Search NASA⌕ Search

SEARCH · Search NASA

Results for “semihydrogenation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Understanding the Reactivity, Selectivity, and Deactivation of Frustrated Lewis Pairs for Semihydrogenation of Acetylene

A good catalyst for semihydrogenation of alkynes must preclude both over-hydrogenation of alkene to alkane and isomerization to the other alkene isomer. In addition, it should balance the trade-off between selectivity and activity. In 2013, the Repo and Pápai groups reported a frustrated Lewis pair (FLP) (1-NMe 2 -2-B(C 6 F 5 ) 2 -C 6 H 4 ), 1, which is a metal-free catalyst and for the first time shows excellent reactivity for the hydrogenation of internal alkynes. However, it is unreactive for terminal alkynes. In this work, we have designed 13 FLPs, a–m, based on 1 by varying the Lewis base site with N and P and the Lewis acid site with B, Al, Ga, and In and replacing pentafluorophenyl with 1,3,5-trifluorophenyl, phenyl, or trifluoromethyl. We apply density functional theory to study the activity, selectivity, and deactivation of FLP 1-m for acetylene semihydrogenation. The catalytic cycle consists of three steps: (1) alkyne insertion, (2) H 2 heterolysis, and (3) intramolecular protonation. We found the activity does not change much by the modification of bulky ligands, while it decreases with the direct replacement of LA and LB sites. The overall activity depends on steps 1 and 3, which are, respectively, positively and negatively linear correlated with the charge of the Lewis acid site. Most of the FLPs in this work show comparable or better selectivity for semihydrogenation of acetylene than 1. FLP deactivation is due to the strong binding of acetylene and the elimination of electron-withdrawing bulky ligands at the preactivated catalyst rather than at activated catalysts. Furthermore, taking the selectivity and stability of FLPs into account, we predict d and k are potentially active for terminal alkynes.

02 PETROLEUM↗
DOE OSTI2026

Synergistic Solvent-Surface Interactions Enable Alkyne Semihydrogenation at Palladium

Enabling higher yield and better selectivity for fine-chemical synthesis through heterogeneous catalysis is intricately linked to the interplay of active sites, reaction conditions, and mass transfer influence provided by the catalyst. Alkyne semihydrogenation is ubiquitous in the production of bulk chemicals in the pharmaceutical, polymer, or fine-chemical industries, but product selectivity remains a major challenge. Here, in this study, we demonstrate that the design of catalysts encompassing nickel (Ni) foams as contiguous monolith supports, decorated with ultralow loading of Pd/PdO x nanoparticles on a carbonized polydopamine interface and tuned with a thin layer of Al 2 O 3 , in conjunction with an optimized reaction environment leads to highly selective alkyne semihydrogenation. The reactions demonstrate good functional group tolerance and applicability to flow reactor systems. Combined computational and experimental studies are presented to describe the synergistic effect between the solvent-surface interaction and the degree of Pd surface reduction that are necessary to promote this selectivity. The system highlights the opportunity for catalyst-solvent codesign as a benign alternative to more complex reactants featuring extrinsic poisons or less-favored dopants.

atomic layer deposition↗
DOE OSTI2025

Selective semihydrogenation of acetylene in ethylene using defect-rich boron nitride catalyst from flux reconstruction

Efficient removal of trace acetylene from ethylene streams is essential for producing polymer-grade ethylene, yet achieving highly selective semihydrogenation without over-hydrogenation remains a long-standing challenge. A key barrier is the lack of a simple, low-cost catalyst that can activate hydrogen effectively while preventing ethylene from reacting further. Here we show that defect-rich boron nitride, prepared through a straightforward flux reconstruction method, serves as a highly selective and metal-free catalyst for acetylene semihydrogenation. The catalyst contains abundant open boron and nitrogen sites that enable efficient hydrogen activation and rapid release of ethylene, thereby avoiding over-hydrogenation. Experiments combined with isotope labeling and theoretical analysis reveal that these defects lower the energy barrier for hydrogen activation while accelerating product desorption. Our findings demonstrate a scalable strategy for defect engineering in boron nitride and highlight its potential as a robust, sustainable alternative to metal-based catalysts in industrial ethylene purification.

Wang, Tao [Oak Ridge National Laboratory (ORNL), O↗
DOE OSTI2020

Spin-Triplet Excitonic Insulator: The Case of Semihydrogenated Graphene

While various excitonic insulators have been studied in the literature, due to the perceived too-small spin splitting, spin-triplet excitonic insulator is rare. In two-dimensional systems such as a semihydrogenated graphene (known as graphone), however, it is possible, as revealed by first-principles calculations coupled with Bethe-Salpeter equation. Here, the critical temperature, given by an effective Hamiltonian, is 11.5 K. While detecting excitonic insulators is still a daunting challenge, the condensation of triplet excitons will result in spin superfluidity, which can be directly measured by a transport experiment. Nonlocal dielectric screening also leads to an unexpected phenomenon, namely, an indirect-to-direct transition crossover between single-particle band and exciton dispersion in the semihydrogenated graphene, which offers yet another test by experiment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Decoding Active Sites for Highly Efficient Semihydrogenation of Acetylene in Palladium–Copper Nanoalloys

Accurately decoding the three-dimensional atomic structure of surface active sites is essential yet challenging for a rational catalyst design. Here, we used comprehensive techniques combining the pair distribution function and reverse Monte Carlo simulation to reveal the surficial distribution of Pd active sites and adjacent coordination environment in palladium-copper nanoalloys. After the fine-tuning of the atomic arrangement, excellent catalytic performance with 98% ethylene selectivity at complete acetylene conversion was obtained in the Pd 34 Cu 66 nanocatalysts, outperforming most of the reported advanced catalysts. Further, t he quantitative deciphering shows a large number of active sites with a Pd-Pd coordination number of 3 distributed on the surface of Pd 34 Cu 66 nanoalloys, which play a decisive role in highly efficient semihydrogenation. This finding not only opens the way for guiding the precise design of bimetal nanocatalysts from atomic-level insight but also provides a method to resolve the spatial structure of active sites.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Discriminating the Role of Surface Hydride and Hydroxyl for Acetylene Semihydrogenation over Ceria through In Situ Neutron and Infrared Spectroscopy

Ceria has been used as a hydrogenation catalyst especially in selective alkyne hydrogenation, but the reaction mechanism regarding the role of different surface hydrogen species remains unclear. Here, we utilized in situ neutron and infrared vibration spectroscopy to show the catalytic role of cerium hydride (Ce–H) and hydroxyl (OH) groups in acetylene hydrogenation over ceria surfaces with different degree of reduction. In situ inelastic neutron scattering spectroscopy (INS) proved that not only Ce–H but also surface atomic hydrogen species on the reduced ceria surface can participate in acetylene semihydrogenation. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results implied that bridging OH groups both on the oxidized and reduced ceria are active in the selective hydrogenation of acetylene. It appears that surface Ce–H is more reactive than the coexisting OH species on the reduced ceria surface, but over-reduction of ceria also results in strongly bound species that may lead to catalyst deactivation. These spectroscopic results clearly explain the reaction mechanism including not only the surface chemistry but also the nature of the active hydrogen species for selective hydrogenation over ceria, providing insights into the design of more active and stable ceria-based catalysts for hydrogenation reactions.

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

Highly Selective Acetylene Semihydrogenation Catalyst with an Operation Window Exceeding 150 °C

The operating window (OW) is a primary performance criterion for the selective hydrogenation of acetylene in excess ethylene. Currently, most state-of-the-art catalyst systems have an OW of less than 50 °C in front-end processes. Selective acetylene hydrogenation catalysts with an OW wider than 100 °C are rare. Here, we demonstrate a facile stepwise chemical method to synthesize calcite-supported PdBi intermetallic compounds (PdBi/Calcite) that feature isolated and electron-rich Pd atoms as active sites for acetylene hydrogenation. Beneficial from the extremely weak ethylene absorption abilities and the stable structures against the formation of β-PdH x , PdBi/Calcite exhibit >99% selectivity to C 2 H 4 in the whole temperature range tested (50–300 °C) and ~100% C 2 H 2 conversion from 150 to 300 °C. Finally, as a result, an operation window exceeding 150 °C has been achieved.

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

Generation and Stabilization of a Dinickel Catalyst in a Metal-Organic Framework for Selective Hydrogenation Reactions

Although many monometallic active sites have been installed in metal–organic frameworks (MOFs) for catalytic reactions, there are no effective strategies to generate bimetallic catalysts in MOFs. Here we report the synthesis of a robust, efficient, and reusable MOF catalyst, MOF-NiH, by adaptively generating and stabilizing dinickel active sites using the bipyridine groups in MOF-253 with the formula of Al(OH)(2,2'-bipyridine-5,5'-dicarboxylate) for Z -selective semihydrogenation of alkynes and selective hydrogenation of C=C bonds in α,β-unsaturated aldehydes and ketones. Spectroscopic studies established the dinickel complex (bpy∙ - )Ni II ( μ 2 -H) 2 Ni II (bpy∙ - ) as the active catalyst. MOF-NiH efficiently catalyzed selective hydrogenation reactions with turnover numbers of up to 192 and could be used in five cycles of hydrogenation reactions without catalyst leaching or significant decrease of catalytic activities. The present work uncovers a synthetic strategy toward solution-inaccessible Earth-abundant bimetallic MOF catalysts for sustainable catalysis.

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

The role of surface chemistry in the synthesis of supported CuPd bimetallic/intermetallic catalysts for selective hydrogenation reactions

Understanding and controlling the structure of supported bimetallic/intermetallic catalysts are crucial for many heterogeneous catalytic reactions. However, commonly used synthesis techniques such as coimpregnation and coadsorption often yield nonuniform alloying and phase segregation, largely owing to the lack of interactions between different metal precursors. Here we show that by adopting sequential adsorption of complex metal cations and anions with the assistance of a proper ligand, the interaction between different metal precursors is enhanced, thus resulting in uniformly alloyed intermetallic catalysts. Importantly, the supported CuPd intermetallic catalyst exhibits greatly improved selectivity towards monoolefins in the semihydrogenation of acetylene and butadiene compared to those random CuPd alloys synthesized via coimpregnation and coadsorption methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Unraveling 1-Hexene Hydrogenation over Dilute Pd-in-Au Alloys

Dilute Pd-in-Au alloys are valuable materials for selectively hydrogenating alkynes and isomerizing alkenes. By diluting Pd in a Au host, the selectivity toward semihydrogenated alkene isomers can be significantly enhanced and the unfavorable overhydrogenation to alkanes is suppressed. However, a detailed mechanistic study on the origin of the enhanced alkene selectivity over dilute alloy catalysts is still missing. Here, we combine experiment and theory to unravel the reaction mechanism, identifying rate-limiting and selectivity-controlling steps in 1-hexene hydrogenation over dilute Pd-in-Au catalysts. Using isotope-exchange hydrogenation experiments, we show that 1-hexene and hydrogen over a bimetallic Pd4Au96 in silica catalyst preferentially form 1-hexene isomers, (trans and cis) 2- and 3-hexene and only a small amounts of hexane. The reaction is consistent with a Horiuti–Polanyi mechanism, similar to a monometallic Pd nanoparticle catalyst. Computation of the free-energy profiles for 1-hexene hydrogenation and isomerization over a single Pd atom in a Au surface using first principles calculations indicated that the isomerization of 1-hexene to 2-hexene is energetically favorable due to the relatively large barrier for H2 dissociation preventing hydrogenation to n-hexane. Microkinetic modeling established that H2 dissociation on the single-atom Pd sites and H spillover from these sites onto the Au host are rate-limiting and key in steering the selectivity of dilute Pd-in-Au alloys toward the hexene isomers. Furthermore, the mechanistic insights from this study contribute to the rational design of optimized dilute alloy catalysts for selective alkene isomerization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

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. Further, 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.

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

Selective chemical looping combustion of acetylene in ethylene-rich streams

Here, the requirement for C 2 H 2 concentrations below 2 parts per million (ppm) in gas streams for C 2 H 4 polymerization necessitates its semihydrogenation to C 2 H 4 . Here, we demonstrate selective chemical looping combustion of C 2 H 2 in C 2 H 4 -rich streams by Bi 2 O 3 as an alternative catalytic pathway to reduce C 2 H 2 concentration below 2 ppm. Bi 2 O 3 combusts C 2 H 2 with a first-order rate constant that is 3000 times greater than the rate constant for C 2 H 4 combustion. In successive redox cycles, the lattice O of Bi 2 O 3 can be fully replenished without discernible changes in local Bi coordination or C 2 H 2 combustion selectivity. Heterolytic activation of C–H bonds across Bi–O sites and the higher acidity of C 2 H 2 results in lower barriers for C 2 H 2 activation than C 2 H 4 , enabling selective catalytic hydrocarbon combustion leveraging differences in molecular deprotonation energies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Facet Preferencing by Chemical Substitution Controls Semi-Hydrogenation Selectivity in Ternary Pyrite-Type Intermetallic Compounds

Intermetallic compounds serve as model catalysts for selective hydrogenation reactions, offering precise control over the active site composition(s), geometric and electronic structure. The addition of a third element to form a ternary intermetallic alters the exposed crystal facet(s), demonstrating a strategy to impart improved catalytic behavior in intermetallic catalysts. The site-specific substitution of a small fraction of Pd atoms with Au in pyrite-type PdSb 2 results in the preferential exposure of the (100) facet over the (111) facet. Electron back scattered diffraction and density functional theory calculations confirm the facet change upon the substitution of Pd with Au to form the ternary Pd 1−x Au x Sb 2 (0.075 ≤ x ≤ 0.25). The (100) facet demonstrates higher net alkene selectivity due to significantly weaker alkene binding compared to the (111) facet. Distinct from our prior work on chemical substitution to directly alter the active site composition, this work demonstrates the indirect modification of active sites via preferential facet exposure.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗