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DOE OSTI2024

MR13A-3183: Microbial and Geochemical Characterization of Groundwater: Implications for Underground Hydrogen Storage Leakage

Underground hydrogen storage (UHS) in geological formations is a key element of the clean energy transition as it enables the decarbonization of the transportation and industrial sectors by decoupling hydrogen production and storage. UHS has many benefits, including low cost, much wider availability, large storage capacity, well-established infrastructure, and increased safety because of geological sealing capabilities. However, the impact of hydrogen (H2) biogeochemical interactions in the presence of subsurface microorganisms is largely neglected from UHS perspectives. These interactions might affect the effectiveness of storage and can even cause H2 to leak into the shallow aquifers. Leakage of H2 into groundwater can change the geochemistry and induce several microbial-driven processes. Microorganisms, such as sulfate-reducers, are naturally abundant in groundwater and consume H2 to produce hydrogen sulfide (H2S), which can contaminate the freshwater drinking groundwater and cause damage to infrastructure. Hydrogen leakage can also trigger microbial reactions responsible for metal mobility, which can impact the water quality. However, the kinetics of these reactions and the temporal impact of hydrogen leakage in groundwater are still unknown. Therefore, a time series hydrogen-groundwater interaction experiment was conducted, and the changes in fluid chemistry and headspace gas composition will be analyzed along with DNA sequencing results to understand the extent and kinetics of biogeochemical reactions that occur if hydrogen leaks into groundwater. In the experiments, Ultra High Purity (UHP) hydrogen gas will be injected into glass vials with groundwater samples, for a designated time period. For each glass-sealed vial, 16S rRNA gene sequencing, IC, ICP-MS, and GC-TCD will be performed. The experiments provide insights into plausible impacts of hydrogen leakage into shallow drinking water aquifers.

Clark, Allison [West Virginia University (WVU)]↗

DOE OSTI2025

The Effect of Flow on CO2 Corrosion of Self-Healing Metallic Coatings

Internal corrosion is an issue that affects natural gas pipelines, a significant part of the United States’ energy infrastructure. Over time, this corrosion has worn away longstanding pipelines due to the original construction materials used for the lines and impurities in the gas and liquid streams flowing through them. The main impurities in natural gas are H2O, CO2, H2S, and O2. One of the leading causes of corrosion is the CO2 dissolved in water, giving rise to carbonic acid formation, which can further dissolve the steel pipe. The National Energy Technology Laboratory (NETL) has been studying different solutions to this problem. One potential answer is a self-healing sacrificial metallic coating applied by a novel cold spray technique. This study explored the impact of flow on corrosion with this coating and carbon steel when exposed to a saturated CO2 environment by simulating the pipeline flow profile in a small-scale lab setting. The samples were evaluated using multiple electrochemical techniques that found corrosion rates and were backed up with surface analysis to conclude the behavior of the corrosion mechanisms. The cold spray coating exhibited steel corrosion protection under flow conditions. This study has significantly advanced our understanding of CO2 corrosion, particularly in the context of natural gas pipelines and coating design.

carbon steel↗

DOE OSTI2025

Corrosion Behavior of Hydrophobic Coatings in Aqueous CO2 Environments

Internal corrosion is caused by gas impurities such as CO2, moisture, and H2S, leading to material degradation. To combat this, the National Energy Technology Laboratory (NETL) developed a novel hydrophobic coating to reduce surface hydrophobicity and enhance the corrosion resistance of steel. NETL’s approach uses multi-layer hydrophobic coatings, a novel and promising coating that could potentially revolutionize the industry's approach to internal corrosion mitigation. This work aims to investigate the corrosion performance of the hydrophobic coating and determine the water uptake. Electrochemical corrosion experiments were carried out on bare X65 carbon steel without and with coating in 3.5 wt.% NaCl saturated with CO2 at 20 °C to follow the water uptake as a function of exposure time. Linear polarization resistance (LPR) was used to determine the corrosion rate for carbon steel immersed in a NaCl electrolyte saturated with CO2. Electrochemical impedance spectroscopy (EIS) of uncoated and coated bare carbon steel was investigated. The analyses of impedance models and water uptake behaviors of hydrophobic coatings were studied for 200 hours during the corrosion process. The water uptake was estimated using the Brasher and Kingsbury relation. The results showed that the superhydrophobic coating that was developed used innovative nano-based materials to act as protection layers on the surface of metallic parts against mechanical aggressors, corrosion, and fouling agents.

corrosion behavior↗

DOE OSTI2025

Investigation of the Mechanical Degradation of Zinc-Based Cold Spray Coatings for Steel Pipelines

adhesion↗

DOE OSTI2026

Upgrading Biogas through in situ Conversion of Carbon Dioxide to Biomethane in Anaerobic Digesters

Organic waste streams generated by wastewater treatment plants, agricultural operations, and food processing industries represent an important yet underutilized opportunity for renewable energy production in the United States. Through anaerobic digestion, these waste streams can produce biogas, a mixture primarily composed of methane (CH4) and carbon dioxide (CO2), that can be upgraded to pipeline-quality natural gas. However, most existing upgrading technologies remove CO2 from biogas rather than utilizing it, leaving a significant portion of the potential energy unused. This project investigates a novel biological upgrading approach that converts CO2 into additional CH4 by supplying hydrogen (H2) to specialized microorganisms capable of performing hydrogenotrophic methanation. The main challenges associated with biological biogas upgrading are related to hydrogen supply, gas-liquid mass transfer, and process stability. First, due to the high cost of hydrogen gas, it is preferable that H2 be produced on-site using renewable energy sources such as wind or solar power. Second, hydrogen has low solubility in liquids, which limits its availability to microorganisms and requires strategies to improve gas dissolution and transfer within the reactor. Third, process inhibition may occur as a result of increased pH caused by CO2 consumption or elevated H2 partial pressure, both of which can negatively affect methanogenic activity. Although research in these areas has advanced during the course of this project, these challenges have not yet been fully resolved. To date, the biological systems that have achieved the highest methane concentrations are typically ex-situ reactors, where operational conditions can be more easily controlled. For this reason, the findings of the present project remain highly relevant. The project goal was to develop an innovative system that can accomplish biogas upgrading via biological conversion of CO2 to CH4, in a novel hybrid approach that combines the advantages of both in-situ and ex-situ systems. The proposed system employs a three-phase upflow anaerobic bioreactor with H2 delivery through a gas-permeable membrane, enabling efficient hydrogen transfer and microbial conversion. Under optimized operating conditions, the system achieved 99% H2 consumption and 90% CO2 conversion. A subsequent gas cleaning stage was implemented to further improve gas quality and meet target purity standards. The upgraded gas composition reached 97.7% CH4, 2.2% CO2, and 0.97% O2, while H2S concentrations remained below detection limits. In addition, a flue gas-driven inorganic thermoelectric generator (TEG) system was designed and experimentally validated as a potential source of electricity for H2 production. The system consisted of six TEG modules connected in series and achieved an open-circuit voltage of 4.5 V and a maximum power output of 224 mW at a temperature difference of approximately 53.5 °C, demonstrating effective conversion of waste heat into electrical power under simulated flue gas conditions. Finally, a comprehensive techno-economic analysis was completed to evaluate the capital and operating costs associated with the proposed system. The results provide important insights to guide future scale-up, optimization, and potential deployment of integrated biological biogas upgrading technologies.

09 BIOMASS FUELS↗

DOE OSTI2021

Permian Basin: in-situ tower greenhouse gas data

The Permian Basin in-situ greenhouse gas network was designed to measure atmospheric mole fractions of methane to be used in conjunction with transport modeling to determine methane emissions from the Permian Basin oil and natural gas extraction area in Texas/New Mexico. The current network includes 5 measurement sites with continuous measurements of CH4, 4 sites with measurements of CO2, 2 sites with measurements of the isotopic ratio of methane, and 1 site with measurements of H2S.

Monteiro, V.↗

DOE OSTI2020

Techno-Economic Assessment of CHP Systems in Wastewater Treatment Plants

Wastewater treatment plant (WWTP) utilization of combined heat and power (CHP) systems allows for the efficient use of on-site biogas production, as well as increased annual savings in utility costs. In this paper, a review of biogas energy recovery options, CHP prime mover technologies, and the costs associated with biogas cleaning give a broad summary of the current state of CHP technology in WWTPs. Even though there are six different prime mover technologies, the main ones currently being implemented in WWTPs are micro turbines, fuel cells and reciprocating engines. Different prime movers offer varying efficiencies, installation costs, and biogas impurity (H2S, siloxanes, HCl) tolerances. To evaluate the long-term savings capabilities, a techno-economic assessment of a CHP installation at a case study WWTP shows the payback, annual savings, and initial costs associated with the installation of a CHP system. In this case, a study a payback of 5.7 years and a net present value of USD 709,000 can be achieved when the WWTP generates over 2,000,000 m3 of biogas per year and utilizes over 36,000 GJ of natural gas per year.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2025

Glancing Angle Deposition in Gas Sensing: Bridging Morphological Innovations and Sensor Performances

Glancing Angle Deposition (GLAD) has emerged as a versatile and powerful nanofabrication technique for developing next-generation gas sensors by enabling precise control over nanostructure geometry, porosity, and material composition. Through dynamic substrate tilting and rotation, GLAD facilitates the fabrication of highly porous, anisotropic nanostructures, such as aligned, tilted, zigzag, helical, and multilayered nanorods, with tunable surface area and diffusion pathways optimized for gas detection. This review provides a comprehensive synthesis of recent advances in GLAD-based gas sensor design, focusing on how structural engineering and material integration converge to enhance sensor performance. Key materials strategies include the construction of heterojunctions and core–shell architectures, controlled doping, and nanoparticle decoration using noble metals or metal oxides to amplify charge transfer, catalytic activity, and redox responsiveness. GLAD-fabricated nanostructures have been effectively deployed across multiple gas sensing modalities, including resistive, capacitive, piezoelectric, and optical platforms, where their high aspect ratios, tailored porosity, and defect-rich surfaces facilitate enhanced gas adsorption kinetics and efficient signal transduction. These devices exhibit high sensitivity and selectivity toward a range of analytes, including NO2, CO, H2S, and volatile organic compounds (VOCs), with detection limits often reaching the parts-per-billion level. Emerging innovations, such as photo-assisted sensing and integration with artificial intelligence for data analysis and pattern recognition, further extend the capabilities of GLAD-based systems for multifunctional, real-time, and adaptive sensing. Finally, current challenges and future research directions are discussed, emphasizing the promise of GLAD as a scalable platform for next-generation gas sensing technologies.

Chemistry↗

DOE OSTI2022

Method for sealing a void in a well using smart gels

Embodiments of the disclosure include swellable smart gel sealants and methods of using smart gel sealants. In certain embodiments, the smart gel sealants reversibly swell when exposed to a certain trigger, such as temperature or pH. In specific embodiments, the smart gel is disposed within voids in a well and triggered to swell in order to seal the voids. One application of the smart gel sealant is to seal the casing of a well against the leakage of gas, such as H2S.

Roback, Robert Clifford↗

DOE OSTI2023

Flexible Gasification of Coal and Biomass to Generate Carbon Free Electric Power and Hydrogen

This paper describes the development of a coal and biomass-fed plant concept to co-produce electric power and hydrogen with net-negative CO2 emissions under the aegis of the 21st Century Power Plant initiative of the U.S. Department of Energy (DOE), whose goal is to advance innovative power plant concepts that are capable of flexible, net-zero carbon emission operations while producing cost-effective “blue” hydrogen to support economy-wide decarbonization goals. The proposed standalone plant will be in Nebraska, USA. The specified design feedstock is a hybrid blend of Powder River Basin (PRB) subbituminous coal from Wyoming and local Nebraska biomass (corn stover), 50 wt.% each (dry basis). Other potential feedstocks, including woody biomass (eastern red cedar) and waste plastic (auto shredder residue) were evaluated or reviewed as alternates. The proposed process block comprises a high-pressure, oxygen-blown fluidized bed gasifier (GTI Energy U-GAS® process) coupled with water gas shift, the Selexol process for acid gas (H2S and CO2) removal, and pressure-swing adsorption (PSA) to yield 8,500 kg/h of high-purity hydrogen. The off gas from the PSA unit is used in the power block (gas turbine combined cycle) to generate electric power to support the gasification process, hydrogen production, and 50 MWe net electric power to the grid. All major plant equipment including the gasifier, gas cleanup system, and power generation are commercially available and proven in other applications and considered at TRL 8-9. However, gasification of corn stover biomass is considered at TRL 6. Overall thermal efficiency of the plant is 50% (net HHV) with net atmospheric CO2 removal at a rate of 250-300,000 tpa. Design activities necessary to provide input to a FEED study (Phase II of the project), including the development of the Environmental Information Volume (EIV) for the host site, and an investment case, based on a pro-forma pre-FEED level cost estimate, have been completed and are described in detail in this paper.

Gülen, S. Can↗

DOE OSTI2024

High-Fidelity and High-Performance Computational Simulations for Rapid Design Optimization of Sulfur Thermal Energy Storage

Industrial process heating (IPH) accounts for approximately 70% of US manufacturing energy use and is primarily produced by fossil fuel combustion. Approximately 1500 TWht (approximately 60%) of IPH demand is in the temperature range of 100-300. Industrial applications in this temperature range include drying, hydrothermal processing, thermal enhanced oil recovery, food and beverage, bioethanol production, etc. Cost-effective thermal energy storage (TES) that increases the utilization of waste and renewable heat (solar, geothermal, etc.) could provide significant energy savings and reliable heat sources, decrease emissions, and increase US manufacturing competitiveness through reductions in fuel consumption. TES development has historically been dominated by technologies suitable for deployment with concentrating solar power (CSP). State-of-the-art thermal storage deployed commercially with power tower CSP plants uses a 60%/40% NaNO3/KNO3 molten salt and operates between temperatures of approximately 280 degrees Celsius and 570 degrees Celsius using a two-tank configuration. However, these nitrate salts are unsuitable for operation outside of this temperature range due to a high freezing point of approximately 220 degrees Celsius, and limits on high-temperature salt stability and corrosion resistance of containment alloys. Other materials being investigated for TES include those based on: (1) sensible energy storage (various molten salt compositions, inert solid particles, rocks or pebble beds, sulfur, water, concrete, graphite, etc.), (2) latent energy storage in materials that undergo solid-liquid phase change at relevant temperatures (organic materials for low-temperature applications, inorganic salts and/or metals for high-temperature applications), or (3) thermochemical energy storage (hydrides, hydroxides, carbonates, metal oxides, etc.). The application temperature and challenges pertaining to storage material and/or containment cost, energy density, long-term thermal and cyclic stability, and charge/discharge heat transfer effectiveness drive material selection for a given IPH or electricity generation application. Sulfur is a cheap commodity at $80/ton compared to $1100 - 1300/ton for conventional salts. When using a metric of storage cost per kWh, sulfur costs around 2-3 $/kWh. Previous sulfur TES development focused on high temperature (>600 degrees) concentrated solar power applications with sulfur encapsulated in pipes and flow of gaseous HTF (air) in the shell side. However, for lower-temperature IPH applications in the range of approximately 100-300 degrees Celsius Element 16 adopted a compact and scalable TES design with molten sulfur in the shell and HTF pipes submerged in the molten sulfur bath. The low-cost molten sulfur TES for dispatchable IPH has deployment potential for broad applications. The spatial and temporal evolution of the HTF and sulfur temperature is critical to the TES system performance, and thus detailed modeling can improve understanding of the performance and facilitate design improvements. Using high performance computing and computational fluid dynamics (CFD) a low-cost molten sulfur thermal energy storage (TES) system for industrial process heating (IPH) applications was developed. The unique challenges in CFD modeling of sulfur TES are the sharp property changes of sulfur relevant to the working temperatures. Above 159, liquid sulfur undergoes polymerization, and the viscosity of sulfur rapidly increases by several orders of magnitude between 159 degrees Celsius and 188 degrees Celsius, followed by a decrease in viscosity beyond 188 degrees Celsius due to thermal bound dissociation. In addition, various concentrations of H2S impurities can also modify sulfur viscosity. This numerical challenge is especially relevant to transient simulation of the sulfur TES charging and discharging processes as the extreme property variations limit the applicability of traditional heat transfer correlations. Transient CFD simulations including the temperature-dependent sulfur properties and geometric complexity of the TES design were used to predict the effect of natural convection during charging and discharging on the heat transfer process, sulfur temperature uniformity, charge/discharge rates, and performance of the storage devices. The CFD model was validated with experimental results for a full charge and discharge cycle. The work will show 3D and 2D simulation comparisons aimed to facilitate rapid design iterations and a machine learning based design optimization approach.

CFD↗

DOE OSTI2025

The Effect of Flow on CO2 Corrosion of Self-Healing Metallic Coatings

Internal corrosion is an issue that affects natural gas pipelines, a significant part of the United States energy infrastructure. Over time, this corrosion has worn away longstanding pipelines due to the original construction materials used for the lines and impurities in the gas and liquid streams flowing through them. The main impurities in natural gas are H2O, CO2, H2S, and O2. One of the leading causes of corrosion is the CO2 dissolved in water, giving rise to carbonic acid formation, which can further dissolve the steel pipe. The National Energy Technology Laboratory (NETL) has been studying different solutions to this problem. One potential answer is a self-healing sacrificial metallic coating applied by a novel cold spray technique. Previous studies at NETL have shown that the zinc-rich self-healing coating can withstand corrosion through passivation and create a barrier to the diffusion of corrosive species. This study explored the impact of flow on corrosion with this coating and carbon steel when exposed to a saturated CO2 environment by simulating the pipeline flow profile in a small-scale lab setting. The samples were evaluated using multiple electrochemical techniques that found corrosion rates and were backed up with surface analysis to conclude the behavior of the corrosion mechanisms.

CO2 corrosion↗

DOE OSTI2025

Investigation of the Mechanical Degradation of Zinc-Based Cold Spray Coatings for Steel Pipelines

Internal corrosion in wet natural gas is a big challenge in the oil and gas industry due to corrosive constituents such as carbon dioxide (CO2), hydrogen sulfide (H2S), other forms of sulfur, and water in the gas stream. To mitigate internal corrosion, zinc-based cold spray coatings were designed for use in natural gas pipelines to increase the lifespan of the pipeline network. However, one of the requirements in designing internal coatings is the resistance of the coatings to mechanical forces applied on the pipeline's internal wall during pigging operations. These forces are primarily compressive and shear/friction forces. This study examines material properties that must be considered when evaluating mechanical considerations. To determine the viability of the developed coatings with respect to the shear/friction forces, the shear adhesion and wear resistance of the materials have been evaluated. Shear adhesion testing was performed with modified clevises to determine the shear stress required to cause adhesion failure at the coating/substrate interface. Scanning electron microscopy was utilized to characterize the interfaces after failure. Wear testing was performed on coatings and pipeline materials utilizing pin-on-drum testing. These tests display the stress limitations and wear that the coatings can tolerate from pigging.

mechanical degradation↗

DOE OSTI2025

Theoretical and kinetic modeling study of H 2 S pyrolysis

Hydrogen sulfide pyrolysis was investigated theoretically and through chemical kinetic modeling. Reactions on the SHH potential energy surface, primarily S + H 2 (+Ar) ⇌ H 2 S (+ Ar) (R1) and S + H 2 ⇌ SH + H (R6b) were characterized by ab initio calculations. Results for k 1 were in good agreement with experiment, but deviated strongly below 2000 K from values previously used in modeling. Collider efficiencies for H 2 S, S 2 , and N 2 compared to Ar were calculated for R1. Hydrogen sulfide decomposition experiments reported in literature were re-examined in terms of an updated detailed chemical kinetic model. Concentration profiles for the atomic S at high temperature in shock tubes supported the present value of k 1 and served to constrain the rate constants for reaction of S with SH and H 2 S. To explain results from batch and flow reactors, conducted at high H 2 S concentrations in the 900–1400 K range, a very fast rate constant was required for HSS + H ⇌ SH + SH. Under dilute conditions, the gas-phase chemistry was too slow to compete and the decomposition of H 2 S was controlled by loss on the reactor surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Experimental and modeling study of water time histories during H 2 S-N 2 O combustion in a shock tube

Here, with the interest in directly burning sour gas in gas turbines, and the fact that even small amounts of H 2 S or its combustion products can alter combustion characteristics, many research studies have been performed to better understand the combustion chemistry of H 2 S. In the present study, the water formation was followed by laser absorption with N 2 O as an oxidant, instead of O 2 . Nitrous Oxide being essentially consumed via N 2 O (+M) ⇌ N 2 + O (+M), the water formation via the H 2 S + O route can then be probed to further validate the models. Three H 2 S/N 2 O mixtures diluted in 98% Ar were studied to cover the following range of equivalence ratios: 0.5, 1.0, and 2.0, over a wide range of temperatures (1580–1940 K) around atmospheric pressure. A chemical kinetic model was then developed first by validating the base N 2 O kinetics mechanism, then by investigating the experimental results presented herein. The N 2 O kinetics mechanism was updated with recent work on the low- and high-pressure limits for N 2 O decomposition (N 2 O (+M) ⇌ N 2 + O (+M)) as well as a review of rate coefficients for N 2 O + H ⇌ N 2 + OH from the literature. Good agreement is shown for H 2 /N 2 O mixtures. Updates were then made to the H 2 S kinetics mechanism, specifically, an update from the literature on SO 2 + H (+M) ⇌ SO + OH (+M) and an adjustment to SO + SH ⇌ S 2 + OH. Additionally, reactions between SH and N 2 O were determined using W1BD data and transition state theory which required the addition of an NNS sub-mechanism. With these updates, the mechanism provides good agreement with the H 2 S/N 2 O experiments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2020

Peptoid-Based Programmable 2D Nanomaterial Sensor for Selective and Sensitive Detection of H 2 S in Live Cells

During the past decades, a variety of two-dimensional (2D) nanosheets have been developed through supramolecular self-assembly. Among them, those assembled from sequence-defined molecules have received particularly attention because they enable a precise displaying of functional groups, including fluorescent dyes, within nanosheet surfaces. On the other hand, due to the fluorescence self-quenching, synthesis of organic 2D nanosheets exhibiting high fluorescence quantum yields is a significant challenge. Herein, we report the utilization of H 2 S-responsive probes as peptoid sidechains to design and synthesize crystalline 2D nanomembranes (2DNMs) as selective and sensitive H 2 S sensors. These 2DNM sensors exhibit a high quantum yield as a result of high crystallinity and tunable probe density. Compared with amorphous state of peptoid assembly and pre-assembled peptoid-probe conjugates, these crystalline 2DNM sensors exhibit a significantly strong fluorescence intensity and a high sensitivity (~ 0.36 nM). By sonication-cutting these 2DNM sensors into a colloidal form in aqueous solution, we further demonstrated the use of colloidal 2DNMs for detecting both exogenous and endogenous H 2 S inside cells or targeted cell organelles. As far as we know, this is the first example of using sequence-defined 2D nanomaterials for selective and sensitive detection of H 2 S. Because peptoids are biocompatible and peptoid-based 2DNMs are highly programmable, we expect that this new class of 2DNM sensors offer great potentials for detecting H 2 S and for biological applications.

2D nanomaterials↗

DOE OSTI2021

Sulfur Tolerant Subnanometer Fe/Alumina Catalysts for Propane Dehydrogenation

A series of Al 2 O 3 -supported Fe-containing catalysts were synthesized by incipient wetness impregnation. The iron surface density was varied from 1 to 13 Fe atoms/nm 2 spanning submonolayer to above-monolayer coverage. Here, the resulting supported Fe-catalysts were characterized by N 2 physisorption, ex situ X-ray diffraction (XRD), X-ray pair distribution function (PDF), X-ray absorption spectroscopy (XAS), aberration corrected scanning transmission electron microscopy (AC-STEM) and chemically probed by hydrogen temperature-programmed reduction (H 2 -TPR). The results suggest that over this entire range of loadings, Fe was present as dispersed species, with only a very small fraction of Fe 2 O 3 aggregates, at the highest Fe loading in oxide phase. The in situ sulfidation of Fe/Al 2 O 3 resulted in the formation of a highly active and selective PDH catalyst. The highest activity with 52% propane conversion and ~99% propylene selectivity at 560 °C was obtained for the 6.4 Fe/Al 2 O 3 -S catalyst, suggesting that this is the highest amount of Fe that could be fully dispersed on the support in sulfided form. XRD and AC-STEM indicated the absence of any crystalline iron sulfide aggregates after sulfidation and reaction. H 2 -TPR results indicated that the amount of the reducible Fe sites in the sulfided catalyst remained constant above monolayer coverage, and increasing loading did not increase the number of reducible Fe sites. Consistent with these results, the reactivity per gram of catalyst showed no increase with Fe loading above monolayer coverage, suggesting that additional Fe remains conformal to the alumina surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Atomically Dispersed Tin-Modified $\gamma$-alumina for Selective Propane Dehydrogenation under H 2 S Co-feed

Developing an earth-abundant catalyst that is sulfur-tolerant, active, and highly selective is of great interest for valorizing natural gas streams containing sour gas. Here, a tin-modified alumina catalyst is reported that is stable and selective for propane dehydrogenation in the presence of percent quantities of H 2 S in the feed. In particular, Sn/Al 2 O 3 –S catalysts with 1.5–5% Sn content exhibit 98% selectivity with up to 16% conversion at 560 °C during the fourth cycle. Experimental and computational characterization shows that the active sites are the defect tricoordinated Al atoms. H 2 S pretreatment further modifies a portion of these sites via exchanging a neighboring oxygen atom with sulfur, thereby rendering them more active and selective. At low loadings, Sn is atomically dispersed and selectively binds to hydroxyl groups or oxygen atoms on Al 2 O 3 . This prevents the formation of original (unmodified) defect sites on Al 2 O 3 and improves overall selectivity. The activity and selectivity of the catalyst are heavily dependent on the chemical potential of sulfur and hydrogen because they influence both the relative concentration of the two types of sites and the overall reaction mechanism. Finally, the catalyst can be regenerated fully under a pure H 2 S stream, thereby precluding treatment under oxygen, which can lead to sintering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗