performance. Accelerating this process may open new opportunities in the scale-up of this new class of materials. In this study, we present an ultrafast surfactant-templating (UST) approach achieved within only a few minutes for the fast production of mesoporous ultra-stable Y (USY) zeolites by combining several favorable factors including high treating temperature, reactors featuring fast heating, and optimized reagent composition. Temperatures in the range of 150–220 °C yielded high quality materials, while too high temperatures (260–280 °C) produced inferior samples. The use of a flow reactor allowed for completing the UST in just one minute, which evidences the remarkable structural flexibility of zeolites that can reorganize in such a short time to accommodate a large amount of intracrystalline mesoporosity, without compromising their integrity or main properties.C. P. is grateful to the Chinese Scholarship Council and the Ministry of Education, Culture, Sports, Science and Technology, Japan for a MonbuKagakusho Scholarship. N. L. acknowledges funding from the University of Alicante, through the “Programa de captación y retención de talento” (ref. UATALENTO17-05). C. A Trujillo acknowledges the Universidad Nacional de Colombia and Ecopetrol for the support of the Laboratorio de Catálisis Heterogénea. Z. L. acknowledges the Japan Society for the Promotion of Science (JSPS) for financial support (a Grant-in-Aid for Young Scientists: 18K14049)

Continuous Flow Synthesis of ZSM-5 Zeolite on the Order of Seconds

Zeolites have typically been synthesized via hydrothermal treatment, a process designed to artificially mimic the geological formation conditions of natural zeolites. This synthesis route, typically carried out in batch reactors like autoclaves, takes a time so long (typically, on the order of days) that the crystallization of zeolites had long been believed to be very slow in nature. Long periods of hydrothermal treatment also cause a burden on both energy efficiency and operational costs. Recently, we have reported the ultrafast syntheses of a class of industrially important zeolites within several minutes.[1,2] Further shortening the crystallization time to the order of seconds would be a great challenge but can significantly benefit the mass product of zeolites as well as the fundamental understanding of the crystallization mechanism

Structure-Directing Behaviors of Tetraethylammonium Cations toward Zeolite Beta Revealed by the Evolution of Aluminosilicate Species Formed during the Crystallization Process

Organic structure-directing agents (OSDAs) have been widely used for the synthesis of zeolites. In most cases, OSDAs are occluded in zeolites as an isolated cation or molecule geometrically fitted within the zeolite cavities. This is not the case for zeolite beta synthesized by using tetraethylammonium (TEA⁺) cation as an OSDA, in which a cluster/aggregate of ca. six TEA⁺ cations is occluded intact in the cavity (i.e., the channel intersection) of zeolite beta. The structure direction of TEA⁺ in such a nontypical, clustered mode has remained elusive. Here, zeolite beta was hydrothermally synthesized using TEA⁺ in the absence of other alkali metal cations in order to focus on the structure-directing behaviors of TEA⁺ alone. The solid products formed throughout the hydrothermal synthesis were analyzed by an array of characterization techniques including argon adsorption–desorption, high-energy X-ray total scattering, Raman and solid-state NMR spectroscopy, and high-resolution transmission electron microscopy. It was revealed that the formation of amorphous TEA⁺–aluminosilicate composites and their structural, chemical, and textural evolution toward the amorphous zeolite beta-like structure during the induction period is vital for the formation of zeolite beta. A comprehensive scheme of the formation of zeolite beta is proposed paying attention to the clustered behavior of TEA⁺ as follows: (i) the formation of the TEA⁺–aluminosilicate composites after heating, (ii) the reorganization of aluminosilicates together with the conformational rearrangement of TEA⁺, yielding the formation of the amorphous TEA⁺–aluminosilicate composites with the zeolite beta-like structure, (iii) the formation of zeolite beta nuclei by solid-state reorganization of such zeolite beta-like, TEA⁺–aluminosilicate composites, and (iv) the subsequent crystal growth. It is anticipated that these findings can provide a basis for broadening the utilization of OSDAs in the clustered mode of structure direction in more effective ways

Ultrafast and Continuous Flow Synthesis of Silicoaluminophosphates

Silicoaluminophosphates are a class of crystalline microporous materials that have been widely used as catalysts and adsorbents. Two representative silicoaluminophosphates, SAPO-CHA (also called SAPO-34) and SAPO-AFI (also called SAPO-5), were synthesized in a tubular reactor within 10 and 5 min, respectively. The addition of a milled seed with small crystal size, the pretreatment of Al and Si sources by mechanical milling, and the employment of a high temperature condition were found to be the critical factors that contributed to the enhancement of crystallization rate of SAPO-CHA. The fast-synthesized SAPO-CHA possesses only isolated Si­(OAl)₄ species, indicating a great potential in catalytic applications. SAPO-CHA and SAPO-AFI usually appear as a pair of competing phases during the synthesis of SAPO-CHA/SAPO-AFI because of similarities in chemical compositions and formation conditions. Here, we show that, owing to the feature of rapid heating, the tubular reactor demonstrated itself as a facile and precise platform to control over the phase selection between SAPO-CHA and SAPO-AFI by tuning the crystallization kinetics, which could not be realized in the conventional autoclaves. A continuous flow process was also established to synthesize these two silicoaluminophosphates with high efficiency and flexibility. These results demonstrate a comprehensive strategy to achieve the minute-order synthesis of two important silicoaluminophosphates and could be very useful to direct the ultrafast synthesis of other crystalline materials