New Class Of Catalysts Research Articles

Better Together: Synergic Effect of Gallium‐Based Catalyst and Porous Support for Reduction Reactions

Liquid metal solutions are a new class of catalysts with outstanding properties in terms of catalytic conversion and resistance to coking. Finding the perfect combination of catalytic particles with homogeneous size distribution and support material able to stabilize them during catalysis is key for preparing model systems to gain understanding of these complex catalytic processes. In this work, we present a method for the preparation of small and narrowly distributed gallium‐palladium particles supported on inverse opals, interconnected 3‐dimensional porous networks with a very narrow pore size distribution. Our platform is a promising candidate as supported liquid metal catalytic system thanks to its permeability to fluids and its confined pore environment, which prevents the coalescence of the metal alloy, thus maximizing the surface area available for the catalytic reaction. We demonstrate their enhanced performance when compared to other state of the art systems giving a proof of concept of their application as catalysts for a simple model reaction, the reduction of methylene blue.

Encapsulating Transition Metal Nanoparticles inside Carbon (TM@C) Chainmail Catalysts for Hydrogen Evolution Reactions: A Review

Green hydrogen energy from electrocatalytic hydrogen evolution reactions (HERs) has gained much attention for its advantages of low carbon, high efficiency, interconnected energy medium, safety, and controllability. Non-precious metals have emerged as a research hotspot for replacing precious metal catalysts due to low cost and abundant reserves. However, maintaining the stability of non-precious metals under harsh conditions (e.g., strongly acidic, alkaline environments) remains a significant challenge. By leveraging the curling properties of two-dimensional materials, a new class of catalysts, encapsulating transition metal nanoparticles inside carbon (TM@C) chainmail, has been successfully developed. This catalyst can effectively isolate the active metal from direct contact with harsh reaction media, thereby delaying catalyst deactivation. Furthermore, the electronic structure of the carbon layer can be regulated through the transfer of electrons, which stimulates its catalytic activity. This addresses the issue of the insufficient stability of traditional non-precious metal catalysts. This review commences with a synopsis of the synthetic advancement of the engineering of TM@C chainmail catalysts. Thereafter, a critical discussion ensues regarding the electrocatalytic performance of TM@C chainmail catalysts during hydrogen production. Ultimately, a comprehensive review of the conformational relationship between the structure of TM@C chainmail catalysts and HER activity is provided, offering substantial support for the large-scale application of hydrogen energy.

Cellulose pyrolysis via liquid metal catalysis

Liquid metals are largely unexplored as catalytic media for biomass conversion. Unlike conventional solid-state catalysts which are prone to deactivation, liquid metals, i.e., low-melting metals operated above their melting point, can show resilience against coking, high thermal conductivity, and enhanced liquid-solid contact between catalyst and biomass feedstocks. This promise motivated the present investigation of liquid metals as catalysts for cellulose pyrolysis. Bismuth, tin, and indium were selected as liquid metal candidates, and their impact on cellulose devolatilization kinetics is studied via thermogravimetric analysis. The results indicate that all three metals show catalytic activity, with bismuth catalyzing volatiles formation, while indium and tin enhance char formation. Quantitative analysis of liquid product reveals that bismuth is selective to dehydration and functional rearrangement reactions, leading to anhydro sugars and functionalized furans formation. In contrast, indium and tin are selective towards dehydration, fragmentation reactions, and Diels Alder chemistry, leading to formation of C2-C4 fragments and aromatic compounds, as further confirmed via infrared spectroscopic analysis of the obtained chars. Finally, the Sn and Bi liquid metals’ stability against deactivation via coking is examined against conventional solid-state zeolite catalyst through multiple cellulose pyrolysis runs in the thermogravimetric analyzer (TGA) with the same batch of catalyst. While ZSM-5 zeolite catalyst's activity and selectivity declined and approached non-catalytic sand results (both the TGA curve and the liquid product distribution) within the first few runs, both Sn and Bi fairly maintained their robustness against coking for the conducted durability runs. Overall, the results show significant promise for this new class of catalysts for biomass pyrolysis.

Highly Stable Cesium Molybdenum Chloride Perovskite Nanocrystals for Photothermal Semihydrogenation Applications.

Metal halide perovskite materials with excellent carrier transport properties have been regarded as a new class of catalysts with great application potential. However, their development is hampered by their instability in polar solvents and high temperatures. Herein, we report a solution-processed Cs2MoCl6 perovskite nanocrystals (NCs) capped with the Mo6+, showing high thermostability in polar solvents. Furthermore, the Pd single atoms (PdSA) can be anchored on the surface of Cs2MoCl6 NCs through the unique coordination structure of Pd-Cl sites, which exhibit excellent semihydrogenation of different alkyne derivatives with high selectivity at full conversion at room temperature. Moreover, the activity could be improved greatly under Xe lamp irradiation. Detailed experimental characterization and DFT calculations indicate the improved activity under light illumination is due to the synergistic effect of photo-to-heat conversion and photoinduced electron transfer from Cs2MoCl6 to PdSA, which facilitates the activation of the C≡C group. This work not only provides a new catalyst for high selective semihydrogenation of alkyne derivatives but also opens a new avenue for metal halides as photothermal catalysts.

Tailoring the d-band center on Ru1Cu single-atom alloy nanotubes for boosting electrochemical non-enzymatic glucose sensing.

The development of cost-effective and highly efficient electrocatalysts is critical to help electrochemical non-enzymatic sensors achieve high performance. Here, a new class of catalyst, Ru single atoms confined on Cu nanotubes as asingle-atom alloy (Ru1Cu NTs), with aunique electronic structure and property, was developed to construct a novel electrochemical non-enzymatic glucose sensor for the first time. The Ru1Cu NTs with a diameter of about 24.0nm showed amuch lower oxidation potential (0.38V) and 9.0-fold higher response (66.5 μA) current than Cu nanowires (Cu NWs, oxidation potential 0.47V and current 7.4 μA) for glucose electrocatalysis. Moreover, as an electrochemical non-enzymatic glucose sensor, Ru1Cu NTs not only exhibited twofold higher sensitivity (54.9 μA mM-1cm-2) and wider linear range (0.5-8mM) than Cu NWs, but also showed alow detection limit (5.0μM), excellent selectivity, and great stability. According to theoretical calculation results, the outstanding catalytic and sensing performance of Ru1Cu NTs could be ascribed to the upshift of the d-band center that helped promote glucose adsorption. This work presents a new avenue for developing highly active catalysts for electrochemical non-enzymatic sensors.

Fast Charge‐Transfer Rates in Li‐CO2 Batteries with a Coupled Cation‐Electron Transfer Process

AbstractLi‐CO2 batteries with a high theoretical energy density (1876 Wh kg−1) have unique benefits for reversible carbon fixation for energy storage systems. However, due to lack of stable and highly active catalysts, the long‐term operation of Li‐CO2 batteries is limited to low current densities (mainly <0.2 mA cm−2) that are far from practical conditions. In this work, it is discovered that, with an ionic liquid‐based electrolyte, highly active and stable transition metal trichalcogenide alloy catalysts of Sb0.67Bi1.33X3 (X = S, Te) enable operation of the Li‐CO2 battery at a very high current rate of 1 mA cm−2 for up to 220 cycles. It is revealed that: i) the type of chalcogenide (Te vs S) significantly affects the electronic and catalytic properties of the catalysts, ii) a coupled cation‐electron charge transfer process facilitates the carbon dioxide reduction reaction (CO2RR) occurring during discharge, and iii) the concentration of ionic liquid in the electrolyte controls the number of participating CO2 molecules in reactions. A combination of these key factors is found to be crucial for a successful operation of the Li‐CO2 chemistry at high current rates. This work introduces a new class of catalysts with potential to fundamentally solve challenges of this type of batteries.

Rise of atomically dispersed metal catalysts: Are they a new class of catalysts?

AbstractAtomically dispersed metal catalysts or single‐atom catalysts have made great strides during the past decade in the catalysis field. While an initial vision of atomically dispersed metal catalysts was to combine the advantages of homogeneous and heterogeneous catalysts, their unexpected potentials continue to be discovered. In this account, we introduce historical backgrounds underpinning the emergence of atomically dispersed metal catalysts. Next, we illustrate some recent examples demonstrating the unusual reactivities of atomically dispersed metal catalysts, which are hard to realize by homogeneous or heterogeneous catalysts. We conclude the account by suggesting the remaining challenges in this exciting field.

Nickel Carbide Nanoparticle Catalyst for Selective Hydrogenation of Nitriles to Primary Amines.

Despite its unique physicochemical properties, the catalytic application of nickel carbide (Ni3 C) in organic synthesis is rare. In this study, we report well-defined nanocrystalline Ni3 C (nano-Ni3 C) as a highly active catalyst for the selective hydrogenation of nitriles to primary amines. The activity of the aluminum-oxide-supported nano-Ni3 C (nano-Ni3 C/Al2 O3 ) catalyst surpasses that of Ni nanoparticles. Various aromatic and aliphatic nitriles and dinitriles were successfully converted to the corresponding primary amines under mild conditions (1 bar H2 pressure). Furthermore, the nano-Ni3 C/Al2 O3 catalyst was reusable and applicable to gram-scale experiments. Density functional theory calculations suggest the formation of polar hydrogen species on the nano-Ni3 C surface, which were attributed to the high activity of nano-Ni3 C towards nitrile hydrogenation. This study demonstrates the utility of metal carbides as a new class of catalysts for liquid-phase organic reactions.

Effect of Polytetrafluorethylene Content in Fe‐N‐C‐Based Catalyst Layers of Gas Diffusion Electrodes for HT‐PEM Fuel Cell Applications

AbstractFe‐N‐C catalysts are a promising alternative to replace cost‐intensive Pt‐based catalysts in high temperature polymer electrolyte membrane fuel cell (HT‐PEMFC) electrodes. However, the electrode fabrication needs to be adapted for this new class of catalysts. In this study, gas diffusion electrodes (GDEs) are fabricated using a commercial Fe‐N‐C catalyst and different polytetrafluorethylene (PTFE) binder ratios, varying from 10 to 50 wt % in the catalyst layer (CL). The oxygen reduction reaction performance is investigated under HT‐PEMFC conditions (160 °C, conc. H3PO4 electrolyte) in a half‐cell setup. The acidophilic character of the Fe‐N‐C catalyst leads to intrusion of phosphoric acid electrolyte into the CL. The strength of the acid penetration depends on the PTFE content, which is visible via the contact angles. The 10 wt % PTFE GDE is less capable to withdraw product water and electrolyte and results into the lowest half‐cell performance. Higher PTFE contents counterbalance the acid drag into the CL and impede flooding. The power density at around 130 mA mgCatalyst−2 increases by 34 % from 10 to 50 wt % PTFE.

Superior catalytic action of high-entropy alloy on hydrogen sorption properties of MgH2

Magnesium hydride (MgH2) is the mostly used material for solid-state hydrogen storage. However, their slow kinetics and highly unfavorable thermodynamics make them unsuitable for the practical applications. The current study describes the unusual catalytic action of a new class of catalyst, a high-entropy alloy (HEA) of Al20Cr16Mn16Fe16Co16Ni16 and its leached version, on the de/re-hydrogenation properties of MgH2. The onset desorption temperature of MgH2 was reduced significantly from 360 °C (for ball-milled MgH2) to 338 °C when it was catalyzed with a leached HEA-based catalyst. On the other hand, a fast de/re-hydrogenation kinetics of MgH2 was observed during the addition of leached HEA-based catalyst. It absorbed ∼6.1 wt% of hydrogen in just 2 min at a temperature of 300 °C under 10 atm hydrogen pressure and desorbed ∼5.4 wt% within 40 min. At moderate temperatures and low pressure, the HEA-based catalyst reduced desorption temperatures and improved re-hydrogenation kinetics. Even after 25 cycles of de/re-hydrogenation, the storage capacity of MgH2 catalyzed with the leached version of HEA degrades negligibly.

Facial synthesis of the trimetallic Au-Pt-Pd nanofluids and performance for methylene blue degradation

The rapid expansion of the chemical industry leads to more environmental pollutants that are difficult to break down through traditional treatment methods. Therefore, it is crucial to introduce a new class of catalysts. The current study examines the simple production and catalytic abilities of Au-Pt-Pd nanofluids (NFs), promising agents for nano catalysts. We have used a one-pot microwave-assisted reduction approach to synthesize the trimetallic NFs. The UV–Vis spectroscopy results indicate that a clear single plasmon resonance peak of NFs has been identified within the 519–545 nm range. Furthermore, the morphological feature of the as-synthesized NFs has been analysed using a transmission electron microscope. The NFs have an average size of 9–12 nm and are spherical in shape. The analysis of the synthesized NFs by energy-dispersive X-ray spectroscopy indicates that they formed in the ratio of 1.3:1:4.3.

Studying, Promoting, Exploiting, and Predicting Catalyst Dynamics: the Next Frontier in Heterogeneous Catalysis

Developing heterogeneous catalysts involves continuous efforts in understanding and designing active sites with improved performance for various applications. In recent years, the recognition and appreciation of the dynamic nature of active sites has permeated the field, leading to renewed efforts in describing dynamic phenomena and exploiting them to go beyond classical barriers of catalyst performance. The challenges in this field are daunting, yet the rewards could lead to new classes of catalysts that outperform traditional systems for critical chemical transformations at the industrial scale. Furthermore, a deeper understanding of the dynamic nature of active sites can lead to fundamental knowledge of practical importance in the field. In this Perspective, we highlight this emerging area of catalysis science using recent examples to motivate the importance of understanding the dynamic nature of heterogeneous catalysts. We predict that this area of study will continue to expand, eventually allowing us to exploit dynamics to control catalytic performance in numerous applications.

Polymeric Carbon Nitride/Iron Oxide Composites: A Novel Class of Catalysts with Reduced Metal Content for Ammonium Perchlorate Thermal Decomposition.

The ever-growing number of space launches triggering an enormous release of metallic dead weight into the atmosphere has become a global concern. Despite technological advancements, the inclusion of environmental concerns in space research has become the need of the hour. Here, we report the impact of iron oxide (Fe2O3)-doped polymeric carbon nitride (gCN) composites with varying metal contents (namely, GF1, GF2, and GF3 with iron contents of 0.1, 0.25, and 2 mmol, respectively) as a new class of catalysts for ammonium perchlorate (AP) thermolysis. Morphology studies revealed the dendritic morphology of the synthesized Fe2O3, and X-ray photoelectron spectroscopy (XPS) analysis confirmed the effective interaction between Fe2O3 and gCN in the composites. Among all of the synthesized composites, GF2 shows superior catalytic competence toward AP decomposition by amalgamating the double-stage decomposition process into a single stage followed by a considerable decrease in the decomposition temperature. The kinetic parameters calculated for the thermal decomposition of AP with and without catalysts using the KAS method substantiated the above results by significantly reducing the activation energy from 173.2 to 151.7 kJ/mol. Later, thermogravimetric and mass-spectrometric (TG-MS) analysis gives a clear idea about the catalytic efficiency of the synthesized catalyst GF2 toward AP decomposition from the accelerated emission of decomposition products NO, NO2, Cl, HCl, Cl2, and N2O in the presence of GF2. In a nutshell, gCN/Fe2O3 will open up new horizons in the field of synthesis of new catalytic systems with minimal metal content for composite solid propellants.

(Digital Presentation) Highly Efficient and Selective CO2 Electroreduction to CO on Novel Metal-Nitrogen-Carbon (M-N-C) Catalyst

The electrocatalytic reduction of CO2 (CO2RR) to CO is an important component of emerging Carbon Capture and Utilization (CCU) technologies. This process often relies on expensive and rare metals such as silver and gold-based materials for high selectivity and conversion rate to CO1,2. It is desired to move away from these metals towards earth-abundant solid materials (e.g., carbon-based) which may serve as heterogeneous electrocatalysts for CO2RR. Herein, a series of novel carbon-based materials with exceptional selectivity/activity for the targeted production of CO is presented. This new class of hybrid catalyst materials have high CO2RR activity which is comparable to the state of the art atomically dispersed Metal-N-C synthesized by the sacrificial support method (SSM). The advantage of this new class of catalysts is that the use of harsh solvents such as nitric acid and potassium hydroxide which are usually required to remove the silica precursor is completely avoided. Not only does this make the immediate process more environmentally friendly, but it also significantly shortens the catalyst synthesis time which increases its industrial viability. The structure and activity of a series of catalysts with different metallic dopants (Fe, Co, Ni, Mn) are investigated. Using this new synthesis technique, a faradaic efficiency for CO formation (FEco) of 96.5 % at -0.3 V vs. RHE is achieved. FEco remains greater than 75 % over the potential range studied from -0.3 V to -1.1 V vs. RHE. By comparison, Fe-N-C by SSM method reaches a maximum FEco of 94.4 % at -0.7 V vs. RHE and FEco remains greater than 85 % over the same potential range.

MOF-based bimetallic diselenide nanospheres as a bifunctional efficient electrocatalysts for overall water splitting

The synthesis of an economical and efficient bifunctional electrocatalyst for general water splitting is necessary for the fabrication of eco-friendly H2 energy. Herein, state-of-the-art ZIF-67-based CoSe/MoSe2 hybrid nanospheres were synthesized and examined as a bifunctional electrocatalyst for Hydrogen evolution reaction (HER) and Oxygen evolution (OER) in basic media. For the first time, a hierarchical well-designed CoSe/MoSe2 hybrid nanospheres designed with the uniform distribution layered of 2D-MoSe2 and conductive CoSe nanoparticles are acquired from CoMoO4via selenization. Due to its large surface area and extraordinary morphology, it exhibited significant catalytic activity, which leads to a small overpotential of 110 mV for HER and for 240 mV OER along with low Tafel values of 54.24 and 51.98 mV dec−1, respectively. Surprisingly, the stability is marvelous and also comparable to the standard of HER and OER. The enhancement is endorsed by the increase in conductivity evolved from the porous nanospheres and the collaborative effect of Co/Mo. To deliver a current density of 10 mA per cm2 for full water splitting 1.56 V is required, which is one of the least reported voltages. Therefore, this work leads to a new class of catalysts for the fabrication of an efficient water electrolyzer.

Synthesis and Reactivity of Copper and Copper Containing Magnetically Separable Catalysts

AbstractThis review endeavours to summarize the emergence of magnetically separable catalysts as a new class of catalyst for the modern developments in the synthesis and reactivity of the nano‐sized magnetically separable copper and copper containing nanomaterials exploited as potent applicant in the field of material science not only for their widespread technological applications but also to realize the fundamentals of nano‐magnetism. This review covers extensively different catalytic reactivity for carbon‐carbon and carbon‐heteroatom bond formation reactions and emphasized on recent developments in the field.

Oxygen‐Functionalized Boron Nitride for the Oxidative Dehydrogenation of Propane – The Case for Supported Liquid Phase Catalysis

AbstractBoron and boron containing materials have created a new class of catalysts for the highly selective conversion of light alkanes to building block olefins. Boron oxide species seem to play an essential role for the oxidative dehydrogenation of propane. For boron nitride they are created through an induction process under reaction conditions. It is still not obvious how different kinds of oxidative pre‐activation influences the observed activity and selectivity. Here we compare two different oxygen activation strategies of boron nitride, a classical activation by calcination at different temperatures and ball‐milling with varying rotation velocity. These treatments allow to control the amount of introduced boron oxide species from 0.2 to 17.5 wt.‐%, as quantified by alkalimetric titration. The catalytic experimental data together with the pre, post as well as in situ characterization, give insights how the catalyst's surface changes under reaction conditions. On this backdrop it can be deduced that molten boron oxide predominantly acts as catalyst under reaction conditions, and boron nitride as catalyst support.

Insights into H2 Activation and Styrene Hydrogenation by Nickel–Borane and Nickel–Alane Bifunctional Catalysts

Lewis acid–transition metal bifunctional complexes have recently emerged as a new class of catalysts. The nickel–borane complex, Ni[(Mes)B(o-Ph2PC6H4)2], has been reported as an efficient catalyst for H2 activation and styrene hydrogenation. Here, we performed density functional theory calculations to investigate the cooperation between nickel and a group 13 element (Z = B and Al), including the effect of its substituent (R = Mes, Ph, and C6F5 in Ni[(R)Z(o-Ph2PC6H4)2]), on H2 activation and styrene hydrogenation. We found that H2 activation by the nickel–borane complex is dominated by charge transfer from the σ-bonding orbital of H2 to the p-based vacant orbital of boron, whereas H2 activation by the nickel–alane complex is governed by charge transfer from the d-based orbital of Ni to the σ*-antibonding orbital of H2. The resulting trans-dihydride nickel–alane complex has higher negative charges on both terminal and bridging hydrogen atoms than the corresponding nickel–borane complex. This accounts for the lower energy barriers observed for the nickel–alane complex toward both H2 activation and the subsequent hydrogenation of styrene. While the C6F5 electron-withdrawing substituent on boron of the nickel–borane complex facilitates H2 activation and styrene hydrogenation better than the phenyl or mesityl substituent, the substituent on aluminum does not affect the reactivity of the nickel–alane complex. As H2 activation and styrene hydrogenation by nickel–alane complexes proceed with lower energy barriers than those by nickel–borane complexes, the nickel–alane complex with [(R)Z(o-Ph2PC6H4)2] ligand scaffold should be more reactive than the nickel–borane counterpart. Insights into the role of Lewis acid in this Z-type σ-acceptor ligand scaffold will assist with the development of metal–ligand bifunctional catalysts.

Exploring the materials space in the smallest particle size range: from heterogeneous catalysis to electrocatalysis and photocatalysis.

Ultrasmall clusters of subnanometer size can possess unique and even unexpected physical and chemical propensities which make them interesting in various fields of basic science and for potential applications, such as catalysis, photocatalysis, electrocatalysis, and optical and chemical sensors, just to name a few examples. These small particles often offer the tunability of their performance in an atom-by-atom fashion and an economic atom-efficient use of the metal loading. In this paper we review recent progress in the characterization and theory of well-defined subnanometer clusters in catalytic processes, and discuss their optical properties and stability, along with the potential of the size-selected clusters for the understanding of catalytic processes and for the development of new classes of catalysts.

5f Covalency Synergistically Boosting Oxygen Evolution of UCoO4 Catalyst.

Electronic structure modulation among multiple metal sites is key to the design of efficient catalysts. Most studies have focused on regulating 3d transition-metal active ions through other d-block metals, while few have utilized f-block metals. Herein, we report a new class of catalyst, namely, UCoO4 with alternative CoO6 and 5f-related UO6 octahedra, as a unique example of a 5f-covalent compound that exhibits enhanced electrocatalytic oxygen evolution reaction (OER) activity because of the presence of the U 5f–O 2p–Co 3d network. UCoO4 exhibits a low overpotential of 250 mV at 10 mA cm–2, surpassing other unitary cobalt-based catalysts ever reported. X-ray absorption spectroscopy revealed that the Co2+ ion in pristine UCoO4 was converted to high-valence Co3+/4+, while U6+ remained unchanged during the OER, indicating that only Co was the active site. Density functional theory calculations demonstrated that the OER activity of Co3+/4+ was synergistically enhanced by the covalent bonding of U6+-5f in the U 5f–O 2p–Co 3d network. This study opens new avenues for the realization of electronic structure manipulation via unique 5f involvement.