Resolving atomic SAPO-34/18 intergrowth architectures for methanol conversion by identifying light atoms and bonds

The micro-structures of catalyst materials basically affect their macro-architectures and catalytic performances. Atomically resolving the micro-structures of zeolite catalysts, which have been widely used in the methanol conversion, will bring us a deeper insight into their structure-property correlations. However, it is still challenging for the atomic imaging of silicoaluminophosphate zeolites by electron microscopy due to the limits of their electron beam sensitivity. Here, we achieve the real-space imaging of the atomic lattices in SAPO-34 and SAPO-18 zeolites, including the Al-O-P atoms and bonds, by the integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM). The spatial distribution of SAPO-34 and SAPO-18 domains in SAPO-34/18 intergrowths can be clearly resolved. By changing the Si contents and templates in feed, we obtain two SAPO-34/18 catalysts, hierarchical and sandwich catalysts, with highly-mixed and separated SAPO-34 and SAPO-18 lattices respectively. The reduced diffusion distances of inside products greatly improve the catalytic performances of two catalysts in methanol conversion. Based on the observed distributions of lattices and elements in these catalysts, we can have a preliminary understanding on the correlation between the synthesis conditions and structures of SAPO-34/18 intergrowth catalysts to further modify their performances based on unique architectures.

Transport Phenomena in Zeolites in View of Graph Theory and Pseudo-Phase Transition

Transport phenomena play an essential role in catalysis. While zeolite catalysis is widely applied in industrial chemical processes, its efficiency is often limited by the transport rate in the micropores of the zeolite. Experimental and theoretical methods are useful for understanding the transport phenomena on multiscale levels. Traditional diffusion models usually use a linear driving force and an isotropic continuum medium, such that transport in a hierarchical catalyst structure and the occurrence of nonlinear deactivation cannot be well understood. Due to the presence of spatial confinement and an ordered structure, some aspects of the transport in a zeolite cannot be regarded as continuum phenomena and discrete models are being developed to explain these. Graph theory and small-world networks are powerful tools that have allowed pseudo-phase transition phenomena and other nontrivial relationships to be clearly revealed. Discrete models that include graph theory can build a bridge between microscopic quantum physics and macroscopic catalyst engineering in both the space and time scales. For a fuller understanding of transport phenomena in diverse fields, several theoretical methods need to be combined for a comprehensive multiscale analysis.

Selective Transformation of CO2 and H2 into Lower Olefins over In2 O3 -ZnZrOx /SAPO-34 Bifunctional Catalysts

Because lower olefins (C₂ ⁼ -C₄ ⁼ ) are important bulk petrochemicals, their direct production from CO₂ hydrogenation is highly attractive. However, the selectivity towards C₂ ⁼ -C₄ ⁼ by the modified Fischer-Tropsch synthesis is restricted to 56.7 % with high undesired methane selectivity. Here, a series of bifunctional catalysts containing In₂ O₃ -ZnZrO_x oxides and various SAPO-34 zeolites with different crystal sizes (0.4-1.5 μm) and pore structures was developed for the production of lower olefins by CO₂ hydrogenation. The C₂ ⁼ -C₄ ⁼ selectivity reached as high as 85 % among all hydrocarbons with very low CH₄ selectivity of only 1 % at a CO₂ conversion of 17 %. This demonstrated that the small crystal size, hierarchical pore structure, and appropriate amount of Brønsted acid sites of SAPO-34 endowed the bifunctional catalysts with high C₂ ⁼ -C₄ ⁼ selectivity. This work shows an efficient way for developing bifunctional catalysts for direct CO₂ hydrogenation to lower olefins.

Highly selective conversion of methanol to propylene: design of an MFI zeolite with selective blockage of (010) surfaces

As an important catalyst of methanol-to-propylene (MTP) conversion, the ZSM-5 zeolite has an anisotropic diffusion path and a large pore size, resulting in the formation of undesirable heavy aromatic by-products. Herein, we developed a surface-specific silica deposition method to block straight channels of nanosized ZSM-5 crystals selectively. By such a coating method, we can selectively suppress the yield of aromatics from the original 13% to 2.4% at 100% conversion of methanol. Trapped hydrocarbon pool species are directly confirmed by aberration-corrected S/TEM for the first time. Such a method of trapping and restricting hydrocarbon pool species in a multiscale zeolite with 10-membered rings would significantly increase its catalytic efficiency and olefin diffusion. Moreover, this provides new methodologies for zeolite structure construction and will be greatly beneficial for the industrial MTP process.

Performance Enhanced SAPO-34 Catalyst for Methanol to Olefins: Template Synthesis Using a CO2-Based Polyurea

Introducing mesopores into the channels and cages of conventional micropores CHA (Chabazite) topological structure SAPO-34 molecular sieves can effectively improve mass transport, retard coke deposition rate and enhance the catalytic performance for methanol to olefins (MTO) reaction, especially lifetime and olefins selectivity. In order to overcome the intrinsic diffusion limitation, a novel CO2-based polyurea copolymer with affluent amine group, ether segment and carbonyl group has been firstly applied to the synthesis of SAPO-34 zeolite under hydrothermal conditions. The as-synthesized micro-mesoporosity SAPO-34 molecular sieve catalysts show heterogeneous size distribution mesopores and exhibit slightly decrease of BET surface area due to the formation of defects and voids. Meanwhile, the catalysts exhibit superior catalytic performance in the MTO reaction with more than twice prolonged catalytic lifespan and improvement of selectivity for light olefins compared with conventional microporous SAPO-34. The methodology provides a new way to synthesize and control the structure of SAPO-34 catalysts.

Mesoporogen-Free Synthesis of Hierarchical SAPO-34 with Low Template Consumption and Excellent Methanol-to-Olefin Conversion

Significant interest has emerged in the development of nanometer-sized and hierarchical silicoaluminophosphate zeolites (SAPO-34) because of their enhanced accessibility and improved catalytic activity for methanol-to-olefin (MTO) conversion. A series of nanometer-sized SAPO-34 catalysts with tunable hierarchical structures was synthesized in a Al₂ O₃ /H₃ PO₄ /SiO₂ /triethylamine(TEA)/H₂ O system by using a mesoporogen-free nanoseed-assisted method. The nanometer-sized hierarchical S_H -3.0 catalyst (TEA/Al₂ O₃ =3.0) possessed the highest crystallinity, highest abundance of intracrystalline meso-/macropores, and the most suitable acidity among all obtained catalysts, showing the highest ethylene and propylene selectivity of 85.4 %. This is the highest reported selectivity for MTO reactions under similar conditions. Detailed analysis of the coke produced during the reaction revealed that the small-sized methyl-substituted benzene and bulky methyl-substituted pyrene were mainly located inside the crystals instead of on the surface of the crystals, which provided further insight into understanding the deactivation of the SAPO-34 catalyst during MTO reaction. Significantly, the simple and cost-effective synthetic process and superb catalytic performance of the nanometer-sized hierarchical SAPO-34 is promising for their practical large-scale application for MTO conversion.

Assembly of Sub-Crystals on the Macroscale and Construction of Composite Building Units on the Microscale for SAPO-34

The nucleation and growth of SAPO-34 crystals with triethylamine (TEA) as a single template was monitored with ex situ time-resolved characterization methods. The investigation focused on the evolution of the intermediate phases at different crystallization stages of SAPO-34. The morphology transformation of the intermediate phases at different crystallization times revealed the unique self-assembly process of the sub-crystals. The cubic SAPO-34 crystals can be constructed from eight pyramidal subunits. Additionally, the construction order of cha cages and double-six-membered ring (d6r) units in the initial crystallization stage was determined. The appearance of cha cages prior to d6r units can be attributed to the structure-directing effect of protonated TEA, which is charge balanced with the negative charge of the framework from Si incorporation. Further analysis showed that Si species were incorporated into the framework by direct participation in the initial crystallization stage and substitution for framework P atoms during the later stage.

Поєднання гри Го і фізичних вправ як фактор розвитку когнітивних і нейродинамічних функцій дітей 6 років

Мета роботи – виявити вплив застосування гри Го в сполученні з фізичними вправами на  показники когнітивних і нейродинамічних властивостей дітей 6 років. Матеріал і методи. В дослідженні взяли участь 30 дітей перших класів, вік 6 років. Діти були поділені на 3 групи по 10 осіб в кожній. Дві групи стали експериментальними, одна група – контрольною. В першій експериментальній групі діти займались грою Го, в другій – грою Го в сполученні з фізичними вправами, в контрольній групі – за звичайною програмою продовженого дня. Діти експериментальних груп займалися грою Го два рази в тиждень протягом місяця. До і після експерименту було проведено тестування за методикою Шульте, і за методикою Єрмакова (комп’ютерна програма «Вибір кнопки»). Експериментальні групи займалися за розробленими методиками, діти контрольної групи займалися за стандартною програмою групи продовженого дня. Результати. Застосування гри Го позитивно впливає на розумову праздатність і на нейродинамічні функції, при цьому вплив на нейродинамічні функції посилюється застосуванням гри Го в сполученні з фізичними вправами. Показано достовірний вплив характеру занять в групах (гра Го; Гра Го в сполученні з фізичними вправами; звичайні заняття за програмою продовженого дня) на когнітивні та нейродинамічні функції дітей 6 років. Достовірний вплив виявлено за тестами Шульте (час роботи на першій таблиці і ефективність роботи) при р<0,001 та за тестом Єрмакова з визначення швидкості реакції вибору при зміні положення об’єкта в просторі в трьох спробах при р<0,001. Висновки. Результати проведених досліджень свідчать про те, що застосування гри Го позитивно впливає на показники когнітивних функцій та нейродинамічних властивостей дітей 6 років. Заняття тільки грою Го найбільш впливає на розумову працездатність, а заняття грою Го в сполученні з фізичними вправами найбільш виражено поліпшує нейродинамічні показники, пов’язані з необхідністю перемикання уваги, швидкості реакції вибору на об’єкти, положення яких змінюється в просторі.

Analyzing transfer properties of zeolites using small-world networks

Hierarchical structures bring efficiency to many processes, including metabolism, plant growth, and even social networks. In society, connectivity among people results in a hierarchical network with a superior efficiency for information transfer. These networks are known as small-world networks. Although the number of people known by a single person is insignificant compared with the total number of people in a society, a small number of long-range connections can bring extremely high information transfer efficiency to the social network. This is the key property of the small-world network. By modeling zeolite structures as small-world networks and regarding vacancies and cracks as long-range connections, we managed to quantify efficiency in hierarchical zeolite structures. We showed the influence of cracks and vacancies on the transfer phenomenon in zeolite structures. By adding 6% vacancies into a perfect 3D zeolite structure, we obtained a 30% equivalent volume reduction in zeolite crystals. This approach might result in new methodology for quantifying zeolite transfer and broaden horizons for zeolite structure design.