Search

Water and nitrogen losses from farmland during the snowmelt process play a vital role in water and nitrogen management in cold regions. To explore the mechanisms and factors contributing to water and nitrogen loss from different sloping farmlands during the snowmelt period, field experiments were conducted under two slope treatments (8° and 15°), two soil water content (SWC) treatments, and two snow water equivalent (SWE) (5 mm and 10 mm) treatments in a seasonal freezing agricultural watershed of Northeast China. The results showed that during the snowmelt process, SWE was the most important factor affecting water and nitrogen production through the surface and total runoff of the sloping farmland, followed by the slope. The water and nitrogen yield in the high snow (HS) treatments ranged from 1.76 to 8.15 and 1.65 to 12.62 times higher than those in the low snow (LS) treatments. The generation of nitrogen was advanced compared with that of water induced by the preferential production of nitrogen. A higher slope promoted this preferential production function of nitrogen. Enhanced infiltration combined with the preferential yield of nitrogen resulted in a greatly decreased yield of water and nitrogen in the gentle slope and LS (GS_LS) treatments. These findings are valuable for accurately describing the water and nitrogen cycling in seasonally freezing sloping farmland. [ABSTRACT FROM AUTHOR]

The light olefin product distribution of the methanol‐to‐olefin (MTO) reaction catalyzed by acid zeolites and zeotypes depends on the nature of the entrapped hydrocarbon pool species that act as co‐catalysts. The preferential stabilization by confinement effects of the cationic intermediates involved in the side‐chain or paring pathways of the aromatics‐based cycle of the MTO mechanism in small‐pore cage‐based zeolites is determined by the topology of the cavity, and can be quantitatively described through the Eint(7/5) parameter obtained from DFT calculations. In this work we extend the study of the Eint(7/5) parameter to a wide range of structures (ERI, LEV, AEI, CHA, DDR, AFX, RTH, ITE, SAV, UFI, RHO, KFI, and LTA) and discuss its applicability in small cages with steric constraints to host bulky intermediates, in zeolites with a tight fitting between the cavity and the hosted cations, and in large cages where confinement effects are lost in part and competitive processes occur. [ABSTRACT FROM AUTHOR]

The methanol‐to‐olefins reaction catalyzed by small‐pore cage‐based acid zeolites and zeotypes produces a mixture of short chain olefins, whose selectivity to ethene, propene and butene varies with the cavity architecture and with the framework composition. The product distribution of aluminosilicates and silicoaluminophosphates with the CHA and AEI structures (H‐SSZ‐13, H‐SAPO‐34, H‐SSZ‐39 and H‐SAPO‐18) has been experimentally determined, and the impact of acidity and framework flexibility on the stability of the key cationic intermediates involved in the mechanism and on the diffusion of the olefin products through the 8r windows of the catalysts has been evaluated by means of periodic DFT calculations and ab initio molecular dynamics simulations. The preferential stabilization by confinement of fully methylated hydrocarbon pool intermediates favoring the paring pathway is the main factor controlling the final olefin product distribution. [ABSTRACT FROM AUTHOR]

Seit den frühen Arbeiten von Barrer in den 1940er Jahren über die Umwandlung natürlicher Mineralien in synthetische Zeolithe ist die Verwendung vorkristallisierter Zeolithe als anorganische strukturdirigierende Agentien für die Synthese anderer kristalliner Zeolithe mit verbesserten physikalisch‐chemischen Eigenschaften zu einem wichtigen Forschungsgebiet geworden. Insbesondere in den letzten Jahren die dabei die Entwicklung neuer industrieller Katalysatoren gelungen. In diesem Aufsatz beschreiben wir, wie das Vorhandensein bestimmter kristalliner Fragmente im Synthesemedium, wie z. B. kleiner Sekundärbausteine (SBUs) oder geschichteter Teilstrukturen, nicht nur die Kristallisation anderer Zeolithe begünstigt, die ähnliche SBUs oder Schichten aufweisen, sondern auch die gezielte Steuerung wichtiger Parameter ermöglicht, die die katalytische Aktivität beeinflussen (chemische Zusammensetzung, Kristallgröße, Porosität usw.). Aktuelle Fortschritte bei der Herstellung von 3D‐ und 2D‐Zeolithen durch Impfen und Zeolith‐Zeolith‐Umwandlungsvorgänge werden ausführlich besprochen, einschließlich der Herstellung mit oder ohne Beteiligung organischer strukturdirigierender Agentien (OSDAs). Ziel ist es, allgemeine Leitlinien für die Entwicklung wirkungsvollerer zukünftiger Syntheseansätze für Zeolithe auszuarbeiten. Zeolith‐Architekten: Eine aktuelle Richtung in der Zeolithforschung sind Synthesemethoden mit vorkristallisierten Materialien, die neue Strukturen mit gut kontrollierter Produktzusammensetzung zugänglich machen. Der Stand der Forschung in der Zeolith‐Zeolith‐Umwandlung und dem molekularen Engineering von Zeolithen wird zusammengefasst. [ABSTRACT FROM AUTHOR]

Since the early reports by Barrer in the 1940s on converting natural minerals into synthetic zeolites, the use of precrystallized zeolites as crucial inorganic directing agents to synthesize other crystalline zeolites with improved physicochemical properties has become a very important research field, allowing the design, particularly in recent years, of new industrial catalysts. This Review highlights how the presence of some crystalline fragments in the synthesis media, such as small secondary building units (SBUs) or layered substructures, not only favors the crystallization of other zeolites with similar SBUs or layers, but also permits control over important parameters affecting their catalytic activity (chemical composition, crystal size, or porosity, etc.). Recent advances in the preparation of 3D and 2D zeolites through seeding and zeolite‐to‐zeolite transformation processes will be discussed extensively in this Review, including their preparation in the presence or absence of organic structure‐directing agents (OSDAs). The aim is to introduce general guidelines for more efficient approaches for target zeolites. Zeolite architectures: A current research direction in the synthesis of zeolites is the use of precrystallized materials as starting materials to obtain new structures with control over the product composition. The state‐of‐the‐art of interzeolite transformation and molecular engineering are summarized. [ABSTRACT FROM AUTHOR]

Abstract: From theoretical calculations and a rational synthesis methodology, it has been possible to prepare nanocrystalline (60–80 nm) chabazite with an optimized framework Al distribution that has a positive impact on its catalytic properties. This is exemplified for the methanol‐to‐olefin (MTO) process. The nanosized material with the predicted Al distribution maximizes the formation of the required MTO hydrocarbon pool intermediates, while better precluding excessive diffusion pathways that favor the rapid catalyst deactivation by coke formation. [ABSTRACT FROM AUTHOR]

Subnanometric PtIn clusters have been synthesized within pure silica MFI zeolites by post-synthetic incorporation of In to Pt@K-MFI. The optimized PtIn@K-MFI catalyst outcompetes state-of-the-art PtSn formulations in ethane and propane dehydrogenations, avoiding the need of large excess of Pt promoters and harsh reductive conditions., (© 2024 Wiley‐VCH GmbH.)

By combining kinetics and theoretical calculations, we show here the benefits of going beyond the concept of static localized and defined active sites on solid catalysts, into a system that globally and dynamically considers the active site located in an environment that involves a scaffold structure particularly suited for a target reaction. We demonstrate that such a system is able to direct the reaction through a preferred mechanism when two of them are competing. This is illustrated here for an industrially relevant reaction, the diethylbenzene-benzene transalkylation. The zeolite catalyst (ITQ-27) optimizes location, density, and environment of acid sites to drive the reaction through the preselected and preferred diaryl-mediated mechanism, instead of the alkyl transfer pathway. This is achieved by minimizing the activation energy of the selected pathway through weak interactions, much in the way that it occurs in enzymatic catalysts. We show that ITQ-27 outperforms previously reported zeolites for the DEB-Bz transalkylation and, more specifically, industrially relevant zeolites such as faujasite, beta, and mordenite.