Screening Cu-Zeolites for Methane Activation Using Curriculum-Based Training

Machine learning (ML), when used synergistically with atomistic simulations, has recently emerged as a powerful tool for accelerated catalyst discovery. However, the application of these techniques has been limited by the lack of interpretable and transferable ML models. In this work, we propose a curriculum-based training (CBT) philosophy to systematically develop reactive machine learning potentials (rMLPs) for high-throughput screening of zeolite catalysts. Our CBT approach combines several different types of calculations to gradually teach the ML model about the relevant regions of the reactive potential energy surface. The resulting rMLPs are accurate, transferable, and interpretable. We further demonstrate the effectiveness of this approach by exhaustively screening thousands of [CuOCu]2+ sites across hundreds of Cu-zeolites for the industrially relevant methane activation reaction. Specifically, this large-scale analysis of the entire International Zeolite Association (IZA) database identifies a set of previously unexplored zeolites (i.e., MEI, ATN, EWO, and CAS) that show the highest ensemble-averaged rates for [CuOCu]2+-catalyzed methane activation. We believe that this CBT philosophy can be generally applied to other zeolite-catalyzed reactions and, subsequently, to other types of heterogeneous catalysts. Thus, this represents an important step toward overcoming the long-standing barriers within the computational heterogeneous catalysis community.

Uncovering the CO2 Capture Mechanism of NaNO3-Promoted MgO by 18O Isotope Labeling

MgO-based CO₂ sorbents promoted with molten alkali metal nitrates (e.g., NaNO₃) have emerged as promising materials for CO₂ capture and storage technologies due to their low cost and high theoretical CO₂ uptake capacities. Yet, the mechanism by which molten alkali metal nitrates promote the carbonation of MgO (CO₂ capture reaction) remains debated and poorly understood. Here, we utilize ¹⁸O isotope labeling experiments to provide new insights into the carbonation mechanism of NaNO₃-promoted MgO sorbents, a system in which the promoter is molten under operation conditions and hence inherently challenging to characterize. To conduct the ¹⁸O isotope labeling experiments, we report a facile and large-scale synthesis procedure to obtain labeled MgO with a high ¹⁸O isotope content. We use Raman spectroscopy and in situ thermogravimetric analysis in combination with mass spectrometry to track the ¹⁸O label in the solid (MgCO₃), molten (NaNO₃), and gas (CO₂) phases during the CO₂ capture (carbonation) and regeneration (decarbonation) reactions. We discovered a rapid oxygen exchange between CO₂ and MgO through the reversible formation of surface carbonates, independent of the presence of the promoter NaNO₃. On the other hand, no oxygen exchange was observed between NaNO₃ and CO₂ or NaNO₃ and MgO. Combining the results of the ¹⁸O labeling experiments, with insights gained from atomistic calculations, we propose a carbonation mechanism that, in the first stage, proceeds through a fast, surface-limited carbonation of MgO. These surface carbonates are subsequently dissolved as [Mg²⁺···CO₃ ^2-] ionic pairs in the molten NaNO₃ promoter. Upon reaching the solubility limit, MgCO₃ crystallizes at the MgO/NaNO₃ interface.

Negative Piezoelectric Coefficient in Ferromagnetic 1H-LaBr2 Monolayer

The discovery of two-dimensional (2D) magnetic materials that have excellent piezoelectric response is promising for nanoscale multifunctional piezoelectric or spintronic devices. Piezoelectricity requires a noncentrosymmetric structure with an electronic band gap, whereas magnetism demands broken time-reversal symmetry. Most of the well-known 2D piezoelectrics, e.g., 1H-MoS₂ monolayer, are not magnetic. Being intrinsically magnetic, semiconducting 1H-LaBr₂ and 1H-VS₂ monolayers can combine magnetism and piezoelectricity. We compare piezoelectric properties of 1H-MoS₂, 1H-VS₂, and 1H-LaBr₂ using density functional theory. The ferromagnetic 1H-LaBr₂ and 1H-VS₂ monolayers display larger piezoelectric strain coefficients, namely, d ₁₁ = -4.527 pm/V for 1H-LaBr₂ and d ₁₁ = 4.104 pm/V for 1H-VS₂, compared to 1H-MoS₂ (d ₁₁ = 3.706 pm/V). 1H-MoS₂ has a larger piezoelectric stress coefficient (e ₁₁ = 370.675 pC/m) than 1H-LaBr₂ (e ₁₁ = -94.175 pC/m) and 1H-VS₂ (e ₁₁ = 298.100 pC/m). The large d ₁₁ for 1H-LaBr₂ originates from the low elastic constants, C ₁₁ = 30.338 N/m and C ₁₂ = 9.534 N/m. The sign of the piezoelectric coefficients for 1H-LaBr₂ is negative, and this arises from the negative ionic contribution of e ₁₁, which dominates in 1H-LaBr₂, whereas the electronic part of e ₁₁ dominates in 1H-MoS₂ and 1H-VS₂. We explain the origin of this large ionic contribution of e ₁₁ for 1H-LaBr₂ through Born effective charges (Z ₁₁) and the sensitivity of the atomic positions to the strain (du/dη). We observe a sign reversal in the Z ₁₁ values of Mo and S compared to the nominal oxidation states, which makes both the electronic and ionic parts of e ₁₁ positive and results in the high value of e ₁₁. We also show that a change in magnetic order can enhance (reduce) the piezoresponse of 1H-LaBr₂ (1H-VS₂).

New 1-(3-nitrophenyl)-5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepines: synthesis and computational study

Triazole derivatives constitute an important group of heterocyclic compounds have have been the subject of extensive study in the recent past. These compounds have shown a wide range of biological and pharmacological activities. In this work, new fused tricyclic 1-(3-nitrophenyl)-5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1,5]-benzodiazepines have been synthesized by the thermal cyclization of N'-(2,3-dihydro-1H-1,5-benzodiazepin-4-yl)-3-nitrobenzohydrazides. After screening ethanol, toluene and 1-butanol as solvents, butanol-1 was found to be the best choice for the cyclization reaction in order to obtain the highest yields of tricyclic derivatives. The chemical structures of the synthesized compounds were elucidated by the analysis of their IR, 1H- and 13C-NMR spectral data. For tentative rationalization of the reaction processes, the global and local reactivity indices of certain compounds, taking part in the reaction pathway, were assessed by means of quantum mechanical calculations using the conceptual density functional theory (DFT) approach. This work could be useful for the synthesis of new heterocyclic compounds bearing a fused triazole ring.

Local electronic and chemical structure of oligo-acetylene derivatives formed through radical cyclizations at a surface

Semiconducting π-conjugated polymers have attracted significant interest for applications in light-emitting diodes, field-effect transistors, photovoltaics, and nonlinear optoelectronic devices. Central to the success of these functional organic materials is the facile tunability of their electrical, optical, and magnetic properties along with easy processability and the outstanding mechanical properties associated with polymeric structures. In this work we characterize the chemical and electronic structure of individual chains of oligo-(E)-1,1'-bi(indenylidene), a polyacetylene derivative that we have obtained through cooperative C1-C5 thermal enediyne cyclizations on Au(111) surfaces followed by a step-growth polymerization of the (E)-1,1'-bi(indenylidene) diradical intermediates. We have determined the combined structural and electronic properties of this class of oligomers by characterizing the atomically precise chemical structure of individual monomer building blocks and oligomer chains (via noncontact atomic force microscopy (nc-AFM)), as well as by imaging their localized and extended molecular orbitals (via scanning tunneling microscopy and spectroscopy (STM/STS)). Our combined structural and electronic measurements reveal that the energy associated with extended π-conjugated states in these oligomers is significantly lower than the energy of the corresponding localized monomer orbitals, consistent with theoretical predictions.

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Transition metal aluminium nitride (TM-Al-N) thin films are valued for their excellent mechanical (e.g. hardness) as well as protective (e.g. oxidation resistance) properties. This paper addresses the structure and phase stability of group IVB TM-Al-N systems Ti(1-x)Al(x)N, Zr(1-x)Al(x)N, and Hf(1-x)Al(x)N. The predicted stability regions of the rock salt cubic structures are x ≤ 0.7, x ≤ 0.45, and x ≤ 0.45, respectively, while the wurtzite-type single phase field is obtained for x ≥ 0.7, x ≥ 0.68, and x ≥ 0.62 respectively. The predicted phase stability regions and the broad dual-phase transition regions in the case of Zr(1-x)Al(x)N and Hf(1-x)Al(x)N are validated by experiments. Furthermore, the phase transition from cubic to wurtzite with increasing Al content in the alloys is correlated with changes of electronic structure and bonding in the systems.

Suzuki-Miyaura cross-coupling reaction on copper-trans-A(2)B corroles with excellent functional group tolerance

The palladium-catalyzed Suzuki-Miyaura cross-coupling reaction has been investigated on meso-substituted trans-A(2)B-corrole using tailored Pd-catalyst systems.We present the first examples of Suzuki-Miyaura cross-coupling reactions on meso-substituted trans-A(2)B-corrole derivatives with neutral, sterically hindered, inactivated and heteroaromatic boronic acids and esters, alkenylboronic acids, as well as quickly deboronating aryl boronic acids and benzo-condensated five membered heterocyclic boronic acids. In addition, we established a high-yield procedure for the Suzuki-Miyaura cross-coupling reaction of corroles with neutral boronic acids.Due to the lability of the free-base corrole macrocycles, functionalization of the corrole periphery was performed with the corresponding Cu-metallated species. meso-Substituted trans-A(2)B-corrole can hence be regarded as highly versatile platform towards more sophisticated corrole systems.X-ray structure analysis of a functionalized meso-substituted trans-A(2)B copper corrole exhibited the typical features of such a Cu-complex: short N-Cu distances and a saddled corrole configuration.Moreover, we observed a sensitivity of the formal oxidation state of the coordinated copper ions towards Suzuki-Miyaura cross-coupling reaction conditions, where the central copper(III) ion approaches the characteristic features of a copper(II) species. This redox behaviour was examined by UV/vis absorption spectra, nuclear magnetic resonance (NMR) experiments and time-dependent density functional theoretical calculations.