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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Atomically dispersed supported metal species as catalysts for alcohol conversion, and hydrogen and chemicals production

Supported single metal atoms are a new class of catalyst in which precious metals can be used at the ultimate limit of atom efficiency. While great strides have been made in demonstrating the potential of single-atom catalysts for many industrial reactions, there remains much debate in the literature over the nature of the active sites and the reaction mechanisms. The major goal of this project was to elucidate how atomic dispersions of metals on oxide supports enable catalytic reactions and how to stabilize such active sites for practical catalyst development. This is particularly important for the reactions of interest to fuel reforming for hydrogen generation in which atomically-dispersed metal ions on various oxide surfaces have been identified as the active sites. Working with trace amounts of precious metals is both fundamentally intriguing and of great practical interest in our continual search for low-cost, efficient and stable catalysts for the conversion of fuels to hydrogen under highly demanding operating conditions. A second major goal of the project was to rationally design and prepare single atom alloy (SAA) catalyst compositions based on information gathered from surface science studies on model catalysts and by catalytic evaluation of nanoparticle SAA analogs under realistic conditions. The overarching goal was to use the knowledge garnered from this project to design and develop new catalysts at the single atom limit, which can be applied to selective hydrogenation reactions (alkynes and dienes to alkenes) and the dehydrogenation of methanol and ethanol to value-added products at near-ambient conditions. Detailed information about the results of the project are given below.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Infrared Spectroscopic Observation of Oxo- and Superoxo-Intermediates in the Water Oxidation Cycle of a Molecular Ir Catalyst

Molecular Ir catalysts have emerged as an important class of model catalysts for understanding structure–activity relationships in water oxidation, a reaction that is central to renewable fuel synthesis. Prior efforts have mostly focused on controlling and elucidating the emergence of active species from prepared precursors. However, the development of efficient and stable molecular Ir catalysts also necessitates probing of reaction intermediates. To date, relatively little is known about the key intermediates in the cycles of the molecular Ir catalysts. Herein, we probed the catalytic cycle of a homogeneous Ir catalyst (“blue dimer”) at a Au electrode/aqueous electrolyte interface by combining surface-enhanced infrared absorption spectroscopy (SEIRAS) with phase-sensitive detection (PSD). Cyclic voltammograms (CVs) from 1.4 to 1.7 VRHE (RHE = reversible hydrogen electrode) give rise to a band at ~818 cm –1 , whereas CVs from 1.4 to ≥1.85 VRHE generate an additional band at ~1146 cm –1 . Isotope labeling experiments indicate that the bands at ~818 and ~1146 cm –1 are attributable to oxo (Ir V =O) and superoxo (Ir IV –OO • ) moieties, respectively. Furthermore, this study establishes PSD-SEIRAS as a sensitive tool for probing water oxidation cycles at electrode/electrolyte interfaces and demonstrates that the relative abundance of two key intermediates can be tuned by the thermodynamic driving force of the reaction.

25 ENERGY STORAGE↗
DOE OSTI2024

Biofuel production from palm oil deoxygenation using nickel-molybdenum on zirconia catalyst using glycerol as a hydrogen donor

The growing demand for renewable energy has generated interest in biofuels as alternatives to fossil fuels. Second-generation biofuels, derived from deoxygenating fats and oils, have garnered a higher level of interest from industry and academia due to their potential for direct replacement of diesel and jet fuels. Palm oil, mostly cultivated in Thailand and composed of C16 and C18 fatty acids, is a primary feedstock sought for biofuel production. Palm oil deoxygenation contains several pathways that may or may not require hydrogen gas. This study aimed to produce biofuels in different fuel ranges, such as gasoline, jet fuel, and diesel, through palm oil deoxygenation using glycerol as a hydrogen source. Glycerol, a low-value byproduct, was used as a hydrogen donor, whereas nickel-molybdenum-supported catalysts were chosen for their high efficiency in deoxygenation and cost-effectiveness. The study investigated the impact of reaction time, temperature, and catalyst activation method on palm oil deoxygenation. Catalyst characterization methods, including XRD, SEM, TEM, XPS, FTIR, TGA, and nitrogen-sorption, were employed to understand the role of catalysts’ activity during palm oil upgrading. Findings indicated that alkane hydrocarbons are the major components in liquid products. The presence of excess hydrogen in post reaction gaseous phase proves the hydrogen donation capability of glycerol. Increased reaction time and temperature facilitated the removal of oxygen from palm oil. Nickel-molybdenum on zirconia activated by sulfidation demonstrated higher stability than by reduction activation.

09 BIOMASS FUELS↗
DOE OSTI2024

Durability of Highly Active PGM Catalyst MEA Tested Via Nitrogen and Air AST Cycling Under HDV Condition

PEMFCs are widely considered as the most promising power sources, particularly for heavy-duty vehicles (HDVs). Unfortunately, the degradation of MEAs under HDV condition remains insufficiently studied. In this work, we systematically investigated two MEAs with catalysts of Pt nanoparticles (NPs) supported over high surface area carbon black. These MEAs were tested for durability under HDV condition in nitrogen using a DOE AST protocol for 180,000 cycles, which is equivalent to 30,000 hours or 1 million miles of operation. The commercial Catalyst MEA also underwent 6,000 AST cycles in air under M2FCT condition. We comprehensively investigated the degradation of catalysts. Our results indicate that both MEAs undergo continuous performance degradation in H 2 /air and H 2 /O 2 during the AST cycling in nitrogen, where analysis employing scanning transmission electron microscopy (STEM) and inductively coupled plasma mass spectrometry (ICP-MS) reveal significant degradation behavior for Pt catalysts. The MEA exhibits more significant degradation, especially within mass transfer region, during the AST process in air. In conclusion, this study describes the long-term degradation behavior and mechanism with AST cycling in nitrogen or air governing highly efficient and durable PGM-catalyst MEA design under HDV conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Nickel Enhances InPd-Catalyzed Nitrate Reduction Activity and N 2 Selectivity

Palladium–indium (PdIn) is a well-established bimetallic composition for reductively degrading nitrate anions, one of the most ubiquitous contaminants in the groundwater. However, the scarcity and the variable price of these rare-earth and platinum group critical metals may hinder their use for water treatment. Nickel (Ni), a nonprecious metal in the same element group as Pd, could partially replace and lower Pd usage if the resulting trimetallic composition is sufficiently catalytically active. Herein, we report the synthesis and nitrate reduction catalysis of activated carbon-supported “In-on-Pd-on-Ni” catalysts (InPdNi/AC). While bimetallic InPd/AC (0.05 wt % In, 1.3 wt % Pd) was expectedly active, trimetallic InPdNi/AC containing the same In amount, much less Pd (0.1 wt %), and 1 wt % Ni was >17 more active (k cat ≈ 20 vs 349 L min –1 g surface metal –1 ). X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations showed that Pd gained electron density from Ni, correlating to the increased nitrate reduction activity. Ammonium byproduct selectivity for InPdNi/AC (18% at 50% nitrate conversion) was lower compared to that of InPd/AC (48%), suggestive of the higher surface coverage of NO or its greater reactivity with NO 2 – , which led to more N 2 . Accounting for the catalyst precursor, manufacturing costs, and spent metal recovery, we calculated that Ni incorporation lowered the net catalyst cost significantly (from $\$$1028/kg to $\$$170/kg). The trimetallic composition lowered, by ∼26 times, the catalyst cost of a stirred tank reactor sized to the same treatment capacity as that for the bimetallic case. In conclusion, the results demonstrate that the partial replacement of the precious metal with an earth-abundant one leads to a higher efficiency and lower cost denitrification catalyst, via a material strategy that should be beneficial for other clean-water catalytic systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mechanistic insight into the active centers of single/dual-atom Ni/Fe-based oxygen electrocatalysts

Single-atom catalysts with maximum metal utilization efficiency show great potential for sustainable catalytic applications and fundamental mechanistic studies. We here provide a convenient molecular tailoring strategy based on graphitic carbon nitride as support for the rational design of single-site and dual-site single-atom catalysts. Catalysts with single Fe sites exhibit impressive oxygen reduction reaction activity with a half-wave potential of 0.89 V vs. RHE. We find that the single Ni sites are favorable to promote the key structural reconstruction into bridging Ni-O-Fe bonds in dual-site NiFe SAC. Meanwhile, the newly formed Ni-O-Fe bonds create spin channels for electron transfer, resulting in a significant improvement of the oxygen evolution reaction activity with an overpotential of 270 mV at 10 mA cm –2 . We further reveal that the water oxidation reaction follows a dual-site pathway through the deprotonation of *OH at both Ni and Fe sites, leading to the formation of bridging O 2 atop the Ni-O-Fe sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Photo-Induced Hydrogen Production from Formic Acid Using a Palladium Catalyst

Liquid organic hydrogen carriers (LOHCs) are recognized as promising sustainable hydrogen (H 2 ) carriers due to their high volumetric capacity and ability to store H 2 at ambient conditions, eliminating the need for energy-intensive liquefaction or compression processes associated with H 2 or ammonia gas. One of the main current drawbacks, however, is LOHCs’ high energy demand for H 2 release. This work presents the photo-induced liberation of H 2 from formic acid (FA) as a liquid H 2 carrier, using visible light and well-established 5 wt% palladium nanoparticles supported over carbon (Pd/C). We show that low-power light-emitting diodes (LEDs) produced higher gas flow than their thermal baseline (35 °C), with 27.2 mL/min and 7.72 mL/min, respectively. Further, the rate of gas evolved with light intensity, catalyst loading, and the concentration of FA. Light-induced dehydrogenation shows similar deactivation as the known thermal mechanisms, such as the decreased Pd 2+ /Pd 0 ratio and Pd nanoparticle agglomeration. Hence, these observations suggest a photothermal mechanism, whereby the LED provides heat efficiently absorbed by the Pd/C catalyst and enhanced by Pd’s ability to absorb light, thereby driving the FA dehydrogenation reaction at ambient conditions.

08 HYDROGEN↗
DOE OSTI2024

Constructing Highly Porous Low Iridium Anode Catalysts Via Dealloying for Proton Exchange Membrane Water Electrolyzers

Iridium (Ir) is the most active and durable anode catalyst for the oxygen evolution reaction (OER) for proton exchange membrane water electrolyzers (PEMWEs). However, their large-scale applications are hindered by high costs and scarcity of Ir. Lowering Ir loadings below 1.0 mgcm -2 causes significantly reduced PEMWE performance and durability. Therefore, developing efficient low Ir-based catalysts is critical to widely commercializing PEMWEs. Herein, an approach is presented for designing porous Ir metal aerogel (MA) catalysts via chemically dealloying IrCu alloys. In this study, the unique hierarchical pore structures and multiple channels of the Ir MA catalyst significantly increase electrochemical surface area (ECSA) and enhance OER activity compared to conventional Ir black catalysts, providing an effective solution to design low-Ir catalysts with improved Ir utilization and enhanced stability. An optimized membrane electrode assembly (MEA) with an Ir loading of 0.5 mg Ir cm -2 generated 2.0 A cm -2 at 1.79 V, higher than the Ir black at a loading of 2.0 mg Ir cm -2 (1.63 A cm -2 ). The low-Ir MEA demonstrated an acceptable decay rate of ≈40 µV h -1 during durability tests at 0.5 (>1200 h) and 2.0 A cm -2 (400 h), outperforming the commercial Ir-based MEA (175 µV h -1 at 2.0 mg Ir cm -2 ).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Isolated copper–tin atomic interfaces tuning electrocatalytic CO 2 conversion

Direct experimental observations of the interface structure can provide vital insights into heterogeneous catalysis. Examples of interface design based on single atom and surface science are, however, extremely rare. Here, we report Cu–Sn single-atom surface alloys, where isolated Sn sites with high surface densities (up to 8%) are anchored on the Cu host, for efficient electrocatalytic CO 2 reduction. The unique geometric and electronic structure of the Cu–Sn surface alloys (Cu 97 Sn 3 and Cu 99 Sn 1 ) enables distinct catalytic selectivity from pure Cu 100 and Cu 70 Sn 30 bulk alloy. The Cu 97 Sn 3 catalyst achieves a CO Faradaic efficiency of 98% at a tiny overpotential of 30 mV in an alkaline flow cell, where a high CO current density of 100 mA cm –2 is obtained at an overpotential of 340 mV. Density functional theory simulation reveals that it is not only the elemental composition that dictates the electrocatalytic reactivity of Cu–Sn alloys; the local coordination environment of atomically dispersed, isolated Cu–Sn bonding plays the most critical role.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Oxygen reduction reaction catalysts prepared by platinizing thermally activated zeolitic imidazolate frameworks

In this study, highly efficient and low-cost oxygen reduction reaction (ORR) catalyst is essential to improve the cost competitiveness of the proton-exchange membrane fuel cells (PEMFCs). One potential approach of cost reduction is to apply low loading Pt over a catalytically active support made of platinum metal group free (PGM-free) material to compensate the overall ORR activity through synergistic catalysis between Pt and PGM-free support. In this report, we investigated a series of catalysts prepared by adding low-loading Pt over ORR active support prepared through thermally activated Co/Zn methyl-imidazolate framework (Co/Zn-ZIF) at various Co/Zn ratios. Catalytic activity measurement and structural characterization were performed in an attempt to gain better understanding of certain structural factors that could influence the catalytic performance.

25 ENERGY STORAGE↗
DOE OSTI2026

Highly Crystalline and Porous Borocarbonitrides as Metal‐Free Catalysts for Boosted N‐Heterocycle Dehydrogenation

Safe and efficient hydrogen storage is pivotal for enabling a clean hydrogen economy. Liquid organic hydrogen carriers (LOHCs) offer a practical solution, but their deployment is hindered by the lack of highly active and economical dehydrogenation catalysts. In this work, we report a metal‐free catalyst design that overcomes the long‐standing trade‐off between crystallinity and surface area in two‐dimensional frameworks for highly efficient dehydrogenation of LOHCs. A flux‐assisted reconstruction strategy transforms amorphous borocarbonitrides (AM‐BCN) into highly crystalline, defect‐rich BCN nanosheets (C‐BCN) with large surface area and accessible porosity, as confirmed by complementary spectroscopic, x‐ray, and neutron analyses. C‐BCN catalyzes the acceptor‐less dehydrogenation of aza‐fused LOHCs with quantitative hydrogen release under mild conditions, outperforming AM‐BCN and previously reported metal‐free scaffolds. Mechanistic insights from x‐ray, neutron scattering, and theoretical calculations identify open C‐B‐N and N‐B‐N defect motifs as the primary active sites. This work establishes a generalizable strategy to engineer crystalline, porous, defect‐rich two‐dimensional lattices and demonstrates a highly active metal‐free platform for LOHC dehydrogenation with high‐purity H 2 generation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Reliable bi-functional nickel-phosphate /TiO2 integration enables stable n-GaAs photoanode for water oxidation under alkaline condition

Abstract Hydrogen is one of the most widely used essential chemicals worldwide, and it is also employed in the production of many other chemicals, especially carbon-free energy fuels produced via photoelectrochemical (PEC) water splitting. At present, gallium arsenide represents the most efficient photoanode material for PEC water oxidation, but it is known to either be anodically photocorroded or photopassivated by native metal oxides in the competitive reaction, limiting efficiency and stability. Here, we report chemically etched GaAs that is decorated with thin titanium dioxide (~30 nm-thick, crystalline) surface passivation layer along with nickel-phosphate (Ni-Pi) cocatalyst as a surface hole-sink layer. The integration of Ni-Pi bifunctional co-catalyst results in a highly efficient GaAs electrode with a ~ 100 mV cathodic shift of the onset potential. In this work, the electrode also has enhanced photostability under 110 h testing for PEC water oxidation at a steady current density J ph > 25 mA·cm −2 . The Et-GaAs/TiO 2 /Ni-Pi║Ni-Pi tandem configuration results in the best unassisted bias-free water splitting device with the highest J ph (~7.6 mA·cm −2 ) and a stable solar-to-hydrogen conversion efficiency of 9.5%.

08 HYDROGEN↗
DOE OSTI2023

Activated carbon supported Ni, Fe, and bimetallic NiFe catalysts for CO x -free H 2 production by microwave methane pyrolysis

The goal of this study was to test the effect of metal-impregnated carbon-based catalysts on the conversion of methane to hydrogen gas and solid carbon using microwave reactor technology. Monometallic and bimetallic catalysts on activated carbon supports (Ni/AC, Fe/AC, Ni-Fe/AC) are compared during methane pyrolysis testing. Catalytic methane pyrolysis was carried out in a microwave reactor at reaction temperatures of 600 °C and 800 °C. For comparison, one of the catalysts (Ni-Fe/AC) was tested in a conventionally heated reactor at 800 °C. The prepared catalysts were characterized by X-ray diffraction (XRD), while post-reaction catalysts were characterized by XRD and SEM. During reaction testing, the monometallic Ni/AC catalyst exhibited the best catalytic activity (CH 4 conversion: 46.0 and H 2 yield: 46.9%) when reacted in the microwave reactor, however, it suffered from rapid deactivation from carbon deposition (carbon yield: 0.39 gC/g catalyst). The bimetallic Ni-Fe/AC catalyst was slightly less active (CH 4 conversion: 36.9 and H 2 yield: 40.5%) but it was more resistant to carbon formation (carbon yield: 0.27 gC/g catalyst) suggesting it may have greater long-term stability. The Ni-Fe/AC catalyst was also the most energy efficient as it required the least microwave power to maintain the 800 °C reaction temperature compared to the other catalysts tested. Methane conversion of the bimetallic Ni-Fe/AC at 800 °C under microwave irradiation was three times the conversion under conventional heating at the same reaction temperature. Finally, this work demonstrates the use of microwave-specific catalysts for catalytic methane pyrolysis in a microwave reactor, and can be used as a foundation for further methane pyrolysis process and catalyst optimization for CO x -free H 2 production.

08 HYDROGEN↗
DOE OSTI2020

Predicting metal–metal interactions. II. Accelerating generalized schemes through physical insights

Operando-computational frameworks that integrate descriptors for catalyst stability within catalyst screening paradigms enable predictions of rates and selectivity on chemically faithful representations of nanoparticles under reaction conditions. These catalyst stability descriptors can be efficiently predicted by density functional theory (DFT)-based models. The alloy stability model, for example, predicts the stability of metal atoms in nanoparticles with site-by-site resolution. In this work, we use physical insights to present accelerated approaches of parameterizing this recently introduced alloy-stability model. These accelerated approaches meld quadratic functions for the energy of metal atoms in terms of the coordination number with linear correlations between model parameters and the cohesive energies of bulk metals. By interpolating across both the coordination number and chemical space, these accelerated approaches shrink the training set size for 12 fcc p- and d-block metals from 204 to as few as 24 DFT calculated total energies without sacrificing the accuracy of our model. We validate the accelerated approaches by predicting adsorption energies of metal atoms on extended surfaces and 147 atom cuboctahedral nanoparticles with mean absolute errors of 0.10 eV and 0.24 eV, respectively. This efficiency boost will enable a rapid and exhaustive exploration of the vast material space of transition metal alloys for catalytic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Metal Independent Correlations for Site-specific Binding Energies of Relevant Catalytic Intermediates

Establishing energy correlations among different metals can accelerate the discovery of efficient and cost-effective catalysts for complex reactions. Using a recently introduced coordination-based model, we can predict site specific metal binding energies (∆EM) that can be used as a descriptor for chemical reactions. In this study, we have examined a range of metals including Ag, Au, Co, Cu, Ir, Ni, Os, Pd, Pt, Rh, and Ru and found linear correlations between predicted ∆EM and adsorption energies of CH and O (∆ECH and ∆EO) at various coordination environment for all the considered metals. Interestingly, all the metals correlate with one another under specific surface site coordination, indicating that different metals are interrelated in a particular coordination environment. Furthermore, we have tested and verified for PtPd and PtIr-based alloys that they follow a similar behavior. Moreover, we have expanded the metal space by taking some early transition metals along with few s-block metals and shown a cyclic behavior of the adsorbate binding energy (∆EA) versus ∆EM. Therefore, ∆ECH and ∆EO can be efficiently interpolated between metals, alloys and intermetallics based on information related to one metal only. This simplifies the process of screening new metal catalyst formulations and their reaction energies.

Density function theory↗
DOE OSTI2023

Fe-N 4 O-C Nanoplates Covalently Bonding on Graphene for Efficient CO 2 Electroreduction and Zn-CO 2 Batteries

Electrochemical carbon dioxide (CO 2 ) reduction into value-added products holds great promise in moving toward carbon neutrality but remains a grand challenge due to lack of efficient electrocatalysts. Herein, the nucleophilic substitution reaction is elaborately harnessed to synthesize carbon nanoplates with a Fe-N 4 O configuration anchored onto graphene substrate (Fe-N 4 O-C/Gr) through covalent linkages. Density functional theory calculations demonstrate the unique configuration of Fe-N 4 O with one oxygen (O) atom in the axial direction not only suppresses the competing hydrogen evolution reaction, but also facilitates the desorption of *CO intermediate compared with the commonly planar single-atomic Fe sites. The Fe-N 4 O-C/Gr shows excellent performance in the electroreduction of CO 2 into carbon monoxide (CO) with an impressive Faradaic efficiency of 98.3% at -0.7 V versus reversible hydrogen electrode (RHE) and a high turnover frequency of 3511 h -1 . Furthermore, as a cathode catalyst in an aqueous zinc (Zn)-CO 2 battery, the Fe-N 4 O-C/Gr achieves a high CO Faradaic efficiency (≈91%) at a discharge current density of 3 mA cm -2 and long-term stability over 74 h. Here this work opens up a new route to simultaneously modulate the geometric and electronic structure of single-atomic catalysts toward efficient CO 2 conversion.

25 ENERGY STORAGE↗
DOE OSTI2025

High-Loading Single-Atom Catalyst via On-Surface Synthesis of a Metal-Covalent Organic Framework for Oxygen Reduction Reaction

The development of active catalysts with both high metal efficiency and use of earth abundant metals is the ultimate goal for advancing the required commercially viable and sustainable energy conversion technologies of the future. Metal-organic frameworks (MOFs) have emerged as promising candidates due to their high surface area and tunable active sites. Here, this study aims to fabricate a new type of high metal loading single-atom catalysts (SACs) based on 2D metal-organic covalent organic frameworks (MCOFs) with uniform, active and stable Fe-N 3 sites. The MCOFs were synthesized through an on-surface polymerization process using Fe and melamine as precursors. The polymerization steps were characterized using operando high-pressure scanning tunneling microscopy (HP-STM), in situ X-ray photoelectron spectroscopy (XPS), low-temperature STM (LT-STM), and computational calculations. The synthesized MCOFs demonstrated favorable adsorption and activation of O 2 at the Fe-N 3 sites, and it is predicted to be active for the oxygen reduction reaction (ORR). The surface chemistry and functionality of 2D MCOFs can be rationally designed by varying the metal atoms and organic linkers, offering a versatile platform for diverse applications.

25 ENERGY STORAGE↗
DOE OSTI2021

Ligand-coordinated Ir single-atom catalysts stabilized on oxide supports for ethylene hydrogenation and their evolution under a reductive atmosphere

In this work, we present a novel series of oxide-supported Ir-ligand single-atom catalysts (SACs) for ethylene hydrogenation. The SACs were created by a metal–ligand self-assembly strategy developed by our group, using one of two ligands, either 1,10-phenanthroline-5,6-dione (PDO) or 3,6-Di-2-pyridyl-1,2,4,5-tetrazine (DPTZ), on powder supports of either CeO 2 or MgO. Characterization by XAS, XPS, and CO adsorption proved that Ir exist principally as highly uniform, cationic single-atoms. Ir SACs show significantly higher durability and metal utilization efficiency than Ir nanoparticle (NP) catalysts during ethylene hydrogenation at 100 °C, as well as excellent stability, as no Ir aggregates were detected after >10 h reaction. The activity can be tuned by ligand and support effects: PDO and CeO 2 are superior to DPTZ and MgO, respectively. This tunability is attributed to differences in H 2 activation capability, which results from differences in support reducibility, electron density on Ir, and, potentially, the local coordination environment of Ir. The Ir SACs lose H 2 activation activity either under inert gas or under H 2 . Through XPS and in situ XAS studies, we attributed the former to the reversible loss of Ir hydride, which is the active species for H 2 activation, and the latter to irreversible over-hydrogenation and loss of Ir–O/N coordination. This work presents a new type of Ir hydrogenation SACs that are more durable, efficient, and tunable than supported Ir NPs, while more stable than homogeneous Ir complexes. It also offers fundamental understanding regarding ligand and support effects, as well as the evolution of Ir single-atoms under H 2 , instructing future design of stable, effective hydrogenation SACs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗