An innovative approach for inserting metal cations into layered perovskite oxides is investigated using a soft-chemistry route that enables controlled incorporation of cations such as Cu²⁺. Starting from the Ruddlesden-Popper...

Highly dispersed Pt/gamma-Al2O3 catalysts play a tremendous role in heterogeneous catalysis, however, synthesizing materials with well-defined Pt nuclearity remains a challenge. In this work, we demonstrate how surface organometallic chemistry (SOMC) can be employed to tune cluster size down to single atoms by selecting an appropriate organometallic precursor (MeCpPtMe3, tmedaPtMe(2), or CODPtMe2) at low platinum loading (0.03 Pt.nm(-2)). FTIR and solution NMR analyses indicate that part of the tmedaPtMe(2) and CODPtMe2 precursors graft through protonolysis with the hydroxyl groups of the gamma-Al2O3 support, while the remaining fraction, along with MeCpPtMe3, is deposited via adsorption onto gamma-Al2O3. Upon calcination, MeCpPtMe3 produces the highest proportion of platinum single atoms, while CODPtMe2 generates the lowest among the series. Following reduction, sub-nanometric clusters (0.6 nm) are formed, significantly smaller than those obtained with a reference catalyst (0.9 nm) prepared by incipient wetness impregnation (IWI) using a conventional Pt(NH3)(4)(NO3)(2) precursor. CO probe adsorption monitored by FTIR reveals distinct electronic properties of the surface metal atoms depending on the chosen metal precursor. Interestingly, an inverse size-frequency trend is observed compared to the results reported in the literature for larger clusters (> 1 nm). This finding opens new avenues for modulating the catalytic properties of these materials.

Deep learning methods are now achieving strong results for segmentation tasks, and the standard metric for evaluating methods is the Intersection over Union (IOU). However, we show in this paper that IOU is not efficient in evaluating the quality of segmentation for electron tomography (ET) images of zeolites. We perform a physics-oriented evaluation to ensure that the segmentation results yield coherent physical measures. We also formalize Mixed Supervised / Self-Supervised Contrastive Learning Segmentation (M3S-CLS), a semi-supervised approach using a contrastive learning approach that uses expert annotations to train the neural network model. A detailed comparison of this method with a standard cross-entropy-based model is provided. In addition, we publish a database of five fully segmented ET volumes along with corresponding baseline results. The code and the database is available at http://gitlab.univ-st-etienne.fr/labhc-iscv/M3S-CLS.

Faujasite Y zeolites (FAU-Y) represent one of the most important categories of heterogeneous catalysts. They are historically known for their crucial role in the refining industry, and they have growing potential for upgrading bio-based products today. However, the thermal stability, acidity, and molecular transport properties of the synthesized zeolite are not ideal for the intended process conditions, activity, selectivity and catalyst deactivation. Consequently, post-synthesis physical-chemical treatments, such as dealuminating treatments, are usually employed to design a more efficient material that combines stronger acidity, better stability, and hierarchical porosity. This material is referred to as Ultrastable Y (USY) zeolite. Nevertheless, the precise mechanisms of mesopore network formation and its relationship with the crystal structure and morphology remain poorly understood. Our research investigates the evolution of the porous system induced by the dealumination in FAU-Y zeolites. Here, we propose a classification, quantification, morphological description and formation scheme of the mesopores with an unprecedented level of detail, that is based on electron tomography data from the main steps of the dealumination process. Four main groups of pores are identified: (1) closed, isolated mesopores with more spherical shapes and diameters of 7-8 nm; (2) open intracrystalline channeling mesopores that often run along crystallographic orientations, vary in diameter, and whose morphology recall a mechanism of isolated mesopore coalescence; (3) intercrystalline mesopores with irregular shapes detected at the boundaries of twinned crystals, and (4) surface roughness. We finally observe that the localization and development of mesopores are associated with structural defects, such as stacking faults and twinning. These results allow us to consider a nucleation/diffusion mechanism for the mesoporous network within zeolite Y during dealumination and provide guidelines for identifying new pathways to optimize hierarchical zeolites.

Single atom catalysts (SACs) appear as a promising class of materials featuring isolated metal atoms anchored to supports, where the advantages of heterogeneous catalysis are combined with a maximized noble metal atom usage. In SACs, each metal atom is fully exposed to the support surface; it is therefore critical to elucidate the nature of the metal-support interface to identify the active species and design tailored, more efficient materials. Among SACs, Pt1/γ-Al2O3, active toward CO oxidation and isomerization of olefins, represents a prototypical system. However, the chemical complexity and poor crystallinity of γ-Al2O3 hinders an atomistic description via conventional techniques (XAS, TEM) only. Here, we report the study, via multinuclear solid-state NMR and DFT modeling, of a series of Pt SACs on γ-Al2O3 supports, prepared by surface organometallic chemistry followed by calcination. This approach clarifies the coordination environment of Pt1/γ-Al2O3, revealing that highly oxidized Pt atoms are preferentially anchored by undercoordinated Al sites at the (110)b-(100) edge. The Pt atoms have a distorted square planar or square pyramidal environment and are stabilized through [4-6]Al-O-Pt and [4]Al-OH-Pt linkages. Pyridine absorption studies reveal the presence of Brønsted acidic sites, assigned to [4]Al-OH-Pt edge moieties, through DFT modeling. The findings establish morphological features of γ-Al2O3 supports needed to stabilize SACs and provide a roadmap for building accurate SAC-support models using NMR and DFT.

Pt/γ-Al 2 O 3 catalysts are prepared by surface organometallic chemistry and treatment under oxidative or reductive atmospheres. They exhibit a smaller particle size and/or a higher single atom/cluster ratio than a conventional catalyst.

This study investigates phase transitions in CuO/Al 2 O 3 oxygen carriers during chemical looping combustion (CLC), aiming to understand performance and stability over extended redox cycles.

Platinum catalysts supported on γ-Al2O3 are central to a variety of applications. The conditions controlling the formation of Pt single atoms and subnanometric clusters remain elusive. The present work, based on surface organometallic chemistry (SOMC), unravels their formation under oxidative and reductive atmospheres. Following the grafting of MeCpPtMe3 as a molecular precursor to generate highly dispersed sites on alumina, the evolution upon thermal treatment under oxidative or reductive conditions is monitored by in situ FTIR, with the ultimate goal to access catalysts with different single atom-to-cluster ratios, comparing SOMC with a conventional preparation method. Under oxidative conditions, all ligands are removed to form CO2 in a multi-step process, while under reductive conditions, ligands likely decompose through hydrogenolysis/hydrogenation reactions. HAADF-STEM characterization and CO adsorption experiments reveal the presence of several states of Pt, depending on the Pt surface density and the treatment applied. Under a reductive atmosphere, the size of platinum clusters remains relatively constant and lower than 0.8 nm, regardless of the Pt surface density (0.03-0.09-0.15 Pt nm-2). Under an oxidative atmosphere, the Pt surface density is a key factor that drives the size of platinum clusters and the relative amount of single atoms, both of which are significantly different from those of a reference conventional catalyst obtained by incipient wetness impregnation of Pt(NH3)4(NO3)2. Notably, the material at 0.03 Pt nm-2 exhibits mainly Pt single atoms after calcination, while increasing Pt density favors cluster formation.

This study investigates phase transitions in CuO/Al2O3 oxygen carriers during chemical looping combustion (CLC), aiming to understand performance and stability over extended redox cycles. In situ quick X-ray assorption spectroscopy (QXAS) was employed to track the transformations of the copper aluminate phase (CuxAlyO4) over 50 redox cycles in various oxidizing (2.5 to 21% O2 in N2) and reducing (H2, CO, CH4) environments. The study reveals that the oxygen carrier undergoes significant phase transitions, reaching a threshold where CuxAlyO4 predominantly converts to copper oxide and alpha-Al2O3, leading to irreversible structural modifications. Complementary SEM analysis further highlights morphological changes, such as particle growth prior to alpha-Al2O3 formation. This cycle-dependent phase evolution provides new insights into accelerated ageing mechanism involving the interplay between copper phase transformations and alpha-Al2O3 formation, which is critical for enhancing the durability of oxygen carriers in CLC applications.

This study explores the morphological and structural transformation of boehmite (AlOOH) into transition aluminas during calcination, a pathway crucial for diverse industrial applications. The primary focus is on the topotactic transformation of boehmite into gamma-Al2O3 and its subsequent transitions into higher temperature polymorphs, culminating in alpha-Al2O3. Utilizing a combination of in situ X-ray diffraction, in situ and ex situ transmission electron microscopy, 27Al solid-state nuclear magnetic resonance, thermogravimetric analysis, nitrogen physisorption, and mercury porosimetry, this work provides insights into the morphological and structural reordering during the calcination process. Furthermore, the study highlights the significant impact of thermal processing on the morphological evolution of boehmite and transition aluminas, characterized by changes in pore structure sizes and shapes. These findings offer valuable insights for optimizing the properties of alumina-based materials for specific applications. This study explores the transformation of boehmite (AlOOH) into transition aluminas during calcination, emphasizing on the progression from gamma-Al2O3 to alpha- Al2O3. Through a combination of in-situ techniques, the research elucidates the pseudomorphic retention of structure during initial dehydration and successive structural ordering at higher temperatures. The results highlight the influence of thermal processing on pore structure development, contributing to our understanding of boehmite derived alumina for industrial applications. image

Silicon-based composite anodes continue to raise interest for their high theoretical specific capacity, but the complexity of their behaviour during battery operation presents an obstacle to both their characterization and their practical application. In this paper we present a comprehensive multiscale model of a Si-based composite anode, based on a detailed characterization and encompassing nano-, micro-, and meso-scale details. The model is used to explore the relationship between the chemo-mechanical changes in the anode components and the electrode stability during battery operation, through the prediction of the morphological evolution of the material during the lithiation process. Through the combined analysis of DFT, FEM, and DEM models we highlight the influence of Si and SiO2 lithiation on electrode swelling and damage, and the predominant influence of particle-level morphology on electrochemical behaviour.

Boehmite (AlOOH) is considered as an important precursor for γ-Al2O3, which when calcinated undergoes topotactic transformation to form the latter. Alumina has extensive applications in fields such as catalysis, abrasives, and cosmetics among others. Boehmite falls under the category of hierarchical structures whose structural and textural properties are a result of its compositional and porous hierarchy. Although research has been carried out extensively to understand the complete representation of its structure, a true morphological model is an important key to understanding and fully explaining its transport properties during catalytic processes. 3D electron microscopy helps us to dive deeper into the different hierarchical entities of boehmite, bridging the gaps between the models and assumptions made using some more traditional characterization techniques. We present here a deep insight into the structural and morphological parameters of several commercial boehmites using 3D transmission electron microscopy. Through the extraction of quantitative descriptors pertaining to hierarchical entities and subsequent comparison with bulk analyses, precise and comprehensive information regarding these microstructures can be obtained. The results of our study indicate that boehmite grades, which appear to be identical in terms of their grades, display discrepancies in the uniformity of particle sizes. Moreover, diverse platelet interactions result in varying types of pores in these grades. Furthermore, it has been observed that the interfacial interactions among various crystallographic planes exhibit variations across different specimens, thereby contributing to the distinctive compositions within the aggregates. The variation in aggregates of different boehmite grades is also reflected in the combination of four distinct quantified morphologies.

Hierarchical zeolites presenting different pore domains have the potential to reduce problems associated with low diffusion in zeolites, thus holding great promise in a wide range of application fields. Nevertheless, efficient transfer between the different porous networks is required for the mesopores (2-50 nm) and macropores (>50 nm) to be effective in promoting the transit of molecules towards the micropores (<2 nm). In this work, the connectivity between the various pore domains in a class of hierarchical zeolites - denominated as nanoparticle aggregates - is investigated through 2D exchange spectroscopy (EXSY) 1H nuclear magnetic resonance (NMR) using paraxylene as a probe molecule. This approach allows to track whether the probe molecule visits distinct pore environments over time, providing unique insight into pore connectivity. The analysis of scanning curves through N2 adsorption/desorption cycles completes the characterization of pore connectivity. Furthermore, electron microscopy and tomography are used as visual techniques to confirm the arrangement of the mesoporous and macroporous networks generated by the nanoparticle aggregates.

Photocatalytic conversion of CO2 with H2O is an attractive application that has the potential to mitigate environmental and energy challenges through the conversion of CO2 to hydrocarbon products such as methane. However, the underlying reaction mechanisms remain poorly understood, limiting real progress in this field. In this work, a mechanistic investigation of the CO2 photocatalytic reduction on Pt/TiO2 is carried out using an operando FTIR approach, combined with chemometric data processing and isotope exchange of ((CO2)-C-12 + H2O) toward ((CO2)-C-13 + H2O). Multivariate curve resolution analysis applied to operando spectra across numerous cycles of photoactivation and the CO2 reaction facilitates the identification of principal chemical species involved in the reaction pathways. Moreover, specific probe-molecule-assisted reactions, including CO and CH3COOH, elucidate the capacity of selected molecules to undergo methane production under irradiation conditions. Finally, isotopic exchange reveals conclusive evidence regarding the nature of the identified species during CO2 conversion and points to the significant role of acetates resulting from the C-C coupling reaction as key intermediates in methane production from the CO2 photocatalytic reduction reaction.

Zeolites are widely used as solid acid catalysts from the laboratory to the industrial scale. Their thermal stability, mesoporous volume, and catalytic properties can be significantly enhanced by framework dealumination, resulting in the formation of framework defects and extra-framework aluminum (EFAL) species, altering surface acidity and microporous volume. Understanding dealumination of as-synthesized zeolite crystals is critical to tuning their catalytic activities. However, the atomic-scale structural evolution of the zeolite surface in the course of dealumination treatments remains elusive. Here, we examined a series of four faujasite zeolite samples, ranging from Y to USY zeolites, collected at key steps of the manufacturing process. High-resolution quantitative 1H NMR spectra were obtained at high field and fast magic angle spinning frequency and interpreted with the help of 1H multiple-quantum (up to four-quanta) and 1H-27Al dipolar-based correlation experiments. An extensive array of surface species was resolved, identified, and monitored during dealumination with a high level of structural detail. This was achieved through a joint interpretation of the NMR data acquired across the entire sample set and DFT calculations spanning an exceptionally broad range of environments. Key insight is provided into the environment of various hydroxyl groups as well as the atomic-scale structure of mononuclear EFAL species. While alumina-like domains are not observed, the presence of multinuclear EFAL species is evidenced. The structures of several defect silanol sites were also characterized. The quantitative evolution of these various surface sites during dealumination is discussed based on the peak intensity changes in the 1H spectra. Ultimately, in situ IR spectra were obtained. Clear correlations were observed between the IR bands and 1H peaks, offering valuable perspectives to refine the interpretation of both IR and NMR spectra.

CH4 production enhancement upon periodic irradiation cycles.