Atomic Insight into the Local Structure and Microenvironment of Isolated Co-Motifs in MFI Zeolite Frameworks for Propane Dehydrogenation

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.

Stable Cobalt-Zeolite Propane-Dehydrogenation Catalysts Enabled by Reaction-Driven Reconstruction

Cobalt-based catalysts have emerged as promising substitutes for Pt- and Cr-based propane dehydrogenation (PDH) catalysts. However, controlling the distribution of Co species and achieving stable active centers remains challenging. Here, we report that reaction-driven reconstruction of metallic cobalt (Co0) species within pure silica MFI zeolite (S-1) into CoOx clusters within silanol nests during PDH yields efficient and durable performance. Atomically dispersed CoOx clusters exhibit exceptional durability and high propylene space-time yield (STY), maintaining an ultrahigh propylene STY of 17.2 mmolC3H6 gcat -1 h-1 for over 260 h under industrially relevant conditions, surpassing previous cobalt-based PDH catalysts. Moreover, the catalyst operates stably at 520 °C for 170 h with near-equilibrium propane conversions. Comprehensive characterizations indicate the dynamic evolution process from the silanol nests effectively capturing and stabilizing Co0 species within S-1 zeolite, thereby promoting the dynamic formation of CoOx clusters during the PDH process. We also demonstrate that stable Co─O active centers formed by this unique anchoring strategy improve catalyst stability by suppressing coke formation and promoting efficient propane dehydrogenation.

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.

Unveiling the Dichotomy Between Cobalt(II)-Exchanged X and Y Faujasite Zeolites via Oxidative Carboxylation of Alkene to Cyclic Carbonate

Cobalt(II)-exchanged X and Y zeolites with varying metal loadings were employed to convert CO2 to cyclic carbonates starting from alkenes. The transformation was carried out using O2 as an oxidant in a mixture of O2 and CO2 under atmospheric pressure, and a maximum yield of 35.7% cyclic carbonate was achieved. Studies revealed a stark difference among both the zeolites, primarily arising from a difference in their ion exchange behaviors. Their catalytic and recyclability properties differed as a result of this variation.

Design of a CrZrOx-Cu2MnOx@Na2WO4 catalyst-oxygen carrier system for efficient chemical looping oxidative dehydrogenation of propane

In the utilisation of most oxide-based propane dehydrogenation (PDH) catalysts, each reaction-regeneration cycle necessitates both coke combustion and hydrogen reduction to achieve complete regeneration of the catalyst. However, the need for hydrogen reduction makes it difficult to use such catalysts in chemical looping oxidative dehydrogenation (CL-ODH) processes. This study prepared a series of CrZrOx catalysts with Cr/Zr atomic ratios ranging from 0.02 to 1 using a co-precipitation method. Electron paramagnetic resonance (EPR) analysis revealed that the catalyst surface in its oxidised state is rich in oxygen vacancies. These vacancies created numerous coordinated unsaturated Zr (Zrcus)-based active sites directly linked to the catalyst's unique catalytic activity. This catalyst was paired with a Cu2MnOx@Na2WO4 oxygen carrier to perform the CL-ODH of propane. The results demonstrated that the catalyst-oxygen carrier coupling system significantly enhanced single-pass propane conversion in the PDH process, increasing the initial propane conversion from 27.2% to 35.9%. The enhanced conversion, along with the observed hydrogen consumption over time, confirmed that the PDH process was coupled with hydrogen oxidation via the lattice oxygen of the oxygen carrier. This coupling broke through the thermodynamic equilibrium, thereby significantly improving the single-pass propane conversion. These findings provide valuable insights for designing novel catalyst systems tailored for the CL-ODH of propane.

Design and engineering of microenvironments of supported catalysts toward more efficient chemical synthesis

Catalytic species such as molecular catalysts and metal catalysts are commonly attached to varieties of supports to simplify their separation and recovery and accommodate various reaction conditions. The physicochemical microenvironments surrounding catalytic species play an important role in catalytic performance, and the rational design and engineering of microenvironments can achieve more efficient chemical synthesis, leading to greener and more sustainable catalysis. In this review, we highlight recent works addressing the topic of the design and engineering of microenvironments of supported catalysts, including supported molecular catalysts and supported metal catalysts. Six types of materials, including oxide nano/microparticle, mesoporous silica nanoparticle (MSN), polymer nanomaterial, reticular material, zeolite, and carbon-based nanomaterial, are widely used as supports for the immobilization of catalytic species. We summarize and discuss the synthesis and modification of supports and the positive effects of microenvironments on catalytic properties such as metal-support interaction, molecular recognition, pseudo-solvent effect, regulating mass transfer, steric effect, etc. These design principles and engineering strategies allow access to a better understanding of structure-property relationships and advance the development of more efficient catalytic processes.

Sustainable Synthesis of MCM-22 Zeolite as a Catalytic Platform for Propane Dehydrogenation

The significant volume of solvent required for the hydrothermal synthesis of zeolites remains the primary hurdle impeding industrial applications. With the benefits of reduced manufacturing costs, safety, and energy savings, reducing the use of solvents is one of the significant sought-after objectives. In this study, borosilicate zeolite B-MCM-22 is successfully obtained using a solvent-free synthesis method. The as-synthesized sample exhibits good long-range order, high crystallinity, and high silica utilization (ca. 95%). Furthermore, the B-MCM-22 precursor serves as a platform for introducing Co active sites via deboronization and impregnation processes. The resulting Co-MCM-22-DB catalyst provides a propylene selectivity of >90% with an initial propane conversion of 38% in the propane dehydrogenation reaction and shows a higher initial catalytic performance than the Co/ITQ-1 catalyst. The essential interplay between the metal-support interaction and catalytic performance is demonstrated by ultraviolet-visible (UV-vis), H2-TPR, and catalytic assessments, further elucidating that Co2+ species are the active sites for propane to propylene conversion. We anticipate that B-MCM-22 will be a versatile and ideal platform for catalyst design through structural manipulation.

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.

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.

Incorporation of enzyme-mimic species in porous materials for the construction of porous biomimetic catalysts

The unique catalytic properties of natural enzymes have inspired chemists to develop biomimetic catalyst platforms for the intention of retaining the unique functions and solving the application limitations of enzymes, such as high costs, instability and unrecyclable ability. Porous materials possess unique advantages for the construction of biomimetic catalysts, such as high surface areas, thermal stability, permanent porosity and tunability. These characteristics make them ideal porous matrices for the construction of biomimetic catalysts by immobilizing enzyme-mimic active sites inside porous materials. The developed porous biomimetic catalysts demonstrate high activity, selectivity and stability. In this feature article, we categorize and discuss the recently developed strategies for introducing enzyme-mimic active species inside porous materials, which are based on the type of employed porous materials, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), molecular sieves, porous metal silicate (PMS) materials and porous carbon materials. The advantages and limitations of these porous materials-based biomimetic catalysts are discussed, and the challenges and future directions in this field are also highlighted.

Modifying the Charge-Density of Tetrahedral Cobalt(II) Centers through Carbon-Layer Modulation Promotes C-H Activation in the Propane Dehydrogenation Reaction (PDH)

The electronic structure of active metal centers plays an indispensable role in regulating catalytic reactivity in heterogeneous catalysis, developing other metals as promoters to decorate electronic state is a common strategy, while non-metal component of carbon as electronic additives to regulate d-band center has rarely been studied in thermal-catalysis field. Herein, we report electron-deficient tetrahedral Co(II) (Td-cobalt(II)) centers through carbon-layer modulation for propane dehydrogenation (PDH). It is indicated that bifunctional sites of both Td-cobalt(II) and metallic-cobalt are designed, and the in situ generated carbon through the disproportionation of CO on metallic-cobalt can cover the inactive metallic-cobalt and tailor d-band of active Td-cobalt(II) simultaneously. More importantly, the pre-deposited carbon-layer is proposed to decrease electron density of Td-cobalt(II) and make d-band center closer to Fermi level, consequently promotes C-H activation in PDH reaction. This study provides new perspective for the utilization of inactive carbon as electronic promoters and unlocks new opportunity to fabricate efficient PDH and other heterogeneous catalysts.

Encapsulation of Pd Single-Atom Sites in Zeolite for Highly Efficient Semihydrogenation of Alkynes

Palladium (Pd)-based single-atom catalysts (SACs) have shown outstanding selectivity for semihydrogenation of alkynes, but most Pd single sites coordinated with highly electronegative atoms (such as N, O, and S) of supports will result in a decrease in the electron density of Pd sites, thereby weakening the adsorption of reactants and reducing catalytic performance. Constructing a rich outer-shell electron environment of Pd single-atom sites by changing the coordination structure offers a novel opportunity to enhance the catalytic efficiency with excellent alkene selectivity. Therefore, in this work, we first propose the in situ preparation of isolated Pd sites encapsulated within Al/Si-rich ZSM-5 structure using the one-pot seed-assisted growth method. Pd1@ZSM-5 features Pd-O-Al/Si bonds, which can boost the domination of d-electron near the Fermi level, thereby promoting the adsorption of substrates on Pd sites and reducing the energy barrier for the semihydrogenation of alkynes. In semihydrogenation of phenylacetylene, Pd1@ZSM-5 catalyst performs the highest turnover frequency (TOF) value of 33582 molC═C/molPd/h with 96% selectivity of styrene among the reported heterogeneous catalysts and nearly 17-fold higher than that of the commercial Lindlar catalyst (1992 molC═C/molPd/h). This remarkable catalytic performance can be retained even after 6 cycles of usage. Particularly, the zeolitic confinement structure of Pd1@ZSM-5 enables precise shape-selective catalysis for alkyne reactants with a size less than 4.3 Å.

Discovery of highly efficient dual-atom catalysts for propane dehydrogenation assisted by machine learning

Propane dehydrogenation (PDH) is a highly efficient approach for industrial production of propylene, and the dual-atom catalysts (DACs) provide new pathways in advancing atomic catalysis for PDH with dual active sites. In this work, we have developed an efficient strategy to identify promising DACs for PDH reaction by combining high-throughput density functional theory (DFT) calculations and the machine-learning (ML) technique. By choosing the γ-Al2O3(100) surface as the substrate to anchor dual metal atoms, 435 kinds of DACs have been considered to evaluate their PDH catalytic activity. Four ML algorithms are employed to predict the PDH activity and determine the relationship between the intrinsic characteristics of DACs and the catalytic activity. The promising catalysts of CuFe, CuCo and CoZn DACs are finally screened out, which are further validated by the whole kinetic reaction calculations, and the highly efficient performance of DACs is attributed to the synergistic effects and interactions between the paired active sites.

Synthesis of Ordered Mesoporous Molecular Sieve-Supported Cobalt Catalyst via Organometallic Complexation for Propane Non-Oxidative Dehydrogenation

Co-based catalysts have shown great promise for propane dehydrogenation (PDH) reactions due to their merits of environmental friendliness and low cost. In this study, ordered mesoporous molecular sieve-supported CoOx species (CoOx/Al-SBA-15 catalyst) were prepared by one-step organometallic complexation. The catalysts show worm-like morphology with regular straight-through mesoporous pores and high external specific surface area. These typical features can substantially enhance the dispersion of CoOx species and mass transfer of reactants and products. Compared with the conventional impregnation method, the 10CSOC (10 wt.% Co/Al-SBA-15 prepared by the organometallic complexation method) sample presents a smaller CoOx size and higher Co2+/Co3+ ratio. When applied to PDH reaction, the 10CSOC delivers higher propane conversion and propylene selectivity. Under the optimal conditions (625 °C and 4500 h-1), 10CSOC achieves high propane conversion (43%) and propylene selectivity (83%). This is attributed to the smaller and better dispersion of CoOx nanoparticles, more suitable acid properties, and higher content of Co2+ species. This work paves the way for the rational design of high-performance catalysts for industrially important reactions.

Co single atom coupled oxygen vacancy on W18O49 nanowires surface to construct asymmetric active site enhanced peroxymonosulfate activation

Enhancing the activation of peroxymonosulfate (PMS) is essential for generating more reactive oxygen species in advanced oxidation process (AOPs). Nevertheless, improving PMS adsorption and expediting interfacial electron transfer to enhance reaction kinetics pose significant challenges. Herein, we construct confined W18O49 nanowires with asymmetric active centers containing Co-Vo-W (Vo: oxygen vacancy). The design incorporates surface-rich Vo and single-atom Co, and the resulting material is employed for PMS activation in water purification. By coupling unsaturated coordinated electrons in Vo with low-valence Co single atoms to construct an the "electron fountainhead", the adsorption and activation of PMS are enhanced. This results in the generation of more active free radicals (SO4•-, •OH, •O2-) and non-free radicals (1O2) for the decomposition of micropollutants. Thereinto, the degradation rate of bisphenol A (BPA) by Co-W18O49 is 32.6 times faster that of W18O49 monomer, which is also much higher than those of other transition-metal-doped W18O49 composites. This work is expected to help to elucidate the rational design and efficient PMS activation of catalysts with asymmetric active centers.

Bimetallic CoCu-modified Pt species in S-1 zeolite with enhanced stability for propane dehydrogenation

Propane dehydrogenation (PDH) has been an outstanding technique with a bright prospect, which can meet the growing global demand for propylene. However, undesired side reactions result in the deactivation of the Pt-based catalysts, which contribute to the insufficient lifetime of the catalysts. Herein, we describe a novel catalyst by encapsulating bimetallic CoCu-modified Pt species in S-1 zeolite for efficient dehydrogenation of propane, which synergizes the confinement of zeolites and the geometric and electronic effects on Pt species for enhancing the catalyst stability. The introduction of bimetallic additives efficiently promotes the dispersion of platinum and the electron transfer between Pt species and the additives, which greatly prolongs the lifetime of the catalysts. Particularly, no obvious deactivation is observed on 0.2Pt0.3Co0.5CuK@S-1 after 93 h on stream with a weight hourly space velocity (WHSV) of 5.4 h-1, revealing an ultralow deactivation constant of 0.0011 h-1 (t = 909 h). The formation rate of propylene still maintains at a high value of 407 mol gPt-1 h-1 (WHSV = 21.6 h-1) at 580 ℃ even after on pure propane stream for 42 h. The catalyst with the bimetallic CoCu-modified Pt species in S-1 zeolite reveals ultra-high activity and stability for PDH, which is ascribed to the highly dispersed Pt species and the stabilization effect of bimetallic additives on Pt species.

Crystal epitaxy-confined Pd, Ti-bimetallic sites in the MFI zeolite for benzylalcohol oxidation

A general strategy for confining Pd, Ti-bimetallic sites in the MFI zeolite by crystal epitaxy was developed. The tailored spatial intimacy of the bimetallic sites demonstrated distinct catalytic performance for the oxidation of benzylalcohol. The related mechanism was clarified and afforded a valuable pathway for rational catalyst design.

Well-Defined Supported ZnOx Species: Synthesis, Structure, and Catalytic Performance in Nonoxidative Dehydrogenation of C3-C4 Alkanes

ConspectusZinc oxide (ZnO) is a multipurpose material and finds its applications in various fields such as rubber manufacturing, medicine, food additives, electronics, etc. It has also been intensively studied in photocatalysis due to its wide band gap and environmental compatibility. Recently, heterogeneous catalysts with supported ZnOx species have attracted more and more attention for the dehydrogenation of propane (PDH) and isobutane (iBDH) present in shale/natural gas. The olefins formed in these reactions are key building blocks of the chemical industry. These reactions are also of academic importance for understanding the fundamentals of the selective activation of C-H bonds. Differently structured ZnOx species supported on zeolites, SiO2, and Al2O3 have been reported to be active for nonoxidative dehydrogenation reactions. However, the structure-activity-selectivity relationships for these catalysts remain elusive. The main difficulty stems from the preparation of catalysts containing only one kind of well-defined ZnOx species.In this Account, we describe the studies on PDH and iBDH over differently structured ZnOx species and highlight our approaches to develop catalysts with controllable ZnOx speciation relevant to their performance. Several methods, including (i) the in situ reaction of gas-phase metallic Zn atoms with OH groups on the surface of supports, (ii) one-pot hydrothermal synthesis, and (iii) impregnation/anchoring methods, have been developed/used for the tailored preparation of supported ZnOx species. The first method allows precise control of the molecular structure of ZnOx through the nature of the defective OH groups on the supports. Using this method, a series of ZnOx species ranging from isolated, binuclear to nanosized ZnOx have been successfully generated on different SiO2-based or ZrO2-based supports as demonstrated by complementary ex/in situ characterization techniques. Based on kinetic studies and detailed characterization results, the intrinsic activity (Zn-related turnover frequency) of ZnOx was found to depend on its speciation. It increases with an increasing number of Zn atoms in a ZnmOn cluster from 1 to a few atoms (less than 10) and then decreases strongly for ZnOx nanoparticles. The latter promote the formation of undesired C1-C2 hydrocarbons and coke, resulting in lower propene selectivity in comparison with the catalysts containing only ZnOx species ranging from isolated to subnanometer ZnmOn clusters. In addition, the strategy for improving the thermal stability of ZnOx species and the consequences of mass-transport limitations for DH reactions were also elucidated. The results obtained allowed us to establish the fundamentals for the targeted preparation of well-structured ZnOx species and the relationships between their structures and the DH performance. This knowledge may inspire further studies in the field of C-H bond activation and other reactions, in which ZnOx species act as catalytically active sites or promoters, such as the dehydroaromatization of light alkanes and the hydrogenation of CO2 to methanol.

Coupled conversion of polyethylene and carbon dioxide catalyzed by a zeolite-metal oxide system

Zeolite-catalyzed polyethylene (PE) aromatization achieves reduction of the aromatic yield via hydrogenation and hydrogenolysis reactions. The hydrogen required for CO2 hydrogenation can be provided by H radicals formed during aromatization. In this study, we efficiently convert PE and CO2 into aromatics and CO using a zeolite-metal oxide catalyst (HZSM-5 + CuZnZrOx) at 380°C and under hydrogen- and solvent-free reaction conditions. Hydrogen, derived from the aromatization of PE over HZSM-5, diffuses through the Brønsted acidic sites of the zeolite to the adjacent CuZnZrOx, where it is captured in situ by CO2 to produce bicarbonate and further hydrogenated to CO. This favors aromatization while inhibiting hydrogenation and secondary hydrogenolysis reactions. An aromatic yield of 62.5 wt % is achieved, of which 60% consisted of benzene, toluene, and xylene (BTX). The conversion of CO2 reaches values as high as 0.55 mmol gPE-1. This aromatization-hydrogen capture pathway provides a feasible scheme for the comprehensive utilization of waste plastics and CO2.

Tricoordinated Single-Atom Cobalt in Zeolite Boosting Propane Dehydrogenation

Propane dehydrogenation (PDH) reaction has emerged as one of the most promising propylene production routes due to its high selectivity for propylene and good economic benefits. However, the commercial PDH processes usually rely on expensive platinum-based and poisonous chromium oxide based catalysts. The exploration of cost-effective and ecofriendly PDH catalysts with excellent catalytic activity, propylene selectivity, and stability is of great significance yet remains challenging. Here, we discovered a new active center, i.e., an unsaturated tricoordinated cobalt unit (≡Si-O)CoO(O-Mo) in a molybdenum-doped silicalite-1 zeolite, which afforded an unprecedentedly high propylene formation rate of 22.6 molC3H6 gCo-1 h-1 and apparent rate coefficient of 130 molC3H6 gCo-1 h-1 bar-1 with >99% of propylene selectivity at 550 °C. Such activity is nearly one magnitude higher than that of previously reported Co-based catalysts in which cobalt atoms are commonly tetracoordinated, and even superior to that of most of Pt-based catalysts under similar operating conditions. Density functional theory calculations combined with the state-of-the-art characterizations unravel the role of the unsaturated tricoordinated Co unit in facilitating the C-H bond-breaking of propane and propylene desorption. The present work opens new opportunities for future large-scale industrial PDH production based on inexpensive non-noble metal catalysts.

Amorphous CeOx Islands on Dealuminated Zeolite Beta to Stabilize Pt Nanoparticles as Efficient and Antisintering Catalysts for Propane Dehydrogenation

Pt-based catalysts have been widely used in propane dehydrogenation due to their superior activation of C-H bonds and weak scission of C-C bonds. However, in the process of repeated calcination to remove deposited coke, the active Pt species tend to sinter, resulting in a significant decline in catalytic activity. In this study, amorphous CeOx islands loaded on dealuminated Beta zeolite were prepared via simple wetness impregnation. Then, partially embedded Pt nanoparticles in CeOx islands were obtained after reduction owing to the affinity of CeOx for Pt. In the propane dehydrogenation reaction, Pt/Ce5-SiBeta with a Ce loading of 4.55 wt % and Pt loading of 0.72 wt % exhibited the highest activity and the lowest inactivation constant at 550 °C. More importantly, due to the anchoring effect of CeOx on Pt, the catalytic activity of Pt could be recovered after a simple calcination-reduction regeneration process, avoiding the chlorination treatment for the redispersion of Pt species used in industry. In addition, to improve the selectivity of the Pt/Ce5-SiBeta catalyst, a PtSn/Ce5-SiBeta catalyst with excellent activity, selectivity, and recycling stability has been prepared by introducing Sn into Pt/Ce5-SiBeta. The use of amorphous CeOx islands to improve the sintering resistance of Pt opens up new prospects for the design of stable industrial dehydrogenation catalysts.

Highly Efficient and Stable Methane Dry Reforming Enabled by a Single-Site Cationic Ni Catalyst

Zeolite-supported nickel (Ni) catalysts have been extensively studied for the dry reforming of methane (DRM). It is generally believed that prior to or during the reaction, Ni is reduced to a metallic state to act as the catalytic site. Here, we employed a ligand-protected synthesis method to achieve a high degree of Ni incorporation into the framework of the MFI zeolite. The incorporated Ni species retained their cationic nature during the DRM reaction carried out at 600 °C, exhibiting higher apparent catalytic activity and significantly greater catalytic stability in comparison to supported metallic Ni particles at the same loading. From theoretical and experimental evidence, we conclude that the incorporation of Ni into the zeolite framework leads to the formation of metal-oxygen (Niδ+-O(2-ξ)-) pairs, which serve as catalytic active sites, promoting the dissociation of C-H bonds in CH4 through a mechanism distinct from that of metallic Ni. The conversion of CH4 on cationic Ni single sites follows the CHx oxidation pathway, which is characterized by the rapid transformation of partial cracking intermediates CHx*, effectively inhibiting coke formation. The presence of the CHx oxidation pathway was experimentally validated by identifying the reaction intermediates. These new mechanistic insights elucidate the exceptional performance of the developed Ni-MFI catalyst and offer guidance for designing more efficient and stable Ni-based DRM catalysts.

Fluoride- and Seed-Free Synthesis of Pure-Silica Zeolite Adsorbent and Matrix Using OSDA-Mismatch Approach

The pure-silica zeolite plays a crucially important role in the gas separation of alkane/alkene, the low-k dielectric material, and the robust matrix for confining metal species during catalysis. However, the environmentally friendly synthesis of pure-silica zeolites is still challenging since (1) the toxic fluoride or dealuminum seeds are inevitably utilized through the hydrothermal synthesis and (2) it will also take a longer crystallization time. Herein, we present an efficient method called the OSDA-mismatch approach for the fluoride- and seed-free synthesis of pure-silica zeolites using Si-SOD (enriched 4-rings) as the sole silica source. This approach allows for the rapid and green synthesis of 15 pure-silica zeolites (CHA, *BEA, EUO, SFF, STF, -SVR, *-SVY, DOH, MTN, NON, *MRE, MEL, MFI, MTW, and *STO). Furthermore, distinct crystallization mechanisms of two significant pure-silica CHA- and *BEA-type zeolites (denoted as Si-CHA and Si-BEA) are investigated in detail by advanced characterization techniques such as FIB, 3D ED, 4D-STEM, HRTEM, Raman, and 29Si MAS NMR. More importantly, Si-CHA displays promising propane/propylene separation performance even better than the one synthesized in the presence of toxic HF. In addition, the incorporation of Zn species within Si-BEA fabricated by this approach also renders superior performance on propane dehydrogenation.

Boosting Propane Dehydrogenation by the Regioselective Distribution of Subnanometric CoO Clusters in MFI Zeolite Nanosheets

Direct dehydrogenation of propane (PDH) has already been implemented worldwide in industrial processes to produce value-added propylene. The discovery of earth-abundant and environmentally friendly metal with high activity in C-H cleavage is of great importance. Co species encapsulated within zeolite are highly efficient for catalyzing direct dehydrogenation. However, exploring a promising Co catalyst remains a nontrivial target. Direct control of the regioselective distribution of Co species in the zeolite framework through altering their crystal morphology gives opportunities to modify the metallic Lewis acidic features, thus providing an active and appealing catalyst. Herein, we achieved the regioselective localization of highly active subnanometric CoO clusters in straight channels of siliceous MFI zeolite nanosheets with controllable thickness and aspect ratio. The subnanometric CoO species were identified by different types of spectroscopies, probe measurements, and density functional theory calculations, as the coordination site for the electron-donating propane molecules. The catalyst showed promising catalytic activity for the industrially important PDH with propane conversion of 41.8% and propylene selectivity higher than 95% and was durable during 10 successive regeneration cycles. These findings highlight a green and facile method to synthesize metal-containing zeolitic materials with regioselective metal distribution and also to open up a future perspectives for designing advanced catalysts with integrated advantages of the zeolitic matrix and metal structures.

Accelerating syngas-to-aromatic conversion via spontaneously monodispersed Fe in ZnCr2O4 spinel

Spontaneous monodispersion of reducible active species (e.g., Fe, Co) and their stabilization in reductive atmospheres remain a key challenge in catalytic syngas chemistry. In this study, we present a series of catalysts including spontaneously monodispersed and enriched Fe on ZnCr₂O₄. Deep investigation shows remarkable performance in the syngas-to-aromatic reaction only when monodispersed Fe coupled with a H-ZSM-5 zeolite. Monodispersed Fe increases the turnover frequency from 0.14 to 0.48 s⁻¹ without sacrificing the record high selectivity of total aromatics (80–90%) at a single pass. The increased activity is ascribed to more efficient activation of CO and H₂ at oxygen vacancy nearest to the isolated Fe site and the prevention of carbide formation. Atomic precise characterization and theoretical calculations shed light on the origin and implications of spontaneous Fe monodispersion, which provide guidance to the design of next-generation catalyst for upgrading small molecules to synthetic fuels and chemicals.

Spontaneous monodispersion of active species and their stabilization in reductive atmospheres remain a challenge in catalytic syngas chemistry. Here the authors demonstrate that syngas-to-aromatic conversion can be significantly accelerated by the spontaneously monodispersed Fe in ZnCr₂O₄ spinel.

HZSM-5 zeolite modification and catalytic reaction mechanism in the reaction of cyclohexene hydration

This study investigated a three-phase (liquid–liquid–solid) reaction system of cyclohexene hydration where the catalyst was hydrophilic at the bottom of the water phase.