Active, Selective, and Durable Catalyst for Alkane Dehydrogenation Based on a Well-Designed Trimetallic Alloy

High-entropy intermetallics: emerging inorganic materials for designing high-performance catalysts

Alloy materials have been used as promising platforms to upgrade catalytic performance that cannot be achieved with conventional monometallic materials. As a result of numerous efforts, the recent progress in the field of alloy catalysis has been remarkable, and a wide range of new advanced alloys have been considered as potential electro/thermal catalysts. Among advanced alloy materials, high-entropy intermetallics are novel materials, and their excellent catalytic performance has recently been reported. High-entropy intermetallics have several advantages over disordered solid-solution high-entropy alloys, that is, greater structural/thermal stability, more facile site isolation, more precise control of electronic structures, tunability, and multifunctionality. A multidimensional compositional space is indeed limitless, but such a compositional space also provides a well-designed surface configuration because of its ordered nature. In this review, we will provide fundamental insights into high-entropy intermetallics, including thermodynamic properties, synthesis requirements, characterization techniques, roles in catalysis, and reaction examples. The comprehensive information provided in this review will highlight the great application potential of high-entropy intermetallics for catalysis, and will accelerate the development of this newly developed field.

Unveiling Atomic-Scaled Local Chemical Order of High-Entropy Intermetallic Catalyst for Alkyl-Substitution-Dependent Alkyne Semihydrogenation

High-entropy intermetallic (HEI) nanocrystals, composed of multiple elements with an ordered structure, are of immense interest in heterogeneous catalysis due to their unique geometric and electronic structures and the cocktail effect. Despite tremendous efforts dedicated to regulating the metal composition and structures with advanced synthetic methodologies to improve the performance, the surface structure, and local chemical order of HEI and their correlation with activity at the atomic level remain obscure yet challenging. Herein, by determining the three-dimensional (3D) atomic structure of quinary PdFeCoNiCu (PdM) HEI using atomic-resolution electron tomography, we reveal that the local chemical order of HEI regulates the surface electronic structures, which further mediates the alkyl-substitution-dependent alkyne semihydrogenation. The 3D structures of HEI PdM nanocrystals feature an ordered (intermetallic) core enclosed by a disordered (solid-solution) shell rather than an ordered surface. The lattice mismatch between the core and shell results in apparent near-surface distortion. The chemical order of the intermetallic core increases with annealing temperature, driving the electron redistribution between Pd and M at the surface, but the surface geometrical (chemically disordered) configurations and compositions are essentially unchanged. We investigate the catalytic performance of HEI PdM with different local chemical orders toward semihydrogenation across a broad range of alkynes, finding that the electron density of surface Pd and the hindrance effect of alkyl substitutions on alkynes are two key factors regulating selective semihydrogenation. We anticipate that these findings on surface atomic structure will clarify the controversy regarding the geometric and/or electronic effects of HEI catalysts and inspire future studies on tuning local chemical order and surface engineering toward enhanced catalysts.

Highly Efficient Iridium-Iron-Molybdenum Catalysts Condensed on Boron Nitride for Biomass-Derived Diols' Hydrogenolysis to Secondary Monoalcohols

A trade-off of activity-selectivity exists in primary C-O hydrogenolysis of biomass-derived diols to secondary alcohols over bimetallic catalysts, especially the combination of noble metal and early transition metal in the metallic state and metal oxide state, respectively. Herein, the combination of high surface concentration of boron nitride (BN)-supported metals and the addition of Mo as third metal broke the trade-off. High yields (>50%) of secondary alcohols were obtained with robust productivity up to 25-fold based on Ir over Ir-Fe0.13-Mo0.08/BN (Ir = 20 wt %, Fe/Ir = 0.13, Mo/Ir = 0.08) than previously reported Ir-Fe catalysts. In contrast, simply increasing the loading amount of Ir-Fe catalysts or the addition of Mo species only enhanced the productivity by <2-4-fold. Various characterizations showed that large Ir loading enables the formation of condensed nanostructures (∼2 nm) on the BN support, which further alloy with Mo and Fe to form an face centred cubic (fcc)-type trimetallic alloy with surface enrichment of Fe. On the other hand, in Ir-Fe0.25-Mo0.08/BN with lower Ir (5 wt %) and lower Ir-based activity, the Mo species were rather bound on the support surface possibly as the MoBx state. These structures were formed by simple impregnation and reduction with H2 at the reaction temperature (453 K). The high activity of Ir-Fe0.13-Mo0.08/BN (20 wt % Ir) is derived from two aspects: (1) the formation of condensed nanostructures (∼2 nm) exposing more active sites and (2) alloying with Mo to modify the electronic state of Ir to enhance the H2 activation ability, as shown by the decreased Ea (82-84 → 67 kJ mol-1).

Recent Advances in Reversible Liquid Organic Hydrogen Carrier Systems: From Hydrogen Carriers to Catalysts

Liquid organic hydrogen carriers (LOHCs) have gained significant attention for large-scale hydrogen storage due to their remarkable gravimetric hydrogen storage capacity (HSC) and compatibility with existing oil and gas transportation networks for long-distance transport. However, the practical application of reversible LOHC systems has been constrained by the intrinsic thermodynamic properties of hydrogen carriers and the performances of associated catalysts in the (de)hydrogenation cycles. To overcome these challenges, thermodynamically favored carriers, high-performance catalysts, and catalytic procedures need to be developed. Here, significant advances in recent years have been summarized, primarily centered on regular LOHC systems catalyzed by homogeneous and heterogeneous catalysts, including dehydrogenative aromatization of cycloalkanes to arenes and N-heterocyclics to N-heteroarenes, as well as reverse hydrogenation processes. Furthermore, with the development of metal complexes for dehydrogenative coupling, a new family of reversible LOHC systems based on alcohols is described that can release H2 under relatively mild conditions. Finally, views on the next steps and challenges in the field of LOHC technology are provided, emphasizing new resources for low-cost hydrogen carriers, high-performance catalysts, catalytic technologies, and application scenarios.

Identifying Noble Metal Catalysts for the Hydrogenation and Dehydrogenation of Dibenzyltoluene: A Combined Theoretical-Experimental Study

We present a comprehensive theoretical and experimental investigation of the hydrogenation and dehydrogenation of dibenzyltoluene (DBT) using Pd-, Pt-, Ru-, and Rh-supported metal catalysts to identify the optimal catalysts for hydrogen storage and release processes. Our results demonstrated significant variation in the catalytic activity of the metal catalysts. 5 wt % Rh/Al2O3 and 5 wt % Pt/Al2O3 showed the highest activity for hydrogenation and dehydrogenation with the highest selectivity and turnover frequency (TOF), respectively. Conversely, 5 wt % Pd/Al2O3 and 5 wt % Ru/Al2O3 exhibited lower catalytic activity toward full hydrogenation and dehydrogenation. Rh/Al2O3 showed the best catalytic hydrogenation activity with a TOF of 26.49 h-1 and a hydrogenation degree of 92.69% in 2 h, while Pt/Al2O3 exhibited the best catalytic dehydrogenation activity with a released H2 volume of 3755 mL, a dehydrogenation degree of 78.23%, and a TOF of 39.56 h-1 in 2 h. Additionally, we estimated the activation energies for hydrogenation and dehydrogenation to be 67.20 and 82.78 kJ/mol, respectively. Notably, the produced hydrogen gas was of high purity and suitable for use in fuel cells. Density functional theory (DFT) calculations were used to analyze the adsorption structure and reaction energy changes of all intermediate products of DBT on the surface of the chosen catalysts. Our research provides valuable insights into developing efficient catalysts for liquid organic hydrogen carriers.

Ethane Dehydrogenation over the Core-Shell Pt-Based Alloy Catalysts: Driven by Engineering the Shell Composition and Thickness

Pt-based catalysts as the commercial catalysts in ethane dehydrogenation (EDH) face one of the main challenges of realizing the balance between coke formation and catalytic activity. In this work, a strategy to drive the catalytic performance of EDH on Pt-Sn alloy catalysts is proposed by rationally engineering the shell surface structure and thickness of core-shell Pt@Pt₃Sn and Pt₃Sn@Pt catalysts from a theoretical perspective. Eight types of Pt@Pt₃Sn and Pt₃Sn@Pt catalysts with different Pt and Pt₃Sn shell thicknesses are considered and compared with the industrially used Pt and Pt₃Sn catalysts. Density functional theory (DFT) calculations completely describe the reaction network of EDH, including the side reactions of deep dehydrogenation and C-C bond cracking. Kinetic Monte Carlo (kMC) simulations reveal the influences of the catalyst surface structure, experimentally related temperatures, and reactant partial pressures. The results show that CHCH* is the main precursor for coke formation, and Pt@Pt₃Sn catalysts generally have higher C₂H₄(g) activity and lower selectivity compared to those of Pt₃Sn@Pt catalysts, which is attributed to the unique surface geometrical and electronic properties. 1Pt₃Sn@4Pt and 1Pt@4Pt₃Sn are screened out as catalysts exhibiting excellent performance; especially, the 1Pt₃Sn@4Pt catalyst has much higher C₂H₄(g) activity and 100% C₂H₄(g) selectivity compared to those of 1Pt@4Pt₃Sn and the widely used Pt and Pt₃Sn catalysts. The two descriptors C₂H₅* adsorption energy and reaction energy of its dehydrogenation to C₂H₄* are proposed to qualitatively evaluate the C₂H₄(g) selectivity and activity, respectively. This work facilitates a valuable exploration for optimizing the catalytic performance of core-shell Pt-based catalysts in EDH and reveals the great importance of the fine control of the catalyst shell surface structure and thickness.

Alloying effect of Ni-Mo catalyst in hydrogenation of N-ethylcarbazole for hydrogen storage

Liquid organic hydrogen storage with N-ethylcarbazole (NEC) as a carrier is a very promising method. The use of precious metal hydrogenation catalysts restricts the development in industrial grade. Efficient and low-cost hydrogen storage catalysts are essential for its application. In this work, a Ni-Mo alloy catalyst supported by commercial activated carbon was synthesized by impregnation method, and the Ni-Mo ratio and preparation conditions were optimized. The catalyst was characterized by XRD, XPS, H₂-TPR, SEM, and TEM. The results showed that the doping of Mo could dramatically promote the catalytic hydrogenation of N-ethylcarbazole by the Ni-based catalyst. More than 5.75 wt% hydrogenation could be achieved in 4 h using the Ni-Mo catalyst, and the selectivity of the fully hydrogenated product 12H-NEC could be effectively improved. This result reduces the cost of hydrogenation catalysts by more than 90% and makes liquid organic hydrogen storage a scaled possibility.

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

High-Entropy Intermetallics Serve Ultrastable Single-Atom Pt for Propane Dehydrogenation

Propane dehydrogenation has been a promising propylene production process that can compensate for the increasing global demand for propylene. However, Pt-based catalysts with high stability at ≥600 °C have barely been reported because the catalysts typically result in short catalyst life owing to side reactions and coke formation. Herein, we report a new class of heterogeneous catalysts using high-entropy intermetallics (HEIs). Pt-Pt ensembles, which cause side reactions, are entirely diluted by the component inert metals in PtGe-type HEIs. The resultant HEI (PtCoCu) (GeGeSn)/Ca-SiO₂ exhibited an outstandingly high catalytic stability, even at 600 °C (k_d^-1 = τ = 4146 h = 173 d), and almost no deactivation of the catalyst was observed for 2 months for the first time. Detailed experimental studies and theoretical calculations demonstrated that the combination of the site-isolation and entropy effects upon multi-metallization of PtGe drastically enhanced the desorption of propylene and the thermal stability, eventually suppressing the side reactions even at high reaction temperatures.

Heterogeneous Trimetallic Nanoparticles as Catalysts

The development and application of trimetallic nanoparticles continues to accelerate rapidly as a result of advances in materials design, synthetic control, and reaction characterization. Following the technological successes of multicomponent materials in automotive exhausts and photovoltaics, synergistic effects are now accessible through the careful preparation of multielement particles, presenting exciting opportunities in the field of catalysis. In this review, we explore the methods currently used in the design, synthesis, analysis, and application of trimetallic nanoparticles across both the experimental and computational realms and provide a critical perspective on the emergent field of trimetallic nanocatalysts. Trimetallic nanoparticles are typically supported on high-surface-area metal oxides for catalytic applications, synthesized via preparative conditions that are comparable to those applied for mono- and bimetallic nanoparticles. However, controlled elemental segregation and subsequent characterization remain challenging because of the heterogeneous nature of the systems. The multielement composition exhibits beneficial synergy for important oxidation, dehydrogenation, and hydrogenation reactions; in some cases, this is realized through higher selectivity, while activity improvements are also observed. However, challenges related to identifying and harnessing influential characteristics for maximum productivity remain. Computation provides support for the experimental endeavors, for example in electrocatalysis, and a clear need is identified for the marriage of simulation, with respect to both combinatorial element screening and optimal reaction design, to experiment in order to maximize productivity from this nascent field. Clear challenges remain with respect to identifying, making, and applying trimetallic catalysts efficiently, but the foundations are now visible, and the outlook is strong for this exciting chemical field.

Reversible dehydrogenation and rehydrogenation of cyclohexane and methylcyclohexane by single-site platinum catalyst

Developing highly efficient and reversible hydrogenation-dehydrogenation catalysts shows great promise for hydrogen storage technologies with highly desirable economic and ecological benefits. Herein, we show that reaction sites consisting of single Pt atoms and neighboring oxygen vacancies (V_O) can be prepared on CeO₂ (Pt₁/CeO₂) with unique catalytic properties for the reversible dehydrogenation and rehydrogenation of large molecules such as cyclohexane and methylcyclohexane. Specifically, we find that the dehydrogenation rate of cyclohexane and methylcyclohexane on such sites can reach values above 32,000 mol_H2 mol_Pt⁻¹ h⁻¹, which is 309 times higher than that of conventional supported Pt nanoparticles. Combining of DRIFTS, AP-XPS, EXAFS, and DFT calculations, we show that the Pt₁/CeO₂ catalyst exhibits a super-synergistic effect between the catalytic Pt atom and its support, involving redox coupling between Pt and Ce ions, enabling adsorption, activation and reaction of large molecules with sufficient versatility to drive abstraction/addition of hydrogen without requiring multiple reaction sites.

Developing highly efficient and reversible hydrogenation-dehydrogenation catalysts shows great promise for hydrogen storage technologies. Here the authors develop a highly efficient and reversible de/rehydrogenation single-site platinum catalyst which exhibits great promise for hydrogen storage technologies with cyclic alkanes/aromatics as liquid organic hydrogen carriers.

Tailoring Single-Atom Platinum for Selective and Stable Catalysts in Propane Dehydrogenation

Propane dehydrogenation has been a promising method for producing propylene that has the potentials to meet the increasing global demand for propylene. However, owing to the restricted equilibrium conversion caused by the high endothermicity, even the Pt-based catalysts, which exhibit high activity and selectivity, severely suffer significantly from coke formation and/or nanoparticle sintering at realistic reaction temperatures, resulting in a short catalyst lifetime. As a result, few innovative catalysts in terms of catalytic activity, selectivity, and stability, have been produced. In this Review, we focus on the characteristics of single-atom-like Pt sites for PDH and attempt to provide suggestions for developing highly efficient catalysts. First, we briefly describe the fundamental strategies. Following that, the remarkable catalysis is addressed by three different distinct sorts of state-of-the-art single-atom-like Pt catalysts are discussed. Additionally, we present other promising catalyst design approaches that are not based on single-atom-like Pt catalysts, as well as future research challenges in this field.

Synthesis and potential applications of trimetallic nanostructures

The present review highlights the synthetic strategies and potential applications of TMNs for organic reactions, environmental remediation, and health-related activities.

Recent Advances in Catalysts and Membranes for MCH Dehydrogenation: A Mini Review

Methylcyclohexane (MCH), one of the liquid organic hydrogen carriers (LOHCs), offers a convenient way to store, transport, and supply hydrogen. Some features of MCH such as its liquid state at ambient temperature and pressure, large hydrogen storage capacity, its well-known catalytic endothermic dehydrogenation reaction and ease at which its dehydrogenated counterpart (toluene) can be hydrogenated back to MCH and make it one of the serious contenders for the development of hydrogen storage and transportation system of the future. In addition to advances on catalysts for MCH dehydrogenation and inorganic membrane for selective and efficient separation of hydrogen, there are increasing research interests on catalytic membrane reactors (CMR) that combine a catalyst and hydrogen separation membrane together in a compact system for improved efficiency because of the shift of the equilibrium dehydrogenation reaction forwarded by the continuous removal of hydrogen from the reaction mixture. Development of efficient CMRs can serve as an important step toward commercially viable hydrogen production systems. The recently demonstrated commercial MCH-TOL based hydrogen storage plant, international transportation network and compact hydrogen producing plants by Chiyoda and some other companies serves as initial successful steps toward the development of full-fledged operation of manufacturing, transportation and storage of zero carbon emission hydrogen in the future. There have been initiatives by industries in the development of compact on-board dehydrogenation plants to fuel hydrogen-powered locomotives. This review mainly focuses on recent advances in different technical aspects of catalytic dehydrogenation of MCH and some significant achievements in the commercial development of MCH-TOL based hydrogen storage, transportation and supply systems, along with the challenges and future prospects.

Synthesis of Co2FeGe Heusler alloy nanoparticles and catalysis for selective hydrogenation of propyne

Although intermetallic compounds are attracting attention of catalysis researchers, ternary intermetallic catalysts have scarcely been investigated due the difficulty of synthesizing supported nanoparticles. In this study, we successfully synthesized SiO₂ supported Co₂FeGe Heuslar alloy nanoparticles. This catalyst exhibited high catalytic performance for selective hydrogenation of propyne by nano-sizing.

Supported nanoparticles of Co₂FeGe Heusler alloy were successfully synthesized. The reaction rate per weight was increased 2000 times by nano-sizing.

Durability and activity of Co2YZ (Y = Mn or Fe, Z = Ga or Ge) Heusler alloy catalysts for dehydrogenation of 2-propanol

Using dehydrogenation of 2-propanol as a test reaction for Heusler alloy catalysts, durability against oxidation and a relationship between activity and electronic structures were revealed.