Propane wet reforming over PtSn nanoparticles on γ-Al2O3 for acetone synthesis

Acetone serves as an important solvent and building block for the chemical industry, but the current industrial synthesis of acetone is generally accompanied by the energy-intensive and costly cumene process used for phenol production. Here we propose a sustainable route for acetone synthesis via propane wet reforming at a moderate temperature of 350 oC with the use of platinum-tin nanoparticles supported on γ-aluminium oxide (PtSn/γ-Al2O3) as catalyst. We achieve an acetone productivity of 858.4 μmol/g with a selectivity of 57.8% among all carbon-based products and 99.3% among all liquid products. Detailed spectroscopic and controlled experiments reveal that the acetone is formed through a tandem catalytic process involving propene and isopropanol as intermediates. We also demonstrate facile ketone synthesis via wet reforming with the use of different alkanes (e.g., n-butane, n-pentane, n-hexane, n-heptane, and n-octane) as substrates, proving the wide applicability of this strategy.

Atomically dispersed Pt1Ir1 pair for synergetic hydrogenation of levulinic acid to γ-valerolactone

Atomically dispersed metal catalysts have attracted considerable attention in various important reactions owing to their high atom utilization and specific coordination environment. However, monometallic single sites sometimes present undesirable catalytic performance, which usually need a synergistic effect with the neighboring metal atoms, such as dimers or trimers. Different metal pairs on various solid carriers have been reported; nonetheless, huge challenges remain to precisely prepare a metal pair-site. Herein, we present a versatile strategy to synthesize an atomically dispersed Pt1Ir1 pair via strong metal-sulfur interaction over porous sulfur-doped carbons. Pt1Ir1 pair sites presented high activity and stability for the hydrogenation of levulinic acid to γ-valerolactone.

Photocatalytic CH4-to-Ethanol Conversion on Asymmetric Multishelled Interfaces

The selective oxidation of methane (CH4) features attractive potentials in both mitigating global warming and producing value-added chemicals. However, due to the short-life and unpaired concentrations of reactive intermediates (such as ·OH, ·CH3, and CO), the selective formation of multicarbon products like ethanol has remained challenging. In this work, we developed a hollow multishelled CeO2@PdO@FeOx nanosphere catalyst with two asymmetric and closely connected interfaces, featuring efficient in-tandem photo-oxidation of CH4 into ethanol with O2 as the oxidant. The outer FeOx surface promotes the photoreduction of the oxazole atoms in O2. In the meantime, the two asymmetric PdO/FeOx and CeO2/PdO catalytic interfaces enable selective photoactivation of CH4 to ·CH3 and then to CO, respectively, and the hollow multishelled structure further facilitates the directional transport and coupling of the as-generated ·CH3 and CO to produce ethanol. Under 100 mW·cm-2 light intensity and ambient conditions, the hollow multishelled CeO2@PdO@FeOx nanosphere photocatalyst exhibited a peak CH4-to-ethanol yield of 728 μmol·g-1·h-1 without photosensitizers or sacrificial agents, almost three times higher than the previous best reports on photocatalytic CH4 oxidation to ethanol, suggesting the attractive potential of the asymmetric multishelled catalytic interfaces.

Highly Stable Propane Dehydrogenation on a Self-Supporting Single-Component Zn2SiO4 Catalyst

Current industrial propane dehydrogenation (PDH) processes predominantly use either toxic Cr-based or expensive Pt-based catalysts, necessitating urgent exploration for alternatives. Herein, we present Zn2SiO4, an easily prepared, cost-effective material, as a highly efficient and stable catalyst for PDH. Uniquely, Zn2SiO4 nanocrystals do not require dispersion on support materials, commonly needed for catalytic active oxide clusters, but function as a self-supporting catalyst instead. During the reaction's induction period, surface Zn species on the Zn2SiO4 crystal reduce to coordinately unsaturated ZnOx single sites, serving as highly active catalytic centers. The Zn2SiO4 catalyst demonstrates a stable performance over 200 hours of PDH operation at 550 °C. We further find that introducing a minuscule amount of CO2 into the propane feed significantly extends the catalyst lifespan to over 2000 hours. This enhancement arises from the special role of CO2 in facilitating the removal of strongly adsorbed H*, preventing the complete reduction of ZnOx. After prolonged reaction, the activity of Zn2SiO4 can be fully restored by etching the surface layer to expose fresh Zn species, available throughout the crystals. The combination of CO2introduction and catalytic site regeneration strategies is expected to enable a year-long PDH operation using a single batch of Zn2SiO4 catalyst.

4d-2p-4f Gradient Orbital Coupling Enables Tandem Catalysis for Simultaneous Abatement of N2O and CO on Atomically Dispersed Rh/CeO2 Catalyst

N2O and CO coexist in various industrial and mobile sources. The synergistic reaction of N2O and CO to generate N2 and CO2 has garnered significant research interest, but it remains extremely challenging. Herein, we constructed an atomically dispersed Rh-supported CeO2 catalyst with asymmetric Rh-O-Ce sites through gradient Rh 4d-O 2p-Ce 4f orbital coupling. This design effectively regulates the 4f electron states of Ce and promotes the electron filling of the O 3π* antibonding orbital to facilitate N-O bond cleavage. Near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) reveals that CO reacts with the surface-adsorbed O* generated by N2O decomposition through self-tandem catalysis, accelerating the rate-limiting step in N2O decomposition and activating the synergistic reaction of N2O and CO at temperatures as low as 115 °C. This work can guide the development of high-performance catalysts using the strategy of high-order orbital hybridization combined with the tandem concept to achieve versatile catalytic applications.

Selective Catalytic Combustion of Hydrogen under Aerobic Conditions on Na2WO4/SiO2

Na2WO4/SiO2, a material known to catalyze alkane selective oxidation including the oxidative coupling of methane (OCM), is demonstrated to catalyze selective hydrogen combustion (SHC) with >97 % selectivity in mixtures with several hydrocarbons (CH4, C2H6, C2H4, C3H6, C6H6) in the presence of gas-phase dioxygen at 883-983 K. Hydrogen combustion rates exhibit a near-first-order dependence on H2 partial pressure and are zero-order in H2O and O2 partial pressures. Mechanistic studies at 923 K using isotopically-labeled reagents demonstrate the kinetic relevance of H-H dissociation and absence of O-atom recombination. In situ X-ray diffraction (XRD) and W LIII-edge X-ray absorption spectroscopy (XAS) studies demonstrate, respectively, a loss of Na2WO4 crystallinity and lack of second-shell coordination with respect to W6+ cations below 923 K; benchmark experiments show that alkali cations must be present for the material to be selective for hydrogen combustion, but that materials containing Na alone have much lower combustion rates (per gram Na) than those containing Na and W. These data suggest a synergy between Na and W in a disordered phase at temperatures below the bulk melting point of Na2WO4 (971 K) during SHC catalysis. The Na2WO4/SiO2 SHC catalyst maintains stable combustion rates at temperatures ca. 100 K higher than redox-active SHC catalysts and could potentially enable enhanced olefin yields in tandem operation of reactors combining alkane dehydrogenation with SHC processes.

Asymmetric Coupled Binuclear-Site Catalysts for Low-Temperature Selective Acetylene Semi-Hydrogenation

Heterogeneous metal catalysts with bifunctional active sites are widely used in chemical industries. Although their improvement process is typically based on trial-and-error, it is hindered by the lack of model catalysts. Herein, we report an effective vacancy-pair capturing strategy to fabricate 12 heterogeneous binuclear-site catalysts (HBSCs) comprising combinations of transition metals on titania. During the synthesis of these HBSCs, proton-passivation treatment and step-by-step electrostatic anchorage enabled the suppression of single-atom formation and the successive capture of two target metal cations on the titanium-oxygen vacancy-pair site. Additionally, during acetylene hydrogenation at 20 °C, the HBSCs (e.g., Pt1Pd1-TiO2) consistently generated more than two times the ethylene produced by their single-atom counterparts (e.g., Pd1-TiO2). Furthermore, the Pt1Pd1 binuclear sites in Pt1Pd1-TiO2 were demonstrated to catalyze C2H2 hydrogenation via a bifunctional active-site mechanism: initially C2H2 chemisorb on the Pt1 site, then H2 dissociates and migrates from Pd1 to Pt1, and finally hydrogenation occurs at the Pt1-Pd1 interface.

Accelerating the electron-transfer of nitrogen electro-fixation through assembling Fe nanoparticles into Fe nanochains

Electrochemically synthesizing NH3 via N2 is a facile and sustainable approach that involves multistep electron and proton transfer processes. Thus, consecutive electron and proton transfer is necessary. Here, a universal method with the assistance of magnetic stirring that can assemble Fe, Co, and Ni nanoparticles into nanochains is developed. Notably, the Fe nanochain, composed of amorphous Fe nanoparticles, facilitates electron and proton transfer, resulting in an enhanced NH3 yield (92.42 μg h-1 mg-1) and faradaic efficiency (20.02%) at -0.4 V vs. RHE during the electrochemical reduction of N2. This work offers new insight into designing tandem electrocatalysts.

Carbon-Boosted and Nitrogen-Stabilized Isolated Single-Atom Sites for Direct Dehydrogenation of Lower Alkanes

Lower olefins are widely used in the chemical industry as basic carbon-based feedstocks. Here, we report the catalytic system featuring isolated single-atom sites of iridium (Ir1) that can function within the entire temperature range of 300-600 °C and transform alkanes with conversions close to thermodynamics-dictated levels. The high turnover frequency values of the Ir1 system are comparable to those of homogeneous catalytic reactions. Experimental data and theoretical calculations both indicate that Ir1 is the primary catalytic site, while the coordinating C and N atoms help to enhance the activity and stability, respectively; all three kinds of elements cooperatively contribute to the high performance of this novel active site. We have further immobilized this catalyst on particulate Al2O3, and we found that the resulting composite system under mimicked industrial conditions could still give high catalytic performances; in addition, we have also developed and established a new scheme of periodical in situ regeneration specifically for this composite particulate catalyst.

Formation of a Porous Crystalline Mg1-xAl2Oy Overlayer on Metal Catalysts via Controlled Solid-State Reactions for High-temperature Stable Catalysis

Catalyst deactivation by sintering and coking is a long-standing issue in metal-catalyzed harsh high-temperature hydrocarbon reactions. Ultrathin oxide coatings of metal nanocatalysts have recently appeared attractive to address this issue, while the porosity of the overlayer is difficult to control to preserve the accessibility of embedded metal nanoparticles, thus often leading to a large decrease in activity. Here, we report that a nanometer-thick alumina coating of MgAl2O4-supported metal catalysts followed by high-temperature reduction can transform a nonporous amorphous alumina overlayer into a porous Mg1-xAl2Oy crystalline spinel structure with a pore size of 2-3 nm and weakened acidity. The high porosity stems from the restrained Mg migration from the MgAl2O4 support to the alumina overlayer through solid-state reactions at high temperatures. The resulting Ni/MgAl2O4 and Pt/MgAl2O4 catalysts with a porous crystalline Mg1-xAl2Oy overlayer achieved remarkably high stability while preserving much higher activity than the corresponding alumina-coated Ni and Pt catalysts on MgO and Al2O3 supports in the reactions of dry reforming of methane and propane dehydrogenation, respectively.

Recovering palladium and gold by peroxydisulfate-based advanced oxidation process

Palladium (Pd) and gold (Au) are the most often used precious metals (PMs) in industrial catalysis and electronics. Green recycling of Pd and Au is crucial and difficult. Here, we report a peroxydisulfate (PDS)-based advanced oxidation process (AOPs) for selectively recovering Pd and Au from spent catalysts. The PDS/NaCl photochemical system achieves complete dissolution of Pd and Au. By introducing Fe(II), the PDS/FeCl2·4H2O solution functioned as Fenton-like system, enhancing the leaching efficiency without xenon (Xe) lamp irradiation. Electron paramagnetic resonance (EPR), 18O isotope tracing experiments, and density functional theory calculations revealed that the reactive oxidation species of SO4·-, ·OH, and Fe(IV)═O were responsible for the oxidative dissolution process. Lixiviant leaching and one-step electrodeposition recovered high-purity Pd and Au. Strong acids, poisonous cyanide, and volatile organic solvents were not used during the whole recovery, which enables an efficient and sustainable precious metal recovery approach and encourage AOP technology for secondary resource recycling.

Advances in morphology-controlled alumina and its supported Pd catalysts: synthesis and applications

Alumina materials, as one of the cornerstones of the modern chemical industry, possess physical and chemical properties that include excellent mechanical strength and structure stability, which also make them highly suitable as catalyst supports. Alumina-supported Pd-based catalysts with the advantages of exceptional catalytic performance, flexible regulated surface metal/acid sites, and good regeneration ability have been widely used in many traditional chemical industry fields and have also shown great application prospects in emerging fields. This review aims to provide an overview of the recent advances in alumina and its supported Pd-based catalysts. Specifically, the synthesis strategies, morphology transformation mechanisms, and structural properties of alumina with various morphologies are comprehensively summarized and discussed in-depth. Then, the preparation approaches of Pd/Al2O3 catalysts (impregnation, precipitation, and other emerging methods), as well as the metal-support interactions (MSIs), are revisited. Moreover, Some promising applications have been chosen as representative reactions in fine chemicals, environmental purification, and sustainable development fields to highlight the universal functionality of the alumina-supported Pd-based catalysts. The role of the Pd species, alumina support, promoters, and metal-support interactions in the enhancement of catalytic performance are also discussed. Finally, some challenges and upcoming opportunities in the academic and industrial application of the alumina and its supported Pd-based are presented and put forward.

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.

Structured Catalysts and Catalytic Processes: Transport and Reaction Perspectives

The structure of catalysts determines the performance of catalytic processes. Intrinsically, the electronic and geometric structures influence the interaction between active species and the surface of the catalyst, which subsequently regulates the adsorption, reaction, and desorption behaviors. In recent decades, the development of catalysts with complex structures, including bulk, interfacial, encapsulated, and atomically dispersed structures, can potentially affect the electronic and geometric structures of catalysts and lead to further control of the transport and reaction of molecules. This review describes comprehensive understandings on the influence of electronic and geometric properties and complex catalyst structures on the performance of relevant heterogeneous catalytic processes, especially for the transport and reaction over structured catalysts for the conversions of light alkanes and small molecules. The recent research progress of the electronic and geometric properties over the active sites, specifically for theoretical descriptors developed in the recent decades, is discussed at the atomic level. The designs and properties of catalysts with specific structures are summarized. The transport phenomena and reactions over structured catalysts for the conversions of light alkanes and small molecules are analyzed. At the end of this review, we present our perspectives on the challenges for the further development of structured catalysts and heterogeneous catalytic processes.

Spectra-Based Machine Learning for Predicting the Statistical Interaction Properties of CO Adsorbates on Surface

Theoretical analyses of small-molecule adsorption on heterogeneous catalyst surfaces often rely on simplified models of molecular adsorption with the most favorable configuration. Given that real-world experimental tests frequently entail multiple molecules interacting with the surface, there is a pressing need for a comprehensive multimolecule adsorption model to bridge the gap between theory and experiment. Using machine learning, we predict the average values of important adsorption properties from conformationally averaged, calculated infrared and Raman spectra and compare these values to those theoretically derived from the conformationally averaged ensemble. Remarkably, our approach yields excellent predictions even when faced with large and indeterminate numbers of surface molecules. These quantitative spectra-averaged property relationships provide a theoretical framework for extracting key interaction properties from the spectra of real chemical environments.

Controlling Pt nanoparticle sintering by sub-monolayer MgO ALD thin films

Metal nanoparticle (NP) sintering is a major cause of catalyst deactivation, as NP growth reduces the surface area available for reaction. A promising route to halt sintering is to deposit a protective overcoat on the catalyst surface, followed by annealing to generate overlayer porosity for gas transport to the NPs. Yet, such a combined deposition-annealing approach lacks structural control over the cracked protection layer and the number of NP surface atoms available for reaction. Herein, we exploit the tailoring capabilities of atomic layer deposition (ALD) to deposit MgO overcoats on archetypal Pt NP catalysts with thicknesses ranging from sub-monolayers to nm-range thin films. Two different ALD processes are studied for the growth of MgO overcoats on Pt NPs anchored on a SiO2 support, using Mg(EtCp)2 and H2O, and Mg(TMHD)2 and O3, respectively. Spectroscopic ellipsometry and X-ray photoelectron spectroscopy measurements reveal significant growth on both SiO2 and Pt for the former process, while the latter exhibits a drastically lower growth per cycle with an initial chemical selectivity towards Pt. These differences in MgO growth characteristics have implications for the availability of uncoated Pt surface atoms at different stages of the ALD process, as probed by low energy ion scattering, and for the sintering behavior during O2 annealing, as monitored in situ with grazing incidence small angle X-ray scattering (in situ GISAXS). The Mg(TMHD)2-O3 ALD process enables exquisite coverage control allowing a balance between physically blocking the Pt surface to prevent sintering and keeping Pt surface atoms free for reaction. This approach avoids the need for post-annealing, hence also safeguarding the structural integrity of the as-deposited overcoat.

Dynamic configurations of metallic atoms in the liquid state for selective propylene synthesis

The use of liquid gallium as a solvent for catalytic reactions has enabled access to well-dispersed metal atoms configurations, leading to unique catalytic phenomena, including activation of neighbouring liquid atoms and mobility-induced activity enhancement. To gain mechanistic insights into liquid metal catalysts, here we introduce a GaSn0.029Ni0.023 liquid alloy for selective propylene synthesis from decane. Owing to their mobility, dispersed atoms in a Ga matrix generate configurations where interfacial Sn and Ni atoms allow for critical alignments of reactants and intermediates. Computational modelling, corroborated by experimental analyses, suggests a particular reaction mechanism by which Sn protrudes from the interface and an adjacent Ni, below the interfacial layer, aligns precisely with a decane molecule, facilitating propylene production. We then apply this reaction pathway to canola oil, attaining a propylene selectivity of ~94.5%. Our results offer a mechanistic interpretation of liquid metal catalysts with an eye to potential practical applications of this technology.

A Data and DFT-Driven Framework for Predicting the Microstructure of Submonolayer Inverse Metal Oxide on Metal Catalysts

Metal oxides on metal (inverse) catalysts can selectively drive many important reactions. However, understanding the active site under experimentally relevant conditions is lacking. Herein, we introduce a computational framework for predicting atomic models of stable inverse catalysts and demonstrate it for WOx on Pt(553) and a Pt79 nanoparticle at variable WOx coverages. An evolutionary algorithm identifies a small (5%) subset of promising atomic configurations on which DFT simulations are performed. We predict a maximum coverage of ∼50% WOx on Pt(553), consisting of small clusters (tetramers and pentamers), which preferentially reside on the terrace, with their oxygen atoms interacting with the Pt step sites. Consistently, WOx does not lie on curved and undercoordinated metal sites of Pt nanoparticles. The oxide clusters prefer a partially reduced oxidation state. Theoretical EXAFS spectra for select configurations provide insights into interpreting experimental spectra of inverse catalysts. The framework applies to other catalysts.

Unveiling Atomic-Scale Product Selectivity at the Cocatalyst-TiO2 Interface Using X-Ray Techniques: Insights into Interface Reactivity

The microstructure at the interface between the cocatalyst and semiconductor plays a vital role in concentrating photo-induced carriers and reactants. However, observing the atomic arrangement of this interface directly using an electron microscope is challenging due to the coverings of the semiconductor and cocatalyst. To address this, multiple metal-semiconductor interfaces on three TiO2 crystal facets (M/TiO2 ─N, where M represents Ag, Au, and Pt, and N represents the 001, 010, and 101 single crystal facets). The identical surface atomic configuration of the TiO2 facets allowed us to investigate the evolution of the microstructure within these constructs using spectroscopies and DFT calculations. For the first time, they observed the transformation of saturated Ti6c ─O bonds into unsaturated Ti5c ─O and Ti6c ─O─Pt bonds on the TiO2 ─010 facet after loading Pt. This transformation have a direct impact on the selectivity of the resulting products, leading to the generation of CO and CH4 at the Ti6c ─O─Pt and Pt sites, respectively. These findings pinpoint the pivotal roles played by the atomic arrangement at the M/TiO2 ─N interfaces and provide valuable insights for the development of new methodologies using conventional lab-grade equipment.

Confinement-Induced Indium Oxide Nanolayers Formed on Oxide Support for Enhanced CO2 Hydrogenation Reaction

An enclosed nanospace often shows a significant confinement effect on chemistry within its inner cavity, while whether an open space can have this effect remains elusive. Here, we show that the open surface of TiO2 creates a confined environment for In2O3 which drives spontaneous transformation of free In2O3 nanoparticles in physical contact with TiO2 nanoparticles into In oxide (InOx) nanolayers covering onto the TiO2 surface during CO2 hydrogenation to CO. The formed InOx nanolayers are easy to create surface oxygen vacancies but are against over-reduction to metallic In in the H2-rich atmospheres, which thus show significantly enhanced activity and stability in comparison with the pure In2O3 catalyst. The formation of interfacial In-O-Ti bonding is identified to drive the In2O3 dispersion and stabilize the metastable InOx layers. The InOx overlayers with distinct chemistry from their free counterpart can be confined on various oxide surfaces, demonstrating the important confinement effect at oxide/oxide interfaces.

Ultrasound-activated piezo-hot carriers trigger tandem catalysis coordinating cuproptosis-like bacterial death against implant infections

Implant-associated infections due to the formation of bacterial biofilms pose a serious threat in medical healthcare, which needs effective therapeutic methods. Here, we propose a multifunctional nanoreactor by spatiotemporal ultrasound-driven tandem catalysis to amplify the efficacy of sonodynamic and chemodynamic therapy. By combining piezoelectric barium titanate with polydopamine and copper, the ultrasound-activated piezo-hot carriers transfer easily to copper by polydopamine. It boosts reactive oxygen species production by piezoelectrics, and facilitates the interconversion between Cu2+ and Cu+ to promote hydroxyl radical generation via Cu+ -catalyzed chemodynamic reactions. Finally, the elevated reactive oxygen species cause bacterial membrane structure loosening and DNA damage. Transcriptomics and metabolomics analysis reveal that intracellular copper overload restricts the tricarboxylic acid cycle, promoting bacterial cuproptosis-like death. Therefore, the polyetherketoneketone scaffold engineered with the designed nanoreactor shows excellent antibacterial performance with ultrasound stimulation and promotes angiogenesis and osteogenesis on-demand in vivo.

Generating active metal/oxide reverse interfaces through coordinated migration of single atoms

Identification of active sites in catalytic materials is important and helps establish approaches to the precise design of catalysts for achieving high reactivity. Generally, active sites of conventional heterogeneous catalysts can be single atom, nanoparticle or a metal/oxide interface. Herein, we report that metal/oxide reverse interfaces can also be active sites which are created from the coordinated migration of metal and oxide atoms. As an example, a Pd1/CeO2 single-atom catalyst prepared via atom trapping, which is otherwise inactive at 30 °C, is able to completely oxidize formaldehyde after steam treatment. The enhanced reactivity is due to the formation of a Ce2O3-Pd nanoparticle domain interface, which is generated by the migration of both Ce and Pd atoms on the atom-trapped Pd1/CeO2 catalyst during steam treatment. We show that the generation of metal oxide-metal interfaces can be achieved in other heterogeneous catalysts due to the coordinated mobility of metal and oxide atoms, demonstrating the formation of a new active interface when using metal single-atom material as catalyst precursor.

Copper Single-Atom Catalysts-A Rising Star for Energy Conversion and Environmental Purification: Synthesis, Modification, and Advanced Applications

Future renewable energy supply and green, sustainable environmental development rely on various types of catalytic reactions. Copper single-atom catalysts (Cu SACs) are attractive due to their distinctive electronic structure (3d orbitals are not filled with valence electrons), high atomic utilization, and excellent catalytic performance and selectivity. Despite numerous optimization studies are conducted on Cu SACs in terms of energy conversion and environmental purification, the coupling among Cu atoms-support interactions, active sites, and catalytic performance remains unclear, and a systematic review of Cu SACs is lacking. To this end, this work summarizes the recent advances of Cu SACs. The synthesis strategies of Cu SACs, metal-support interactions between Cu single atoms and different supports, modification methods including modification for carriers, coordination environment regulating, site distance effect utilizing, and dual metal active center catalysts constructing, as well as their applications in energy conversion and environmental purification are emphatically introduced. Finally, the opportunities and challenges for the future Cu SACs development are discussed. This review aims to provide insight into Cu SACs and a reference for their optimal design and wide application.

Ferric Single-Site Catalyst Confined in a Zeolite Framework for Propane Dehydrogenation

Non-oxidative dehydrogenation of propane is a highly efficient approach for industrial preparation of propene that is commonly catalyzed by noble Pt or toxic Cr catalysts and suffers from coking. In this work, ferric catalyst confined in a zeolite framework was synthesized by a hydrothermal procedure. The isolated Fe in the framework formed distorted tetrahedra, which were beneficial for the selective dehydrogenation of propane and reached over 95 % propene selectivity and over 99 % total olefins selectivity. This catalyst had a silanol-free structure and was oxygen tolerant, hydrothermally stable, and coke free, with a deactivation constant of 0.01 h-1 . This study provided guidance for the synthesis of structural heteroatomic zeolite and efficient propane non-oxidative dehydrogenation over early transition metals.

Tandem propane dehydrogenation and surface oxidation catalysts for selective propylene synthesis

Direct propane dehydrogenation (PDH) to propylene is a desirable commercial reaction but is highly endothermic and severely limited by thermodynamic equilibrium. Routes that oxidatively remove hydrogen as water have safety and cost challenges. We coupled chemical looping-selective hydrogen (H2) combustion and PDH with multifunctional ferric vanadate-vanadium oxide (FeVO4-VOx) redox catalysts. Well-dispersed VOx supported on aluminum oxide (Al2O3) provides dehydrogenation sites, and adjacent nanoscale FeVO4 acts as an oxygen carrier for subsequent H2 combustion. We achieved an integral performance of 81.3% propylene selectivity at 42.7% propane conversion at 550°C for 200 chemical looping cycles for the reoxidization of FeVO4. Based on catalytic experiments, spectroscopic characterization, and theory calculations, we propose a hydrogen spillover-mediated coupling mechanism. The hydrogen species generated at the VOx sites migrated to adjacent FeVO4 for combustion, which shifted PDH toward propylene. This mechanism is favored by the proximity between the dehydrogenation and combustion sites.

Thermodynamically and Kinetically Stabilized Pt Clusters Against Sintering on CeO2 Nanofibers Through Enclosing CeO2 Nanocubes

Sintering is a major concern for the deactivation of supported metals catalysts, which is driven by the force of decreasing the total surface energy of the entire catalytic system. In this work, a double-confinement strategy is demonstrated to stabilize 2.6 nm-Pt clusters against sintering on electrospun CeO2 nanofibers decorated by CeO2 nanocubes (m-CeO2 ). Thermodynamically, with the aid of CeO2 -nanocubes, the intrinsically irregular surface of polycrystalline CeO2 nanofibers becomes smooth, offering adjacent Pt clusters with decreased chemical potential differences on a relatively uniform surface. Kinetically, the Pt clusters are physically restricted on each facet of CeO2 nanocubes in a nanosized region. In situ high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation reveals that the Pt clusters can be stabilized up to 800 °C even in a high density, which is far beyond their Tammann temperature, without observable size growth or migration. Such a sinter-resistant catalytic system is endowed with boosted catalytic activity toward both the hydrogenation of p-nitrophenol after being aged at 500 °C and the sinter-promoting exothermic oxidation reactions (e.g., soot oxidation) at high temperatures over 700 °C. This work offers new opportunities for exploring sinter-resistant nanocatalysts, starting from the rational design of whole catalytic system in terms of thermodynamic and kinetic aspects.

Homologous RuO2-Ru heterostructures for tandem catalytic upgrading of ethanol

The homologous RuO₂-Ru heterostructure was demonstrated as an efficient tandem catalyst for upgrading ethanol. The adjacent RuO₂ and Ru separately serve as aldol condensation/dehydration and dehydrogenation/hydrogenation sites for ethanol conversion.

Tailored Cl- Ligation on Supported Pt Catalysts for Selective Primary C-H Bond Oxidation

It is challenging to achieve high selectivity over Pt-metal-oxide catalysts widely used in many selective oxidation reactions because Pt is prone to over-oxidize substrates. Herein, our sound strategy for enhancing the selectivity is to saturate the under-coordinated single Pt atoms with Cl^- ligands. In this system, the weak electronic metal-support interactions between Pt atoms and reduced TiO₂ cause electron extraction from Pt to Cl^- ligands, resulting in strong Pt-Cl bonds. Therefore, the two-coordinate single Pt atoms adopt a four-coordinate configuration and thus inactivated, thereby inhibiting the over-oxidation of toluene over Pt sites. The selectivity for the primary C-H bond oxidation products of toluene was increased from 50.1 to 100%. Meanwhile, the abundant active Ti³⁺ sites were stabilized in reduced TiO₂ by Pt atoms, leading to a rising yield of the primary C-H oxidation products of 249.8 mmol g_cat^-1. The reported strategy holds great promise for selective oxidation with enhanced selectivity.

Concerted oxygen diffusion across heterogeneous oxide interfaces for intensified propane dehydrogenation

Propane dehydrogenation (PDH) is an industrial technology for direct propylene production which has received extensive attention in recent years. Nevertheless, existing non-oxidative dehydrogenation technologies still suffer from the thermodynamic equilibrium limitations and severe coking. Here, we develop the intensified propane dehydrogenation to propylene by the chemical looping engineering on nanoscale core-shell redox catalysts. The core-shell redox catalyst combines dehydrogenation catalyst and solid oxygen carrier at one particle, preferably compose of two to three atomic layer-type vanadia coating ceria nanodomains. The highest 93.5% propylene selectivity is obtained, sustaining 43.6% propylene yield under 300 long-term dehydrogenation-oxidation cycles, which outperforms an analog of industrially relevant K-CrO_x/Al₂O₃ catalysts and exhibits 45% energy savings in the scale-up of chemical looping scheme. Combining in situ spectroscopies, kinetics, and theoretical calculation, an intrinsically dynamic lattice oxygen "donator-acceptor" process is proposed that O^2- generated from the ceria oxygen carrier is boosted to diffuse and transfer to vanadia dehydrogenation sites via a concerted hopping pathway at the interface, stabilizing surface vanadia with moderate oxygen coverage at pseudo steady state for selective dehydrogenation without significant overoxidation or cracking.

Site Diversity and Mechanism of Metal-Exchanged Zeolite Catalyzed Non-Oxidative Propane Dehydrogenation

Metal-exchanged zeolites are well-known propane dehydrogenation (PDH) catalysts; however, the structure of the active species remains unresolved. In this review, existing PDH catalysts are first surveyed, and then the current understanding of metal-exchanged zeolite catalysts is described in detail. The case of Ga/H-ZSM-5 is employed to showcase that advances in the understanding of structure-activity relations are often accompanied by technological or conceptional breakthroughs. The understanding of Ga speciation at PDH conditions has evolved owing to the advent of in situ/operando characterizations and to the realization that the local coordination environment of Ga species afforded by the zeolite support has a decisive impact on the active site structure. In situ/operando quantitative characterization of catalysts, rigorous determination of intrinsic reaction rates, and predictive computational modeling are all significant in identifying the most active structure in these complex systems. The reaction mechanism could be both intricately related to and nearly independent of the details of the assumed active structure, as in the two main proposed PDH mechanisms on Ga/H-ZSM-5, that is, the carbenium mechanism and the alkyl mechanism. Perspectives on potential approaches to further elucidate the active structure of metal-exchanged zeolite catalysts and reaction mechanisms are discussed in the final section.

Coupling acid catalysis and selective oxidation over MoO3-Fe2O3 for chemical looping oxidative dehydrogenation of propane

Redox catalysts play a vital role in chemical looping oxidative dehydrogenation processes, which have recently been considered to be a promising prospect for propylene production. This work describes the coupling of surface acid catalysis and selective oxidation from lattice oxygen over MoO₃-Fe₂O₃ redox catalysts for promoted propylene production. Atomically dispersed Mo species over γ-Fe₂O₃ introduce effective acid sites for the promotion of propane conversion. In addition, Mo could also regulate the lattice oxygen activity, which makes the oxygen species from the reduction of γ-Fe₂O₃ to Fe₃O₄ contribute to selectively oxidative dehydrogenation instead of over-oxidation in pristine γ-Fe₂O₃. The enhanced surface acidity, coupled with proper lattice oxygen activity, leads to a higher surface reaction rate and moderate oxygen diffusion rate. Consequently, this coupling strategy achieves a robust performance with 49% of propane conversion and 90% of propylene selectivity for at least 300 redox cycles and ultimately demonstrates a potential design strategy for more advanced redox catalysts.

Mechanistic Insight into the Synergy between Platinum Single Atom and Cluster Dual Active Sites Boosting Photocatalytic Hydrogen Evolution

In the energy transition context, the design and synthesis of high-performance Pt-based photocatalysts with low Pt content and ultrahigh atom-utilization efficiency for hydrogen production are essential. Herein, a facile approach for decorating atomically dispersed Pt cocatalysts having single-atom (SA) and atomic cluster (C) dual active sites on CdS nanorods (Pt_SA+C /CdS) via atomic layer deposition is reported. The size of the cocatalyst and the spatial intimacy of the cocatalyst active sites are precisely engineered at the atomic scale. The Pt_SA+C /CdS photocatalysts show the optimized photocatalytic hydrogen evolution activity, achieving a reaction rate of 80.4 mmol h^-1 g^-1 , which is 1.6- and 7.3-fold higher than those of the Pt_SA /CdS and Pt_NP /CdS photocatalysts, respectively. Thorough characterization and theoretical calculations reveal that the enhanced photocatalytic activity is due to a remarkable synergy between SAs and atomic clusters as dual active sites, which are responsible for water adsorption-dissociation and hydrogen desorption, respectively. A similar synergetic effect is found in a representative Pt/TiO₂ system, indicating the generality of the strategy. This study demonstrates the significance of the synergy between active sites for enhancing the reaction efficiency, opening a new avenue for the rational design of atomically dispersed photocatalysts with high efficiency.

Antiexfoliating h-BN⊃In2O3 Catalyst for Oxidative Dehydrogenation of Propane in a High-Temperature and Water-Rich Environment

Hexagonal boron nitride (h-BN) is regarded as one of the most efficient catalysts for oxidative dehydrogenation of propane (ODHP) with high olefin selectivity and productivity. However, the loss of the boron component under a high concentration of water vapor and high temperature seriously hinders its further development. How to make h-BN a stable ODHP catalyst is one of the biggest scientific challenges at present. Herein, we construct h-BN⊃xIn₂O₃ composite catalysts through the atomic layer deposition (ALD) process. After high-temperature treatment in ODHP reaction conditions, the In₂O₃ nanoparticles (NPs) are dispersed on the edge of h-BN and observed to be encapsulated by ultrathin boron oxide (BO_x) overlayer. A novel strong metal oxide-support interaction (SMOSI) effect between In₂O₃ NPs and h-BN is observed for the first time. The material characterization reveals that the SMOSI not only improves the interlayer force between h-BN layers with a pinning model but also reduces the affinity of the B-N bond toward O^• for inhibiting oxidative cutting of h-BN into fragments at a high temperature and water-rich environment. With the pinning effect of the SMOSI, the catalytic stability of h-BN⊃70In₂O₃ has been extended nearly five times than that of pristine h-BN, and the intrinsic olefin selectivity/productivity of h-BN is well maintained.

Concepts Relevant for the Kinetic Analysis of Reversible Reaction Systems

The net rate of a reversible chemical reaction is the difference between unidirectional rates of traversal along forward and reverse reaction paths. In a multistep reaction sequence, the forward and reverse trajectories, in general, are not the microscopic reverse of one another; rather, each unidirectional route is comprised of distinct rate-controlling steps, intermediates, and transition states. Consequently, traditional descriptors of rate (e.g., reaction orders) do not reflect intrinsic kinetic information but instead conflate unidirectional contributions determined by (i) the microscopic occurrence of forward/reverse reactions (i.e., unidirectional kinetics) and (ii) the reversibility of reaction (i.e., nonequilibrium thermodynamics). This review aims to provide a comprehensive resource of analytical and conceptual tools which deconvolute the contributions of reaction kinetics and thermodynamics to disambiguate unidirectional reaction trajectories and precisely identify rate- and reversibility-controlling molecular species and steps in reversible reaction systems. The extrication of mechanistic and kinetic information from bidirectional reactions is accomplished through equation-based formalisms (e.g., De Donder relations) grounded in principles of thermodynamics and interpreted in the context of theories of chemical kinetics developed in the past 25 years. The aggregate of mathematical formalisms detailed herein is general to thermochemical and electrochemical reactions and encapsulates a diverse body of scientific literature encompassing chemical physics, thermodynamics, chemical kinetics, catalysis, and kinetic modeling.

Ultra-thin ZrO2overcoating on CuO-ZnO-Al2O3catalyst by atomic layer deposition for improved catalytic performance of CO2hydrogenation to dimethyl ether

An ultra-thin overcoating of zirconium oxide (ZrO₂) film on CuO-ZnO-Al₂O₃(CZA) catalysts by atomic layer deposition (ALD) was proved to enhance the catalytic performance of CZA/HZSM-5 (H form of Zeolite Socony Mobil-5) bifunctional catalysts for hydrogenation of CO₂to dimethyl ether (DME). Under optimal reaction conditions (i.e. 240 °C and 2.8 MPa), the yield of product DME increased from 17.22% for the bare CZA/HZSM-5 catalysts, to 18.40% for the CZA catalyst after 5 cycles of ZrO₂ALD with HZSM-5 catalyst. All the catalysts modified by ZrO₂ALD displayed significantly improved catalytic stability of hydrogenation of CO₂to DME reaction, compared to that of CZA/HZSM-5 bifunctional catalysts. The loss of DME yield in 100 h of reaction was greatly mitigated from 6.20% (loss of absolute value) to 3.01% for the CZA catalyst with 20 cycles of ZrO₂ALD overcoating. Characterizations including hydrogen temperature programmed reduction, x-ray powder diffraction, and x-ray photoelectron spectroscopy revealed that there was strong interaction between Cu active centers and ZrO₂.

Atomically Thick Oxide Overcoating Stimulates Low-Temperature Reactive Metal-Support Interactions for Enhanced Catalysis

Reactive metal-support interactions (RMSIs) induce the formation of bimetallic alloys and offer an effective way to tune the electronic and geometric properties of metal sites for advanced catalysis. However, RMSIs often require high-temperature reductions (>500 °C), which significantly limits the tuning of bimetallic compositional varieties. Here, we report that an atomically thick Ga₂O₃ coating of Pd nanoparticles enables the initiation of RMSIs at a much lower temperature of ∼250 °C. State-of-the-art microscopic and in situ spectroscopic studies disclose that low-temperature RMSIs initiate the formation of rarely reported Ga-rich PdGa alloy phases, distinct from the Pd₂Ga phase formed in traditional Pd/Ga₂O₃ catalysts after high-temperature reduction. In the CO₂ hydrogenation reaction, the Ga-rich alloy phases impressively boost the formation of methanol and dimethyl ether ∼5 times higher than that of Pd/Ga₂O₃. In situ infrared spectroscopy reveals that the Ga-rich phases greatly favor formate formation as well as its subsequent hydrogenation, thus leading to high productivity.

Oxidative Cleavage and Ammoxidation of Unsaturated Hydrocarbons via Heterogeneous Auto-Tandem Catalysis

The oxidative cleavage and functionalization of unsaturated C-C bonds are important processes for synthesis of carbonyl compounds from hydrocarbon feedstocks, yet there has been no report of direct amidation of unsaturated hydrocarbons via an oxidative cleavage of unsaturated C-C bonds with molecular oxygen as an environmentally benign oxidant. Herein, for the first time, we describe a manganese oxide-catalyzed auto-tandem catalysis strategy that enables direct synthesis of amides from unsaturated hydrocarbons by coupling oxidative cleavage with amidation. With oxygen as an oxidant and ammonia as a nitrogen source, a wide range of structurally diverse mono- and multisubstituted activated and unactivated alkenes or alkynes can smoothly undergo unsaturated C-C bond cleavage to deliver one- or multiple-carbon shorter amides. Moreover, a slight modification of the reaction conditions also allows for the direct synthesis of sterically hindered nitriles from alkenes or alkynes. This protocol features excellent functional group tolerance, a broad substrate scope, flexible late-stage functionalization, facile scalability, and a cost-effective and recyclable catalyst. Detailed characterizations reveal that the high activity and selectivity of the manganese oxides are attributed to the large specific surface area, abundant oxygen vacancies, better reducibility, and moderate acid sites. Mechanistic studies and density functional theory calculations indicate that the reaction proceeds through divergent pathways depending on the structure of substrates.

Auto-accelerated dehydrogenation of alkane assisted by in-situ formed olefins over boron nitride under aerobic conditions

Oxidative dehydrogenation (ODH) of alkane over boron nitride (BN) catalyst exhibits high olefin selectivity as well as a small ecological carbon footprint. Here we report an unusual phenomenon that the in-situ formed olefins under reactions are in turn actively accelerating parent alkane conversion over BN by interacting with hydroperoxyl and alkoxyl radicals and generating reactive species which promote oxidation of alkane and olefin formation, through feeding a mixture of alkane and olefin and DFT calculations. The isotope tracer studies reveal the cleavage of C-C bond in propylene when co-existing with propane, directly evidencing the deep-oxidation of olefins occur in the ODH reaction over BN. Furthermore, enhancing the activation of ethane by the in-situ formed olefins from propane is successfully realized at lower temperature by co-feeding alkane mixture strategy. This work unveils the realistic ODH reaction pathway over BN and provides an insight into efficiently producing olefins.

Emerging laser-assisted vacuum processes for ultra-precision, high-yield manufacturing

Laser technology is a cutting-edge process with a unique photothermal response, precise site selectivity, and remote controllability. Laser technology has recently emerged as a novel tool in the semiconductor, display, and thin film industries by providing additional capabilities to existing high-vacuum equipment. The in situ and in operando laser assistance enables using multiple process environments with a level of complexity unachievable with conventional vacuum equipment. This broadens the usable range of process parameters and directly improves material properties, product precision, and device performance. This review paper examines the recent research trends in laser-assisted vacuum processes (LAVPs) as a vital tool for innovation in next-generation manufacturing processing equipment and addresses the unique characteristics and mechanisms of lasers exclusively used in each study. All the findings suggest that the LAVP can lead to methodological breakthroughs in dry etching, 2D material synthesis, and chemical vapor deposition for optoelectronic devices.

Atomically Dispersed Dual Metal Sites Boost the Efficiency of Olefins Epoxidation in Tandem with CO2 Cycloaddition

Tandem catalysis provides an economical and energy-efficient process for the production of fine chemicals. In this work, we demonstrate that a rationally synthesized carbon-based catalyst with atomically dispersed dual Fe-Al sites (ADD-Fe-Al) achieves superior catalytic activity for the one-pot oxidative carboxylation of olefins (conversion ∼97%, selectivity ∼91%), where the yield of target product over ADD-Fe-Al is at least 62% higher than that of monometallic counterparts. The kinetic results reveal that the excellent catalytic performance arises from the synergistic effect between Fe (oxidation site) and Al sites (cycloaddition site), where the efficient CO₂ cycloaddition with epoxides in the presence of Al sites (3.91 wt %) positively shifts the oxidation equilibrium to olefin epoxidation over Fe sites (0.89 wt %). This work not only offers an advanced catalyst for oxidative carboxylation of olefins but also opens up an avenue for the rational design of multifunctional catalysts for tandem catalytic reactions in the future.

Light olefin synthesis from a diversity of renewable and fossil feedstocks: state-of the-art and outlook

Light olefins are important feedstocks and platform molecules for the chemical industry. Their synthesis has been a research priority in both academia and industry. There are many different approaches to the synthesis of these compounds, which differ by the choice of raw materials, catalysts and reaction conditions. The goals of this review are to highlight the most recent trends in light olefin synthesis and to perform a comparative analysis of different synthetic routes using several quantitative characteristics: selectivity, productivity, severity of operating conditions, stability, technological maturity and sustainability. Traditionally, on an industrial scale, the cracking of oil fractions has been used to produce light olefins. Methanol-to-olefins, alkane direct or oxidative dehydrogenation technologies have great potential in the short term and have already reached scientific and technological maturities. Major progress should be made in the field of methanol-mediated CO and CO₂ direct hydrogenation to light olefins. The electrocatalytic reduction of CO₂ to light olefins is a very attractive process in the long run due to the low reaction temperature and possible use of sustainable electricity. The application of modern concepts such as electricity-driven process intensification, looping, CO₂ management and nanoscale catalyst design should lead in the near future to more environmentally friendly, energy efficient and selective large-scale technologies for light olefin synthesis.

Main-Group Catalysts with Atomically Dispersed In Sites for Highly Efficient Oxidative Dehydrogenation

Transition metal oxides are well-known catalysts for oxidative dehydrogenation thanks to their excellent ability to activate alkanes. However, they suffer from an inferior alkene yield due to the trade-off between the conversion and selectivity induced by more reactive alkenes than alkanes, which obscures the optimization of catalysts. Herein, we attempt to overcome this challenge by activating a selective main-group indium oxide considered to be inactive for oxidative dehydrogenation in conventional wisdom. Atomically dispersed In sites with the local structure of [InOH]²⁺ anchored by substituting the protons of supercages in HY are enclosed to be active centers that enable the activation of ethane with a metal-normalized turnover number of almost one magnitude higher than those of their supported In₂O₃ counterparts. Furthermore, the structure of isolated [InOH]²⁺ sites could be stabilized by in situ formed H₂O from the selective oxidation of hydrogen by In₂O₃ nanoparticles. As a result, the as-designed main-group In catalysts exhibit 80% ethene selectivity at 80% ethane conversion, thus achieving 60% ethene yield due to active isolated [InOH]²⁺ sites and selective In₂O₃ nanoparticles, outperforming state-of-the-art transition metal oxide catalysts. This study unlocks new opportunities for the utilization of main-group elements and could pave the way toward a more rational design of catalysts for highly efficient selective oxidation catalysis.