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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Activity of Silica-Alumina for the Conversion of Polyethylene into Tunable Aromatics Below Pyrolytic Temperatures

Plastic waste is a mounting problem that lacks global strategy, largely due to inadequate recycling capabilities. One alternative gaining traction in the heterogeneous catalysis community is the upcycling of polyolefins into value-added products, such as hydrogen-free conversion to alkylaromatic compounds over Pt/Al 2 O 3 . Here, we examined the activity of nominally metal-free, mesoporous silica-alumina mixed oxide materials (SiO 2 –Al 2 O 3 ) for the conversion of polyethylene into aromatic compounds at temperatures of and below 280 °C. Yields with the silica-alumina catalysts are comparable to those obtained over Pt(1 wt %)/Al 2 O 3 under identical conditions, and product selectivity can be tuned by altering reaction conditions or the acid site density of the SiO 2 –Al 2 O 3 . Notably, the fraction of polyaromatic products increases with the Brønsted acid site density of the catalyst, as does the degree of polymer deconstruction. These catalysts can be reused without regeneration, and their activity improves with each recycling event, producing soluble product yields up to 83%. Preliminary work on the mechanism of the reaction suggests that acid sites are responsible for initiating depolymerization and aromatization reactions, in analogy to previous work in the literature. Finally, this work showcases the activity of SiO 2 –Al 2 O 3 for polyolefin deconstruction/aromatization at subpyrolytic temperatures and lays the foundation for future studies involving solid acid and bifunctional catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Size Transformation of the Au 22 (SG) 18 Nanocluster and Its Surface-Sensitive Kinetics

For many applications of well-defined gold nanoclusters, it is desirable to understand their structural evolution behavior under working conditions with molecular precision. Here we report the first systematic investigation of the size transformation products of the Au 22 (SG) 18 nanocluster under representative working conditions and highlight the surface effect on the transformation kinetics. Under thermal and aerobic conditions, the consecutive and pH-dependent transformation from Au 22 to both well-defined clusters and small Au(I)SR species was identified by ESI-MS and UV-vis spectroscopy. By introducing a perturbation onto the Au 22 surface, significant changes in the activation parameters were determined from the kinetic study of the Au 22 transformation. This indicates the sensitivity of the nanocluster transformation pathway to the cluster surface. Finally, the systematic study of cluster transformation and the sensitivity of cluster transformation to the surface revealed herein has significant implications for future attempts to design gold nanoparticles with adaptation to the working environment and the regeneration of active nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Perspectives on Dye Sensitization of Nanocrystalline Mesoporous Thin Films

Recent advances in our mechanistic understanding of dye-sensitized electron transfer reactions occurring at metal oxide interfaces are described. These advances were enabled by the advent of mesoporous thin films, comprised of anatase TiO 2 nanocrystallites, that are amenable to spectroscopic and electrochemical characterization in unprecedented molecular-level detail. The metal-to-ligand charge transfer (MLCT) excited states of Ru polypyridyl compounds serve as the dye sensitizers. Excited-state injection often occurs on ultrafast time scales with yields that can be tuned from unity to near zero through modification of the sensitizer or the electrolyte composition. Transport of the injected electron and the oxidized sensitizer (hole hopping) are both operative in the composite mechanism for charge recombination between the injected electron and the oxidized sensitizer. Sensitizers that contain a pendant electron donor, as well as core/shell SnO 2 /TiO 2 nanostructures, often prolong the lifetime of the injected electron and provide fundamental insights into adiabatic and nonadiabatic electron transfer mechanisms. Regeneration of the oxidized sensitizer by iodide is enhanced through halogen bonding, orbital pathways, and ion pairing. A substantial ~10 MV cm –1 electric field is created by electron injection into TiO 2 nanocrystallites that induces ion migration, reports on the sensitizer dipole orientation, and (in some cases) reorients or flips the sensitizer. Dye-sensitized conductive oxides also promote long-lived charge separation with bias dependent kinetics that provide insights into the reorganization energies associated with electron and proton-coupled electron transfer in the electric double layer.

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

Ene Reactivity of an Fe=NR Bond Enables the Catalytic α-Deuteration of Nitriles and Alkynes

Herein, we report the reactions of an Fe(II) imido complex [Ph 2 B( t BuIm) 2 Fe=NDipp] – (1) with internal alkynes and isobutyronitrile, affording the Fe amido allenyl complexes [Ph 2 B( t BuIm) 2 Fe(NHDipp)((R 1 )C=C=C(R 2 )(H))] – (R 1 = Et or n Pr; R 2 = Me or Et, 2–5) and the Fe amido keteniminate complex [Ph 2 B( t BuIm) 2 Fe(NHDipp)(N=C=CMe 2 )K(THF)] n (8-K), respectively. These transformations represent the previously unknown ene-like reactivity of a metal–ligand multiple bond. Stoichiometric reactions of 2 and 8-K with DippNH 2 lead to the regeneration of 3-hexyne and isobutyronitrile, respectively, with concomitant formation of the bis(anilido) complex [Ph 2 B( t BuIm) 2 Fe(NHDipp) 2 ] – (9). These results provide the platform for 1 as an efficient catalyst for the selective α-deuteration of nitriles and alkynes by RND 2 . Furthermore, these results demonstrate a new reaction mode for metal imido complexes and suggest new avenues for using the imido ligand in catalysis.

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

Catalytic Chemical Recycling of Post-Consumer Polyethylene

Among commercial plastics, polyolefins are the most widely produced worldwide but have limited recyclability. Here, we report a chemical recycling route for the conversion of post-consumer high-density polyethylene (HDPE) into telechelic macromonomers suitable for circular reprocessing. Unsaturation was introduced into HDPE by catalytic dehydrogenation using an Ir-POCOP catalyst without an alkene acceptor. Cross-metathesis with 2-hydroxyethyl acrylate followed by hydrogenation transformed the partially unsaturated HDPE into telechelic macromonomers. The direct repolymerization of the macromonomers gave a brittle material due to the low overall weight-average molecular weight. Aminolysis of telechelic macromonomers with a small amount of diethanolamine increased the overall functionality. The resulting macromonomers were repolymerized through transesterification to generate a polymer with comparable mechanical properties to the starting post-consumer HDPE waste. Finally, depolymerization of the repolymerized material catalyzed by an organic base regenerated the telechelic macromonomers, thereby allowing waste polyethylene materials to enter a chemical recycling pathway.

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

Molecular Switch Cobalt Redox Shuttle with a Tunable Hexadentate Ligand

Strong-field hexadentate ligands were synthesized and coordinated to cobalt metal centers to result in three new low-spin to low-spin Co(III/II) redox couples. The ligand backbone has been modified with dimethyl amine groups to result in redox potential tuning of the Co(III/II) redox couples from –200 to –430 mV versus Fc +/0 . The redox couples surprisingly undergo a reversible molecular switch rearrangement from five-coordinate Co(II) to six-coordinate Co(III) despite the ligands being hexadentate. The complexes exhibit modestly faster electron self-exchange rate constants of 2.2–4.2 M –1 s –1 compared to the high-spin to low-spin redox couple [Co(bpy) 3 ] 3 + /2 + at 0.27 M –1 s –1 , which is attributed to the change in spin state being somewhat offset by this coordination switching behavior. The complexes were utilized as redox shuttles in dye-sensitized solar cells with the near-IR AP25 + D35 dye system and exhibited improved photocurrents over the [Co(bpy) 3 ] 3 + /2 + redox shuttle (19.8 vs 18.0 mA/cm 2 ). Finally, future directions point toward pairing the low-spin to low-spin Co(II/III) tunable series to dyes with significantly more negative highest occupied molecular orbital potentials that absorb into the near-IR where outer sphere redox shuttles have failed to produce efficient dye regeneration.

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

Adaptive Pore Opening to Form Tailored Adsorption Sites in a Cooperatively Flexible Framework Enables Record Inverse Propane/Propylene Separation

A proposed low-energy alternative to the separation of alkanes from alkenes by energy-intensive cryogenic distillation is separation by porous adsorbents. Unfortunately, most adsorbents preferentially take up the desired, high-value major component alkene, requiring frequent regeneration. Adsorbents with inverse selectivity for the minor component alkane would enable the direct production of purified, reagent-grade alkene, greatly reducing global energy consumption. However, such materials are exceedingly rare, especially for propane/propylene separation. Here, we report that through adaptive and spontaneous pore size and shape adaptation to optimize an ensemble of weak noncovalent interactions, the structurally responsive metal-organic framework CdIF-13 (sod-Cd(benzimidazolate) 2 ) exhibits inverse selectivity for propane over propylene with record-setting separation performance under industrially relevant temperature, pressure, and mixture conditions. Powder synchrotron X-ray diffraction measurements combined with first-principles calculations yield atomic-scale insight and reveal the induced fit mechanism of adsorbate-specific pore adaptation and ensemble interactions between ligands and adsorbates. Dynamic column breakthrough measurements confirm that CdIF-13 displays selectivity under mixed-component conditions of varying ratios, with a record measured selectivity factor of α ≈ 3 at 95:5 propylene:propane at 298 K and 1 bar. When sequenced with a low-cost rigid adsorbent, we demonstrated the direct purification of propylene under ambient conditions. In conclusion, this combined atomic-level structural characterization and performance testing firmly establishes how cooperatively flexible materials can be capable of unprecedented separation factors.

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

Reduction of CO to Methanol with Recyclable Organic Hydrides

We report the reaction steps for the selective conversion of a transition metal carbonyl complex to a hydroxymethyl complex that releases methanol upon irradiation with visible light have been successfully quantified in acetonitrile solution with dihydrobenzimidazole organic hydride reductants. Dihydrobenzimidazole reductants have been shown to be inactive toward H 2 generation in the presence of a wide range of proton sources and have been regenerated electrochemically or photochemically. Specifically, the reaction of cis-[Ru(bpy) 2 (CO) 2 ] 2+ (bpy = 2,2'-bipyridine) with one equivalent of a dihydrobenzimidazole quantitatively yields a formyl complex, cis-[Ru(bpy) 2 (CO)(CHO)] + , and the corresponding benzimidazolium on a seconds time scale. Kinetic experiments revealed a first-order dependence on the benzimidazole hydride concentration and an unusually large kinetic isotope effect, inconsistent with direct hydride transfer and more likely to occur by an electron transfer-proton-coupled electron transfer (EΤ-PCET) or related mechanism. Further reduction/protonation of cis-[Ru(bpy) 2 (CO)(CHO)] + with two equivalents of the organic hydride yields the hydroxymethyl complex cis-[Ru(bpy) 2 (CO)(CH 2 OH)] + . Visible light excitation of cis-[Ru(bpy) 2 (CO)(CH 2 OH)] + in the presence of excess organic hydride was shown to yield free methanol. Identification and quantification of methanol as the sole CO reduction product was confirmed by 1 H NMR spectroscopy and gas chromatography. The high selectivity and mild reaction conditions suggest a viable approach for methanol production from CO, and from CO 2 through cascade catalysis, with renewable organic hydrides that bear similarities to Nature's NADPH/NADP + .

14 SOLAR ENERGY↗
DOE OSTI2024

Supramolecular Motion Enables Chondrogenic Bioactivity of a Cyclic Peptide Mimetic of Transforming Growth Factor-β1

Transforming growth factor (TGF)-β1 is a multifunctional protein that is essential in many cellular processes that include fibrosis, inflammation, chondrogenesis, and cartilage repair. In particular, cartilage repair is important to avoid physical disability since this tissue does not have the inherent capacity to regenerate beyond full development. We report here on supramolecular coassemblies of two peptide amphiphile molecules, one containing a TGF-β1 mimetic peptide, and another which is one of two constitutional isomers lacking bioactivity. Using human articular chondrocytes, we investigated the bioactivity of the supramolecular copolymers of each isomer displaying either the previously reported linear form of the mimetic peptide or a novel cyclic analogue. Based on fluorescence depolarization and 1 H NMR spin–lattice relaxation times, we found that coassemblies containing the cyclic compound and the most dynamic isomer exhibited the highest intracellular TGF-β1 signaling and gene expression of cartilage extracellular matrix components. Here, we conclude that control of supramolecular motion is emerging as an important factor in the binding of synthetic molecules to receptors that can be tuned through chemical structure.

Antigens↗
DOE OSTI2025

Photodriven Ammonia Synthesis from N 2 and H 2 : Recycling of a Molecular Molybdenum Nitride

Here, the synthesis of ammonia from its elements, N 2 and H 2 , is the most atom-economical and thermodynamically preferred route but presents a high kinetic barrier and thus is rare using molecular compounds. Irradiation of a molecular molybdenum nitride prepared from N 2 cleavage with visible light in the presence of an iridium photocatalyst and 1–4 atm of H 2 produced high yields of ammonia along with the formation of a cationic, formally molybdenum(VI) pentahydride as the major molybdenum-containing product. Continued irradiation of the molybdenum hydride under an N 2 atmosphere resulted in regeneration of the molybdenum nitride that was recycled and used for additional hydrogenation to generate more ammonia, demonstrating superstoichiometric batch ammonia synthesis using only N 2 and H 2 with molecular compounds under ambient conditions.

Hydrogenation↗
DOE OSTI2025

CO Adsorbates Induced Framework-Associated Low-Valence Co δ+ Sites in Co-ZSM-5 for Ethane Dehydrogenation

The dynamic structural evolution of heterogeneous catalysts is a ubiquitous phenomenon that has attracted a lot of interest. Catalyst reconstruction can occur after appropriate pretreatment, resulting in more efficient active catalysts, which is an attractive but challenging issue. Here, we reveal a CO activation strategy that controls the microenvironment of the Co sites in the high-silica Co-ZSM-5 catalyst (denoted as 0.50Co-Z5(340)), resulting in three times higher initial conversion and superior regeneration durability in the ethane dehydrogenation reaction compared to the same catalyst without CO pretreatment. In situ spectroscopy and metadynamics simulations reveal that the Co 2+ sites in 0.50Co-Z5(340) dislodge from the framework and move toward the nearby Brønsted acid sites, forming framework-associated low-valence Co δ+ species. Mechanistic studies indicate that the Co δ+ species catalyze ethane C–H bond cleavage via an oxidative addition mechanism, and ethylene is produced simultaneously with H* coupling (direct pathway). The promoted C–H bond activation and facile ethylene desorption explain the superior ethane dehydrogenation performance of the herein CO preactivated 0.50Co-Z5(340) catalyst.

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

Metal–Metal Bonding Influences Hydride Reactivity in [Sn–Rh] 3+ and [Sn–Ni] 2+ Bimetallics

Heavier group 14 metal hydrides serve as key intermediates in catalytic transformations, such as hydroboration. Regenerating such intermediates via a clean hydride source like dihydrogen could provide catalytic processes with a more economical alternative to, e.g., silanes and hydridoborane reagents. Herein, we report our efforts toward this goal using a [Sn–Rh] 3+ bimetallic system with the formal Rh I center acting as a potential dihydrogen activator. Targeting the introduction of a hydride ligand to the bimetallic core, our reactivity studies have revealed a preference for the hydride ligand to be bound to the Rh center, instead of the Sn center. Finally, examination of the electronic structures of these complexes via theoretical and experimental methods has revealed the electron acceptor nature of the Rh center within the bimetallic core and offers an explanation for the localization of the hydride between metal centers.

anions↗
DOE OSTI2026

Hydrophobic Metal–Organic Frameworks Enable Superior High-Pressure Ammonia Storage through Geometric Design

Hydrophobic metal–organic frameworks (MOFs) are typically overlooked for ammonia storage due to weak host–guest interactions. Here, we demonstrate that four structurally analogous aluminum-based MOFs exhibit a counterintuitive behavior whereby framework geometry, rather than ligand hydrophilicity, determines high-pressure NH 3 adsorption performance. The hydrophobic CAU-23 achieved an exceptional capacity matching hydrophilic analogs despite its poor low-pressure uptake. This pressure-dependent enhancement stems from the unique 4-cis-4-trans geometry of CAU-23 compared to the purely cis arrangement of MIL-160 and KMF-1 and the alternating cis-trans configuration of MOF-303. Critically, CAU-23 retained 95% capacity over three high-pressure cycles, whereas hydrophilic MOFs suffered 39–46% irreversible losses due to strong NH 3 -framework interactions that compromise structural integrity. Grand canonical Monte Carlo simulations reveal that high pressure enables NH 3 clustering through intermolecular hydrogen bonding, bypassing the need for strong host–guest interactions. High-pressure powder X-ray diffraction measurements confirm the exceptional mechanical resilience of CAU-23, showing complete structural recovery upon decompression despite exhibiting the highest pressure sensitivity among the studied MOFs. An extended analog, HE-CAU-23, validates this design principle with further enhanced capacity. Furthermore, these findings reveal a paradigm shift toward hydrophobic MOFs with optimized geometry for high-performance and regenerable gas storage applications.

MOFs↗
DOE OSTI2026

Sulfite Is Not Required for N 2 Reduction Catalyzed by Mo-Nitrogenase

Mo-nitrogenase catalyzes the reduction of dinitrogen (N 2 ) to two ammonia (NH 3 ) at the active-site FeMo-cofactor. Substrate activation requires the accumulation of three or four electrons and protons as two Fe-bound hydrides and is coupled to obligatory H 2 release through reductive hydride elimination. Subsequent delivery of four or five additional electrons and protons to the bound N 2 yields two NH 3 molecules. Increasing evidence suggests that at least one belt sulfide within FeMo-cofactor is dynamically involved in the catalytic cycle. A recent report further proposed that sulfite (SO 3 2− ) is required for N 2 reduction, with sulfite binding required for NH 3 release and a subsequent six-electron reduction of the bound sulfite to regenerate the resting cofactor. To test this proposal, we conducted turnover studies of Mo-nitrogenase under sulfite-free conditions using a reduced viologen as reductant and protein preparations devoid of dithionite or sulfite. Under these conditions, nitrogenase effectively catalyzed both N 2 reduction and proton reduction, exhibiting steady-state turnover under N 2 for 6 min, with a turnover number exceeding 150, approaching that observed with dithionite as reductant. The same H 2 -formed/N 2 -reduced ratio was observed whether dithionite or the viologen species was used as reductant. Further, EPR spectroscopic analyses showed that the FeMo-cofactor returned to its resting state after multiple catalytic cycles in the absence of sulfite. Finally, physiological bypass of sulfite formation does not affect the capacity for diazotrophic growth of the model nitrogen-fixing organism Azotobacter vinelandii . Finally, these results demonstrate that sulfite is not required for Mo-nitrogenase-catalyzed N 2 reduction either in vitro or in vivo .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Pore-Space-Partition-Enabled Exceptional Ethane Uptake and Ethane-Selective Ethane–Ethylene Separation

A modell material for C 2 H 6 /C 2 H 4 separation would simultaneously have the highest C 2 H 6 uptake capacity and the highest C 2 H 6 /C 2 H 4 selectivity. But such material is elusive. A benchmark material for ethane-selective C 2 H 6 /C 2 H 4 separation is peroxo-functionalized MOF-74-Fe that exhibits the best known separation performance due to its high C 2 H 6 /C 2 H 4 selectivity (4.4), although its C 2 H 6 uptake capacity is moderate (74.3 cm 3 /g). Here, we report a family of pore-space-partitioned crystalline porous materials (CPMs) with exceptional C 2 H 6 uptake capacity and C 2 H 6 /C 2 H 4 separation potential (i.e., C 2 H 4 recovered from the mixture) despite their moderate C 2 H 6 /C 2 H 4 selectivity (up to 1.75). The ethane uptake capacity as high as 166.8 cm 3 /g at 1 atm and 298 K, more than twice that of peroxo-MOF-74-Fe, was previously achieved even though the isosteric heat of adsorption (21.9–30.4 kJ/mol) for these CPMs is as low as about one-third of that for peroxo-MOF-74-Fe (66.8 kJ/mol). While the overall C 2 H 6 /C 2 H 4 separation potentials have not yet surpassed peroxo-MOF-74-Fe, these robust CPMs exhibit outstanding properties including high thermal stability (up to 450 °C) and aqueous stability, low regeneration energy, and a high degree of chemical and geometrical tunability within the same isoreticular framework.

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

Integrated CO 2 Capture and Conversion to Formate with a Molecular Platinum Bis(diphosphine) Electrocatalyst

Carbon dioxide is a potentially valuable feedstock for carbon-based fuels or commodities but is only available in dilute streams. Many studies have focused on either the capture and concentration of CO 2 or the reduction of pure CO 2 streams. The direct reduction of sorbent-captured CO 2 in an integrated process would skip the energy-intensive CO 2 concentration and sorbent regeneration step. Herein, we report the electrocatalytic reduction of 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-carboxylate (IPr·CO 2 ), which forms quantitatively from the reaction of sorbent 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with 10% and 0.04% CO 2 streams, by catalyst [Pt(dmpe) 2 ](PF 6 ) 2 (dmpe = 1,2-bis(dimethylphosphino)ethane) to formate with >70% Faradaic efficiencies. Unexpectedly, experimental studies indicate that the proton source phenol facilitates rapid decarboxylation of IPr·CO 2 to release CO 2 , which is the substrate for reduction. Kinetic studies determined the rate of hydride transfer from a catalytic intermediate [HPt(dmpe) 2 ](PF 6 ) to form the C–H bond in formate to be 0.22 M –1 s –1 . Further details on the mechanism, transition state energy, and structure for hydride transfer to CO 2 , a common step in CO 2 reduction, were explored using computational methods.

Chemistry↗
DOE OSTI2026

Aqueous Carbon Capture Using Guanidinium-Functionalized Hollow Fiber Sorbent Contactors

As part of the growing suite of technologies aimed at combatting rising temperatures, negative emissions technologies have become a powerful tool in the global effort to minimize the consequences of human-induced climate change. Among these, carbon removal from aqueous sources, which contain much higher carbon concentrations than the atmosphere, remains largely unexplored. Indeed, developing robust and efficient carbon capture materials for usage in complex aqueous environments remains a significant challenge. Here, we explore the potential of functionalizing polyvinylidene fluoride (PVDF) hollow fiber contactors grafted with a guanidinium-derived polymer sorbent for carbon removal from aqueous sources, including saline waters. Computational screening against amine-based analogs is utilized to identify guanidinium as a promising motif for bicarbonate (HCO 3 – ) ions binding. To leverage this finding, synthesis of a guanidinium polymer and subsequent covalent grafting onto PVDF hollow fibers is employed to structured polymer–sorbent–grafted hollow fiber contactors. Our prototype achieves an initial HCO 3 – removal of 34% with an increase to 98% after four cycles. The functionalized fibers demonstrate aqueous stability over 13 adsorption/desorption cycles in model NaHCO 3 solutions where regeneration is facilitated by a mild pH swing. Importantly, the system maintains selective performance in the presence of competitive chloride ions over multiple cycles; carbon removal remained above 10% even at high (10:1) NaCl/NaHCO 3 ratios. These findings demonstrate the feasibility of sorbent-based aqueous carbon removal and highlight its potential as a promising approach for negative emissions.

carbon capture↗
DOE OSTI2022

Ecological and genomic responses of soil microbiomes to high-severity wildfire: linking community assembly to functional potential

Increasing wildfire severity, which is common throughout the western United States, can have deleterious effects on plant regeneration and large impacts on carbon (C) and nitrogen (N) cycling rates. Soil microbes are pivotal in facilitating these elemental cycles, so understanding the impact of increasing fire severity on soil microbial communities is critical. Here, we assess the long-term impact of high-severity fires on the soil microbiome. We find that high-severity wildfires result in a multi-decadal (>25 y) recovery of the soil microbiome mediated by concomitant differences in aboveground vegetation, soil chemistry, and microbial assembly processes. Our results depict a distinct taxonomic and functional successional pattern of increasing selection in post-fire soil microbial communities. Changes in microbiome composition corresponded with changes in microbial functional potential, specifically altered C metabolism and enhanced N cycling potential, which related to rates of potential decomposition and inorganic N availability, respectively. Based on metagenome-assembled genomes, we show that bacterial genomes enriched in our earliest site (4 y since fire) harbor distinct traits such as a robust stress response and a high potential to degrade pyrogenic, polyaromatic C that allow them to thrive in post-fire environments. Taken together, these results provide a biological basis for previously reported process rate measurements and explain the temporal dynamics of post-fire biogeochemistry, which ultimately constrains ecosystem recovery.

59 BASIC BIOLOGICAL SCIENCES↗