The increasing concentration of atmospheric CO2 is a major contributor to global increase in temperature, which motivates the development of efficient materials for car- bon capture. Alkali metal oxides, due to their intrinsic surface basicity and low cost, have emerged as promising candidates for CO2 adsorption. However, the exception- ally strong binding of CO2 to bulk alkali oxides hinders its controlled desorption as a concentrated stream for sequestration. In this study, we investigate the interaction of CO2 with potassium oxide K2O clusters of varying sizes ranging from monomoer to tetramer through density functional theory modeling to understand the role of clus- ter size on adsorption strength. The resulting models show that CO2 adsorption is weaker on exceedingly small K2O clusters than on bulk K2O. Empirical thermogravi- metric and differential scanning calorimetry measurements similarly showed stronger COadsorptionon larger K2O clusters. The cooperative electronic and geometric effects that cause strong CO2 binding on continuous surfaces may be beneficially disrupted on highly constrained active surfaces, allowing controlled desorption of captured emis- sions with lower process energy input. K2O clusters on γ-alumina were evaluated to understand the effect of metal oxide supports used in practice to achieve high active site dispersion. Incorporation of a γ-alumina support significantly strengthened CO2 binding energies, which highlights the significant influence of underlying supports on the adsorption chemistry of highly dispersed active clusters.

The rising concentration of atmospheric CO2 significantly contributes to global temperature increases, prompting the need for efficient carbon capture materials. Alkali metal oxides, known for their intrinsic surface basicity and low cost, are promising candidates for CO2 adsorption. However, the strong binding of CO2 to bulk alkali oxides necessitates high energy input for its controlled desorption as a concentrated stream fit for sequestration. This study investigates the interaction of CO2 with potassium oxide (K2O) bulk surfaces and clusters of varying sizes, from monomer to tetramer, using density functional theory modeling to assess how cluster size affects adsorption strength. Our models indicate that CO2 adsorption is weaker on very small K2O clusters compared to bulk K2O. Empirical thermogravimetric and differential scanning calorimetry measurements corroborate that larger K2O clusters exhibit stronger CO2 adsorption. The cooperative electronic and geometric effects responsible for strong CO2 binding on continuous surfaces may be disrupted on highly constrained active surfaces, facilitating controlled desorption with reduced energy input. Additionally, K2O clusters supported on γ-alumina were evaluated to examine the impact of metal oxide supports. The incorporation of γ-alumina significantly enhanced CO2 binding energies, underscoring the critical role of supports in the adsorption chemistry of dispersed active clusters.

A vast number of industrial catalytic processes rely on noble metals, also called platinum group metals (PGMs), which are scarce and expensive. Replacing these expensive noble metals with Earth abundant metals represents a major challenge. Although nickel is known to be an effective catalyst for certain reactions, like hydrogenation, it is unselective in metallic form and is inactive when oxidized. Here, we show that many of the reactions catalyzed by PGMs, such as oxidation or hydrogenation, can also be carried out by a base metal such as nickel, when it is stabilized in the form of isolated single atoms in square planar coordination within the fluorite lattice of CeO2. Incorporating Ni into the CeO2 lattice (Ce0.9Ni0.1O2-x) creates a versatile and robust Ni single atom catalyst. The working catalyst contains atomically dispersed Ni2+ sites that are stable under reaction conditions. Unlike metallic Ni, this single atom catalyst is not pyrophoric, can be handled in air, and easily activated for hydrogenation reactions. The synthesis described here is scalable and yields a high loading of Ni (similar to 3 wt %) within the fluorite CeO2 lattice while also allowing facile substitution of Ce with co-dopants, such as Zr, to further tune the environment of the active sites.

The dry reforming of methane reaction is a promising means to convert two potent greenhouse gases, methane and carbon dioxide, into industrially valuable synthesis gas. However, the presence of reducing gases and high operating temperatures degrade conventional nickel catalysts via excessive coke formation and particle sintering. These catalysts are not readily regenerated because the oxidative heat treatments employed to remove coke further promote active particle sintering. Herein, we designed high entropy aluminate spinel oxides (MAl2O4 where M = Co, Mg, Ni, and divalent site vacancies in nominal equimolar concentration) as selective and regenerable reforming catalysts. Under reaction conditions, reducible nickel and cobalt cations exsolved from the spinel lattice to form highly selective bimetallic particles on the oxide surface. Instead of sintering, these particles uniquely redissolved back into the aluminate lattice upon reoxidation and regained the original spinel structure. This phenomenon is ascribed to entropic stabilization, wherein an increase in configurational entropy creates a thermodynamic driving force for redispersing supported metal particles back into the multi‐cationic oxide structure, which was not seen on the NiAl2O4 sample where Ni sintered during oxidation to burn off coke. High entropy materials thus provide a unique mechanism of regeneration, which is inaccessible in conventional catalysts.

Conventional methods for extracting rare earth metals (REMs) from mined mineral ores are inefficient, expensive, and environmentally damaging. Recent discovery of lanmodulin (LanM), a protein that coordinates REMs with high-affinity and selectivity over competing ions, provides inspiration for new REM refinement methods. Here, we used quantum mechanical (QM) methods to investigate trivalent lanthanide cation (Ln3+) interactions with coordination systems representing bulk solvent water and protein binding sites. Energy decomposition analysis (EDA) showed differences in the energetic components of Ln3+ interaction with representatives of solvent (water, H2O) and protein binding sites (acetate, CH3COO-), highlighting the importance of accurate description of electrostatics and polarization in computational modeling of REM interactions with biological and bioinspired molecules. Relative binding free energies were obtained for Ln3+ with coordination complexes originating from binding sites in PDB structures of a lanthanum binding peptide (PDB entry 7CCO) and LanM, with explicit consideration of the first hydration shell waters, according to quasi-chemical theory (QCT). Beyond the first shell, the bulk solvent environment was represented with an implicit continuum model. Ln3+ interactions with (H2O)9 and both binding site models became more favorable, moving down the periodic series. This trend was more pronounced with the protein binding site models than with water, resulting in affinity increasing with periodic number, except for the last REM, Lu3+, which bound less favorably than the preceding element, Yb3+. Using the truncated 7CCO binding site model, the magnitude and trend of the experimental Ln3+ relative binding free energies for the whole 7CCO peptide were reproduced. Conversely, the previously reported experimental data for LanM show a preference for the earlier lanthanides; this is likely due to longer-range interactions and cooperative effects, which are not represented by the reduced models. Using the truncated 7CCO binding site model, the magnitude and trend of the experimental Ln3+ relative binding free energies for the whole 7CCO peptide were reproduced. In contrast to the previously reported experimental data for LanM, the peptide preferentially binds the earlier lanthanides. This difference likely arises due to longer-range interactions and cooperative effects not represented by the peptide. Further investigation of Ln3+ interactions with whole proteins using polarizable molecular mechanics models with explicit solvent is warranted to understand the influence of longer-ranged interactions, cooperativity, and bulk solvent. Nevertheless, the present work provides new insights into Ln3+ interactions with biomolecules and presents an effective computational platform for designing specific single-site REM binding peptides more efficiently.

Concentrating solar power plants can generate renewable heat at temperatures well above those of most industrial processes. Ceramic particles irradiated with concentrated sunlight can store high-quality sensible heat and transfer this to power generation systems. These concepts and materials hold great potential to also enable thermal processes in the chemical industry, but effective strategies for transferring heat from thermal energy storage media into chemical reactors are still under development. This present work evaluated the thermal and chemical compatibility of various solid particle media (including quartz, bauxite, and alumina particles) integrated directly into tube reactors and the subsequent effects on reactor performance for the nonoxidative dehydrogenation of ethane reaction. Empty tube reactors without loaded particles (representing conventional ethane cracking coils) showed significant heat transfer limitations as the tube diameter was scaled. The incorporation of media into the reactor significantly aided heat transfer to the gaseous ethane reactant and increased its conversion by as much as 10% at similar space velocities. Despite direct contact with hydrocarbon gases, alumina and quartz media showed negligible coke formation. Even during reaction in 100% ethane feed gas at 825 degrees C, the average selectivity of the coke product was only 0.57% when using the quartz media. These materials further demonstrated excellent thermal stability during subsequent reoxidation in air at 800 degrees C, which simulated the reheating of particles in a circulating particle solar receiver. Conversely, high rates of coke formation, with a product selectivity of 27.5%, were observed on sintered bauxite particles during the reaction, likely promoted by transition metal constituents. These particles fractured upon reoxidation due to exotherms generated from coke combustion. While the use of cofed steam could mitigate attrition of redox-active particles, the ability of inert metal oxide particles to efficiently transfer heat to concentrated ethane reactant gas while suppressing side reactions or degradation suggests that these media could effectively couple solar thermal plants to reactors for next-generation production of ethylene and other critical chemicals.

Several recent studies on the nonoxidative dehydrogenation of ethane to form ethylene have suggested this may be a promising pathway to upgrade products from ethane. The experiments of Riley et al. provide conversion, selectivity, and yield data for ethylene synthesis using bench-scale reactors with three different materials of construction at furnace temperature settings in the range of 575-700 degrees C. Despite being a gas phase reaction, there were significant differences between the quartz, alumina, and stainless-steel reactor tubes. Here, we present an analysis by simulation of the reported experimental results via simplified 1-step kinetic modeling using thermal and flow solvers. The stainless steel and alumina reactor results were fit to one reaction rate, while the quartz tube necessitated a separate mechanism to best fit the experimental results. The quartz tube reactions are faster than the Riley et al. stainless and alumina data as well as the published rate data from other sources. Alumina and stainless tube results, which were fit together, were also significantly faster than those suggested by published rates.

Thermal degradation is a leading cause of automotive catalyst deactivation. Because high-entropy oxides are uniquely stabilized at high temperatures via an increase in configurational entropy, these materials may offer new mechanisms for preventing the thermal deactivation of precious metal catalysts. In this work, we evaluated platinum loaded on simple and high-entropy aluminate spinels (MAl2O4, where M = Co, Cu, Mg, Ni, or mixtures thereof) in carbon monoxide oxidation before and after aging at 800 °C. Pt supported on all simple spinels showed significant deactivation after thermal aging compared to the fresh samples, with T90 increasing by at least 60 °C. However, Pt on high-entropy spinels had nearly the same or better activity after aging, with T90 increasing by only 6 °C at most. During aging and reduction, copper exsolved from the spinel supports and alloyed with platinum. This interaction promoted low temperature oxidation activity, presumably through weakened CO binding, but did not prevent deactivation. On the other hand, Co, Mg, and Ni constituents promoted stronger CO bonding, as evidenced by apparent negative order kinetics and poor activity at low temperatures. High-entropy spinels, containing a variety of active metals, displayed synergetic reactant adsorption capacity and cooperative effects with supported platinum particles, which collectively prevented thermal deactivation.

Computational fluid dynamics simulations of solar-thermal dry reforming of methane using a parabolic trough configuration were performed. Parametric simulations of different combinations of gas flow rate, receiver tube emissivity, and geometric concentration ratio were conducted to determine configurations that could achieve the required catalyst temperatures of at least 700 °C to achieve high conversion of CH4 and CO2 to H2 and CO. Results showed that the concentration ratio of the parabolic trough collector had to be increased from ~70 to ~120 and the receiver-tube emissivity had to be reduced to ~0.2 to achieve bulk average catalyst temperatures of greater than 700 °C. Lower gas flow rates also reduced enthalpic heat losses and increased catalyst temperatures.

Despite significant recent developmentsin the field of high entropyoxides, previously reported HEOs are overwhelmingly stoichiometricstructures containing a single cationic site and are stabilized solelyby intermixing increasing numbers of cations. For the first time,we demonstrate here that cationic vacancies can significantly increaseconfigurational entropy and stabilize phase-pure HEOs. Aluminate spinelHEOs with AB(2)O(4) stoichiometry are used as amodel crystal structure. These spinels tolerate large divalent cationdeficiencies without changing phase, allowing for high concentrationsof cationic vacancies. Stoichiometric and sub-stoichiometric spinels(with A:B molar ratios <0.5), which contained various mixturesof Co, Cu, Mg, Mn, Ni, and cationic vacancies in nominal equimolarconcentration, were systematically compared as a function of heattreatment temperature and number of unique cationic species. We foundthat the same number of cationic species were needed to stabilizeboth stoichiometric and sub-stoichiometric nickel-containing spinelsat 800 degrees C calcination, as exemplified by (CoCuMgNi)Al2O4 and (CoMgNi)(0.75)Al2Ox samples, signifying that vacancies stabilize phase-pure spinelssimilarly to cations. The chromatic, structural, and chemical propertiesof these complex spinels were highly tunable via incorporation ofcationic vacancies and multiple divalent metals, promoting their potentialapplication as unique pigments, catalysts, and thermal coatings.

The role of a solid surface for initiating gas-phase reactions is still not well understood. The hydrogen atom (H) is an important intermediate in gas-phase ethane dehydrogenation and is known to interact with surface sites on catalysts. However, direct measurements of H near catalytic surfaces have not yet been reported. Here, we present the first H measurements by laser-induced fluorescence in the gas-phase above catalytic and noncatalytic surfaces. Measurements at temperatures up to 700 degrees C show H concentrations to be at the highest above inert quartz surfaces compared to stainless steel and a platinum-based catalyst. Additionally, H concentrations above the catalyst decreased rapidly with time on stream. These newly obtained observations are consistent with the recently reported differences in bulk ethane dehydrogenation reactivity of these materials, suggesting H may be a good reporter for dehydrogenation activity.

conduction in the solid phase, and convection between the fluid and solid phases. A number of upgrades to the model and improved property values are presented here. Model predictions are shown to bound the experimental axial thermocouple data when experimental uncertainties are included. Global predictions are made using a technique in which the incident solar flux distribution is subdivided into flux contour bands. Model predictions for each band are then spatially integrated to provide global predictions such as reactor efficiencies and methane conversions. Global predictions are shown to compare well with experimental data. Reactor predictions for anticipated operating conditions suggest a further decrease in optical density at the front of the absorber inner disk may be beneficial. The need to conduct code-validation experiments is identified as essential to improve the confidence in the capability to predict large-scale reactor operation.

The chemical complexity of single-phase multicationic oxides, commonly termed high entropy oxides (HEOs), enables the integration of conventionally incompatible metal cations into a single-crystalline phase. However, few studies have effectively leveraged the multicationic nature of HEOs for optimization of disparate physical and chemical properties. Here, we apply the HEO concept to design robust oxidation catalysts in which multicationic oxide composition is tailored to simultaneously achieve catalytic activity, oxygen storage capacity, and thermal stability. Unlike conventional catalysts, HEOs maintain single-phase structure, even at high temperature, and do not rely on the addition of expensive platinum group metals (PGM) to be active. The HEOs are synthesized through a facile, relatively low temperature (500 °C) sol-gel method, which avoids excessive sintering and catalyst deactivation. Nanostructured high entropy oxides with surface areas as high as 138 m2/g are produced, marking a significant structural improvement over previously reported HEOs. Each HEO contained Ce in varying concentrations, as well as four other metals among Al, Fe, La, Mn, Nd, Pr, Sm, Y, and Zr. All samples adopted a fluorite structure. First row transition metal cations were most effective at improving CO oxidation activity, but their incorporation reduced thermal stability. Rare earth cations were necessary to prevent thermal deactivation while maintaining activity. In sum, our work demonstrates the utility of entropy in complex oxide design and a low-energy synthetic route to produce nanostructured HEOs with cations selected for a cooperative effect toward robust performance in chemically and physically demanding applications.

Steam cracking of ethane, a non-catalytic thermochemical process, remains the dominant means of ethylene production. The severe reaction conditions and energy expenditure involved in this process incentivize the search for alternative reaction pathways and reactor designs which maximize ethylene yield while minimizing cost and energy input. Herein, we report a comparison of catalytic and non-catalytic non-oxidative dehydrogenation of ethane. We achieve ethylene yields as high as 67 % with an open tube quartz reactor without the use of a catalyst at residence times similar to 4 s. The open tube reactor design promotes simplicity, low cost, and negligible coke formation. Pristine quartz tubes were most effective, since coke formation was detected when defects were introduced by scratching the surface of the quartz. Surprisingly, the addition of solids to the quartz tube, such as quartz sand, alumina powder, or even Pt-based intermetallic catalysts, led to lower ethylene yield. Pt alloy catalysts are effective at lower temperatures, such as at 575 degrees C, but conversion is limited due to thermodynamic constraints. When operated at industrially relevant temperatures, such as 700 degrees C and above, these catalysts were not stable in our tests, causing ethylene yield to drop below that of the open tube. These results suggest that future research on non-oxidative dehydrogenation should be directed at optimizing reactor designs to improve the conversion of ethane to ethylene, since this approach shows promise for decentralized production of ethylene from natural gas deposits.