Catalyst Libraries Research Articles

General synthesis of a dual-atomic-site catalyst library

General synthesis of a dual-atomic-site catalyst library

Molli: A General Purpose Python Toolkit for Combinatorial Small Molecule Library Generation, Manipulation, and Feature Extraction.

The construction, management, and analysis of large in silico molecular libraries is critical in many areas of modern chemistry. Herein, we introduce the MOLecular LIibrary toolkit, "molli", which is a Python 3 cheminformatics module that provides a streamlined interface for manipulating large in silico libraries. Three-dimensional, combinatorial molecule libraries can be expanded directly from two-dimensional chemical structure fragments stored in CDXML files with high stereochemical fidelity. Geometry optimization, property calculation, and conformer generation are executed by interfacing with widely used computational chemistry programs such as OpenBabel, RDKit, ORCA, NWChem, and xTB/CREST. Conformer-dependent grid-based feature calculators provide numerical representation and interface to robust three-dimensional visualization tools that provide comprehensive images to enhance human understanding of libraries with thousands of members. The package includes a command-line interface in addition to Python classes to streamline frequently used workflows. Parallel performance is benchmarked on various hardware platforms, and common workflows are demonstrated for different tasks ranging from optimized grid-based descriptor calculation on catalyst libraries to an NMR chemical shift prediction workflow from CDXML files.

General negative pressure annealing approach for creating ultra-high-loading single atom catalyst libraries

Catalyst systems populated by high-density single atoms are crucial for improving catalytic activity and selectivity, which can potentially maximize the industrial prospects of heterogeneous single-atom catalysts (SACs). However, achieving high-loading SACs with metal contents above 10 wt% remains challenging. Here we describe a general negative pressure annealing strategy to fabricate ultrahigh-loading SACs with metal contents up to 27.3–44.8 wt% for 13 different metals on a typical carbon nitride matrix. Furthermore, our approach enables the synthesis of high-entropy single-atom catalysts (HESACs) that exhibit the coexistence of multiple metal single atoms with high metal contents. In-situ aberration-corrected HAADF-STEM (AC-STEM) combined with ex-situ X-ray absorption fine structure (XAFS) demonstrate that the negative pressure annealing treatment accelerates the removal of anionic ligand in metal precursors and boosts the bonding of metal species with N defective sites, enabling the formation of dense N-coordinated metal sites. Increasing metal loading on a platinum (Pt) SAC to 41.8 wt% significantly enhances the activity of propane oxidation towards liquid products, including acetone, methanol, and acetic acid et al. This work presents a straightforward and universal approach for achieving many low-cost and high-density SACs for efficient catalytic transformations.

Thermodynamic H-Abstraction Abilities of Nitrogen Centered Radical Cations as Potential Hydrogen Atom Transfer Catalysts in Y-H Bond Functionalization.

Y-H bond functionalization has always been the focus of research interest in the area of organic synthesis. Direct hydrogen atom transfer (HAT) from the Y-H bond is one of the most efficient and practical methods to activate the Y-H bond. Recently, nitrogen centered radical cations were broadly utilized as H-abstraction catalysts to activate Y-H bonds via the HAT process. As a type of HAT catalyst, the H-affinity of nitrogen centered radical cations is a significant thermodynamic parameter to quantitatively evaluate the thermodynamic H-abstraction potentials of nitrogen centered radical cations. In this work, the pK a values of 120 protonated N-containing compounds in acetonitrile (AN) are predicted, and the H-affinities of 120 nitrogen centered radical cations in AN are derived from the reduction potentials of nitrogen centered radical cations and pK a of protonated N-containing compounds using Hess' law. This work focuses on the H-abstraction abilities of 120 nitrogen centered radical cations in AN to enrich the molecule library of novel HAT catalysts or H-abstractors and provides valuable thermodynamic guidelines for the application of nitrogen centered radical cations in Y-H bond functionalization.

Doubling the life of Cu/ZnO methanol synthesis catalysts via use of Si as a structural promoter to inhibit sintering.

Cu/ZnO/Al2O3 catalysts used to synthesize methanol undergo extensive deactivation during use, mainly due to sintering. Here, we report on formulations wherein deactivation has been substantially reduced by the targeted use of a small quantity of a Si-based promoter, resulting in accrued activity benefits that can exceed a factor of 1.8 versus unpromoted catalysts. This enhanced stability also provides longer lifetimes, up to double that of prior generation catalysts. Detailed characterization of a library of aged catalysts has allowed the most important deactivation mechanisms to be established and the chemical state of the silicon promoter to be identified. We show that silicon is incorporated within the ZnO lattice, providing a pronounced improvement in the hydrothermal stability of this component. These findings have important implications for sustainable methanol production from H2 and CO2.

Effect of a phase transfer catalyst structure on the alkaline hydrolysis of poly(ethylene terephthalate)

The evaluation of a library of phase transfer catalysts in the alkaline hydrolysis of polyethylene terephthalate revealed the key interplay between catalyst structure/properties and the reaction conditions.

Electrochemical trends of a hybrid platinum and metal–nitrogen–carbon catalyst library for the oxygen reduction reaction

Pt nanoparticles supported on a library of 3d, 4d, 5d and f metal M–N–C catalysts for the ORR.

Parallel Catalyst Synthesis Protocol for Accelerating Heterogeneous Olefin Polymerization Research.

The data scientific approach has become an indispensable tool for capturing structure-performance relationships in complex systems, where the quantity and quality of data play a crucial role. In heterogeneous olefin polymerization research, the exhaustive and multi-step nature of Ziegler-Natta catalyst synthesis has long posed a bottleneck in synthetic throughput and data generation. In this contribution, a custom-designed 12-parallel reactor system and a catalyst synthesis protocol were developed to achieve the parallel synthesis of a magnesium ethoxide-based Ziegler-Natta catalyst. The established system, featuring a miniature reaction vessel with magnetically suspended stirring, allows for over a tenfold reduction in synthetic scale while ensuring the consistency and reliability of the synthesis. We demonstrate that the established protocol is highly efficient for the generation of a catalyst library with diverse compositions and physical features, holding promise as a foundation for the data-driven establishment of the structure-performance relationship in heterogeneous olefin polymerization catalysis.

Bent and Twisted: Synthesis of an Alkoxy-Substituted (1,5)Naphthalene-paracyclophanediene.

This contribution describes the synthesis of [2.2](1,5)naphthalenoparacyclophane-1,13-diene in four steps from 1,5-bis(bromomethyl)naphthalene and 1,4-benzenedimethanethiol. Consisting of 2,6-dioctyloxynaphthalene and benzene moieties, the effects of differing arene size on the structure, strain energy, and chemical reactivity of the cyclophanediene are examined. Despite a strain energy of 24.3 kcal/mol, the naphthalenoparacyclophanediene was unreactive toward a library of olefin metathesis catalysts. This diminished reactivity can be explained by the steric hindrance of the twisted olefin. Incorporation of an electron donor (naphthalene) into the rigid paracyclophanediene structure can allow for applications in optoelectronics, chiral ligands, and planar chiral materials.

Aspartyl β-Turn-Based Dirhodium(II) Metallopeptides for Benzylic C(sp3)-H Amination: Enantioselectivity and X-ray Structural Analysis.

Amination of C(sp3)-H bonds is a powerful tool to introduce nitrogen into complex organic frameworks in a direct manner. Despite significant advances in catalyst design, full site- and enantiocontrol in complex molecular regimes remain elusive using established catalyst systems. To address these challenges, we herein describe a new class of peptide-based dirhodium(II) complexes derived from aspartic acid-containing β-turn-forming tetramers. This highly modular system can serve as a platform for the rapid generation of new chiral dirhodium(II) catalyst libraries, as illustrated by the facile synthesis of a series of 38 catalysts. Critically, we present the first crystal structure of a dirhodium(II) tetra-aspartate complex, which unveils retention of the β-turn conformation of the peptidyl ligand; a well-defined hydrogen-bonding network is evident, along with a near-C4 symmetry that renders the rhodium centers inequivalent. The utility of this catalyst platform is illustrated by the enantioselective amination of benzylic C(sp3)-H bonds, in which state-of-the-art levels of enantioselectivity up to 95.5:4.5 er are obtained, even for substrates that present challenges with previously reported catalyst systems. Additionally, we found these complexes to be competent catalysts for the intermolecular amination of N-alkylamides via insertion into the C(sp3)-H bond α to the amide nitrogen, yielding differentially protected 1,1-diamines. Of note, this type of insertion was also observed to occur on the amide functionalities of the catalyst itself in the absence of the substrate but did not appear to be detrimental to reaction outcomes when the substrate was present.

High-Throughput Approach in the Ring-Opening Polymerization of β-Butyrolactone Enables Rapid Evaluation of Yttrium Salan Catalysts

Poly(3-hydroxybutyrate) (PHB) is a material produced naturally by bacteria but is also chemically accessible via ring-opening polymerization (ROP) of β-butyrolactone (β-BL). In ROP, catalyst design plays a key role in the production of PHB with different stereomicrostructures, i.e., syndiotactic, isotactic, or atactic PHB. In this work, we demonstrate a simple procedure for generating the catalysts in situ by conveniently combining a suitable yttrium precursor with the respective salan pro-ligand. This approach circumvents the elaborate isolation of the catalyst and enables the high-throughput screening of a library of yttrium salan catalysts for the ROP of β-BL. Electronic and steric influences of the ligand framework on stereoselectivity and activity of the catalyst as well as limitations could be determined, and structure–property relationships were established. Depending on the substitution pattern, these in situ-generated catalysts produced syndiotactic-enriched, isotactic-enriched, or atactic PHB with high activity.

Oxygen-Bridged Vanadium Single-Atom Dimer Catalysts Promoting High Faradaic Efficiency of Ammonia Electrosynthesis

Single-atom catalysts have already been widely investigated for the nitrogen reduction reaction (NRR). However, the simplicity of a single atom as an active center encounters the challenge of modulating the multiple reaction intermediates during the NRR process. Moving toward the single-atom-dimer (SAD) structures can not only buffer the multiple reaction intermediates but also provide a strategy to modify the electronic structure and environment of the catalysts. Here, a structure of a vanadium SAD (V-O-V) catalyst on N-doped carbon (O-V2-NC) is proposed for the electrochemical nitrogen reduction reaction, in which the vanadium dimer is coordinated with nitrogen and simultaneously bridged by one oxygen. The oxygen-bridged metal atom dimer that has more electron deficiency is perceived to be the active center for nitrogen reduction. A loop evolution of the intermediate structure was found during the theoretical process simulated by density functional theory (DFT) calculation. The active center V-O-V breaks down to V-O and V during the protonation process and regenerates to the original V-O-V structure after releasing all the nitrogen species. Thus, the O-V2-NC structure presents excellent activity toward the electrochemical NRR, achieving an outstanding faradaic efficiency (77%) along with the yield of 9.97 μg h-1 mg-1 at 0 V (vs RHE) and comparably high ammonia yield (26 μg h-1 mg-1) with the FE of 4.6% at -0.4 V (vs RHE). This report synthesizes and proves the peculiar V-O-V dimer structure experimentally, which also contributes to the library of SAD catalysts with superior performance.

Peroxidase-like biomimetic epoxidation and subsequent alcoholysis of olefins by Fe(III)tetrakis(4-sulphonatophenyl) porphyrin (Fe4SP) encapsulated in the metal-organic framework HKUST-1

The efficiency and diverse functionality of biological catalysts has inspired the synthetic design of systems to mimic the stabilizing and catalytic properties of enzyme substrate binding protein pockets. One such system is the Fe4SP@HKUST-1 metal organic framework (MOF) system, also known as MOMzyme-1, in which Fe(III)tetrakis(4-sulphonatophenyl)porphyrin (Fe4SP) is encapsulated within the cuboctahedral cavities of the HKUST-1 MOF. Within this system the Fe4SP heme active site is encapsulated in a pseudo protein pocket within the MOF. Here, the ability of the Fe4SP@HKUST-1 to catalyze the tandem epoxidation of olefins followed by selective alcoholysis is examined. It is observed that encapsulation of Fe4SP within the MOF framework significantly enhances the turnover number (TON) of peroxide-driven epoxidation of styrene while greatly reducing metalloporphyrin degradation and maintaining stereoisomer selectivity. The Fe4SP@HKUST-1 catalyzes both the olefin epoxidation and the subsequent ring opening through the addition of CH3OH. The epoxidation of styrene occurs through the hydrogen peroxide generated high valent Fe(IV) = O of the encapsulated Fe4SP while the corresponding ring opening and methanolysis takes place at the Cu metallo building blocks of the HKUST-1 framework. These results provide a framework through which to develop a more extensive library of bio-inspired heme-based MOF catalysts.

Synthesis of platinum intermetallic nanoparticle fuel cell catalysts within secure inter-particle distance on carbon blacks

Supported ordered intermetallic nanoparticles are of significant interest for catalysis applications owing to their unique surface/near-surface structures and electronic properties. However, the synthesis of small-sized intermetallic catalysts with high mass activity remains a formidable challenge, as high temperatures annealing treatments are generally requisite to achieve ordered intermetallic structures but lead to undesired larger crystallites. Here, we report an industrially relevant impregnation approach for the scalable synthesis of small-sized platinum-based intermetallic nanoparticle catalysts by regulating inter-particle distance on carbon black supports to mitigate metal sintering in high-temperature annealing. We construct a library consisting of 18 binary Pt-based intermetallic nanoparticle catalysts with an average size of < 5 nm. The prepared intermetallic catalyst libraries exhibit outstanding proton-exchange-membrane fuel cells performance, including high mass activities of 1.3–1.8 A mgPt–1, large peak power densities of 1.2–1.4 W cm–2 in H2-air cells, and efficient Pt utilization of ∼0.07 g kW–1 at rated power.

Copper-Catalyzed Chemo- and Enantioselective Radical 1,2-Carbophosphonylation of Styrenes.

The copper-catalyzed enantioselective radical difunctionalization of alkenes from readily available alkyl halides and organophosphorus reagents possessing a P-H bond provides an appealing approach for the synthesis of α-chiral alkyl phosphorus compounds. The major challenge arises from the easy generation of a P-centered radical from the P-H-type reagent and its facile addition to the terminal side of alkenes, leading to reverse chemoselectivity. We herein disclose a radical 1,2-carbophosphonylation of styrenes in a highly chemo- and enantioselective manner. The key to the success lies in not only the implementation of dialkyl phosphites with a strong bond dissociation energy to promote the desired chemoselectivity but also the utilization of an anionic chiral N,N,N-ligand to forge the chiral C(sp3 )-P bond. The developed Cu/N,N,N-ligand catalyst has enriched our library of single-electron transfer catalysts in the enantioselective radical transformations.

General Synthesis of a Diatomic Catalyst Library via a Macrocyclic Precursor-Mediated Approach.

Heterogeneous catalysts containing diatomic sites are often hypothesized to have distinctive reactivity due to synergistic effects, but there are limited approaches that enable the convenient production of diatomic catalysts (DACs) with diverse metal combinations. Here, we present a general synthetic strategy for constructing a DAC library across a wide spectrum of homonuclear (Fe2, Co2, Ni2, Cu2, Mn2, and Pd2) and heteronuclear (Fe-Cu, Fe-Ni, Cu-Mn, and Cu-Co) bimetal centers. This strategy is based on an encapsulation-pyrolysis approach, wherein a porous material-encapsulated macrocyclic complex mediates the structure of DACs by preserving the main body of the molecular framework during pyrolysis. We take the oxygen reduction reaction (ORR) as an example to show that this DAC library can provide great opportunities for electrocatalyst development by unlocking an unconventional reaction pathway. Among all investigated sites, Fe-Cu diatomic sites possess exceptional high durability for ORR because the Fe-Cu pairs can steer elementary steps in the catalytic cycle and suppress the troublesome Fenton-like reactions.

Electrochemical Screening of Au/Pt Catalysts for the Thermocatalytic Synthesis of Hydrogen Peroxide Based on Their Oxygen Reduction and Hydrogen Oxidation Activities Probed via Voltammetric Scanning Electrochemical Microscopy

Electrochemical analysis provides a convenient way to screen active materials for thermocatalytic processes involving implicit electrochemical redox mechanisms. Here, we show how a combinatorial method based on scanning electrochemical microscopy (SECM) rapidly screens multiple catalysts for hydrogen peroxide direct synthesis reaction by independently analyzing their hydrogen oxidation and oxygen reduction reactivities on the same chip. We present a reproducible and quantifiable procedure to fabricate catalyst spot array samples using photolithography and microdispensing. This procedure enables the exploration of up to 10 catalysts with three replicates each on one chip, allowing us to study 30 compositions to identify reactive trends in a vast compositional space. SECM imaging with linear sweep voltammetry improved the accuracy and efficiency of data collection. Kinetic parameters of both half-reactions for each catalyst were extracted from experimental data with the help of established analytical theory and finite element analysis simulation. A library of AuxPty catalysts with a range of Au/Pt ratios from 1200:1 to 120:12 were examined. For the synthesized AuxPty catalysts, the rate constants of oxygen reduction and hydrogen reduction increase as Pt content increases and then level off beyond Au120Pt7. Therefore, to achieve the highest activity while keeping the cost low, Au120Pt7 would be a promising composition to further investigate. We believe this SECM-based technique will expedite the catalyst design and discovery process for classes of thermochemical reactions involving underlying heterolytic electrochemical mechanisms, thus assisting in the synthesis and utilization of sustainable fuels and commodity chemicals.

Exploring Structure-Function Relationships of Aryl Pyrrolidine-Based Hydrogen-Bond Donors in Asymmetric Catalysis Using Data-Driven Techniques.

Hydrogen bond-based organocatalysts rely on networks of attractive noncovalent interactions (NCIs) to impart enantioselectivity. As a specific example, aryl pyrrolidine substituted urea, thiourea, and squaramide organocatalysts function cooperatively through hydrogen bonding and difficult-to-predict NCIs as a function of the reaction partners. To uncover the synergistic effect of the structural components of this catalyst class, we applied data science tools to study various model reactions using a derivatized, aryl pyrrolidine-based, hydrogen-bond donor (HBD) catalyst library. Through a combination of experimentally collected data and data mined from previous reports, statistical models were constructed, illuminating the general features necessary for high enantioselectivity. A distinct dependence on the identity of the electrophilic reaction partner and HBD catalyst is observed, suggesting that a general interaction is conserved throughout the reactions analyzed. The resulting models also demonstrate predictive capability by the successful improvement of a previously reported reaction using out-of-sample reaction components. Overall, this study highlights the power of data science in exploring mechanistic hypotheses in asymmetric HBD catalysis and provides a prediction platform applicable in future reaction optimization.

Regulation of Chiral Phosphoric Acid Catalyzed Asymmetric Reaction through Crown Ether Based Host-Guest Chemistry.

Supramolecular asymmetric catalysis has arisen from the in-depth intersection of supramolecular chemistry and asymmetric catalysis due to its unique advantages in building chiral catalyst libraries and regulating performance of catalysts. Herein, we combine crown ether based host-guest chemistry with chiral phosphoric acid mediated asymmetric catalysis to actualize the supramolecular regulation of catalytic asymmetric two-component tandem acetalization reactions. By comparison with the catalytic reaction without host-guest interaction, improvement of up to 72% in yield and increases of up to 13% in enantioselectivity were acquired after addition of the alkali metal guests, which demonstrated the great advantages of this supramolecular regulation strategy.

Automated high-throughput activity and stability screening of electrocatalysts

Common high-throughput (HT) approaches rapidly assess the activity of electrocatalyst libraries toward electrochemical conversion reactions. The short time regime on which individual measurements are performed creates a false perception of catalyst durability, masking the true catalyst performance by the omission of detailed stability assessments during HT campaigns. Here, an automated scanning flow cell coupled to an inductively coupled plasma mass spectrometer was developed, allowing a simultaneous HT determination of the catalyst activity and stability. Fe-Ni and Fe-Ni-Co oxide libraries were automatically synthesized by a custom-programmed pipetting robot and examined as an oxygen evolution catalyst in neutral media, the advancement of which remains a great challenge. Ni-rich compositions in Fe-Ni oxides show higher activity but also significant catalyst loss due to the major Ni dissolution, which triggers Fe dissolution. Co-rich compositions in Fe-Ni-Co oxides attain the best synergy between activity and stability. • Automated scanning flow cell linked to inductively coupled plasma mass spectrometer • High-throughput platform allowing simultaneous activity and stability measurement • Neutral OER activity and in situ stability of Fe-Ni and Fe-Ni-Co oxides libraries • Automated synthesis using liquid-handling robot Transition metal oxides are an abundant and low-cost material class suitable as catalyst for electrochemical conversion reactions. The vast space of possible elemental combinations to construct such catalysts necessitates the use of accelerated laboratory experiments to rapidly screen material libraries for compositions with suitable properties. Activity and stability parameters of an electrocatalyst are key metrics that are decisive for their consideration as a promising candidate. Screening both performance indicators simultaneously in a high-throughput manner is crucial. The automation of an electrochemical flow cell coupled to an inductively coupled plasma mass spectrometer allows the rapid assessment of key catalyst parameters at the same time. Accelerating the material discovery exploration can help advancing key scientific areas and scientific knowledge needed for the energy transition of the society. High-throughput screening of multicompositional catalysts for electrocatalytic reactions significantly accelerates material development and discovery. While the activity of such catalyst libraries is the prime target of high-throughput investigations, the stability is often neglected, which plays a crucial role in defining the performance of electrocatalysts. The development of an automated platform involving a scanning flow cell coupled to an inductively coupled plasma mass spectrometer allows for a rapid measurement of the catalyst activity and stability simultaneously.