Separating ammonia from the reactor effluent remains a major energy bottleneck in industrial synthesis processes, where cryogenic condensation is typically employed. This method is energy-intensive, and alternative approaches such as pressure swing adsorption have not been widely adopted due to challenges associated with ammonia’s high affinity for adsorbents and the difficulty of complete regeneration under practical conditions. Here, we introduce pure- silica zeolites for this application. We determine first the high-pressure high-temperature adsorption data using a specially designed adsorption equipment. Our findings indicate that pure-silica zeolites exhibit high ammonia working adsorption capacity compared to previously reported commercial adsorbents. Molecular simulations provide information on adsorbate distribution and explain observed trends in adsorbed amounts and enthalpies. A 4-column 4- step pressure and temperature swing adsorption is designed and modeled at process relevant conditions, achieving ammonia purity above 99 % and recovery over 98 %, demonstrating the potential of replacing the energy intensive cryogenic separation.

Rare-earth element (REE) incorporation into dealuminated zeolites has been shown to catalyze a variety of selective oxygenate transformations, including ethanol to olefins, yet the structure and function of REE-incorporated Lewis acid zeotypes remain unclear. In this study, we proposed five yttrium acid site configurations and evaluated each against experimental physicochemical characterization techniques including X-ray absorption spectroscopy and pyridine Fourier transformed infrared spectroscopy (FTIR). Our analysis identified three fundamental site motifs, defect-open, dehydrated defect-open, and geminal hydroxyl, stabilized by adjacent silanol defects and hydroxyl groups that agreed with spectroscopic characterization. By comparing ethanol dehydration kinetics, we identified that interconvertible defect-open and dehydrated defect-open sites are kinetically relevant for catalytic turnovers. The three yttrium open site structural motifs from Y/deAlBeta were extended to 14 other REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) to explore trends in Lewis acid strength, assessed via pyridine adsorption energies and supported by experimentally measured pyridine FTIR. A linear correlation between Lewis acid strength and highest occupied molecular orbital + lowest unoccupied molecular orbital energies was established, offering a predictive framework for understanding structure-function relationships in REEs incorporated into dealuminated Beta zeotypes. These findings provide molecular-level insight into REE incorporation and its role in tuning Lewis acid strength for the selective catalytic transformation of biomass-derived oxygenates into chemicals and liquid fuels.

Developing advanced catalytic materials for mild-condition ammonia (NH3) synthesis is essential for improving the energy efficiency of this key industrial process. Here, we report a ζ-phase manganese-nitride (MnN0.43) catalyst for low-temperature NH3 synthesis. The as-synthesized MnN0.43 catalyst is protected by a carbon shell, allowing for storage and processing of the air-sensitive metal nitride under ambient conditions. After activation in situ, the MnN0.43 catalyst exhibits high activity for NH3 synthesis at 250-350 °C, surpassing the conventional noble metal based Ru/MgO catalyst. A combination of kinetic, chemisorption and computational studies indicate that a nitrogen vacancy-mediated associative mechanism accounts for the catalytic enhancements. Our work highlights the great potential of earth-abundant transition metal nitrides for catalyzing mild-condition NH3 synthesis.

Improving the efficiency of ammonia synthesis processes by integrating reaction with separation is a topic of long-standing interest. One approach is the use of sorption-enhanced catalytic reactors, where in situ ammonia sorption removes it from the vapor phase and allows reaction to proceed with ammonia yields beyond those dictated by thermodynamic equilibrium in the absence of sorption. While many sorbents have been used for this purpose, challenges remain with full regeneration at practical ammonia pressures limiting the potential benefits of sorption-enhanced reactors. Here, we introduce pure-silica zeolites for this application. First, we determine high-pressure high-temperature adsorption data using a specially designed adsorption equipment. Our findings indicate that pure-silica zeolites exhibit high ammonia working adsorption capacity compared to previously reported commercial adsorbents. Molecular simulations provide information on adsorbate distribution and explain observed trends in adsorbed amounts and enthalpies. A proof of concept is demonstrated using a batch sorption-enhanced catalytic reactor.

The development of energy-efficient catalysts for ammonia synthesis under mild conditions is crucial for reducing the energy demands and carbon footprint of the industrial Haber-Bosch process. In this study, we investigated ammonia synthesis via the associative Mars-van Krevelen (MvK) mechanism using B1-structured metal nitrides, focusing on manganese nitride (MnN) due to its low vacancy formation energy and potential as a metal-support interface. Density functional theory (DFT) calculations identified the MnN (100) facet as the most stable, with a nickel (Ni) nanowire implemented on the surface to facilitate H2 dissociation while surface nitrogen vacancies activate N2. A free energy diagram for Ni-MnN (100) at 350 degrees C was constructed and a dual-site microkinetic model was developed to determine reaction orders, apparent activation energies and the rate limiting step (RDS). To capture temperature-induced catalyst restructuring, ab initio molecular dynamics (AIMD) simulations and machine learning interatomic potentials (MLPs) were employed to improve the sampling of interfacial active sites over longer timescales. We found significant active site fluxionality leading to active site structural rearrangements that reduced vacancy formation energies. A hydrogen coverage analysis at reaction temperatures revealed coverage-dependent dynamic restructuring of Ni active sites, with lowered free energy change of the RDS that correlates with Ni p-Band center. MLPs were observed to predict coverage-dependent fluxionality with training data exclusive to high coverage regimes. By integrating DFT, AIMD, and MLP-based molecular dynamics, we established a computational framework for understanding dynamic metal-support interactions in transition metal nitride catalysts, demonstrating its applicability not only to ammonia synthesis under mild conditions but also to broader classes of supported catalysts and reactions.

Adenosine triphosphate (ATP) and other nucleotides can be irreversibly bound to the metal-organic framework (MOF) MIL-101(Cr). Analysis of X-ray diffraction data suggests that the location of the adsorbed ATP molecule is in proximity of the Cr3 clusters. Solid-state NMR and DFT calculations indicate that ATP is bound to MIL-101(Cr) through linkages of the terminal phosphate group with Cr(III) of the framework. In the presence of Cu(II) ions, the MOF-supported nucleotides can function as stable and reusable enantioselective heterogeneous catalysts for reactions like Diels-Alder and Michael addition. Compared to the corresponding homogeneous nucleotide-based artificial metalloenzymes (ArMs), the MOF-supported nucleotide-based ArMs exhibit significantly enhanced activity and selectivity in certain cases, demonstrating their potential as a new class of enantioselective heterogeneous catalysts.

Understanding the dynamic evolution of Cu species under varying environmental conditions is critical for addressing challenges related to the activity and the stability of copper-based catalysts in thermo-, photo-, and electrocatalysis. However, metal–metal interactions between dual single atoms and their effects on Cu evolution after exposure to different environmental molecules remain underexplored. Herein, we synthesized bimetallic Cu-Y/Beta catalysts with dual single-atom Cu and Y sites and monometallic Cu-Beta catalysts with isolated Cu sites in dealuminated Beta zeolites. By varying Cu and Y compositions, diatomic interactions were studied under H 2 and ethanol atmospheres. With 6 wt% Y loading, approximately 0.4 wt% of Cu species in Cu-Y/Beta remained partially oxidized as Cu(I) after reduction in pure H 2 at 350 °C, in contrast to the full transition to metallic Cu observed in Cu-Beta. Combining X-ray absorption spectroscopy with kinetic studies revealed that metallic Cu became the predominant species after reduction with H 2 as Cu loading increased from 0.4 to 1.7 wt%, quadrupling the initial ethanol dehydrogenation rate and demonstrating the dominant role of Cu(0) sites. Scanning transmission electron microscopy and density functional theory simulations indicated spatial proximity between dual single-atom Cu and Y sites and elucidated Cu speciation controlled by diatomic interactions.

Water plays a pivotal role in numerous chemical processes, especially in the production of fuels and fine chemicals de-rived from bio-based feedstocks. Zeolites are porous catalysts used extensively due to their shape-selective adsorption and confinement interactions; However the kinetics of zeolite-catalyzed reactions are significantly impacted by the presence of water, which may affect product selectivity and intrinsic rate constants depending on transition state polarity. In this study, we employed machine learning force fields (MLFFs) to accelerate ab initio molecular dynamics (AIMD) simulations and enhance the phase space exploration of water configurations in a model Brønsted acid zeolite, H-AFI. We interrogated the structure of adsorbed water based on the Si/Al ratio and acid site distribution to disentangle the impact of acid site density and distribution on water matrix organization as a function of water loading. We integrated adsorption thermodynamics, vibrational spectroscopy simulations, and local density maps to interrogate the spatial orientation of adsorbed water clusters and their degree of hydrogen bonding. Our analysis unveiled the intricate interplay between zeolite structure, Brønsted acid site location, and water where spatially disparate acid sites nucleate extended clusters that span siliceous regions of the zeolite. We found that the length scale of ordered water regions is directly related to the Si/Al ratio and spatial distribution of Al sites. These findings provide insights into the molecular-level structure of water in microporous aluminosilicate micropores and demonstrate how acid sites can be used to control water activity which has applications to heterogeneous catalysis and adsorptive separations.

Microporous catalysts are ubiquitous in chemical processes including sustainable transformations of biobased feedstocks into fuels and fine chemicals. The mechanistic insights needed to design next-generation microporous catalysts can be obtained with ab initio simulations coupled with microkinetic modeling, yet active site confinement complicates an accurate determination of adsorbate entropies, which, in turn, affect predictions of rate and equilibrium constants. In this study, we developed a machine learning force field (MLFF) strategy to rapidly predict temperature-dependent quasi-harmonic adsorbate entropies in zeolite Beta, reducing the number of compute-intensive ab initio molecular dynamics calculations needed to construct a microkinetic model. These entropies directly impacted the kinetics of a model parallel reaction mechanism. We chose lactic acid dehydration to acrylic acid on aluminosilicate zeolite Beta to explore the pathway dependence of unselective product formation and initial deactivation mechanisms using microkinetic modeling with our MLFF entropy strategy. The resulting quasi-harmonic entropy approximations led to shifts in steady-state coverages that impacted reaction orders and product selectivity. At low lactic acid partial pressures, concerted monomolecular decarbonylation is favored over Br & oslash;nsted acid sites, which then shifts at high lactic acid partial pressures to concerted bimolecular condensations into lactic acid oligomers. Sequential pathways mediated by adsorbed alkoxide or carbonyl intermediates have no kinetic relevance at these conditions. These findings provide a strategy to integrate quasi-harmonic entropies into microkinetic modeling that is scalable with reaction temperature and applicable to a wide range of catalysts and catalytic cycles.

Glyphosate, the most widely used herbicide globally, is accumulating in the environment and poses significant potential eco- and bio-toxicity risks. While natural attenuation of glyphosate has been reported, the efficacy varies considerably and the dominant metabolite, aminomethylphosphonic acid (AMPA), is potentially more persistent and toxic. This study investigated the bioelectrochemical system (BES) for glyphosate degradation under anaerobic, reductive conditions. Atomistic simulations using density functional theory (DFT) predicted increased thermodynamic favorability for the non-dominant C-P lyase degradation pathway under external charge, which suppressed AMPA production. Experimental results confirmed that cathodic poised potential (-0.4V vs. Ag/AgCl) enhanced glyphosate degradation compared to abiotic and non-electric control conditions (75% vs. ∼40% degradation after 37 days), and lowered the AMPA yield (0.52 mol AMPA yield per mol glyphosate removed in BES vs. 0.77-0.86 mol/mol in the control conditions). Geobacter lovleyi was likely the active species driving the C-P lyase pathway, as evidenced by the increase of its relative abundance, the preservation of its electron transfer genes (most notably ferredoxin) and the up-regulation of its phnJ and hydroxylamine reductase (hcp) genes.

The molecular mechanisms that drive adsorption are critical for engineering new adsorbents to capture environmental contaminants, such as perfluoroalkyl substances (PFAS). Metal-organic frameworks (MOFs) have been shown to adsorb some classes of PFAS, yet a fundamental understanding of how PFAS identity and water competition affect adsorption capacity is unknown. Here, grand canonical Monte Carlo simulations of perfluoroalkanoic acids (PFAAs) adsorption in the MOF NU-1000 were performed with coadsorbed water and varying carbon chain length sizes to interrogate how PFAS structure affects adsorption capacity. We found that larger PFAAs adsorb favorably into NU-1000 than shorter chain PFAAs due to the formation of pore-filling aggregates that stabilize anionic adsorption to the node. Due to their size and hydrophilicity, shorter chains tend to limit interactions with the adsorbent. These insights offer directions for developing novel materials that promote aggregate formation to capture and retain a wider set of PFAS from aqueous solutions.

Adenosine triphosphate (ATP) and other nucleotides can be irreversibly bound to the metal-organic framework (MOF) MIL-101(Cr). Analysis of X-ray diffraction data suggests that the location of the adsorbed ATP molecule is in proximity of the Cr3 clusters. Solid-state NMR and DFT calculations indicate that ATP is bound to MIL-101(Cr) through linkages of the terminal phosphate group with Cr(III) of the framework. In the presence of Cu(II) ions, the MOF-supported nucleotides can function as stable and reusable enantioselective heterogeneous catalysts for reactions like Diels-Alder and Michael addition. Compared to the corresponding homogeneous nucleotide-based artificial metalloenzymes (ArMs), the MOF-supported nucleotide-based ArMs exhibit significantly enhanced activity and selectivity in certain cases, demonstrating their potential as a new class of enantioselective heterogeneous catalysts.

Amorphous porous organic polymers show promise for energy-efficient adsorptive separations, but it is difficult to understand or improve their performance through intentional structural modification. Herein, we report the synthesis of porous aromatic frameworks (PAFs) with pore structures tailored by the incorporation of a monofunctionalized end-capping monomer that disrupts framework topology. Combining experimental characterization with molecular simulations, we show that this defect engineering strategy yields less densely crosslinked networks, which leads to pore collapse and the presence of unique adsorption sites. These defect-engineered PAFs exhibit enhanced removal of 1,4-dioxane, an important environmental pollutant, from water. Increasing the concentration of end-capping monomers produces PAFs with narrower pore size distributions and improved 1,4-dioxane uptake. These results illustrate that defect engineering can effectively modulate polymer connectivity and porosity for applications in selective adsorptive separations. This technique avoids post-synthetic treatments and presents another approach to tailor amorphous polymeric adsorbents.

Synchrotron spectroscopy and Density Functional Theory (DFT) are combined to develop a new descriptor for the stability of adsorbed chemical intermediates on metal alloy surfaces. This descriptor probes the separation of occupied and unoccupied d electron density in platinum and is related to shifts in Resonant Inelastic X-ray Scattering (RIXS) signals. Simulated and experimental spectroscopy are directly compared to show that the promoter metal identity controls the orbital shifts in platinum electronic structure. The associated RIXS features are correlated with the differences in the band centers of the occupied and unoccupied d bands, providing chemical intuition for the alloy ligand effect and providing a connection to traditional descriptions of chemisorption. The ready accessibility of this descriptor to both DFT calculations and experimental spectroscopy, and its connection to chemisorption, allow for deeper connections between theory and characterization in the discovery of new catalysts.

Lithium-sulfur (Li-S) batteries are one promising alternative to Li-ion batteries due to their higher theoretical specific capacity and energy density. However, several technical challenges such as polysulfide shuttling remain. As liquid polysulfide diffusion into the electrolyte causes a loss of capacity, different material classes have been explored to anchor lithium polysulfides and reduce active material loss. The metal-organic framework (MOF) UiO-66 has been identified as one candidate material due to its porosity, high surface area, and zirconium oxide nodes that could anchor liquid polysulfides. MOFs also allow for post-synthetic modifications that can increase their adsorption specificity towards liquid polysulfides and reduce shuttling. In this work, we combined atomistic simulations and experimental characterization to probe the molecular interactions between lithium polysulfides and functionalized UiO-66 nodes. We explored how lithium polysulfides adsorb to open sites caused by missing linker defects, as well as sites functionalized with alkali cations. Our results demonstrate that lithium polysulfides adsorb favorably to UiO-66 through Li-O electrostatic interactions. In addition, we found that nodes functionalized with alkali metals demonstrated stronger adsorption of long chain lithium polysulfides (Li2S4-8) by facilitating charge transfer to the nodes. Experimental UV-Vis and 7Li-NMR measurements on Zr polyoxometallates and UiO-66 provided further evidence that lithiation favors adsorption of long chain polysulfides. Our findings show how UiO-66 functionalization may inhibit the shuttle effect through polysulfide adsorption, and consequently im-prove Li-S battery performance. The fundamental insights into polysulfide adsorption shown here provide quantitative principles to design functionalized moieties and further inhibit polysulfide shuttling.

Postsynthetic modification (PSM) of metal-organic frameworks (MOFs) enables incorporation of diverse functionalities in pores for chemical separations, drug delivery, and heterogeneous catalysis. However, the effect of PSM on molecular transport, which is essential for most applications of MOFs, has been rarely studied. In this paper, we used perfluoroalkane-functionalized Zr-MOF NU-1008 as a platform to systematically interrogate transport processes and mechanisms in solvated pores. We anchored perfluoroalkanes onto NU-1008 nodes by solvent-assisted ligand incorporation (SALI-n, with n = 3, 5, 7, and 9 denoting the number of fluorinated carbons). Transport of a luminescent molecule, BODIPY, through individual crystallites of four versions of methanol-filled SALI-n was monitored by confocal fluorescence microscopy as a function of time and location. In comparison with the parent NU-1008, the diffusivity of the probe molecules within SALI-n declined by 2- to 7-fold depending on chain length and loading, presumably due to the reduction in pore diameter or adsorptive interactions with perfluoroalkyl chains. Atomistic simulations were performed to uncover the microscopic behavior of the BODIPY diffusion in SALI-n. The perfluoroalkyl chains are observed to stay close to the pore walls, instead of extending toward the pore center. BODIPY molecules, which preferably interact with linkers, were pushed to the interior of the channels as the chain length increased, resulting in solvated diffusion and minor differences in the short-time mobility of BODIPY in SALI-n. This suggested that the observed decline of transport diffusivity in SALI-n mainly stemmed from the reduction in the pore size when these flexible chains are present. We anticipate that this proof of concept will assist in understanding how pore functionalization can physically and chemically affect mass transport in MOFs and will be useful in further guiding the design of PSM to realize the optimal performance of MOFs for various applications.

The complexation kinetics between quinoneradicals and CO2 have been measured under different electrochemicalconditionsto inform the design of electrochemically mediated carbon capturesystems. Carbon capture driven by renewable electricity representsa promisingapproach to mitigate carbon dioxide (CO2) emissions andcombat climate change. Electrochemically mediated carbon capture canbe achieved by developing redox-active Lewis bases, with quinonesbeing the most representative chemistry. In aprotic electrolytes,a subset of quinoid species can selectively uptake CO2 froma dilute feed upon electro-reduction via a nucleophilic addition reactionand release a concentrated CO2 product stream upon oxidation.However, there is a lack of quantitative understanding of the reactionkinetics landscape of redox-active CO2 sorbents, especiallyconsidering the complex nature of the multi-component electrolytemedia they must be deployed in. To bridge this knowledge gap, we investigatethe bimolecular reaction rate constant between CO2 andradical anions of various quinones in a range of electrolytes usingan electroanalytical technique. Combined with molecular dynamics anddensity functional theory calculations, we provide insights into thecomplex interplay between quinone chemistry, supporting salt composition,and electrolyte solvents on the intrinsic CO2 adduct formationkinetics. To summarize some key observations, we found that the reactionrate is affected by both the identity and concentration of the cationicand anionic species in the supporting electrolyte, the presence ofhydrogen-bonding additives may accelerate the kinetics, and ortho-isomersof quinones have a faster reaction rate than para-isomers. We believethe work can help guide the rational design of electrochemical microenvironmentsfor enhanced electrochemically mediated carbon capture performance.

Microporous zeolites have pores of molecular dimension that can stabilize desired chemical pathways but may also introduce mass-transfer limitations. Now, synthesis protocols allow for greater control of catalyst active-site location via elemental zoning, enabling an alternative strategy to reduce mass-transfer limitations and consequently improve catalyst performance for methanol-to-hydrocarbon reactions.