Screening heteroatom distributions in zeotype materials using an effective Hamiltonian approach: the case of aluminogermanate PKU-9

We introduce a method to allow the screening of large configurational spaces of heteroatom distributions in zeotype materials. Based on interatomic potential calculations of configurations containing up to three heteroatoms, we parameterize an atomistic effective Hamiltonian to describe the energy of multiple substitutions, with consideration of both short- and long-range interactions. Then, the effective Hamiltonian is used to explore the full configurational space at other compositions, allowing the identification of the most stable structures for further analysis. We illustrate our approach with the aluminogermanate PKU-9, where we show that increasing the aluminium concentration changes the likely siting of Al, in agreement with experiment

Activation of molecular oxygen over binuclear iron centers in Al-rich *BEA zeolite

Here, we present the unique redox properties of distant binuclear iron centers in Al-rich *BEA zeolite in O2 splitting and CH4 oxidation. Al-rich *BEA was obtained via a template-free synthesis procedure guaranteeing low-defected structure and a high fraction of Al-pairs enabling stabilization of binuclear iron centers. By employment of a multispectroscopic in-situ approach (Mössbauer and X-ray absorption) the formation of active oxygen over binuclear iron centers in Al-rich *BEA was confirmed and subsequent CH4 oxidation was studied. Spontaneous release of the reaction products to the gas stream, representing a significant advantage of the studied system, was proved by the results of in-situ FTIR and mass spectrometry. This is the first experimental proof of the formation of fully-functioned binuclear iron centers (able to split O2, stabilize active oxygen forms, and subsequently oxidize CH4) in zeolite of *BEA topology.This work was supported by the Grant Agency of the Czech Republic under project # 19-02901S, 21-45567L, and project RVO: 61388955nd. This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic through the e-INFRA CZ (ID:90140). Chemical analysis was provided in the frame of CATPRO (Ministry of Education, Youth and Sports, ref. no. MSMT-1000/2016, under Project No. LM2015039), which has been integrated into the National Program for Sustainability I of the Ministry of Education, Youth and Sports of the Czech Republic through the project Development of the UniCRE Centre, Project Code LO1606. This research was funded in part by the National Science Centre, Poland grant no. 2020/39/I/ST4/02559

Efficient Approach for the Computational Study of Alcohol and Nitrile Adsorption in H-ZSM-5

Since many industrially important processes start with the adsorption of guest molecules inside the pores of an acidic zeolite catalyst, a proper estimate of the adsorption enthalpy is of paramount importance. In this contribution, we report ab initio calculations on the adsorption of water, alcohols, and nitriles at the bridging Bronsted sites of H-ZSM-5, using both cluster and periodic models to account for the zeolite environment. Stabilization of the adsorption complexes results from hydrogen bonding between the guest molecule and the framework, as well as from embedding, i.e., van der Waals interactions with the pore walls. Large-cluster calculations with different DFT methods, in particular B3LYP(-D), PBE(-D), M062X(-D), and omega B97X-D, are tested for their ability to reproduce the experimental heats of adsorption available in the literature (J. Phys. Chem. B 1997, 101, 3811-3817). A proper account of dispersion interactions is found to be crucial to describe the experimental trend across a series of adsorbates of increasing size, i.e., an increase in adsorption enthalpy by 10-15 kJ/mol for each additional carbon atom. The extended-cluster model is shown to offer an attractive alternative to periodic simulations on the entire H-ZSM-5 unit cell, resulting in virtually identical final adsorption enthalpies. Comparing calculated stretch frequencies of the zeolite acid sites and the adsorbate functional groups with experimental IR data additionally confirms that the cluster approach provides an appropriate representation of the adsorption complexes

On the possible formation of Si=O, Si=S, and Si=Se double bonds via the reaction of silylenes with oxirane, thiirane, and selenirane, respectively. An ab initio theoretical study

The reactions between silylene, H2Si, and the three-membered ring compounds, oxirane (9), thiirane (10), and selenirane (11), which provide possible routes to Si=X (X = O, S, Se) double bonds were studied by ab initio calculations at the MP2 and QCISD correlated levels of theory employing the polarized 6-31G** basis set. The calculations show that the three reactions are all highly exothermic, (–61.8, –45.2, –52.9 kcal/mol at MP2/6-31G**//MP2/6-31G** for X = O, S, Se, respectively). In the gas phase, at 0 K, these reactions are predicted to be also spontaneous (i.e., the calculated transition states are lower in energy than the reactants). At 298 K, entropy contributions result in small barriers on the ΔG surface for X = O, S (7.4 kcal/mol for both reactions at QCISD (full)/6-31G**), but for X = Se the reaction remains spontaneous. Thus, the calculations suggest that these reactions are viable routes for the preparation of compounds with Si=X (X = O, S, Se) double bonds. The first step in all the reactions is the barrier-less formation of an encounter-complex between the silylene and the X atom of the precursor. For X = O, S, these complexes are predicted to be sufficiently stable to be observed in a matrix. The reaction steps which follow depend on X; for X = O fragmentation of the silylene-XC2H4 complex proceeds in two steps via a biradical intermediate, while for X = S and X = Se the fragmentation occurs in a single step. The first ab initio calculations for H2Si=Se are reported.Key words: silylene, silanone, silanethione, silaneselone. </jats:p

Analyse der Wirkmechanismen im fluidfreien Wälzkontakt mit beschichteten Oberflächen

ZusammenfassungDer Zahnkontakt wird in Zahnradgetrieben in der Regel mit flüssigem Schmierstoff, wie beispielsweise Öl oder Fett geschmiert. Jedoch führen extreme Betriebsbedingungen, wie beispielsweise hohe Druck- und Temperaturschwankungen, bei flüssigen Schmierstoffen zum Ausfall der positiven Schmiereigenschaften. Für den Einsatz von Zahnradgetrieben unter fluidfreien Betriebsbedingungen bieten Festschmierstoffe eine alternative Schmierung im Wälzkontakt. Das Ziel dieser Arbeit ist die Kenntnis über die Wirkmechanismen im PVD-beschichteten (Physical Vapour Deposition – Physikalische Gasphasenabscheidung) und fluidfreien Wälzkontakt. Für den fluidfreien Einsatz im Zahnkontakt wurde ein Schichtsystem auf Basis von Molybdändisulfid im Zahnrad-Analogieversuch auf dem Zwei-Scheiben-Reibkrafttribometer untersucht. Anhand der Charakteristik der Reibkraft kann zwischen einer Gebrauchs- und Lebensdauer unterschieden werden. Dabei zeigt die Lebensdauer eine bessere Wiederholgenauigkeit als die Gebrauchsdauer. Für die Kenntnisse über die Verschleißmechanismen wurden in Bezug auf Gebrauchsdauer und Lebensdauer Versuche mit Intervallbetrieb durchgeführt und ausgewertet. Die Verschleißanalyse der Kontaktfläche auf der Prüfwelle zeigt, dass sich bereits zu Beginn einer instationären Reibungsphase im Prüflauf ein starker Verschleiß in einem großen Teil der Laufbahn entwickelt hat.</jats:p