Regioselective generation and reactivity control of subnanometric platinum clusters in zeolites for high-temperature catalysis

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.

Dynamic evolution of metal structures on/in zeolites for catalysis

Dynamic changes of metal species always occur during catalysis, and primarily rely on forming mobile metal species initiated by thermal or chemical conditions. During these processes, a support is important in affecting the catalyst stability and dynamic change pathways. Among several supports, zeolites provide ideal features for regulating the migration of metal species due to their unique pore structures and specific defect sites. This review provides a comprehensive summary of typical cases about dynamic migration of metal species on/in metal-zeolite catalysts, analyzing the mechanisms and driving factors of metal migration under different reaction conditions. We discuss the roles of zeolite supports in the migration process of metal species, particularly their crucial contributions to the stability of metal species and the optimization of active sites. In addition, the potential mechanism of the dynamic migration of metal species, theoretical studies, and practical guidance for designing highly efficient catalysts are also included in this review.

Topological Placement of Metal Nanoparticles in MFI Zeolitic Framework With Intriguing Mesoporous Architecture

The efficient utilization of nanoporous zeolites requires careful tuning of the inherent physicochemical attributes of crystals such as porosity, diffusion pathlengths, and chemical composition. The metal loading in the zeolite imparts extra functional multiplicity owing to additional Lewis's acid centers. However, the higher catalytic performance is strongly determined by the spatial location of metal nanoparticles and their sizes. Here, modified desilication routes in the presence of Ethylene Diamine (EDA) is explored to generate mesopores and core-shell architecture for both Silicalite-1 (S-1) and ZSM-5. EDA helped in stabilizing the zeolitic core of MFI for controlled desilication. Interestingly, evidence of layered depletion of the inner core and recrystallization of the partially ordered external surface is provided. Subsequently, multiple EDA-assisted synthetic protocols are used to load metals on topologically different locations of MFI crystals (S-1 and ZSM-5). Here, explicit metal loading on the external surface and inside the core is showcased. Through the in situ method, metal can deposit on both the external surface and the inner core. The study presents a comprehensive picture using two metals (Pd and Ag), where EDA helps in ensuring uniform distribution. Overall, the complementary methodology is established for controlled porosity tuning and selective metal placement in MFI framework.

Atomic surface structure for unraveling the trade-off between the propane dehydrogenation activity and anti-deactivation of PtSn catalysts

In commercial Pt-based propane dehydrogenation catalysts, Sn doping is a fascinating strategy to suppress side reactions and optimize selectivity. Nevertheless, excessive Sn incorporation results in a decline in surface Pt sites, leading to a significant reduction in catalytic activity. It challenges the precision of surface chemical design and the atomic unraveling of surface coordination is critical to resolving the inherent trade-off between catalytic activity and anti-deactivation. In this work, we modulated PtSn catalyst surface structures by controlling the Sn content, achieving optimal activity, anti-deactivation, and selectivity. Building upon the average structural characterization, we further resolved three-dimensional atomic configurations and extracted surface structures of catalysts by integrating the Reverse Monte Carlo method with pair distribution function analysis. It was found that the increasing Sn content enhances anti-deactivation by reducing surface Pt-Pt coordination numbers; this effect reaches saturation when the coordination number on the surface approaches approximately 3. Beyond this critical threshold, additional Sn incorporation compromises activity through Pt site blockage while offering a negligible effect on anti-deactivation. These findings provide clear guidelines for the rational surface design of nanocatalysts and synthesis of high-performance platinum-based catalysts with superior catalytic properties.

A self-regenerating Pt/Ge-MFI zeolite for propane dehydrogenation with high endurance

Supported noble metal cluster catalysts are typically operated under severe conditions involving switching between reducing and oxidizing atmospheres, causing irreversible transformation of the catalyst structure and thereby leading to permanent deactivation. We discovered that various platinum (Pt) precursors spontaneously disperse in a germanium-MFI (Ge-MFI) zeolite, which opposes the Ostwald ripening phenomenon, producing self-regenerating Pt/Ge-MFI catalysts for propane dehydrogenation. These catalysts reversibly switch between Pt clusters and Pt single atoms in response to reducing reaction and oxidizing regeneration conditions. This environmental adaptability allows them to completely self-regenerate over 110 reaction and regeneration cycles in propane dehydrogenation, and they exhibited unprecedented sintering resistance when exposed to air at 800°C for 10 days. Such spontaneous metal dispersion in a Ge-MFI zeolite is a robust and versatile methodology for fabricating various rhodium, ruthenium, iridium, and palladium cluster catalysts.

Data-driven discovery of Pt single atom embedded germanosilicate MFI zeolite catalysts for propane dehydrogenation

Zeolite-confined metal is an important class of heterogeneous catalysts, demonstrating exceptional catalytic performance in many reactions, but the identification of a stable metal-zeolite combination with a simple synthetic method remains a top challenge. Here artificial intelligence methods, particularly global neural network potential based large-scale atomic simulation, are utilized to design Pt-containing zeolite frameworks for propane-to-propene conversion. We show that out of the zeolite database (>220 structure framework) and more than 100,000 Pt/Ge differently distributed configurations, there are only three Ge-containing zeolites, germanosilicate (MFI, IWW and SAO) that are predicted to be capable of stabilizing Pt single atom embedded in zeolite skeleton and at the meantime allowing propane fast diffusion. Among, the Pt1@Ge-MFI catalyst is successfully synthesized via a simple one-pot synthesis without a lengthy post-treatment procedure, and characterized by high-resolution experimental techniques. We demonstrate that the catalyst features an in-situ formed [GePtO3H2] active site under the reductive reaction condition that can achieve long-term (>750 h) high activity and selectivity (98%) for propane dehydrogenation. Our simple catalyst synthesis holds promise for scale-up industrial applications that can now be rooted in first principles via data-driven catalyst design.

Advanced Zeolite-Based Catalysts for CO2 Hydrogenation to Targeted High-Value Chemicals and Fuels

The excessive use of fossil fuels has resulted in elevated CO2 emissions in the atmosphere, significantly impacting the climate and global environment. The catalytic conversion of CO2 into high-value chemicals has been recognized as a promising strategy to mitigate CO2 emissions. Light olefins, aromatics, and alcohols, etc. are widely used high-value chemicals as fuels and chemical synthesis intermediates. To enhance the catalytic efficiency and selectivity for producing these chemicals, various catalysts have been developed. Among them, zeolite-based catalysts have garnered significant attention due to their unique microporous structure, shape-selective catalysis capability, high thermal stability, and tunable acidity. This article focuses on the distinctive structural characteristics of zeolites and their notable representative applications, with particular emphasis on the impact of zeolite structural properties on catalytic performance and reaction mechanism. Additionally, we discuss the current challenges of fabricating highly efficient zeolite-based catalysts and future development prospects in improving the catalytic performance and industrial-scale applications. We propose rational and strategic insights to pave the way for the efficient utilization of CO₂ as a valuable resource.

Resolving Complex K-Pt-Sn Interactions in PtSn@K-MFI Catalysts for Alkane Dehydrogenation

K and Sn contents were rationalized during the synthesis of PtSn@K-MFI to maximize metal dispersion and stability along the MFI crystallites. Experimental results and theoretical calculations reveal a stoichiometry of ∼1 K per unit cell of MFI, limiting then the final K incorporation within siliceous MFI crystals at ∼0.7 wt %. Above this stoichiometry, K is not incorporated into the final solids unless significant amounts of Sn are simultaneously present, leading to the formation of tin-silicate precipitates. The optimized PtSn@K-MFI catalysts improve the catalytic performance of well-established references, as PtSn/SiO2, for the propane dehydration (PDH) reaction. In particular, low Sn loadings (below 0.5 wt %) result in higher time-on-stream (TOS) deactivation catalytic profiles but excellent regenarability after consecutive PDH reaction, while higher Sn content (close to 1 wt %) minimizes TOS deactivation due to the maximization of Pt-Sn bonds but consecutive regenerations result in significant metal sintering. Increasing Sn contents within MFI crystallites facilitates Pt sintering and, thus, occurring catalyst deactivation upon regeneration cycles. As a result of complex interconnected nucleation/crystallization processes, fine-tuning rationalizations of one-pot synthesis approaches can substantially influence the final atomic and subnanometric metal interactions and, consequently, the catalytic and sintering-resistance properties when exposed to highly demanding industrial conditions.

Phase Changes of Multielemental Alloy Nanoparticles at Elevated Temperatures

Multielemental alloy (MEA) nanomaterials, such as medium and high entropy alloys, display promising catalytic performance in a range of chemical reactions due to their multicomponent structural configurations. These complex structural and chemical arrangements can be influenced by several factors, such as mechanical stress, irradiation, and high temperatures, which impact the performance of MEAs in various applications. Here, we investigated the effect of high temperatures on MEA nanoparticles composed of noble and transition metals (quaternary PtPdFeCo) at the atomic scale and found the material undergoes a series of phase transitions between solid solution and intermetallic phases at elevated temperatures ranging from room temperature to 1073 K. In contrast, the binary PtFe nanoalloy displays a one-way solid solution to intermetallic transition at these temperatures. Our findings, rationalized by density functional theory (DFT) studies, demonstrate how the varied migration energies of elements govern the solid solution to intermetallic transition and how differences in the bonding energies of elemental pairs influence the Gibbs free energy change (ΔG), which dictates the intermetallic to solid-solution transition. Overall, this work provides better guidance in the design, development, and usage of nano-MEAs for high-temperature-based applications.

Design and synthesis of Pt/TiO2 catalyst with abundant surface hydroxyl for formaldehyde oxidation

Catalytic oxidation of formaldehyde (HCHO) is a highly effective method for indoor HCHO removal. However, many aspects of the catalytic mechanism remain unclear, making the optimization of catalysts largely empirical. Herein, we report a coupled experimental and computational study of Pt/TiO2 catalysts, with special focus on the functional roles of surface oxygen vacancies and hydroxyl groups in the catalytic oxidation of HCHO. DFT calculations combined with control experiments revealed that the formation of surface oxygen vacancies on TiO2 and their capability in facilitating H2O dissociation are strongly dependent on the exposed facets. Correlating these facet-dependent properties with the determined activity further indicated that the catalytic performance is directly related to the abundance of surface hydroxyl groups, rather than surface oxygen vacancies as commonly assumed. Guided by these insights, we employed a combination of facet-engineering and alkali metal modification strategies to design a potassium-modified Pt/TiO2 catalyst with predominantly exposed {100} facets (denoted as Pt/TiO2{100}-K). The Pt/TiO2{100}-K catalyst showed an impressively high mass-specific reaction rate of 105.7 μmol gPt-1 s-1, along with fairly good stability and moisture tolerance. Further investigations using in situ DRIFTS coupled with on-line GC provided additional insight into the reaction mechanism of HCHO oxidation over the Pt/TiO2{100}-K catalyst.

Construction of Pt─O Sites on Pt Nanoclusters in Silicalite-1 Zeolite for Efficient Catalytic Oxidation of Hydrogen Isotope Gases

The construction, use, and maintenance of tritium-related equipment will inevitably produce tritium-containing radioactive waste gas, and the production of efficient catalysts for tritium removal remains a difficult problem. Herein, silicalite-1 zeolite with entrapped Pt nanoclusters is skillfully post-oxidized at an appropriate temperature, building highly active Pt─O sites on the nanoclusters to achieve efficient oxidation of hydrogen isotopes at low temperatures. The designed Pt─O sites can directly participate in the oxidation reaction of hydrogen isotopes. Compared to the case without Pt─O sites, the presence of these sites significantly reduces the reaction energy barrier to 0.55 eV, enabling the catalyst to achieve a hydrogen conversion rate of 99% at a low temperature of 40 °C. Specifically, the O atoms consumed by the Pt─O sites in the reaction are replaced by O2 gas and this cycle repeats, which is consistent with the Mars-van Krevelen (M-K) theory. This ensures efficient catalytic oxidation of hydrogen isotopes, and provides an astonishingly high conversion rate of 99% in the nearly 34 days restart performance test. The results of this study provide insights into the strategic design of efficient catalysts for hydrogen isotope oxidation.

Light-driven propane dehydrogenation by a single-atom catalyst under near-ambient conditions

Propane dehydrogenation is an energy-intensive industrial reaction that requires high temperatures (550-750 °C) to overcome thermodynamic barriers. Here we overcome these limits and demonstrate that near-ambient propane dehydrogenation can be achieved through photo-thermo-catalysis in a water-vapour environment. We reduce the reaction temperature to 50-80 °C using a single-atom catalyst of copper supported on TiO2 and a continuous-flow fixed-bed reactor. The mechanism differs from conventional propane dehydrogenation in that hydrogen is produced from the photocatalytic splitting of water vapour, surface-bound hydroxyl radicals extract propane hydrogen atoms to form propylene without over-oxidation, and water serves as a catalyst. This route also works for the dehydrogenation of other small alkanes. Moreover, we demonstrate sunlight-driven water-catalysed propane dehydrogenation operating at reaction temperatures as low as 10 °C. We anticipate that this work will be a starting point for integrating solar energy usage into a wide range of high-temperature industrial reactions.

Destabilization of Single-Atom Catalysts: Characterization, Mechanisms, and Regeneration Strategies

Numerous in situ characterization studies have focused on revealing the catalytic mechanisms of single-atom catalysts (SACs), providing a theoretical basis for their rational design. Although research is relatively limited, the stability of SACs under long-term operating conditions is equally important and a prerequisite for their real-world energy applications, such as fuel cells and water electrolyzers. Recently, there has been a rise in in situ characterization studies on the destabilization and regeneration of SACs; however, timely and comprehensive summaries that provide the catalysis community with valuable insights and research directions are still lacking. This review summarizes recent advances in the destabilization mechanisms and regeneration strategies of SACs, specifically highlighting various state-of-the-art characterization techniques employed in the studies. The factors that induce destabilization in SACs are identified by discussing the failure of active sites, coordination environments, supports, and reaction conditions under long-term operating scenarios. Next, the primary regeneration strategies for SACs are introduced, including redispersion, surface poison desorption, and exposure of subsurface active sites. Additionally, the advantages and limitations of both in situ and ex situ characterization techniques are discussed. Finally, future research directions are proposed, aimed at constructing structure-stability relationships and guiding the design of more stable SACs.

Interfacial Catalysis at Atomic Level

Heterogeneous catalysts are pivotal to the chemical and energy industries, which are central to a multitude of industrial processes. Large-scale industrial catalytic processes rely on special structures at the nano- or atomic level, where reactions proceed on the so-called active sites of heterogeneous catalysts. The complexity of these catalysts and active sites often lies in the interfacial regions where different components in the catalysts come into contact. Recent advances in synthetic methods, characterization technologies, and reaction kinetics studies have provided atomic-scale insights into these critical interfaces. Achieving atomic precision in interfacial engineering allows for the manipulation of electronic profiles, adsorption patterns, and surface motifs, deepening our understanding of reaction mechanisms at the atomic or molecular level. This mechanistic understanding is indispensable not only for fundamental scientific inquiry but also for the design of the next generation of highly efficient industrial catalysts. This review examines the latest developments in atomic-scale interfacial engineering, covering fundamental concepts, catalyst design, mechanistic insights, and characterization techniques, and shares our perspective on the future trajectory of this dynamic research field.

Ideal Bifunctional Catalysis for Propane Dehydrogenation over Pt-Promoted Gallia-Alumina and Minimized Use of Precious Elements

Gallia-alumina (GaxAl2-xO3), promoted with a trace amount of Pt, exhibits excellent activity and selectivity in propane dehydrogenation (PDH) due to a bifunctional mechanism. Tetrahedrally coordinated Ga (GaIV) catalyzes C-H dissociation, while Pt facilitates H recombination into H2. To maximize the utilization of precious Pt and Ga, it is crucial to understand the optimal balance between the two catalytic functions or determine the 'ideal regime.' Here, we developed techniques to quantify the catalytic functions of Pt and GaIV sites. H2-D2 exchange rates (rHD) and propylene chemisorption (Q(GaIV,surf)) were used as effective measures of the catalytic functions of Pt and GaIV, respectively. When Pt is sufficient relative to GaIV (rHD/Q(GaIV,surf) ratio >0.3 molHD molGaIV,surf-1 s-1), the catalysts exhibit ideal catalytic properties. During repeated reaction and regeneration cycles, the catalysts deactivated mainly due to Pt sintering, which leads to an imbalance between the two catalytic functions. Notably, catalysts with higher Pt contents lost catalytic activity faster than those with lower Pt contents, eventually exhibiting reversed activities. This is because increased Pt loading facilitates sintering. Doping a small amount of Ce3+ onto GaxAl2-xO3 effectively suppresses Pt sintering via strong metal-support interaction. Thus, optimal loadings of Ga and Pt, combined with Ce3+ doping to stabilize Pt, enabled the minimized use of precious elements while maintaining excellent catalytic properties. Even with 100 ppm Pt and 1 wt % Ga, the catalyst exhibited superior activity, selectivity, and stability compared to the benchmark catalyst, PtSn/γ-Al2O3, with 7000 ppm (0.7 wt %) Pt.

Boosting Propane Dehydrogenation to Propylene via Electron Hole-Hydrogen Coupling on Cobalt Metal Surface

Nonoxidative dehydrogenation of propane is useful for the high selectivity to propylene but is suffering from the heavy coke deposition on the catalyst surface. Herein, we present a proof-of-concept application of a hole-hydrogen (H) couple on a metallic cobalt surface to decrease the deactivation rate. The coupled H atoms on the Cobalt (Co) surface, partially resulting from propane dehydrogenation, enabled the desorption of propylene to avoid deep hydrogenolysis and coke deposition and realize selective and durable propylene production, while conventional Co metal-based catalysts do not generate propylene. The optimized hole-H coupled Co catalyst provided a low deactivation rate (0.0036 h-1) and a high turnover frequency (55.6 h-1) for propylene production with a high propane flux (48 vol.% C3H8 in gas feeds) at 550 °C.

Deep Learning-Enabled STEM Imaging for Precise Single-Molecule Identification in Zeolite Structures

Observing chemical reactions in complex structures such as zeolites involves a major challenge in precisely capturing single-molecule behavior at ultra-high spatial resolutions. To address this, a sophisticated deep learning framework tailored has been developed for integrated Differential Phase Contrast Scanning Transmission Electron Microscopy (iDPC-STEM) imaging under low-dose conditions. The framework utilizes a denoising super-resolution model (Denoising Inference Variational Autoencoder Super-Resolution (DIVAESR)) to effectively mitigate shot noise and thereby obtain substantially clearer atomic-resolved iDPC-STEM images. It supports advanced single-molecule detection and analysis, such as conformation matching and elemental clustering, by incorporating object detection and Density Functional Theory (DFT) configurational matching for precise molecular analysis. the model's performance is demonstrated with a significant improvement in standard image quality evaluation metrics including Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM). The test conducted using synthetic datasets shows its robustness and extended applicability to real iDPC-STEM images, highlighting its potential in elucidating dynamic behaviors of single molecules in real space. This study lays a critical groundwork for the advancement of deep learning applications within electron microscopy, particularly in unraveling chemical dynamics through precise material characterization and analysis.

Elucidating Confinement and Microenvironment of Ru Clusters Stably Confined in MFI Zeolite for Efficient Propane Oxidation

Achieving active and stable heterogeneous catalysts by encapsulating noble metal species within zeolites is highly promising for high utilization and cost efficiency in thermal and environmental catalytic reactions. Ru, considered an economical noble metal alternative with comparable performance, faces great challenges within MFI-type microporous zeolites due to its high cohesive energy and mobility. Herein, an innovative strategy was explored that couples hydrothermal in situ ligand protection with stepwise calcination in a flowing atmosphere to embed ultrasmall Ru clusters anchored at K+-healed silanol sites (≡Si-Ruδ+-O-K complexes) within 10-membered ring sinusoidal channels of MFI. Comprehensive experiments and theoretical calculations unveiled that the interplay between confined Ru clusters and MFI induces local strain in MFI, creating a unique catalytic microenvironment around the Ru clusters. This synergy interaction enhances alkane deep oxidation as the confined Ru clusters and the MFI microenvironment collectively pre-activate C3H8 and O2, facilitate the cleavage of C-H and C-C bonds at low temperatures. Notably, the stable geometric and electronic properties of the confined Ru show exceptional thermal stability up to 1000 °C, rivaling fresh catalysts. These findings shed vital methodological and mechanistic insights for developing efficacious heterogeneous catalysts for thermal catalysis.

Substance migration in the synthesis of single-atom catalysts

Substance migration is universal and crucial in the synthesis of catalysts, which directly affects their existing form and the micro-structure of their active sites. Realizing migration during the synthesis of single-atom catalysts (SACs) is beneficial for not only increasing their metal loading capacity but also manipulating the electronic structures (coordination structure, long-range interactions, etc.) of their metal sites. This review summarizes the thermodynamics and kinetic processes involved in the synthesis of SACs to unveil the fundamental principles involved in their synthesis. For a better understanding of the effect of migration, the migration of both metal (including ions, atoms, and molecules) and nonmetal species is outlined. Moreover, we propose the research directions to guide the rational design of SACs in the future and deepen the fundamental understanding in the formation of catalysts.

Structure-Reactivity Relationship of Zeolite-Confined Rh Catalysts for Hydroformylation of Linear α-Olefins

Substituting the molecular metal complexes used in the industrial olefin hydroformylation process is of great significance in fundamental research and practical application. One of the major difficulties in replacing the classic molecular metal catalysts with supported metal catalysts is the low chemoselectivity and regioselectivity of the supported metal catalysts because of the lack of a well-defined coordination environment of the metal active sites. In this work, we have systematically studied the influences of key factors (crystallinity, alkali promoters, etc.) of the Rh-MFI zeolite catalysts on their performances for the hydroformylation of long-chain α-olefins (LAOs). With the help of comprehensive spectroscopy and electron microscopy characterization results, we can correlate the structural features of various Rh-MFI catalysts and their catalytic performances. The resultant structure-reactivity relationship guides us to prepare a nanosized Rh-MFI catalyst, which exhibits about a 3-fold improvement in specific activity compared to the Rh-MFI catalyst with conventional crystallite sizes and maintains very high regioselectivity for hydroformylation of LAOs.

Functionalization of zeolite-encapsulated Cu5 clusters as visible-light photoactive sub-nanomaterials

The unique structural properties of zeolites make them ideal environments for encapsulating subnanometric metal clusters on their microporous channels and cavities, showing an enhanced catalytic performance. As a first step towards the functionalization of these clusters as photocatalysts as well, this work addresses the optical properties of zeolite-encapsulated Cu5-TiO2 nanoparticles as well as their application in the photo-induced activation of CO2 by sunlight. Model density functional theory (DFT) calculations indicate the stability of the Cu5 cluster adsorbed on the TiO2 nanoparticles filling the pores of a model zeolite structure. Second, it is shown that while TiO2 nanoparticles absorb in the UV, the photo-absorption spectrum of the Cu5-TiO2 nanoparticle composite is peaked at the visible region, where the sun has its maximum energy input, also allowing for the photo-induced activation of CO2 adsorbed onto the Cu5 cluster.

Highly Stable Subnanometric PtIn Clusters for the Selective Dehydrogenation of Alkanes

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.

Propane Dehydrogenation on PtxZny Active Sites in Silicalite-1

The improvement of Pt-based catalysts for propane dehydrogenation (PDH) has progressed by recent investigations that have identified Zn as a promising promoter for Pt subnanometer catalysts. It is desirable to gain insights into the structure, stability, and activity of such active sites and the factors that influence them, such as Zn : Pt ratio, Pt coordination and nuclearity. Here, we employ density functional theory and microkinetic simulations to investigate the stability of PtxZny (x=1-3, y=0-3) active sites grafted on silanols of Silicalite-1 and the PDH activity of Pt. We find that the coordination of a Pt atom to a nest of grafted Zn(II) atoms increases the stability of the Pt1Zny sites, whose activity is similar for y=0-2 and drops dramatically for y>2. We further demonstrate, via linear scaling relations and microkinetic simulations, that the turnover frequency obeys a volcano law as a function of propylene binding strength. The Pt2Zn1 and Pt3Zn1 sites are stable and exhibit activity similar to Pt1Zn2, but only Pt1Zn2 manifests reaction kinetics consistent with experimental data, strongly suggesting the active site composition in the synthesized catalyst samples. The methodology presented here suggests a general strategy for deducing active site information such as composition through simple kinetic experiments.

Synergize Strong and Reactive Metal-Support Interactions to Construct Sub-2 nm Metal Phosphide Cluster for Enhanced Selective Hydrogenation Activities

Strong metal-support interactions (SMSI) are crucial for stabilizing sub-2 nm metal sites, e.g. single atom (M1) or cluster (Mn). However, further optimizing sub-2 nm sites to break the activity-stability trade-off due to excessive interactions remains significant challenges. Accordingly, for the first time, we propose synergizing SMSI with reactive metal-support interactions (RMSI). Comprehensive characterization confirms that the SMSI stabilizes the metal and regulates the aggregation of Ni1 into Nin site within sub-2 nm. Meanwhile, RMSI modulates Nin through sufficiently activating P in the support and eventually generates sub-2 nm metal phosphide Ni2P cluster (Ni2Pn). The synergetic metal-support interactions triggered the adaptive coordination and electronic structure optimization of Ni2Pn, leading to the desired substrate adsorption-desorption kinetics. Consequently, the activity of Ni2Pn site greatly enhanced towards the selective hydrogenations of p-chloronitrobenzene and alkynyl alcohol. The formation rates of target products are up to 20.2 and 3.0 times greater than that of Ni1 and Nin site, respectively. This work may open a new direction for metal-support interactions and promote innovation and application of active sites below 2 nm.

High-purity hydrogen production from dehydrogenation of methylcyclohexane catalyzed by zeolite-encapsulated subnanometer platinum-iron clusters

Liquid organic hydrogen carriers (LOHCs) are considered promising carriers for large-scale H2 storage and transportation, among which the toluene-methylcyclohexane cycle has attracted great attention from industry and academia because of the low cost and its compatibility with the current infrastructure facility for the transportation of chemicals. The large-scale deployment of the H2 storage/transportation plants based on the toluene-methylcyclohexane cycle relies on the use of high-performance catalysts, especially for the H2 release process through the dehydrogenation of methylcyclohexane. In this work, we have developed a highly efficient catalyst for MCH dehydrogenation reaction by incorporating subnanometer PtFe clusters with precisely controlled composition and location within a rigid zeolite matrix. The resultant zeolite-encapsulated PtFe clusters exhibit the up-to-date highest reaction rate for dehydrogenation of methylcyclohexane to toluene, very high chemoselectivity to toluene (enabling the production of H2 with purity >99.9%), remarkably high stability (>2000 h) and regenerability over consecutive reaction-regeneration cycles.

Pt-ZnOx Interfacial Effect on the Performance of Propane Dehydrogenation and Mechanism Study

Bimetallic Pt-based catalysts, for example, PtZn and PtSn catalysts, have gained significant attention for addressing the poor stability and low selectivity of pristine Pt catalysts over propane dehydrogenation (PDH). However, the structures of the active sites and the corresponding catalytic mechanism of PDH are still elusive. Here, we demonstrate a spatially confined Pt-ZnmOx@RUB-15 catalyst (where "m" is the mole ratio of Zn/Pt and RUB-15 is a layered silica), which exhibited high catalytic activity, ultrahigh selectivity (>99%), and resistance to coking at 550 °C for PDH. Significantly different from the preliminary studies over the PtZn catalysts, through the assistance of quasi-in situ X-ray photoelectron spectroscopy (XPS), in situ Fourier transform infrared spectroscopy (CO-FTIR), in situ X-ray absorption spectroscopy (XAS), and CO titration, we discovered that the active sites for PDH were the Pt-ZnOx interfaces, characterized by a structure of Ptδ+-Zn2+-O-Si. Density functional theory (DFT) calculations showed that Pt atoms positioned at Pt-ZnOx interfaces with coordinatively unsaturated ZnOx sites facilitate the C-H bond breaking of propane while concurrently suppressing deep dehydrogenation processes. This study suggests that engineering the interfaces of Pt-metal oxides under spatially confined conditions holds promise for developing highly efficient Pt-based catalysts for light alkane dehydrogenation.

Tuning the Selectivity in the Nonoxidative Alkane Dehydrogenation Reaction by Potassium-Promoted Zeolite-Encapsulated Pt Catalysts

The significance of the nonoxidative dehydrogenation of middle-chain alkanes into corresponding alkenes is increasing in the context of the world's declining demands on transportation fuels and the growing demand for chemicals and materials. The middle-chain alkenes derived from the dehydrogenation reaction can be transformed into value-added chemicals in downstream processes. Due to the presence of multiple potential reaction sites, the reaction mechanism of the dehydrogenation of middle-chain alkanes is more complicated than that in the dehydrogenation of light alkanes, and there are few prior studies on elucidating their detailed structure-reactivity relationship. In this work, we have employed Pt catalysts encapsulated in pure-silica MFI zeolite crystallites as model catalysts and studied how the catalytic performances for dehydrogenation of n-pentane can be modulated by the K+ promotor in the Pt-MFI catalyst. A combination of comprehensive structural characterizations by aberration-corrected electron microscopy, X-ray absorption spectroscopy, in situ CO-IR, X-ray photoelectron spectroscopy, and kinetic studies shows that K+ promoter can not only influence the particle size but also modify the electronic properties of Pt species, which further affect the activity and selectivity in the dehydrogenation of n-pentane.

Subnanometric Pt-W Bimetallic Clusters for Efficient Alkaline Hydrogen Evolution Electrocatalysis

Rational design and synthesis of subnanometric bimetallic clusters (SBCs) within a narrow size distribution, along with achieving full SBCs exposure on supporting materials, are formidable challenges that must be overcome to realize potential applications. This work details a facile strategy to synthesize fully exposed PtW SBCs with an average size of 0.81 nm on the surface of spherical N-doped carbon (PtW/NC), which is underpinned by the electrostatic interactions between the negatively charged [H3PtW6O24]5- polyanions and the positively charged closed-pore metal-organic framework (MOF) [Zn5(OH)2(AmTRZ)6]2+. The PtW/NC exhibits significant electrocatalytic performance and stability for the alkaline hydrogen evolution reaction with an ultralow overpotential of 4 mV at 10 mA cm-2, a low Tafel slope of 29 mV dec-1, and a long-term electrolysis stability exceeding 140 h. The Pt mass activity of PtW/NC is 34 times higher than that of commercial 20 wt % Pt/C at the 100 mV overpotential. Both theoretical calculations and electrochemical measurements indicate that a synergistic effect between Pt and W is responsible for this notable catalytic performance. The synthetic approach outlined in this work can be applied to other MOFs and coordination networks that lack pores or have limited porosity.

Comparative Study of PtM (M=Cu, Zn, Ga, Mn, Fe, In, Ce) Bimetals on Zincosilicate for Propane Dehydrogenation Reaction

Silicoaluminate zeolites have relatively strong Brönsted (B) acid properties that can easily lead to deep cracking reactions, making them less favourable as carriers for propane dehydrogenation. Here, we utilise zincosilicate zeolite with less B-acid produced by the introduction of the heteroatom Zn into the framework as a carrier, followed by simultaneous ion exchange (IE) of M monometallic or PtM bimetallic (M=Cu, Zn and Ga, etc.). The optimized PtZn/Zn-4 exhibits a superior propane dehydrogenation performance over PtCu/Zn-4 and PtGa/Zn-4, which can achieve a propane conversion of about 30 % in a pure propane atmosphere at 550 °C and can be operated for at least 168 h without significant deactivation. Characterization techniques such as spherical aberration corrected transmission electron microscopy, in situ X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared fourier transform spectroscopy with different gas adsorptions are used to investigate these PtM@zeolite catalysts in order to deepen the understanding of acid site identification, promoter effect and catalysis.

Design of Supported Metal Catalysts and Systems for Propane Dehydrogenation

Propane dehydrogenation (PDH) is currently an approach for the production of propylene with high industrial importance, especially in the context of the shale gas revolution and the growing global demands for propylene and downstream commodity chemicals. In this Perspective article, we comprehensively summarize the recent advances in the design of advanced catalysts for PDH and the new understanding of the structure-performance relationship in supported metal catalysts. Furthermore, we discuss the gaps between fundamental research and practical industrial applications in the catalyst developments for the PDH process. In particular, we overview some critical issues regarding catalyst regeneration and the compatibility of the catalyst and reactor design. Finally, we make perspectives on the future directions of PDH research, including the efforts toward achieving a unified understanding of the structure-performance relationship, innovation in reactor engineering, and translation of the knowledge accumulated on PDH studies to other important alkane dehydrogenation reactions.

Facile and Environmentally Friendly Synthesis of Ga2O3/MFI Catalysts for Propane Dehydrogenation

A GaOx-based catalyst is recognized as a promising catalyst for dehydrogenation of light alkanes. Conventionally, impregnation and calcination are necessary processes for the loading of GaOx. However, the incomplete impregnation of gallium salt solution would generate wastewater, and the calcination for the dissociation of gallium salt would release harmful gases, such as SOx, NOx, and HCl. Meanwhile, the high temperature results in an excessive energy cost and undesired GaOx particle aggregation. Here, we report a facile and environmentally friendly method for the synthesis of GaOx-based catalysts. The gallium salt solution was replaced directly with liquid gallium (LG). Through a simple physical mixing method at room temperature, uniform GaOx nanoparticles with diameters of around 3.5 nm were loaded onto the surface of silicalite-1 (S-1). With the optimal GaOx/MFI catalyst, the propane conversion and propylene selectivity reached 22.9 and 90.1%, respectively, in the propane dehydrogenation reaction. The work offers a clean and economical strategy utilizing liquid metal (LM) as an impregnation solution for the preparation of GaOx-based catalysts.

Metal-Organic Framework Supported Low-Nuclearity Cluster Catalysts for Highly Selective Carbon Dioxide Electroreduction to Ethanol

It is still a great challenge to achieve high selectivity of ethanol in CO2 electroreduction reactions (CO2RR) because of the similar reduction potentials and lower energy barrier of possible other C2+ products. Here, we report a MOF-based supported low-nuclearity cluster catalysts (LNCCs), synthesized by electrochemical reduction of three-dimensional (3D) microporous Cu-based MOF, that achieves a single-product Faradaic efficiency (FE) of 82.5 % at -1.0 V (versus the reversible hydrogen electrode) corresponding to the effective current density is 8.66 mA cm-2. By investigating the relationship between the species of reduction products and the types of catalytic sites, it is confirmed that the multi-site synergism of Cu LNCCs can increase the C-C coupling effect, and thus achieve high FE of CO2-to-ethanol. In addition, density functional theory (DFT) calculation and operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy further confirmed the reaction path and mechanism of CO2-to-EtOH.

Preparation of Metal-Supported Nanostructured Zeolite Catalysts and their Applications in the Upgrading of Biomass-Derived Furans: Advances and Prospects

The development of platform chemicals derived from biomass, in particular, 5-hydroxymethylfurfural (5-HMF) and furfural (FUR), is of crucial importance in biorefinery. Over the past decades, metal-supported nanostructured zeolites, in particular, metal-supported hierarchically porous zeolites or metal-encapsulated zeolites, have been extensively elaborated because of their multiple functionalities and superior properties, for example, shape-selectivity, (hydro)thermal stability, tunable acidity and basicity, redox properties, improved diffusion, and intimacy of multiple active sites. In this review, the effects of such properties of metal-supported nanostructured zeolites on the enhanced catalytic performances in furanic compound upgrading are discussed. In addition, the recent rational design of metal-supported nanostructured zeolites is exemplified. Consequently, the ongoing challenges for further developing metal-supported nanostructured zeolites-based catalysts and their applications in HMF and FUR upgrading are identified.

Water-promoted oxidative coupling of aromatics with subnanometer palladium clusters confined in zeolites

A fundamental understanding of the active sites in working catalysts can guide the rational design of new catalysts with improved performances. In this work, we have followed the evolution of homogeneous and heterogeneous Pd catalysts under the reaction conditions for aerobic oxidative coupling of toluene for the production of 4,4'-bitolyl. We have found that subnanometer Pd clusters made with a few Pd atoms are the working active sites in both homogeneous and heterogeneous catalytic systems. Moreover, water can promote the activity of Pd clusters by nearly one-order magnitude for oxidative coupling reaction by facilitating the activation of O2. These new insights lead to the preparation of a catalyst made with Pd clusters supported on a two-dimensional zeolite, which expands the scope of the oxidative coupling of aromatics to larger substrates.

An Active and Regenerable Nanometric High-Entropy Catalyst for Efficient Propane Dehydrogenation

Propane dehydrogenation (PDH) is crucial for propylene production, but commercially employed Pt-based catalysts face susceptibility to deactivation due to the Pt sintering during reaction and regeneration steps. Here, we report a SiO2 supported nanometric (MnCoCuZnPt) high-entropy PDH catalyst with high activity and stability. The catalyst exhibited a super high propane conversion of 56.6 % with 94 % selectivity of propylene at 600 °C. The propylene productivity reached 68.5 molC3H6 ⋅ gPt -1 ⋅ h-1, nearly three times that of Pt/SiO2 (23.5 molC3H6 ⋅ gPt -1 ⋅ h-1) under a weight hourly space velocity of 60 h-1. In a high-entropy nanoparticle, Pt atoms were atomically dispersed through coordination with other metals and exhibited a positive charge, thereby showcasing remarkable catalytic activity. The high-entropy effect contributes to the catalyst a superior stability with a low deactivation constant of 0.0004 h-1 during 200 hours of reaction under the industrial gas composition at 550 °C. Such high-entropy PDH catalyst is easy regenerated through simple air combustion of deposited coke. After the fourth consecutive regeneration cycle, satisfactory catalytic stability was observed, and the element distribution of spent catalysts almost returned to their initial state, with no detectable Pt sintering. This work provides new insights into designing active, stable, and regenerable novel PDH catalysts.

Boosting the Stability of Subnanometer Pt Catalysts by the Presence of Framework Indium(III) Sites in Zeolite

Subnanometer metal clusters show advantages over conventional metal nanoparticles in numerous catalytic reactions owing to their high percentage of exposed surface sites, abundance of under-coordinated metal sites and unique electronic structures. However, the applications of subnanometer metal clusters in high-temperature catalytic reactions (>600 °C) are still hindered, because of their low stability under harsh reaction conditions. In this work, we have developed a zeolite-confined bimetallic PtIn catalyst with exceptionally high stability against sintering. A combination of experimental and theoretical studies shows that the isolated framework In(III) species serve as the anchoring sites for Pt species, precluding the migration and sintering of Pt species in the oxidative atmosphere at ≥650 °C. The catalyst comprising subnanometer PtIn clusters exhibits long-term stability of >1000 h during a cyclic reaction-regeneration test for ethane dehydrogenation reaction.

Isolated Pt Atoms Stabilized by Ga2O3 Clusters Confined in ZSM-5 for Nonoxidative Activation of Ethane

Selective activation of light alkanes is an essential reaction in the petrochemical industry for producing commodity chemicals, such as light olefins and aromatics. Because of the much higher intrinsic activities of noble metals in comparison to non-noble metals, it is desirable to employ solid catalysts with low noble metal loadings to reduce the cost of catalysts. Herein, we report the introduction of a tiny amount of Pt (at levels of hundreds of ppm) as a promoter of the Ga2O3 clusters encapsulated in ZSM-5 zeolite, which leads to ∼20-fold improvement in the activity for ethane dehydrogenation reaction. A combination of experimental and theoretical studies shows that the isolated Pt atoms stabilized by small Ga2O3 clusters are the active sites for activating the inert C-H bonds in ethane. The synergy of atomically dispersed Pt and Ga2O3 clusters confined in the 10MR channels of ZSM-5 can serve as a bifunctional catalyst for the direct ethane-benzene coupling reaction for the production of ethylbenzene, surpassing the performances of the counterpart catalysts made with PtGa nanoclusters and nanoparticles.

Silanol-Stabilized Atomically Dispersed Ptδ+-Ox-Sn Active Sites in Protozeolite for Propane Dehydrogenation

Crystalline zeolites have been proven to be excellent supports for confining subnanometric metal catalysts to boost the propane dehydrogenation (PDH) reaction. However, the introduced metallic species may suffer from severe sintering and limited stability during the catalytic process, especially when utilizing an industrial impregnation method for metal incorporation. In this study, we developed a new type of support based on amorphous protozeolite (PZ), taking advantage of its adjustable silanol chemistry and zeolitic microporous characteristic for stabilizing atomically dispersed PtSn catalyst via a simple, cost-effective coimpregnation process. The combination of X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy under CO atmosphere, and density functional theory calculations confirmed the formation of highly dispersed active Ptδ+-Ox-Sn species in PtSn/PZ. The PtSn/PZ catalyst exhibited a high propane conversion of 45.4% and a high propylene selectivity of 99% (WHSV= 3.6 h-1, 550 °C), with a high apparent rate coefficient of 565 molC3H6·gPt-1·h-1·bar-1 at a high WHSV of 108 h-1, presenting a top-level performance among the state-of-the-art Pt-based catalysts prepared by in situ synthesis and impregnation methods. The silanol density determined the chemical state of PtSn species, showing a change from atomically dispersed Ptδ+-Ox-Sn sites to PtSn alloy with decreasing silanol density of supports. This work provides a general strategy using silanol-rich amorphous protozeolite as support for stabilizing various metal catalysts by the simple impregnation method and also offers an effective way for fine tailoring the chemical state of metallic species via a silanol-engineered approach.

Confining platinum clusters in indium-modified ZSM-5 zeolite to promote propane dehydrogenation

Designing highly active and stable catalytic sites is often challenging due to the complex synthesis procedure and the agglomeration of active sites during high-temperature reactions. Here, we report a facile two-step method to synthesize Pt clusters confined by In-modified ZSM-5 zeolite. In-situ characterization confirms that In is located at the extra-framework position of ZSM-5 as In+, and the Pt clusters are stabilized by the In-ZSM-5 zeolite. The resulting Pt clusters confined in In-ZSM-5 show excellent propane conversion, propylene selectivity, and catalytic stability, outperforming monometallic Pt, In, and bimetallic PtIn alloys. The incorporation of In+ in ZSM-5 neutralizes Brønsted acid sites to inhibit side reactions, as well as tunes the electronic properties of Pt clusters to facilitate propane activation and propylene desorption. The strategy of combining precious metal clusters with metal cation-exchanged zeolites opens the avenue to develop stable heterogeneous catalysts for other reaction systems.

Directional Construction of the Highly Stable Active-Site Ensembles at Sub-2 nm to Enhance Catalytic Activity and Selectivity

Precise control over the size, species, and breakthrough of the activity-selectivity trade-off are great challenges for sub-nano non-noble metal catalysts. Here, for the first time, a "multiheteroatom induced SMSI + in situ P activation" strategy that enables high stability and effective construction of sub-2 nm metal sites for optimizing selective hydrogenation performance is developed. It is synthesized the smallest metal phosphide clusters (<2 nm) including from unary to ternary non-noble metal systems, accompanied by unprecedented thermal stability. In the proof-of-concept demonstration, further modulation of size and species results in the creation of a sub-2 nm site platform, directionally achieving single atom (Ni1), Ni1+metal cluster (Ni1+Nin), or novel Ni1+metal phosphide cluster synergistic sites (Ni1+Ni2Pn), respectively. Based on thorough structure and mechanism investigation, it is found the Ni1+Ni2Pn site is motivated to achieve electronic structure self-optimizing through synergistic SMSI and site coupling effect. Therefore, it speeds up the substrate adsorption-desorption kinetics in semihydrogenation of alkyne and achieves superior catalytic activity that is 56 times higher than the Ni1 site under mild conditions. Compared to traditional active sites, this may represent the highly effective integration of atom utilization, thermal stability, and favorable site requirements for chemisorption properties and reactivities of substrates.

Insight into the Catalytic Oxidation Mechanism of Hydrogen Isotopes by Pt Clusters Confined by Silicalite-1

Highly efficient removal of low concentrations of hydrogen isotope gas in air is crucial for the safe operation of nuclear energy plants. Herein, silicalite-1-confined Pt cluster catalysts were used for the catalytic oxidation of hydrogen isotopes, and the related catalytic mechanism was revealed. Increased temperature in direct hydrogen reduction treatment slightly increased the size of Pt clusters from 1.6 nm at 400 °C to 1.8 nm at 600 °C. The catalyst reduced at 600 °C exhibited excellent performance (99%) in hydrogen isotope oxidation at 75 °C, as well as high stability and catalytic efficiency in continuous and intermittent operation for 7200 min. X-ray absorbance spectroscopy confirmed the existence of Pt clusters in the catalysts, and the theoretical results showed that the total net charge was -0.07 e, indicating a slight charge transfer from the zeolite to the Pt atoms. The metal-support interaction thermally stabilized Pt clusters and altered the metal electronic structure, which enhanced the catalytic activity following a hydroperoxyl (OOH)-mediated route. Based on the low reaction temperature, efficient hydrogen conversion rate, and high stability, the silicalite-1-confined Pt cluster catalyst is expected to be used in hydrogen isotope oxidation treatment to achieve nuclear safety.

RhRu Bimetallic Oxide Cluster Catalysts for Cross-Dehydrogenative Coupling of Arenes and Carboxylic Acids

Noble-metal-based bimetallic oxide clusters are promising novel catalysts. In this study, we developed carbon-supported RhRu bimetallic oxide clusters (RhRuOx/C) with a mean diameter of 1.2 nm, which showed remarkable catalytic activity for the cross-dehydrogenative coupling (CDC) of arenes and carboxylic acids with O2 as the sole oxidant. RhRu bimetallic oxide cluster formation was confirmed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy and synchrotron X-ray absorption spectroscopy. Kinetic isotope and substituent effects indicated that arene C-H bond cleavage was the rate-determining step and proceeded via electrophilic concerted metalation-deprotonation mechanism, with a carboxylate as an internal base. Density functional theory calculations supported the proposed mechanism and indicated that the active center for C-H bond activation was Rh(V) rather than Rh(III), while Ru enhanced the electrophilicity of the Rh(V) site by decreasing the negative charge of the surrounding oxygen atoms. Electron-rich arenes showed relatively high reactivity for the RhRuOx/C-catalyzed CDC reaction, and both aliphatic and aromatic carboxylic acids were applicable to the reaction. The RhRuOx/C catalyst is promising for the CDC reaction of arenes and carboxylic acids to produce aryl esters. This work promotes the development of noble-metal-based bimetallic oxide clusters for C-H bond activation reactions.

Exploring the Interfacial Hydrogen Transfer between Pt and the Siliceous Framework and Its Promotional Effect on the Isotope Catalytic Exchange

Interfacial hydrogen transfer between metal particles and catalyst supports is a ubiquitous phenomenon in heterogeneous catalysis, and this occurrence on reducible supports has been established, yet controversies remain about how hydrogen transfer can take place on nonreducible supports, such as silica. Herein, highly dispersed Pt clusters supported on a series of porous silica materials with zeolitic or/and amorphous frameworks were prepared to interrogate the nature of hydrogen transfer and its promotional effect on H2-HDO isotope catalytic exchange. The formation of zeolitic frameworks upon these porous silica supports by hydrothermal crystallization greatly promotes the interfacial hydrogen bidirectional migration between metal clusters and supports. Benefiting from this transfer effect, the isotope exchange rate is enhanced by 10 times compared to that on the amorphous counterpart (e.g., Pt/SBA-15). In situ spectroscopic and theoretical studies suggest that the defective silanols formed within the zeolite framework serve as the reactive sites to bind HDO or H2O by hydrogen bonds. Under the electrostatic attraction interaction, the D of hydrogen-bonded HDO scrambles to the Pt site and the dissociated H on Pt simultaneously spills back to the electronegative oxygen atom of adsorbed water to attain H-D isotope exchange with an energy barrier of 0.43 eV. The reverse spillover D on Pt combines with the other H on Pt to form HD in the effluent. We anticipate that these findings are able to improve our understanding of hydrogen transfer between metal and silica supports and favor the catalyst design for the hydrogen-involving reaction.

Acceleration of Zeolite Crystallization: Current Status, Mechanisms, and Perspectives

Zeolites are important classes of crystalline materials and possess well-defined channels and cages with molecular dimensions. They have been extensively employed as heterogeneous catalysts and gas adsorbents due to their relatively large specific surface areas, high pore volumes, compositional flexibility, definite acidity, and hydrothermal stability. The zeolite synthesis normally undergoes high-temperature hydrothermal treatments with a relatively long crystallization time, which exhibits low synthesis efficiency and high energy consumption. Various strategies, e.g., modulation of the synthesis gel compositions, employment of special silica/aluminum sources, addition of seeds, fluoride, hydroxyl (·OH) free radical initiators, and organic additives, regulation of the crystallization conditions, development of new approaches, etc., have been developed to overcome these obstacles. And, these achievements make prominent contributions to the topic of acceleration of the zeolite crystallization and promote the fundamental understanding of the zeolite formation mechanism. However, there is a lack of the comprehensive summary and analysis on them. Herein, we provide an overview of the recent achievements, highlight the significant progress in the past decades on the developments of novel and remarkable strategies to accelerate the crystallization of zeolites, and basically divide them into three main types, i.e., chemical methods, physical methods, and the derived new approaches. The principles/acceleration mechanisms, effectiveness, versatility, and degree of reality for the corresponding approaches are thoroughly discussed and summarized. Finally, the rational design of the prospective strategies for the fast synthesis of zeolites is commented on and envisioned. The information gathered here is expected to provide solid guidance for developing a more effective route to improve the zeolite crystallization and obtain the functional zeolite-based materials with more shortened durations and lowered cost and further promote their applications.

Close Intimacy between PtIn Clusters and Zeolite Channels for Ultrastability toward Propane Dehydrogenation

Propane dehydrogenation (PDH) serves as a pivotal intentional technique to produce propylene. The stability of PDH catalysts is generally restricted by the readsorption of propylene which can subsequently undergo side reactions for coke formation. Herein, we demonstrate an ultrastable PDH catalyst by encapsulating PtIn clusters within silicalite-1 which serves as an efficient promoter for olefin desorption. The mean lifetime of PtIn@S-1 (S-1, silicalite-1) was calculated as 37317 h with high propylene selectivity of >97% at 580 °C with a weight hourly space velocity (WHSV) of 4.7 h-1. With an ultrahigh WHSV of 1128 h-1, which pushed the catalyst away from the equilibrium conversion to 13.3%, PtIn@S-1 substantially outperformed other reported PDH catalysts in terms of mean lifetime (32058 h), reaction rates (3.42 molpropylene gcat-1 h-1 and 341.90 molpropylene gPt-1 h-1), and total turnover number (14387.30 kgpropylene gcat-1). The developed catalyst is likely to lead the way to scalable PDH applications.

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.

Strengthening the Metal-Acid Interactions by Using CeO2 as Regulators of Precisely Placing Pt Species in ZSM-5 for Furfural Hydrogenation

Understanding the synergism between the metal site and acid site is of great significance in boosting the efficiency of bi-functional catalysts in many heterogeneous reactions, particularly in biomass upgrading. Herein, a "confined auto-redox" strategy is reported to fix CeO2-anchored Pt atoms on the inner wall of a ZSM-5 cage, achieving the target of finely controlling the placements of the two active sites. Compared with the conventional surface-supported counterpart, the encapsulated Pt/CeO2@ZSM-5 catalyst possesses remarkably-improved activity and selectivity, which can convert >99% furfural into cyclopentanone with 97.2% selectivity in 6 h at 160 °C. Besides the excellent catalytic performance, the ordered metal-acid distribution also makes such kind of catalyst an ideal research subject for metal-acid interactions. The following mechanization investigation reveals that the enhancement is strongly related to the unique encapsulation structure, which promotes the migration of the reactants over different active sites, thereby contributing to the tandem reaction.

Regioselective hydroformylation of propene catalysed by rhodium-zeolite

Hydroformylation is an industrial process for the production of aldehydes from alkenes1,2. Regioselective hydroformylation of propene to high-value n-butanal is particularly important, owing to a wide range of bulk applications of n-butanal in the manufacture of various necessities in human daily life3. Supported rhodium (Rh) hydroformylation catalysts, which often excel in catalyst recyclability, ease of separation and adaptability for continuous-flow processes, have been greatly exploited4. Nonetheless, they usually consist of rotationally flexible and sterically unconstrained Rh hydride dicarbonyl centres, only affording limited regioselectivity to n-butanal5-8. Here we show that proper encapsulation of Rh species comprising Rh(I)-gem-dicarbonyl centres within a MEL zeolite framework allows the breaking of the above model. The optimized catalyst exhibits more than 99% regioselectivity to n-butanal and more than 99% selectivity to aldehydes at a product formation turnover frequency (TOF) of 6,500 h-1, surpassing the performance of all heterogeneous and most homogeneous catalysts developed so far. Our comprehensive studies show that the zeolite framework can act as a scaffold to steer the reaction pathway of the intermediates confined in the space between the zeolite framework and Rh centres towards the exclusive formation of n-butanal.