Atomic Insights into the Cu Species Supported on Zeolite for Direct Oxidation of Methane to Methanol via Low-Damage HAADF-STEM

Blocking the Operando Formation of Single-Atom Spectators by Interfacial Engineering

Aside from activity and selectivity, catalyst stability is a key focus in heterogeneous catalysis research. Although sintering of metal species has been considered the primary cause for deactivation of metal catalysts, our study reveals that the loss of activity at low reaction temperatures in the CeO2-supported Pt (Pt/CeO2) catalyst in complete propane oxidation is due to the dispersion of Pt ensemble sites (nanoclusters) and their subsequent operando conversion into Pt single atoms under reaction conditions. These Pt single-atom species exhibit low reactivity and act as spectators in the low-temperature reaction region. To address this issue, we engineered the surface of CeO2 by introducing NbOx, which does not directly interact with Pt. Instead, NbOx blocks the strong binding sites for Pt on CeO2, thereby preventing Pt redispersion/fragmentation and preserving reactive Pt ensembles. This strategy led to a remarkable 37-fold increase in the reaction rate compared to the Pt/CeO2 catalyst. Our findings emphasize the importance of suppressing the formation of noble metal single-atom spectators through innovative surface engineering strategy. These mechanistic insights not only advance the understanding of the materials science of Pt/CeO2 but also extend to critical technological fields such as energy conversion systems and environmental remediation technologies.

Exploring guest species in zeolites using transmission electron microscopy: a review and outlook

Zeolites, with their well-defined microporous frameworks, accommodate diverse guest species, including metal ions, atoms, clusters, complexes, and organic molecules. Direct imaging of these species and their interactions with the framework is crucial for understanding their structural and functional roles. Transmission electron microscopy (TEM), particularly aberration-corrected scanning TEM (STEM), has become an indispensable tool, offering atomic-resolution real-space insights. This review summarizes key (S)TEM techniques for probing guest species in zeolites, with a focus on low-dose strategies to minimize beam damage. We discuss the principles, applications, and limitations of various imaging modalities and highlight recent advances in visualizing metallic and organic species. Finally, we explore future directions for (S)TEM in zeolite research, emphasizing the opportunities and challenges of in situ, three-dimensional, and cryogenic imaging for resolving host-guest interactions with greater precision.

Confined Cu Single Sites in ZSM-5 for Photocatalytic Hydroxylation of Benzene to Phenol

Zeolites with band-like charge transport properties have exhibited their potential activities in sensing, optics, and electronics. Herein, a precisely designed Cu@ZSM-5 catalyst is presented with an ultra-wide bandgap of 4.27 eV, showing excellent photocatalytic activity in hydroxylation of benzene with benzene conversion 27.9% and phenol selectivity 97.6%. The SXRD and Rietveld refinement results illustrate that Cu@ZSM-5 has an average of 0.8 Cu atoms per unit cell and the single Cu atoms located in the cross-section of the sinusoidal and straight channels. XANES and EXAFS further demonstrate that the Cu atoms have an oxidation state of +2, coordinated with three OMFI-framework atoms and one ─OH group. Detailed characterizations demonstrate that the Cu@ZSM-5 with tailored bandgap is able to enhance the photoinduced electron-hole separation and hence promote selective hydroxylation of benzene to phenol via the superoxide radical route. This work may open a new way for designing electrically conductive zeolite-supported photocatalysts.

The beginning of iron corrosion - high-resolution visualization with 3D electron tomography

Understanding the genesis and early-phase reactions of iron corrosion is essential for the early detection, mitigation and prevention of metal degradation. In this work, high-resolution 3D tomography of metallic iron oxidation was acquired using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In particular, dendritic capillaries (<0.5 nm) were observed during the initial oxidation of fresh nanoscale zero-valent iron due to the differential oxygen diffusion and iron atoms migration. This observation led to the proposal of a nanoscale "pothole" model for early-phase corrosion, wherein hollowing out of the metal nanoparticle and formation of nanovoids beneath the iron/oxide interface through Kirkendall effect. Coalescence of the nanocapillaries results in the ultimate collapse of metal structure and/or functional failure. Using nanoscale zero-valent iron as a research model, this work provides unprecedented insights into the nano- and atomic-scale mechanisms of iron oxidation, paving the way for advanced detection and prevention strategies for iron corrosion.

Exploring the Facet-Dependent Structural Evolution of Pt/CeO2 Catalysts Induced by Typical Pretreatments for CO Oxidation

Atomic-scale insights into the interactions between metals and supports play a crucial role in optimizing catalyst design, understanding catalytic mechanisms, and enhancing chemical conversion processes. The effects of oxide support on the dynamic behavior of supported metal species during pretreatments or reactions have been attracting a lot of attention; however, very less systematic integrations are carried out experimentally using real catalysts. In this study, we here utilized facet-controlled CeO2 as examples to explore their influence on the supported Pt species (1.0 wt %) during the reducing and oxidizing pretreatments that are typically applied in heterogeneous catalysts. By employing a combination of microscopy, spectroscopy, and first-principles calculations, it is demonstrated that the exposed crystal facets of CeO2 govern the evolution behavior of supported Pt species under different environmental conditions. This leads to distinct local coordinations and charge states of the Pt species, which directly influence the catalytic reactivity and can be leveraged to control the catalytic performance for CO oxidation reactions.

Copper-oxygen adducts: new trends in characterization and properties towards C-H activation

This review summarizes the latest discoveries in the field of C-H activation by copper monoxygenases and more particularly by their bioinspired systems. This work first describes the recent background on copper-containing enzymes along with additional interpretations about the nature of the active copper-oxygen intermediates. It then focuses on relevant examples of bioinorganic synthetic copper-oxygen intermediates according to their nuclearity (mono to polynuclear). This includes a detailed description of the spectroscopic features of these adducts as well as their reactivity towards the oxidation of recalcitrant Csp3 -H bonds. The last part is devoted to the significant expansion of heterogeneous catalytic systems based on copper-oxygen cores (i.e. within zeolite frameworks).

Enabling direct oxidation of ethane to acetaldehyde with oxygen using supported PdO nanoparticles

Industrial-scale production of acetaldehyde relies heavily on homogeneous catalysts. Here, we used ethane as the feedstock and developed ZSM-5-supported PdO nanoparticles for the direct oxidation of ethane to acetaldehyde by utilizing O2 and CO. PdO nanoparticles clearly demonstrate effective activity and prevent the further deep oxidation of acetaldehyde.

Solvent-Free Synthesis Enables Encapsulation of Subnanometric FeOx Clusters in Pure Siliceous Zeolites for Efficient Catalytic Oxidation Reactions

Metal/metal oxide clusters possess a higher count of unsaturated coordination sites than nanoparticles, providing multiatomic sites that single atoms do not. Encapsulating metal/metal oxide clusters within zeolites is a promising approach for synthesizing and stabilizing these clusters. The unique feature endows the metal clusters with an exceptional catalytic performance in a broad range of catalytic reactions. However, the encapsulation of stable FeOx clusters in zeolite is still challenging, which limits the application of zeolite-encapsulated FeOx clusters in catalysis. Herein, we design a modified solvent-free method to encapsulate FeOx clusters in pure siliceous MFI zeolites (Fe@MFI). It is revealed that the 0.3-0.4 nm subnanometric FeOx clusters are stably encapsulated in the 5/6-membered rings intersectional voids of the pure siliceous MFI zeolites. The encapsulated Fe@MFI catalyst with a Fe loading of 1.4 wt % demonstrates remarkable catalytic activity and recycle stability in the direct oxidation of methane, while also promoting the direct oxidation of cyclohexane, surpassing the performance of conventional zeolite-supported Fe catalysts.

Nanoparticles as an antidote for poisoned gold single-atom catalysts in sustainable propylene epoxidation

The development of sustainable and anti-poisoning single-atom catalysts (SACs) is essential for advancing their research from laboratory to industry. Here, we present a proof-of-concept study on the poisoning of Au SACs, and the antidote of Au nanoparticles (NPs), with trace addition shown to reinforce and sustain propylene epoxidation. Multiple characterizations, kinetics investigations, and multiscale simulations reveal that Au SACs display remarkable epoxidation activity at a low propylene coverage, but become poisoned at higher coverages. Interestingly, Au NPs can synergistically cooperate with Au SACs by providing distinct active sites required for H2/O2 and C3H6 activations, as well as hydroperoxyl radical to restore poisoned SACs. The difference in reaction order between C3H6 and H2 (nC3H6-nH2) is identified as the descriptor for establishing the volcano curves, which can be fine-tuned by the intimacy and composition of SACs and NPs to achieve a rate-matching scenario for the formation, transfer, and consumption of hydroperoxyl. Consequently, only trace addition of Au NPs antidote (0.3% ratio of SACs) stimulates significant improvements in propylene oxide formation rate, selectivity, and H2 efficiency compared to SACs alone, offering a 56-fold, 3-fold, and 22-fold increase, respectively, whose performances can be maintained for 150 h.

CO-Induced Dimer Decay Responsible for Gem-Dicarbonyl Formation on a Model Single-Atom Catalyst

The ability to coordinate multiple reactants at the same active site is important for the wide-spread applicability of single-atom catalysis. Model catalysts are ideal to investigate the link between active site geometry and reactant binding, because the structure of single-crystal surfaces can be precisely determined, the adsorbates imaged by scanning tunneling microscopy (STM), and direct comparisons made to density functional theory. In this study, we follow the evolution of Rh1 adatoms and minority Rh2 dimers on Fe3O4(001) during exposure to CO using time-lapse STM at room temperature. CO adsorption at Rh1 sites results exclusively in stable Rh1CO monocarbonyls, because the Rh atom adapts its coordination to create a stable pseudo-square planar environment. Rh1(CO)2 gem-dicarbonyl species are also observed, but these form exclusively through the breakup of Rh2 dimers via an unstable Rh2(CO)3 intermediate. Overall, our results illustrate how minority species invisible to area-averaging spectra can play an important role in catalytic systems, and show that the decomposition of dimers or small clusters can be an avenue to produce reactive, metastable configurations in single-atom catalysis.

Contact-separation-induced self-recoverable mechanoluminescence of CaF2:Tb3+/PDMS elastomer

Centrosymmetric-oxide/polydimethylsiloxane elastomers emit ultra-strong non-pre-irradiation mechanoluminescence under stress and are considered one of the most ideal mechanoluminescence materials. However, previous centrosymmetric-oxide/polydimethylsiloxane elastomers show severe mechanoluminescence degradation under stretching, which limits their use in applications. Here we show an elastomer based on centrosymmetric fluoride CaF2:Tb3+ and polydimethylsiloxane, with mechanoluminescence that can self-recover after each stretching. Experimentation indicates that the self-recoverable mechanoluminescence of the CaF2:Tb3+/polydimethylsiloxane elastomer occurs essentially due to contact electrification arising from contact-separation interactions between the centrosymmetric phosphors and the polydimethylsiloxane. Accordingly, a contact-separation cycle model of the phosphor-polydimethylsiloxane couple is established, and first-principles calculations are performed to model state energies in the contact-separation cycle. The results reveal that the fluoride-polydimethylsiloxane couple helps to induce contact electrification and maintain the contact-separation cycle at the interface, resulting in the self-recoverable mechanoluminescence of the CaF2:Tb3+/polydimethylsiloxane elastomer. Therefore, it would be a good strategy to develop self-recoverable mechanoluminescence elastomers based on centrosymmetric fluoride phosphors and polydimethylsiloxane.

Significance of Epitaxial Growth of PtO2 on Rutile TiO2 for Pt/TiO2 Catalysts

TiO2-supported Pt species have been widely applied in numerous critical reactions involving photo-, thermo-, and electrochemical-catalysis for decades. Manipulation of the state of the Pt species in Pt/TiO2 catalysts is crucial for fine-tuning their catalytic performance. Here, we report an interesting discovery showing the epitaxial growth of PtO2 atomic layers on rutile TiO2, potentially allowing control of the states of active Pt species in Pt/TiO2 catalysts. The presence of PtO2 atomic layers could modulate the geometric configuration and electronic state of the Pt species under reduction conditions, resulting in a spread of the particle shape and obtaining a Pt/PtO2/TiO2 structure with more positive valence of Pt species. As a result, such a catalyst exhibits exceptional electrocatalytic activity and stability toward hydrogen evolution reaction, while also promoting the thermocatalytic CO oxidation, surpassing the performance of the Pt/TiO2 catalyst with no epitaxial structure. This novel epitaxial growth of the PtO2 structure on rutile TiO2 in Pt/TiO2 catalysts shows its potential in the rational design of highly active and economical catalysts toward diverse catalytic reactions.

Versatile Structural Engineering of Metal-Organic Frameworks Enabling Switchable Catalytic Selectivity

The structure engineering of metal-organic frameworks (MOFs) forms the cornerstone of their applications. Nonetheless, realizing the simultaneous versatile structure engineering of MOFs remains a significant challenge. Herein, a dynamically mediated synthesis strategy to simultaneously engineer the crystal structure, defect structure, and nanostructure of MOFs is proposed. These include amorphous Zr-ODB nanoparticles, crystalline Zr-ODB-hz (ODB = 4,4'-oxalyldibenzoate, hz = hydrazine) nanosheets, and defective d-Zr-ODB-hz nanosheets. Aberration-corrected scanning transmission electron microscopy combined with low-dose high-angle annular dark-field imaging technique vividly portrays these engineered structures. Concurrently, the introduced hydrazine moieties confer self-reduction properties to the respective MOF structures, allowing the in situ installation of catalytic Pd nanoparticles. Remarkably, in the hydrogenation of vanillin-like biomass derivatives, Pd/Zr-ODB-hz yields partially hydrogenated alcohols as the primary products, whereas Pd/d-Zr-ODB-hz exclusively produces fully hydrogenated alkanes. Density functional theory calculations, coupled with experimental evidence, uncover the catalytic selectivity switch triggered by the change in structure type. The proposed strategy of versatile structure engineering of MOFs introduces an innovative pathway for the development of high-performance MOF-based catalysts for various reactions.

Sn-based materials in photocatalysis: A review

Development and the application of Sn-based materials have become more prevalent in recent years due to concerns regarding the energy crisis, environmental pollution, and the urgent need of constructing inexpensive and highly effective photocatalysis. The recent advancement in Sn-based materials for efficient photocatalysts, such as Sn alloys, Sn oxides, Sn sulfides, Sn selenides, Sn niobates, Sn tantalites, and Sn tungstates, is summarized in this study. Several design ideas for increasing the photoactivity of Sn-based materials in various photocatalytic applications are emphasized. In addition, we considered their present applications in energy generation (H2 evolution, CO2 reduction, and N2 fixation) and environmental remediation (air purification and wastewater treatment). As a result, the current review will deepen the reader's understanding of the properties and potential uses of Sn-based materials in photocatalysis. Hence, this paper will serve as a guide in promoting the domain of Sn-based materials for future photocatalytic technologies.

Structural Analysis of Cu+ and Cu2+ Ions in Zeolite as a Nanoreactor with Antibacterial Applications

In this work, we report the structural analysis of Cu+ and Cu2+ ions in zeolite as a nanoreactor with antibacterial applications. A simple one-step process was implemented to obtain Cu ions in zeolite A (ZA4) by controlling the temperature in the solutions to guarantee the ions' stability. Samples were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, showing the characteristic zeolite elements as well as the characteristic bands with slight modifications in the chemical environment of the zeolite nanoreactor attributed to Cu ions by FT-IR spectroscopy. In addition, a shift of the characteristic peaks of ZA4 in X-ray diffraction was observed as well as a decrease in relative peak intensity. On the other hand, the antibacterial activity of Cu ions in the zeolite nanoreactor was evaluated.