Tuning the Selectivity of Catalytic Carbon Dioxide Hydrogenation over Iridium/Cerium Oxide Catalysts with a Strong Metal-Support Interaction

Using In situ Transmission Electron Microscopy to Study Strong Metal-Support Interactions in Heterogeneous Catalysis

Precisely controlling the microstructure of supported metal catalysts and regulating metal-support interactions at the atomic level are essential for achieving highly efficient heterogeneous catalysts. Strong metal-support interaction (SMSI) not only stabilizes metal nanoparticles and improves their resistance to sintering but also modulates the electrical interaction between metal species and the support, optimizing the catalytic activity and selectivity. Therefore, understating the formation mechanism of SMSI and its dynamic evolution during the chemical reaction at the atomic scale is crucial for guiding the structural design and performance optimization of supported metal catalysts. Recent advancements in in situ transmission electron microscopy (TEM) have shed new light on these complex phenomena, providing deeper insights into the SMSI dynamics. Here, the research progress of in situ TEM investigation on SMSI in heterogeneous catalysis is systematically reviewed, focusing on the formation dynamics, structural evolution during the catalytic reactions, and regulation methods of SMSI. The significant advantages of in situ TEM technologies for SMSI research are also highlighted. Moreover, the challenges and probable development paths of in situ TEM studies on the SMSI are also provided.

Tuning Catalytic Activity of CO2 Hydrogenation to C1 Product via Metal Support Interaction Over Metal/Metal Oxide Supported Catalysts

The metal supported catalysts are emerging catalysts that are receiving a lot of attention in CO2 hydrogenation to C1 products. Numerous experiments have demonstrated that the support (usually an oxide) is crucial for the catalytic performance. The support metal oxides are used to aid in the homogeneous dispersion of metal particles, prevent agglomeration, and control morphology owing to the metal support interaction (MSI). MSI can efficiently optimize the structural and electronic properties of catalysts and tune the conversion of key reaction intermediates involved in CO2 hydrogenation, thereby enhancing the catalytic performance. There is an increasing attention is being paid to the promotion effects in the catalytic CO2 hydrogenation process. However, a systematically understanding about the effects of MSI on CO2 hydrogenation to C1 products catalytic performance has not been fully studied yet due to the diversities in catalysts and reaction conditions. Hence, the characteristics and modes of MSI in CO2 hydrogenation to C1 products are elaborated in detail in our work.

Hydrogenation of CO2 into Value-added Chemicals Using Solid-Supported Catalysts

Reducing CO2 emissions is an urgent global priority. In this context, several mitigation strategies, including CO2 tax and stringent legislation, have been adopted to halt the deterioration of the natural environment. Also, carbon recycling procedures undoubtedly help reduce net emissions into the atmosphere, enhancing sustainability. Utilizing Earth's abundant CO2 to produce high-potential green chemicals and light fuels opens new avenues for the chemical industry. In this context, many attempts have been devoted to converting CO2 as a feedstock into various value-added chemicals, such as CH4, lower methanol, light olefins, gasoline, and higher hydrocarbons, for numerous applications involving various catalytic reactions. Although several CO2-conversion methods have been used, including electrochemical, photochemical, and biological approaches, the hydrogenation method allows the reaction to be tuned to produce the targeted compound without significantly altering infrastructure. This review discusses the numerous hydrogenation routes and their challenges, such as catalyst design, operation, and the combined art of structure-activity relationships for the various product formations.

Hierarchical Carbon Nanocages as Superior Supports for Photothermal CO2 Catalysis

The exploitation of hierarchical carbon nanocages with superior light-to-heat conversion efficiency, together with their distinct structural, morphological, and electronic properties, in photothermal applications could provide effective solutions to long-standing challenges in diverse areas. Here, we demonstrate the discovery of pristine and nitrogen-doped hierarchical carbon nanocages as superior supports for highly loaded, small-sized Ru particles toward enhanced photothermal CO2 catalysis. A record CO production rate of 3.1 mol·gRu-1·h-1 with above 90% selectivity in flow reactors was reached for hierarchical nitrogen-doped carbon-nanocage-supported Ru clusters under 2.4 W·cm-2 illumination without external heating. Detailed studies reveal that the enhanced performance originates from the strong broadband sunlight absorption and efficient light-to-heat conversion of nanocage supports as well as the excellent intrinsic catalytic reactivity of sub-2 nm Ru particles. Our study reveals the great potential of hierarchical carbon nanocages in photothermal catalysis to reduce the fossil fuel consumption of various industrial chemical processes and stimulates interest in their exploitation for other demanding photothermal applications.

Enrooted-Type Metal-Support Interaction Boosting Oxygen Evolution Reaction in Acidic Media

Supported metal catalysts with appropriate metal-support interactions (MSIs) hold a great promise for heterogeneous catalysis. However, ensuring tight immobilization of metal clusters/nanoparticles on the support while maximizing the exposure of surface active sites remains a huge challenge. Herein, we report an Ir/WO3 catalyst with a new enrooted-type MSI in which Ir clusters are, unprecedentedly, atomically enrooted into the WO3 lattice. The enrooted Ir atoms decrease the electron density of the constructed interface compared to the adhered (root-free) type, thereby achieving appropriate adsorption toward oxygen intermediates, ultimately leading to high activity and stability for oxygen evolution in acidic media. Importantly, this work provides a new enrooted-type supported metal catalyst, which endows suitable MSI and maximizes the exposure of surface active sites in contrast to the conventional adhered, embedded, and encapsulated types.

Thermally Stable Oxide-Capsulated Metal Nanoparticles Structure for Strong Metal-Support Interaction via Ultrafast Laser Plasmonic Nanowelding

Strong metal-support interaction (SMSI) has drawn much attention in heterogeneous catalysts due to its stable and excellent catalytic efficiency. However, construction of high-performance oxide-capsulated metal nanostructures meets great challenge in materials thermodynamic compatibility. In this work, dynamically controlled formation of oxide-capsulated metal nanoparticles (NPs) structures is demonstrated by ultrafast laser plasmonic nanowelding. Under the strong localized electromagnetic field interaction, metal (Au) NPs are dragged by an optical force toward oxide NPs (TiO2). Intense energy is simultaneously injected into this heterojunction area, where TiO2 is precisely ablated. With the embedding of metal into oxide, optical force on Au gradually turned from attractive to repulsive due to the varied metal-dielectric environment. Meanwhile, local ablated oxides are redeposited on Au NP. Upon the whole coverage of metal NP, the implantation behavior of metal NP is stopped, resulting in a controlled metal-oxide eccentric structure with capsulated oxide layer thickness ≈0.72-1.30 nm. These oxide-capsulated metal NPs structures can preserve their configurations even after thermal annealing in air at 600 °C for 10 min. This ultrafast laser plasmonic nanowelding can also extend to oxide-capsulated metal nanostructure fabrication with broad materials combinations (e.g., Au/ZnO, Au/MgO, etc.), which shows great potential in designing/constructing nanoscale high-performance catalysts.

Strong Interactions between Au Nanoparticles and BiVO4 Photoanode Boosts Hole Extraction for Photoelectrochemical Water Splitting

Strong metal-support interaction (SMSI) is widely proposed as a key factor in tuning catalytic performances. Herein, the classical SMSI between Au nanoparticles (NPs) and BiVO4 (BVO) supports (Au/BVO-SMSI) is discovered and used innovatively for photoelectrochemical (PEC) water splitting. Owing to the SMSI, the electrons transfer from V4+ to Au NPs, leading to the formation of electron-rich Au species (Auδ-) and strong electronic interaction (i.e., Auδ--Ov-V4+), which readily contributes to extract photogenerated holes and promote charge separation. Benefitted from the SMSI effect, the as-prepared Au/BVO-SMSI photoanode exhibits a superior photocurrent density of 6.25 mA cm-2 at 1.23 V versus the reversible hydrogen electrode after the deposition of FeOOH/NiOOH cocatalysts. This work provides a pioneering view for extending SMSI effect to bimetal oxide supports for PEC water splitting, and guides the interfacial electronic and geometric structure modulation of photoanodes consisting of metal NPs and reducible oxides for improved solar energy conversion efficiency.

One-pot Synthesis of PdCuAg and CeO2 Nanowires Hybrid with Abundant Heterojunction Interface for Ethylene Glycol Electrooxidation

Introducing CeO2 into Pd-based nanocatalysts for electrocatalytic reactions is a good way to solve the intermediate toxicity problem and improve the catalytic performance. Here we reported a simple strategy to synthesize the PdCuAg and CeO2 nanowires hybrid via a one-pot synthesis process under strong nanoconfined effect of specific surfactant as templates. Owing to the structural (ultrathin nanowires, abundant heterojunction/interfaces between metal and metal oxide) and compositional (Pd, Cu, Ag, CeO2) advantages, the hybrid showed significantly enhanced catalytic activity (6.06 A mgPd -1) and stability, accelerated reaction rate, and reduced activation energy toward electrocatalytic ethylene glycol oxidation reaction.

Facilitating the dry reforming of methane with interfacial synergistic catalysis in an Ir@CeO2-x catalyst

The dry reforming of methane provides an attractive route to convert greenhouse gases (CH4 and CO2) into valuable syngas, so as to resolve the carbon cycle and environmental issues. However, the development of high-performance catalysts remains a huge challenge. Herein, we report a 0.6% Ir/CeO2-x catalyst with a metal-support interface structure which exhibits high CH4 (~72%) and CO2 (~82%) conversion and a CH4 reaction rate of ~973 μmolCH4 gcat-1 s-1 which is stable over 100 h at 700 °C. The performance of the catalyst is close to the state-of-the-art in this area of research. A combination of in situ spectroscopic characterization and theoretical calculations highlight the importance of the interfacial structure as an intrinsic active center to facilitate the CH4 dissociation (the rate-determining step) and the CH2* oxidation to CH2O* without coke formation, which accounts for the long-term stability. The catalyst in this work has a potential application prospect in the field of high-value utilization of carbon resources.

Non-Photochemical Origin of Selectivity Difference between Light and Dark Catalytic Conditions

The interest in introducing light into heterogeneous catalysis is driven not only by the urgent need of replacing fossil energy but also by the promise of controlling product selectivity by light. The product selectivity differences observed in recent studies between light and dark reactions are often attributed to photochemical effects. Here, we report the discovery of a non-photochemical origin of selectivity difference, at essentially the same CO2 conversion rate, between photothermal and thermal CO2 hydrogenation reactions over a Ru/TiO2-x catalyst. While the presence of the photochemical effect from ultraviolet light is confirmed, it merely enhances the catalytic activity. Systematic investigation reveals that the gradual formation of an adsorbate-mediated strong metal-support interaction under catalytic conditions is responsible for the variation in the catalytic selectivity. We demonstrate that differences in product selectivity under light/dark reactions do not necessarily originate from photochemical effects. Our study refines the basis for determining photochemical effects and highlights the importance of excluding non-photochemical effects in mechanistic studies of light-controlled product selectivity.

Theoretical Insights into Amido Group-Mediated Enhancement of CO2 Hydrogenation to Methanol on Cobalt Catalysts

Catalytic reduction of carbon dioxide into high-value-added products, such as methanol, is an effective approach to mitigate the greenhouse effect, and improving Co-based catalysts is anticipated to yield potential catalysts with high performance and low cost. In this study, based on first-principles calculations, we elucidate the promotion effects of surface *NHx (x = 1, 2, and 3) on the carbon dioxide hydrogenation to methanol from both activity and selectivity perspectives on Co-based catalysts. The presence of *NHx reduced the energy barrier of each elementary step on Co(100) by regulating the electronic structure to alter the binding strength of intermediates or by forming a hydrogen bond between surface oxygen-containing species and *NHx to stabilize transition states. The best promotion effect for different steps corresponds to different *NHx. The energy barrier of the rate-determining step of CO2 hydrogenation to methanol is lowered from 1.55 to 0.88 eV, and the product selectivity shifts from methane to methanol with the assistance of *NHx on the Co(100) surface. A similar phenomenon is observed on the Co(111) surface. The promotion effect of *NHx on Co-based catalysts is superior to that of water, indicating that the introduction of *NHx on a Co-based catalyst is an effective strategy to enhance the catalytic performance of CO2 hydrogenation to methanol.

Noble Metal Phosphides Supported on CoNi Metaphosphate for Efficient Overall Water Splitting

Transition metal metaphosphates and noble metal phosphides prepared under similar conditions are potential hybrid catalysts for electrocatalytic water splitting, which is of great significance for H2 production. Herein, the structure and electrocatalytic activity of different noble metal species (i.e., Rh, Pd, Ir) on CoNiP4O12 nanoarrays have been systematically studied. Due to the different formation energies of noble metal phosphides, the phosphides of Rh (RhPx) and Pd (PdPx) as well as the noble metal Ir are obtained under the same phosphorylation conditions perspectively. RhPx/CoNiP4O12 and PdPx/CoNiP4O12 exhibit much better HER activity than Ir/CoNiP4O12 due to the advantages of phosphides. Density functional theory (DFT) calculations reveal that the extraordinary activity of RhPx/CoNiP4O12 originated from the strong affinity to H2O and optimal adsorption for H*. The best RhPx/CoNiP4O12 only requires a low overpotential of 30 and 234 mV to deliver 10 mA cm-2 for HER and OER, respectively, and therefore is effective for overall water splitting (requiring 1.57 V to achieve a current density of 10 mA cm-2). This work not only develops a novel RhPx/CoNiP4O12 electrocatalyst for overall water splitting but also provides deep insight into the formation mechanism of noble metal phosphides.

Novel heterogeneous Fe-based catalysts for carbon dioxide hydrogenation to long chain α-olefins-A review

The thermocatalytic conversion of carbon dioxide (CO2) into high value-added chemicals provides a strategy to address the environmental problems caused by excessive carbon emissions and the sustainable production of chemicals. Significant progress has been made in the CO2 hydrogenation to long chain α-olefins, but controlling C-O activation and C-C coupling remains a great challenge. This review focuses on the recent advances in catalyst design concepts for the synthesis of long chain α-olefins from CO2 hydrogenation. We have systematically summarized and analyzed the ingenious design of catalysts, reaction mechanisms, the interaction between active sites and supports, structure-activity relationship, influence of reaction process parameters on catalyst performance, and catalyst stability, as well as the regeneration methods. Meanwhile, the challenges in the development of the long chain α-olefins synthesis from CO2 hydrogenation are proposed, and the future development opportunities are prospected. The aim of this review is to provide a comprehensive perspective on long chain α-olefins synthesis from CO2 hydrogenation to inspire the invention of novel catalysts and accelerate the development of this process.

Renaissance of Strong Metal-Support Interactions

Strong metal-support interactions (SMSIs) have emerged as a significant and cutting-edge area of research in heterogeneous catalysis. They play crucial roles in modifying the chemisorption properties, interfacial structure, and electronic characteristics of supported metals, thereby exerting a profound influence on the catalytic properties. This Perspective aims to provide a comprehensive summary of the latest advancements and insights into SMSIs, with a focus on state-of-the-art in situ/operando characterization techniques. This overview also identifies innovative designs and applications of new types of SMSI systems in catalytic chemistry and highlights their pivotal role in enhancing catalytic performance, selectivity, and stability in specific cases. Particularly notable is the discovery of SMSI between active metals and metal carbides, which opens up a new era in the field of SMSI. Additionally, the strong interactions between atomically dispersed metals and supports are discussed, with an emphasis on the electronic effects of the support. The chemical nature of SMSI and its underlying catalytic mechanisms are also elaborated upon. It is evident that SMSI modification has become a powerful tool for enhancing catalytic performance in various catalytic applications.

Highly Stable Pt/CeO2 Catalyst with Embedding Structure toward Water-Gas Shift Reaction

Strong metal-support interaction (SMSI) has been extensively studied in heterogeneous catalysis because of its significance in stabilizing active metals and tuning catalytic performance, but the origin of SMSI is not fully revealed. Herein, by using Pt/CeO2 as a model catalyst, we report an embedding structure at the interface between Pt and (110) plane of CeO2, where Pt clusters (∼1.6 nm) are embedded into the lattice of ceria within 3-4 atomic layers. In contrast, this phenomenon is absent in the CeO2(100) support. This unique geometric structure, as an effective motivator, triggers more significant electron transfer from Pt clusters to CeO2(110) support accompanied by the formation of interfacial structure (Ptδ+-Ov-Ce3+), which plays a crucial role in stabilizing Pt nanoclusters. A comprehensive investigation based on experimental studies and theoretical calculations substantiates that the interfacial sites serve as the intrinsic active center toward water-gas shift reaction (WGSR), featuring a moderate strength CO activation adsorption and largely decreased energy barrier of H2O dissociation, accounting for the prominent catalytic activity of Pt/CeO2(110) (a reaction rate of 15.76 molCO gPt-1 h-1 and a turnover frequency value of 2.19 s-1 at 250 °C). In addition, the Pt/CeO2(110) catalyst shows a prominent durability within a 120 h time-on-stream test, far outperforming the Pt/CeO2(100) one, which demonstrates the advantages of this embedding structure for improving catalyst stability.

Review of Carbon Support Coordination Environments for Single Metal Atom Electrocatalysts (SACS)

This topical review focuses on the distinct role of carbon support coordination environment of single-atom catalysts (SACs) for electrocatalysis. The article begins with an overview of atomic coordination configurations in SACs, including a discussion of the advanced characterization techniques and simulation used for understanding the active sites. A summary of key electrocatalysis applications is then provided. These processes are oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO2 RR). The review then shifts to modulation of the metal atom-carbon coordination environments, focusing on nitrogen and other non-metal coordination through modulation at the first coordination shell and modulation in the second and higher coordination shells. Representative case studies are provided, starting with the classic four-nitrogen-coordinated single metal atom (MN4 ) based SACs. Bimetallic coordination models including homo-paired and hetero-paired active sites are also discussed, being categorized as emerging approaches. The theme of the discussions is the correlation between synthesis methods for selective doping, the carbon structure-electron configuration changes associated with the doping, the analytical techniques used to ascertain these changes, and the resultant electrocatalysis performance. Critical unanswered questions as well as promising underexplored research directions are identified.

Carbonate Hydrogenated to Formate in the Aqueous Phase over Nickel/TiO2 Catalysts

Carbonate hydrogenation to formate is a promising route to convert captured carbon dioxide into valuable chemicals, thus reducing carbon emissions and creating a revenue return. Developing inexpensive catalysts with high activity, selectivity, and stability remains challenging. We report a supported non-noble metal catalyst, Ni/TiO2 , with great selectivity over 96 % and excellent stability in catalyzing the conversion of carbonate into formate in aqueous solution. Ni0 and Ni2+ species are both observed in Ni/TiO2 catalysts, and the synergistic effect of these two Ni components leads to high activity and high selectivity of carbonate hydrogenation to formate.

Enhancing CO2 reduction through the catalytic effect of a novel silicon haeckelite-inspired 2D material

We propose a novel 2D material based on silicon haeckelite (Hck), whose structure contains a silicon atom arranged in a periodic pattern of pentagons and heptagons. Stacking the two layers gives rise to a planar geometry of the layers that compose it. This new structure presents a semiconductor character with a band gap of 0.17 eV. Furthermore, we studied CO2 reduction using molecular hydrogen to form formic acid, carbon monoxide, formaldehyde, methanol, and methane. All these have been studied theoretically at the Grimme D3BJ corrected TPSS/def2-SVP level. A massive biflake containing 132 Si atoms was used to model the Hck surface. According to the results, CO2 capture with Hck is a spontaneous step; in contrast, the same process for silicene mono- and bi-flakes studied previously was endergonic. After the capture of CO2, the addition of H2 to the substrate passes through an intermediate containing a Si-H bond. The formation of Si-H intermediates is the origin of the catalytic effect, facilitating H2 dissociation and acting as the hydrogen atom donor for the substrate. These intermediates are transformed by adding hydrogen atoms and losing water molecules, producing formic acid and formaldehyde as the most probable products, with rate-controlling steps of 29.2 and 27 kcal mol-1, whose values were less than those exhibited by the silicene biflake. This means that the silicon haeckelite biflake presents better catalytic activity than the silicene biflake. The results show that the novel 2D silicon hackelite material has remarkable potential for CO2 capture and reduction. The theoretical analysis of this innovative 2D structure provides valuable insights into the potential applications of silicene-based materials.

Structure Sensitivity of CO2 Hydrogenation on Ni Revisited

Despite the large number of studies on the catalytic hydrogenation of CO2 to CO and hydrocarbons by metal nanoparticles, the nature of the active sites and the reaction mechanism have remained unresolved. This hampers the development of effective catalysts relevant to energy storage. By investigating the structure sensitivity of CO2 hydrogenation on a set of silica-supported Ni nanoparticle catalysts (2-12 nm), we found that the active sites responsible for the conversion of CO2 to CO are different from those for the subsequent hydrogenation of CO to CH4. While the former reaction step is weakly dependent on the nanoparticle size, the latter is strongly structure sensitive with particles below 5 nm losing their methanation activity. Operando X-ray diffraction and X-ray absorption spectroscopy results showed that significant oxidation or restructuring, which could be responsible for the observed differences in CO2 hydrogenation rates, was absent. Instead, the decreased methanation activity and the related higher CO selectivity on small nanoparticles was linked to a lower availability of step edges that are active for CO dissociation. Operando infrared spectroscopy coupled with (isotopic) transient experiments revealed the dynamics of surface species on the Ni surface during CO2 hydrogenation and demonstrated that direct dissociation of CO2 to CO is followed by the conversion of strongly bonded carbonyls to CH4. These findings provide essential insights into the much debated structure sensitivity of CO2 hydrogenation reactions and are key for the knowledge-driven design of highly active and selective catalysts.

A strong bimetal-support interaction in ethanol steam reforming

The metal-support interaction (MSI) in heterogeneous catalysts plays a crucial role in reforming reaction to produce renewable hydrogen, but conventional objects are limited to single metal and support. Herein, we report a type of RhNi/TiO₂ catalysts with tunable RhNi-TiO₂ strong bimetal-support interaction (SBMSI) derived from structure topological transformation of RhNiTi-layered double hydroxides (RhNiTi-LDHs) precursors. The resulting 0.5RhNi/TiO₂ catalyst (with 0.5 wt.% Rh) exhibits extraordinary catalytic performance toward ethanol steam reforming (ESR) reaction with a H₂ yield of 61.7%, a H₂ production rate of 12.2 L h^-1 g_cat^-1 and a high operational stability (300 h), which is preponderant to the state-of-the-art catalysts. By virtue of synergistic catalysis of multifunctional interface structure (Rh-Ni^δ--O_v-Ti³⁺; O_v denotes oxygen vacancy), the generation of formate intermediate (the rate-determining step in ESR reaction) from steam reforming of CO and CH_x is significantly promoted on 0.5RhNi/TiO₂ catalyst, accounting for its ultra-high H₂ production.

Does Cluster Encapsulation Inhibit Sintering? Stabilization of Size-Selected Pt Clusters on Fe3O4(001) by SMSI

The metastability of supported metal nanoparticles limits their application in heterogeneous catalysis at elevated temperatures due to their tendency to sinter. One strategy to overcome these thermodynamic limits on reducible oxide supports is encapsulation via strong metal-support interaction (SMSI). While annealing-induced encapsulation is a well-explored phenomenon for extended nanoparticles, it is as yet unknown whether the same mechanisms hold for subnanometer clusters, where concomitant sintering and alloying might play a significant role. In this article, we explore the encapsulation and stability of size-selected Pt5, Pt10, and Pt19 clusters deposited on Fe3O4(001). In a multimodal approach using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM), we demonstrate that SMSI indeed leads to the formation of a defective, FeO-like conglomerate encapsulating the clusters. By stepwise annealing up to 1023 K, we observe the succession of encapsulation, cluster coalescence, and Ostwald ripening, resulting in square-shaped crystalline Pt particles, independent of the initial cluster size. The respective sintering onset temperatures scale with the cluster footprint and thus size. Remarkably, while small encapsulated clusters can still diffuse as a whole, atom detachment and thus Ostwald ripening are successfully suppressed up to 823 K, i.e., 200 K above the Hüttig temperature that indicates the thermodynamic stability limit.

Filtration of the preferred catalyst for reverse water-gas shift among Rhn- (n = 3-11) clusters by mass spectrometry under variable temperatures

The key to optimizing energy-consuming catalytic conversions lies in acquiring a fundamental understanding of the nature of the active sites and the mechanisms of elementary steps at an atomically precise level, while it is challenging to capture the crucial step that determines the overall temperature of a real-life catalytic reaction. Herein, benefiting from a newly-developed high-temperature ion trap reactor, the reverse water-gas shift (CO₂ + H₂ → CO + H₂O) reaction catalyzed by the Rh_n^- (n = 3-11) clusters was investigated under variable temperatures (298-783 K) and the critical temperature that each elementary step (Rh_n^- + CO₂ and Rh_nO^- + H₂) requires to take place was identified. The Rh₄^- cluster strikingly surpasses other Rh_n^- clusters to drive the catalysis at a mild starting temperature (∼440 K). This finding represents the first example that a specifically sized cluster catalyst that works under an optimum condition can be accurately filtered by using state-of-the-art mass spectrometric experiments and rationalized by quantum-chemical calculations.

Synergistic Catalysis at the Ni/ZrO2-x Interface toward Low-Temperature CO2 Methanation

The CO₂ methanation reaction, which achieves the carbon cycle and gains value-added chemicals, has attracted much attention, but the design and exploitation of highly active catalysts remain a big challenge. Herein, zirconium dioxide-supported Ni catalysts toward low-temperature CO₂ methanation are obtained via structural topological transformation of NiZrAl-layered double hydroxide (LDH) precursors, which have the feature of an interfacial structure (Ni-O-Zr³⁺-Vö) between Ni nanoparticles and ZrO_2-x support (0 < x < 1). The optimized catalyst (Ni/ZrO_2-x-S2) exhibits exceptional CO₂ conversion (∼72%) at a temperature as low as 230 °C with a ∼100% selectivity to CH₄, without obvious catalyst deactivation within a 110 h reaction at a high gas hourly space velocity of 30,000 mL·g^-1·h^-1. Markedly, the space-time yield of CH₄ reaches up to ∼0.17 molCH4·g_cat^-1·h^-1, which is superior to previously reported Ni catalysts evaluated under similar reaction conditions. Both in situ/operando investigations (diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption fine structure) and catalytic evaluations substantiate the interfacial synergistic catalysis at the Ni/ZrO_2-x interface: the Zr³⁺-Vö facilitates the activation adsorption of CO₂, while the H₂ molecule experiences dissociation at the metallic Ni sites. This work demonstrates that the metal-support interface effect plays a key role in improving the catalytic behavior toward CO₂ methanation, which can be extended to other high-performance heterogeneous catalysts toward structure-sensitive systems.

Review on supported metal catalysts with partial/porous overlayers for stabilization

Heterogeneous catalysts of supported metals are important for both liquid-phase and gas-phase chemical transformations which underpin the petrochemical sector and manufacture of bulk or fine chemicals and pharmaceuticals. Conventional supported metal catalysts (SMC) suffer from deactivation resulting from sintering, leaching, coking and so on. Besides the choice of active species (e.g. atoms, clusters, nanoparticles) to maximize catalytic performances, strategies to stabilize active species are imperative for rational design of catalysts, particularly for those catalysts that work under heated and corrosive reaction conditions. The complete encapsulation of metal active species within a matrix (e.g. zeolites, MOFs, carbon, etc.) or core-shell arrangements is popular. However, the use of partial/porous overlayers (PO) to preserve metals, which simultaneously ensures the accessibility of active sites through controlling the size/shape of diffusing reactants and products, has not been systematically reviewed. The present review identifies the key design principles for fabricating supported metal catalysts with partial/porous overlayers (SMCPO) and demonstrates their advantages versus conventional supported metals in catalytic reactions.

Stabilizing Single-Atomic Pt by Forming PtFe Bonds for Efficient Diboration of Alkynes

Precisely tailoring the oxidation state of single-atomic metal in heterogeneous catalysis is an efficient way to stabilize the single-atomic site and promote their activity, but realizing this approach remains a grand challenge to date. Herein, a class of stable single-atomic catalysts with well-tuned oxidation state of Pt by forming PtFe atomic bonds is reported, which are supported by defective Fe₂ O₃  nanosheets on reduced graphene oxide (PFARFNs). These as-synthesized materials can greatly enhance the catalytic activity, stability, and selectivity for the diboration of alkynes. The PFARFNs exhibit high conversion of 99% at 100 °C with an outstanding turnover frequency (TOF) of 545 h^-1 , and a relatively high conversion of 58% at room temperature (25 °C) with a TOF of 310 h^-1 , which has been hardly achieved previously. Through both experimental and theoretical investigation, it is demonstrated that the fast electron transfer from Fe to Pt in Fe-Pt-O atomic sites in PFARFNs can not only stabilize the single-atomic Pt, but also significantly improve their catalytic activity.

Understanding the Copper-Iridium Nanocrystals as Highly Effective Bifunctional pH-universal Electrocatalysts for Water Splitting

It is pivotal to develop an economical, effective, and stable catalyst to promote the oxygen/hydrogen evolution reaction (OER/HER) throughout pH electrolytes, as the demand for hydrogen energy will increase greatly with the future development. Herein, a series of Ir-Cu nanoparticle composite carbon (Ir_xCu_y/C) catalysts are successfully synthesized using ethylene glycol reduction. In addition, the structure, morphology and composition of the electrocatalysts were systematically characterized, and the OER/HER performance of the catalysts was also tested under different pH conditions. According to experimental findings, amorphous Ir₃Cu/C has superior competent performance to catalyze oxygen (O₂) production in alkaline and acidic environments. The comparatively low overpotentials required are 222 mV and 304 mV, respectively, while generating a current density of 10 mA cm^-2. The reduced amount of precious metal and the further improvement in activity and durability make Ir₃Cu/C an excellent noble metal-based electrocatalyst. Meanwhile, IrCu/C has significant electrocatalytic performance for the HER in acidic media.

Oxygen Vacancy Induced Strong Metal-Support Interactions on Ni/Ce0.8Zr0.2O2 Nanorod Catalysts for Promoting Steam Reforming of Toluene: Experimental and Computational Studies

To develop an efficient Ni-based steam reforming catalyst for tar removal from the products of biomass gasification, Ni/Ce_0.8Zr_0.2O₂ nanorods were designed. The Ni/Ce_0.8Zr_0.2O₂ nanorod was used as a catalyst in steam reforming of toluene, which was regarded as a model compound of biomass gasification tar. At gas hourly space velocity (GHSV) of 24,000 h^-1 and Ni loading of 5 wt %, the 5Ni/Ce_0.8Zr_0.2O₂ nanorod catalyst achieved 100% of toluene conversion at 600 °C. After 10 h of operation, toluene conversion still reached 87.6%, and the carbon deposition rate was only 1.9 mg/g_cat h^-1. The experimental results demonstrated that the 5Ni/Ce_0.8Zr_0.2O₂ nanorod catalyst showed much higher catalytic activity and coking resistance than other Ni-based catalysts reported in the literature. Through different characterization technologies and density functional theory calculations, it was confirmed that the excellent catalytic performance was attributed to the strong metal-support interaction (SMSI) between Ni and the {100} facet of Ce_0.8Zr_0.2O₂. The special surface structure of {100} allowed Ni atoms to anchor to the surface oxygen vacancies and maintained its reduced state by electron transport between surface atoms. The anchored Ni facilitated oxygen vacancies formation and H₂O dissociation on the support, while the support modulated the electronic structure of Ni, which promoted its ability to toluene activation.

Confinement Effects in Well-Defined Metal-Organic Frameworks (MOFs) for Selective CO2 Hydrogenation: A Review

Decarbonization has become an urgent affair to restrain global warming. CO₂ hydrogenation coupled with H₂ derived from water electrolysis is considered a promising route to mitigate the negative impact of carbon emission and also promote the application of hydrogen. It is of great significance to develop catalysts with excellent performance and large-scale implementation. In the past decades, metal-organic frameworks (MOFs) have been widely involved in the rational design of catalysts for CO₂ hydrogenation due to their high surface areas, tunable porosities, well-ordered pore structures, and diversities in metals and functional groups. Confinement effects in MOFs or MOF-derived materials have been reported to promote the stability of CO₂ hydrogenation catalysts, such as molecular complexes of immobilization effect, active sites in size effect, stabilization in the encapsulation effect, and electron transfer and interfacial catalysis in the synergistic effect. This review attempts to summarize the progress of MOF-based CO₂ hydrogenation catalysts up to now, and demonstrate the synthetic strategies, unique features, and enhancement mechanisms compared with traditionally supported catalysts. Great emphasis will be placed on various confinement effects in CO₂ hydrogenation. The challenges and opportunities in precise design, synthesis, and applications of MOF-confined catalysis for CO₂ hydrogenation are also summarized.

Engineering nanoscale H supply chain to accelerate methanol synthesis on ZnZrOx

Metal promotion is the most widely adopted strategy for enhancing the hydrogenation functionality of an oxide catalyst. Typically, metal nanoparticles or dopants are located directly on the catalyst surface to create interfacial synergy with active sites on the oxide, but the enhancement effect may be compromised by insufficient hydrogen delivery to these sites. Here, we introduce a strategy to promote a ZnZrO_x methanol synthesis catalyst by incorporating hydrogen activation and delivery functions through optimized integration of ZnZrO_x and Pd supported on carbon nanotube (Pd/CNT). The CNT in the Pd/CNT + ZnZrO_x system delivers hydrogen activated on Pd to a broad area on the ZnZrO_x surface, with an enhancement factor of 10 compared to the conventional Pd-promoted ZnZrO_x catalyst, which only transfers hydrogen to Pd-adjacent sites. In CO₂ hydrogenation to methanol, Pd/CNT + ZnZrO_x exhibits drastically boosted activity-the highest among reported ZnZrO_x-based catalysts-and excellent stability over 600 h on stream test, showing potential for practical implementation.

Engineering Heterogeneous Catalysis with Strong Metal-Support Interactions: Characterization, Theory and Manipulation

Strong metal-support interactions (SMSI) represent a classic yet fast-growing area in catalysis research. The SMSI phenomenon results in the encapsulation and stabilization of metal nanoparticles (NPs) with the support material that significantly impacts the catalytic performance through regulation of the interfacial interactions. Engineering SMSI provides a promising approach to steer catalytic performance in various chemical processes, which serves as an effective tool to tackle energy and environmental challenges. Our Minireview covers characterization, theory, catalytic activity, dependence on the catalytic structure and inducing environment of SMSI phenomena. By providing an overview and outlook on the cutting-edge techniques in this multidisciplinary research field, we not only want to provide insights into the further exploitation of SMSI in catalysis, but we also hope to inspire rational designs and characterization in the broad field of material science and physical chemistry.

Insight into Key Parameters for Fabricating Stable Single-Atom Pt-Nix Alloy by Reduction Environment-Induced Anti-Ostwald Effects

Developing single-atom catalysts with superior stability under reduction conditions is essential for hydrogenation/dehydrogenation catalysis and green hydrogen generation. In this contribution, single-atom Pt catalysts were achieved via a reduction environment-induced anti-Ostwald approach in the highly confined Ni species (Pt-Ni_x ) on nonreducible Al₂ O₃ matrix. In-situ X-ray absorption spectroscopy indicated that the isolated Pt-Ni_x metallic bonds, generated at high reduction temperature, dominated the formation of single Pt atoms. A relatively large cluster of metallic Ni would benefit the stabilization of Pt single atom as observed via high-angle annular dark-field scanning transmission electron microscopy and validated by density functional theory simulation. Excellent performance on cellulose hydrogenolysis was demonstrated under harsh reductive and hydrothermal conditions, potentially expandable to other hydrogen involved reactions like CO₂ hydrogenation, green hydrogen production from different hydrogen carriers, and beyond.

Uncovering Structure-Activity Relationships in Pt/CeO2 Catalysts for Hydrogen-Borrowing Amination

The hydrogen-borrowing amination of alcohols is a promising route to produce amines. In this study, experimental parameters involved in the preparation of Pt/CeO₂ catalysts were varied to assess how physicochemical properties influence their performance in such reactions. An amination reaction between cyclopentanol and cyclopentylamine was used as the model reaction for this study. The Pt precursor used in the catalyst synthesis and the properties of the CeO₂ support were both found to strongly influence catalytic performance. Aberration corrected scanning transmission electron microscopy revealed that the most active catalyst comprised linearly structured Pt species. The formation of these features, a function result of epitaxial Pt deposition along the CeO₂ [100] plane, appeared to be dependent on the properties of the CeO₂ support and the Pt precursor used. Density functional theory calculations subsequently confirmed that these sites were more effective for cyclopentanol dehydrogenation-considered to be the rate-determining step of the process-than Pt clusters and nanoparticles. This study provides insights into the desirable catalytic properties required for hydrogen-borrowing amination but has relevance to other related fields. We consider that this study will provide a foundation for further study in this atom-efficient area of chemistry.

Thermal-Driven Optimization of the Strong Metal-Support Interaction of a Platinum-Manganese Oxide Octahedral Molecular Sieve to Promote Toluene Oxidation: Effect of the Interface Pt2+-Ov-Mnδ. ACS APPLIED MATERIALS & INTERFACES 2022;14:56790-56800. [PMID: 36524882 DOI: 10.1021/acsami.2c16923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Strong metal-support interactions (SMSIs) have a significant effect on the performance of supported noble-metal catalysts for volatile organic compound (VOC) elimination. Herein, the strength of the SMSI of Pt/OMS-2 between Pt and the OMS-2 support is regulated by simply changing calcination temperatures, and the catalyst calcined at 300 °C (Pt/OMS-2-300) performs the best in the catalytic combustion of toluene. Through systematic structural characterizations, it is revealed that much more Pt²⁺-O_v-Mn^δ+ species are formed in Pt/OMS-2-300, which can help facilitate the generation of more reactive oxygen species and promote lattice oxygen mobility. Moreover, the results of in situ DRIFTS experiments further confirm that abundant Pt²⁺-O_v-Mn^δ+ species at the Pt-MnO₂ interface on Pt/OMS-2-300 can better enhance the adsorption and activation of toluene, thus boosting the catalytic performance in toluene combustion. This newly developed strategy of thermal-driven regulation of the SMSI provides a novel perspective for constructing highly efficient catalysts for VOC emission control.

Ordered Mesopore Confined Pt Nanoclusters Enable Unusual Self-Enhancing Catalysis

As an important kind of emerging heterogeneous catalyst for sustainable chemical processes, supported metal cluster (SMC) catalysts have received great attention for their outstanding activity; however, the easy aggregation of metal clusters due to their migration along the substrate's surface usually deteriorates their activity and even causes catalyst failure during cycling. Herein, stable Pt nanoclusters (NCs, ∼1.06 nm) are homogeneously confined in the uniform spherical mesopores of mesoporous titania (mpTiO2) by the interaction between Pt NCs and metal oxide pore walls made of polycrystalline anatase TiO2. The obtained Pt-mpTiO2 exhibits excellent stability with well-retained CO conversion (∼95.0%) and Pt NCs (∼1.20 nm) in the long term water-gas shift (WGS) reaction. More importantly, the Pt-mpTiO2 displays an unusual increasing activity during the cyclic catalyzing WGS reaction, which was found to stem from the in situ generation of interfacial active sites (Ti3+-Ov-Ptδ+) by the reduction effect of spillover hydrogen generated at the stably supported Pt NCs. The Pt-mpTiO2 catalysts also show superior performance toward the selective hydrogenation of furfural to 2-methylfuran. This work discloses an efficient and robust Pt-mpTiO2 catalyst and systematically elucidates the mechanism underlying its unique catalytic activity, which helps to design stable SMC catalysts with self-enhancing interfacial activity in sustainable heterogeneous catalysis.

Two-Step Conversion of CO2 to Light Olefins: Laboratory-Scale Demonstration and Scale-Up Considerations

The highly selective production of light olefins from CO2 was demonstrated for the first time with a laboratory-scale process comprising consecutive reverse water gas shift (RWGS) and Fischer–Tropsch (FT) reactors. The RWGS reaction, catalyzed by rhodium washcoated catalyst at 850 °C yielded good quality syngas with conversion values close to the thermodynamic equilibrium and without experiencing catalyst deactivation from carbon formation or sintering. For the FT synthesis, a packed bed Fe-Na-S/α-Al2O3 catalyst was used. The highest light olefin selectivity observed for the FT-synthesis was 52% at 310 °C, GHSV of 2250 h−1 and H2/CO ratio of 1. However, the optimal conditions for the light olefin production were determined to be at 340 °C, a GHSV of 3400 h−1 and a H2/CO ratio of 2, as the CO conversion was markedly higher, while the light olefin selectivity remained at a suitably high level. In addition to the experimental results, considerations for the further optimization and development of the system are presented. The combined RWGS–FT process seems to work reasonably well, and initial data for basic process design and modeling were produced.

A Comprehensive Review on Graphitic Carbon Nitride for Carbon Dioxide Photoreduction

Inspired by natural photosynthesis, harnessing the wide range of natural solar energy and utilizing appropriate semiconductor-based catalysts to convert carbon dioxide into beneficial energy species, for example, CO, CH₄ , HCOOH, and CH₃ COH have been shown to be a sustainable and more environmentally friendly approach. Graphitic carbon nitride (g-C₃ N₄ ) has been regarded as a highly effective photocatalyst for the CO₂ reduction reaction, owing to its cost-effectiveness, high thermal and chemical stability, visible light absorption capability, and low toxicity. However, weaker electrical conductivity, fast recombination rate, smaller visible light absorption window, and reduced surface area make this catalytic material unsuitable for commercial photocatalytic applications. Therefore, certain procedures, including elemental doping, structural modulation, functional group adjustment of g-C₃ N₄ , the addition of metal complex motif, and others, may be used to improve its photocatalytic activity towards effective CO₂ reduction. This review has investigated the scientific community's perspectives on synthetic pathways and material optimization approaches used to increase the selectivity and efficiency of the g-C₃ N₄ -based hybrid structures, as well as their benefits and drawbacks on photocatalytic CO₂ reduction. Finally, the review concludes a comparative discussion and presents a promising picture of the future scope of the improvements.

Switchable Tuning CO2 Hydrogenation Selectivity by Encapsulation of the Rh Nanoparticles While Exposing Single Atoms

The switch of CO₂ hydrogenation selectivity from CH₄ to CO over TiO₂ supported Rh catalysts is accomplished via selective encapsulation of Rh nanoparticles while exposing Rh single atoms by high-temperature reduction (HTR) according to their different strong metal-support interaction (SMSI) occurrence conditions, which can be reversed by subsequent oxidation treatment.

Metal-Metal Oxide Catalytic Interface Formation and Structural Evolution: A Discovery of Strong Metal-Support Bonding, Ordered Intermetallics, and Single Atoms

In-depth investigation of metal-metal oxide interactions and their corresponding evolution is of paramount importance to heterogeneous catalysis as it allows the understanding and maneuvering of the structure of catalytic motifs. Herein, using a series of core/shell metal/iron oxide (M/FeO_x, M = Pd, Pt, Au) nanoparticles and through a combination of in situ and ex situ electron and X-ray investigations, we revealed anomalous and dissimilar M-FeO_x interactions among different systems under reducing conditions. Pd interacts strongly with FeO_x after high-temperature reductive treatment, featured by the formation of Pd single atoms in the FeO_x matrix and increased Pd-Fe bonding, while Pt transforms into ordered PtFe intermetallics and Pt single atoms immediately upon the coating of FeO_x. In contrast, Au does not manifest strong bonding with FeO_x. As a proof of concept of tailoring metal-metal oxide interactions for catalysis, optimized Pd/FeO_x demonstrates 100% conversion and 86.5% selectivity at 60 °C for acetylene semihydrogenation.

Atomic-Scale Structure Dynamics of Nanocrystals Revealed By In Situ and Environmental Transmission Electron Microscopy

Nanocrystals are of great importance in material sciences and industry. Engineering nanocrystals with desired structures and properties is no doubt one of the most important challenges in the field, which requires deep insight into atomic-scale dynamics of nanocrystals during the process. The rapid developments of in situ transmission electron microscopy (TEM), especially environmental TEM, reveal insights into nanocrystals to digest. According to the considerable progress based on in situ electron microscopy, a comprehensive review on nanocrystal dynamics from three aspects: nucleation and growth, structure evolution, and dynamics in reaction conditions are given. In the nucleation and growth part, existing nucleation theories and growth pathways are organized based on liquid and gas-solid phases. In the structure evolution part, the focus is on in-depth mechanistic understanding of the evolution, including defects, phase, and disorder/order transitions. In the part of dynamics in reaction conditions, solid-solid and gas-solid interfaces of nanocrystals in atmosphere are discussed and the structure-property relationship is correlated. Even though impressive progress is made, additional efforts are required to develop the integrated and operando TEM methodologies for unveiling nanocrystal dynamics with high spatial, energy, and temporal resolutions.

Controllable Construction of IrCo Nanoclusters and the Performance for Water Electrolysis

Finding a suitable catalyst is an important research direction in hydrogen (H2) production from water electrolysis. We report a synthetic method to obtain IrxCo/C clusters by polyol reduction. The catalyst is small in size and can be evenly distributed. The Ir3Co/C cluster catalyst had very good activity under acidic conditions. The overpotential of the best-performing Ir3Co/C cluster for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is only 290 mV and 91 mV when 10 mA cm−2 and 100 mA cm−2. The catalyst performance may be improved because of the synergistic effect and the small size of the prepared catalyst, which accelerates proton transfer. This approach offers a strategy to reduce costs while improving catalytic activity.