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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Tuning the activity of Cu-containing rare earth oxide catalysts for CO oxidation reaction: Cooling while heating paradigm in microwave-assisted synthesis

Highlights: • Organic chemistry synthesis concepts have been smartly tailored to catalysts’ development. • Enhanced microwave synthesis of (Ce-La-10Cu)O{sub 2} led to an one phase system. • CO{sub 2}-philicity, and oxygen vacancies can be tuned by synthesis. • Coupling microwave with air cooling led to T{sub 50} decrease by 32% in the CO oxidation reaction. - Abstract: (Ce-La-xCu)O{sub 2} catalysts with low (3 at.%) and high (10 at.%) Cu content were prepared by conventional microwave (MW) and enhanced microwave methods where air cooling (AC), while heating, was applied. The catalysts were tested for the CO oxidation reaction in the 25–500 °C range using 4%CO/20%O{sub 2}/He feed gas. Varying spectroscopic, microscopic and catalytic studies were used to probe the effect of synthesis on the nanostructure and the CO oxidation performance. It was found that the synthesis method adopted impacts on the extent of the Cu doping into the (Ce-La)O{sub 2} fluorite lattice, hence leading to one and two phases system in the case of catalyst prepared through enhanced (AC) and conventional (MW) microwave methods, respectively. Furthermore, only Ce{sup 4+} species were found on the surface of the (Ce-La-10Cu)O{sub 2} catalysts synthesized using MW and AC (XPS studies), whereas oxygen vacant sites which are associated with Ce{sup 3+} ions were indicated in the sub-surface/bulk (Raman studies). Ultimately, the catalysts with the low and high Cu loading, prepared under the AC-promoted microwave method, presented a superior performance against CO oxidation, exhibiting an overall improvement of the catalytic activity by 16% and 32%, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Water-gas shift reaction on alumina-supported Pt-CeO x catalysts prepared by supercritical fluid deposition

Alumina-supported platinum catalysts, both with and without ceria, were prepared by supercritical fluid deposition and evaluated for activity for water-gas shift reaction. The organometallic precursor, platinum(II) acetylacetonate, was deposited from solution in supercritical carbon dioxide. Analysis of the catalysts by high resolution scanning transmission electron microscopy indicated that platinum was present in the form of highly dispersed metal nanoparticles. Pretreatment of the alumina-supported ceria in hydrogen prior to the deposition of the platinum precursor resulted in more platinum nucleated on ceria than non-pretreated alumina-supported ceria but varied in both particle size and structure. The ceria-containing catalyst that was not pretreated exhibited a more uniform particle size, and the Pt particles were encapsulated in crystalline ceria. Reaction rate measurements showed that the catalyst was more active for water-gas shift, with reaction rates per mass of platinum that exceeded most literature values for water-gas shift reaction on Pt-CeO x catalysts. The high activity was attributed to the significant fraction of platinum/ceria interfacial contact. We found that these results show the promise of supercritical fluid deposition as a scalable means of synthesizing highly active supported metal catalysts that offer efficient utilization of precious metals.

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

Application of Single-Site Catalysts in the Hydrogen Economy

Catalysts development is an evolutionary process. The generation of new single-metal-site catalysts, with isolated metal atoms dispersed on the surface of substrates, offers maximum atom-utilization efficiency, high specific activity, and novel properties. The unique structure of single-site catalysts also enables their potential to bridge the gap between homogeneous and heterogeneous catalysis. This field is at an early stage, characterized by important discoveries and novel demonstrations of catalytic properties associated with the fine structure of single metal sites; however, specific applications, especially catalytic hydrogenation reactions, are still lacking. Here, we focus on applications of single-site catalysts in the hydrogen economy based on our studies of hydrogen generation/storage via single-metal-site catalysts. We hope this work will inspire the development of single-site catalysts for other applications.

08 HYDROGEN↗
DOE OSTI2025

Stimulus-Responsive Modulation of Solvation Environments in Solid Catalysts

Liquid environments play a crucial role in the biological processes occurring in living organisms as well as in many human-made processes involving electrochemistry, photo-, and thermocatalysis. In the majority of these systems, aqueous phases are ubiquitous due to water’s natural abundance. Water molecules, however, can exert large changes in the chemical environment of catalytically active sites, altering the reaction rates, selectivity, and catalyst stability. These solvation effects induced by water molecules near catalytic sites can drastically change the energy landscape and unlock unique reaction pathways with far more favorable kinetics. In nature, living organisms couple these complex interactions with detection, communication, and actuation mechanisms to induce self-regulatory behavior, ensuring stability of the system and thus long-term durability. Extrapolating this behavior to heterogeneous catalysis is desirable because the resulting “smart materials” can potentially unlock new chemical conversion processes with higher atom efficiency, rates, and stability. The combination of polymer chemistry and heterogeneous catalysis has introduced versatile approaches for creating materials that can respond to cues in the reaction medium that alter the accessibility, intrinsic activity, and selectivity of the catalyst. To achieve this, one could combine stimulus-responsive polymers, which undergo a large volumetric phase transition in response to an external stimulus, with a solid catalyst. This chemo-mechanical response has been employed to create a variety of nanoreactor vessels with stimulus-responsive character that turn on- and off- depending on the reaction conditions. In this Account, we focus on the impact of these polymer coatings on the solvation environment around the active site and the implications of these effects on the reaction energy landscape, molecular arrangement of the solvent, electric fields at the catalyst–liquid interface, binding energy, and mobility of surface reaction intermediates. These seemingly subtle changes in solvent molecules induced by the presence of polymers can have a tremendous impact on the development of bioinspired heterogeneous catalysts, reliable chemical clocks, micro/nanoreactors, and robots. The large library of polymer chemistries offers a plethora of combinations of stimulus-responsive mechanisms (e.g., temperature, pH, light, magnetic field, solvent composition), providing the possibility of creating homeostatic catalysts à la carte.

catalysts↗
DOE OSTI2022

Molecular Catalysts with Diphosphine Ligands Containing Pendant Amines

Pendant amines play an invaluable role in chemical reactivity, especially for molecular catalysts based on Earth-abundant metals. As inspired by [FeFe]-hydrogenases, which contain a pendant amine positioned for cooperative bifunctionality, synthetic catalysts have been developed to emulate this multifunctionality through incorporation of a pendant amine in the second coordination sphere. Cyclic diphosphine ligands containing two amines serve as the basis for a class of catalysts that have been extensively studied and used to demonstrate the impact of a pendant base. These 1,5-diaza-3,7-diphosphacyclooctanes, now often referred to as “P 2 N 2 ” ligands, have profound effects on the reactivity of many catalysts. The resulting [Ni(P R 2 N R ´ 2 ) 2 ] 2+ complexes are electrocatalysts for both the oxidation and production of H 2 . Achieving the optimal benefit of the pendant amine requires that it has suitable basicity and is properly positioned relative to the metal center. In addition to the catalytic efficacy demonstrated with [Ni(P R 2 N R ´ 2 )2] 2+ complexes for the oxidation and production of H2, catalysts with diphosphine ligands containing pendant amines have also be demonstrated for a variety of metals for many different reactions, both in solution and immobilized on surfaces. Here, the impact of pendant amines in catalyst design has been demonstrated and continues to expand.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Cobalt-Based Catalysts for Ethanol Steam Reforming: An Overview

Cobalt has been extensively studied for its use as an alternative catalyst to noble metals for ethanol steam reforming. Among the many other catalyst supports tested, cerium oxide contributed significantly to the catalytic activity and stability of the Co/CeO 2 catalyst as a result of its high oxygen mobility and storage capacity. In this paper, an overview of the research conducted in our laboratory during the past decade on ethanol steam reforming using the Co/CeO 2 catalyst is presented. Here, the role of the support oxygen mobility and storage capacity of the Co/CeO 2 catalyst and how the addition of calcium to the ceria support changes the oxygen vacancies in the catalyst structure are discussed. Results from in situ characterization techniques, such as X-ray diffraction, Raman spectroscopy, X-ray absorption near edge structure, and extended X-ray absorption fine structure, are summarized, showing the evolution of the cobalt phases during synthesis, pretreatment, and ethanol steam reforming reaction. Also, how the synthesis parameters, such as synthesis method, impregnation medium, choice of cobalt precursor, support morphology, and particle size, could alter the catalytic activity and selectivity have been outlined.

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

Numerical Investigation of Susceptor-Catalyst Design for Ethylene Generation in Radio Frequency Based Reactors

Ethylene is the most widely produced petrochemical component in the world. Whether reactors are heated directly or indirectly via steam, manufacturers use economies of scale to overcome inherent thermodynamic inefficiencies when burning fossil fuels. While allowing large-scale operations to use alternative sources of energy and raw materials, new methods of supplying energy to chemical reactor systems can reduce the energy waste produced by conventional processes. One viable method for effectively supplying energy to reactor systems is electromagnetic (EM) induction heating. Using the properties of radio frequency (RF) waves, heterogeneous catalysts can be precisely targeted for heating inside reactors. Site-selective heating can greatly lower the energy requirements of the process by supplying heat to reaction sites while reducing needless heat transfer elsewhere. In this study, a microscale model was used to help create guidelines for susceptors and catalysts to improve ethylene production. The oxidative dehydrogenation of ethane is investigated by utilizing several catalysts and potential catalyst/susceptor combinations, with heat provided by an EM susceptor. Having the susceptors and catalyst function separately results in higher gradients in both heat and mass transfer, which drives transport through the catalyst region, while still providing adequate heating for endothermic reactions. However, using a susceptive core with a catalyst covering produces the maximum ethylene concentration.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Selective Hydrogenation of Acetylene to Ethylene over Bimetallic Catalysts

Ni/α-Al 2 O 3 catalyst and a series of bimetallic catalysts including Pd–Ag, Ni–Pd, Ni–Zn, Ni–Ag, and Ni–Ga were synthesized, characterized, and tested in selective hydrogenation of acetylene to ethylene. The bimetallic catalyst Ni–Ga exhibited almost the same ethylene selectivity compared to Pd–Ag based catalyst. The effect of the Ni/Ga ratio on the catalytic activity and selectivity to ethylene in acetylene hydrogenation was evaluated. Characterization by transmission electron microscopy, X-ray diffraction, hydrogen temperature-programmed reduction, and X-ray photoelectron spectroscopy was carried out to identify active phases on Ni–Ga based catalysts, which was correlated with catalytic performance and the reaction mechanism occurring over the catalyst. Here, the presence of Ga in Ni–Ga lattice structure confined the movement of dissociated H* and reduced the adsorption binding energy of ethylene, which could prevent overhydrogenation of acetylene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Surface chemistry of aromatic reactants on Pt- and Mo-modified Pt catalysts

Supported catalysts containing an oxophilic metal such as Mo and a noble metal such as Pt have shown promising activity and selectivity for deoxygenation of biomass-derived compounds. Here, we report that PtMo catalysts also promote hydrogenolysis of the model compound benzyl alcohol, while decarbonylation is most prevalent over unmodified Pt. A combination of single crystal surface science studies, density functional theory (DFT) calculations, and vapor phase upgrading experiments using supported catalysts was carried out to better understand the mechanism by which Mo promotes deoxygenation. Molybdenum was deposited in submonolayer quantities on a Pt(111) surface and reduced at high temperature. Temperature-programmed desorption (TPD) experiments using benzyl alcohol as a reactant showed greatly enhanced yields of the deoxygenation product toluene at moderate Mo coverages. To understand how the interaction of the aromatic group with the surface influenced this reactivity, we investigated the adsorption of toluene as a probe molecule. We found that the addition of Mo to Pt(111) resulted in a significant decrease in toluene decomposition. DFT calculations indicated that this decrease was consistent with decreased aromatic adsorption strengths that accompany incorporation of Mo into the Pt subsurface. The weaker aromatic-surface interaction on Pt/Mo surfaces led to a tilted adsorption geometry for benzyl alcohol, which presumably promotes hydrogenolysis to produce toluene instead of decarbonylation to produce benzene and CO. Alumina-supported Pt and PtMo catalysts were also tested for benzyl alcohol deoxygenation. PtMo catalysts had a higher rate of toluene production and lower rates of benzene and benzaldehyde production. Additionally, when benzaldehyde was used as the reactant to measure decarbonylation activity the mass-normalized rate of benzene production was 2.5 times higher on Pt than PtMo. Altogether, the results of TPD, DFT, and supported catalyst experiments suggest that subsurface Mo sites weaken the binding of aromatic rings on PtMo surfaces; the weakened aromatic-surface interaction is correlated with an improvement in selectivity to C-O bond scission.

09 BIOMASS FUELS↗
DOE OSTI2021

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Polymer–Particle Interactions and Spinnability

We investigate the effect of the poly(acrylic acid) (PAA) carrier polymer concentration on the microstructure and rheological properties of catalyst inks for electrospun polymer–electrolyte membrane fuel-cell catalyst layers. Characterization of an ink microstructure using oscillatory shear rheology showed that the catalyst particles (platinum on carbon) are significantly agglomerated in the absence of PAA or an ionomer. Both the ionomer and PAA promoted the stability of the particles against agglomeration via electrosteric stabilization by adsorbing onto the particle surface. Increasing the PAA concentration increased the stability of the particles (or reduced the agglomerated structure) due to increasing PAA coverage onto the free surface area of the particles. However, beyond a certain increase in concentration, PAA was found to predominantly remain as an excess free polymer in the ink due to an insufficient free/available surface area on the particles for further PAA coverage. Extensional rheology measurements demonstrated that PAA enhances the extensional viscosities of the inks. Consequently, increasing the PAA concentration in the ink promoted the evolution of uniform nanofibers. However, beyond a certain concentration, a significant increase in the shear viscosities of the inks led to defective fiber morphologies because of the onset of flow instabilities. Electrochemical performance comparisons between catalyst layers with different PAA concentrations showed maximum performance at the PAA concentration that led to the least agglomerated structure of the catalyst, most uniform fiber morphologies, and low concentrations of free (non-adsorbing) PAA in the electrode. These results provide a rationale for optimization of electrospun catalyst nanofibers for both spinnability and electrochemical performance.

25 ENERGY STORAGE↗
DOE OSTI2020

Correlating Oxidation State and Surface Area to Activity from Operando Studies of Copper CO Electroreduction Catalysts in a Gas-Fed Device

Copyright © 2020 American Chemical Society. The rational design of high-performance electrocatalysts requires a detailed understanding of dynamic changes in catalyst properties, including oxidation states, surface area, and morphology under realistic working conditions. Oxide-derived Cu catalysts exhibit a remarkable selectivity toward multicarbon products for the electrochemical CO reduction reaction (CORR), but the exact role of the oxide remains elusive for explaining the performance enhancements. Here, we used operando X-ray absorption spectroscopy (XAS) coupled with simultaneous measurements of the catalyst activity and selectivity by gas chromatography (GC) to study the relationship between oxidation states of Cu-based catalysts and the activity for ethylene (C2H4) production in a CO gas-fed cell. By utilizing a custom-built XAS cell, oxidation states of Cu catalysts can be probed in device-relevant settings and under high current densities (>80 mA cm-2) for the CORR. By employing an electrochemical oxidation process, we found that the Cu oxidation states and specific ion species do not correlate with C2H4 production. The difference in the CORR activity is also investigated in relation to electrochemical surface area (ECSA) changes. While the hydrogen evolution reaction (HER) activity is positively correlated to the ECSA changes, the increased C2H4 activity is not proportional to the ECSA. Ex situ characterization from microscopic techniques suggests that the changes in the C2H4 activity and selectivity may arise from a morphological transformation that evolves into a more active structure. These comprehensive results give rise to the development of a cell regeneration method that can restore the performance of the Cu catalyst without cell disassembly. Our study establishes a basis for the rational design of highly active electrocatalysts for broad-range reactions in a gas-fed device.

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

Atomic Structural Origin of the High Methanol Selectivity over In 2 O 3 –Metal Interfaces: Metal–Support Interactions and the Formation of a InO x Overlayer in Ru/In 2 O 3 Catalysts during CO 2 Hydrogenation

CO 2 hydrogenation to methanol is of great environmental and economic interest due to its potential to reduce carbon emissions and produce valuable chemicals in one single reaction. Compared with the unmodified traditional Cu/ZnO/Al 2 O 3 catalyst, an indium oxide (In 2 O 3 )-based catalyst can double the methanol selectivity from 30–50 to 60–100%. It is worth noting that over catalysts involving various active metals dispersed on indium oxide (M/In 2 O 3 , M = Pd, Ni, Au, etc.), although the methanol yield is boosted, the selectivity remains similar to that of plain In 2 O 3 despite the distinct chemical properties of the added metals. Here, to investigate the phenomena behind this behavior, we used RuO 2 /In 2 O 3 as a test catalyst. The results of ambient pressure photoelectron spectroscopy, in situ X-ray absorption fine structure, and time-resolved X-ray diffraction indicate that the structure of the RuO 2 /In 2 O 3 catalyst is highly dynamic in the presence of a reactive environment. Specifically, under CO 2 hydrogenation conditions, Ru clusters facilitate the reduction of In 2 O 3 to generate In 2 O 3–x aggregates, which encapsulate the Ru systems in a migration driven by thermodynamics. In this way, the Ru O sites for CH 4 production are blocked while creating RuO x –In 2 O 3–x interfacial sites with tunable metal–oxide interactions for selective methanol production. In an inverse oxide/metal configuration, indium oxide has properties not seen in its bulk phase that are useful for the binding and conversion of CO 2 . This work reveals the dynamic nature of In 2 O 3 -based catalysts, providing insights for a rational design of materials for the selective synthesis of methanol.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiO x Oxygen Evolution Reaction Catalysts

Iridium has emerged as the leading catalyst material for the anodic oxygen evolution reaction (OER) in acidic media. Often, iridium is mixed with more stable materials such as titanium. For these materials, the electronic structure of titanium plays a crucial role since with varying degrees of oxidation titanium transforms to semiconducting or even insulating phases. Yet, the electronic properties of mixed Ir-TiO x catalysts have never been systematically studied. In this study, we correlate the catalytic performance of mixed Ir-TiO x -based OER catalysts with the electronic structure of the surface layers. For this, a thin film material library with a 20-70 at. % Ir (Ir/[Ir + Ti]) compositional gradient was prepared. We used inductively coupled plasma mass spectrometry to test the OER activity and stability of the set of mixed Ir-TiO x catalyst candidate materials. Complementary, Ti L 2,3 - and O K-edge X-ray absorption spectroscopy and depth-dependent X-ray photoelectron spectroscopy measurements were performed to correlate the catalytic performance with the composition and electronic property profiles of these mixed Ir-TiO x OER anode catalysts. The spectroscopic analysis reveals that titanium is present as an intermixed matrix of semiconductive but stable TiO 2 , conductive but less stable titanium-suboxides (TiO x ), and highly conductive but highly unstable metallic Ti(0). The extent of the titanium oxidation strongly depends on the titanium content, with a lower degree of oxidation observed for lower titanium (and thus higher iridium) contents. For an iridium loading of 70 at. %, the respective mixed Ir-TiO x catalyst showed a similar OER activity to that of the pure metallic iridium (1.74 vs 1.59 VRHE, respectively) but with a 71% lower iridium dissolution rate relative to the pure metallic iridium. This demonstrates the stabilization effect of titanium addition while maintaining high OER activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Single-Site Palladium(II) Catalyst for Oxidative Heck Reaction: Catalytic Performance and Kinetic Investigations

ABSTRACT: The development of organometallic single-site catalysts (SSCs) has inspired the designs of new heterogeneous catalysts with high efficiency. Nevertheless, the application of SSCs in certain modern organic reactions, such as C-C bond formation reactions, has still been less investigated. In this study, a single-site Pd(II) catalyst was developed, where 2,2'-bipyridine-grafted periodic mesoporous organosilica (PMO) was employed as the support of a Pd(II) complex. The overall performance of the single-site Pd(II) catalyst in the oxidative Heck reaction was then investigated. The investigation results show that the catalyst displays over 99% selectivity for the product formation with high reaction yield. Kinetic profiles further confirm its high catalytic efficiency, showing that the rate constant is nearly 40 times higher than that for the free Pd(II) salt. X-ray absorption spectroscopy reveals that the catalyst has remarkable lifetime and recyclability.

cross-coupling reactions↗
DOE OSTI2018

Dry Reforming of Methane on Single-Site Ni/MgO Catalysts: Importance of Site Confinement

Single-site catalysts (SSCs) have drawn considerable attention, because of their superior behaviors in catalysis. However, the origin of promoting the effect of a single site is not well understood. Here in this paper, we take the single-atom Ni1/Mg(100) and single-site Ni4/Mg(100) catalysts as a case study to elucidate their behaviors under the complex dry reforming of methane (DRM, CO 2 + CH 4 → 2CO + 2H 2 ) reaction by combining theoretical modeling (density functional theory and kinetic Monte Carlo simulation) and experimental studies. The synergy between single Ni atom and MgO is found to improve the binding property of MgO; yet, it is not enough to dissociate CO 2 and CH 4 . It can be achieved by the single-site Ni 4 /MgO(100) catalyst, enabling the formations of CO, H 2 , and H 2 O under the DRM conditions. During this process, coking, as observed for bulklike Ni particles, is eliminated. By confining the reaction to occur at the isolated Ni sites in the SSC, the Ni 4 /MgO(100) catalyst is able to balance the CO 2 and CH 4 activations, which is identified as the key for tuning the DRM activity and selectivity of Ni/MgO catalysts. The theory-identified promotion introduced by increasing the size of MgO-supported Ni clusters from Ni 1 to Ni 4 and the MgO-introduced site confinement of single-site catalysts are verified by corresponding experimental studies, highlighting the essential roles of confined sites in tuning the performance of SSCs during complex catalytic processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

“Intelligent” Pt Catalysts Studied on High-Surface-Area CaTiO 3 Films

CaTiO 3 -supported Pt is sometimes referred to as an “Intelligent” catalyst because Pt can reversibly leave or enter the perovskite lattice following high-temperature reduction or oxidation; however, slow egress-ingress kinetics associated with large perovskite crystallites make these systems impractical. In this study, thin films (~1 nm) of CaTiO 3 were deposited onto MgAl 2 O 4 and then examined as catalyst supports for Pt and Pd. While Pd/CaTiO 3 /MgAl 2 O 4 showed adsorption and CO-oxidation properties that were essentially the same as Pd/MgAl 2 O 4 , the Pt/CaTiO 3 /MgAl 2 O 4 catalyst exhibited evidence for strong support interactions. Pt/CaTiO 3 /MgAl 2 O 4 showed high activity for CO oxidation following reduction at 1073 K, even though CO adsorption was suppressed; but the catalysts were dramatically less active after oxidation at 1073 K and reduction at 773 K. Both Pt/CaTiO 3 /MgAl 2 O 4 and a catalyst formed by ex-solution of CaTi 0.95 Pt 0.05 O 3 exhibited very low rates for toluene hydrogenation in comparison to Pt/MgAl 2 O 4 . Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive Spectroscopy (EDS) showed that the CaTiO 3 films uniformly covered the MgAl 2 O 4 surface after both reduction and oxidation at 1073 K. Pt particles on reduced Pt/CaTiO 3 /MgAl 2 O 4 exhibited an unusual rhombohedral shape and may be flat, a further indication of strong interactions between the metal and the support. Low Energy Ion Scattering (LEIS) indicated that high-temperature reduction caused a restructuring of the CaTiO 3 . Lastly, the implications of these results for understanding catalysts formed by ex-solution of metals from a perovskite lattice are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

CO 2 Hydrogenation to Methanol over ZrO 2 -Containing Catalysts: Insights into ZrO 2 Induced Synergy

Catalytic hydrogenation of CO 2 with renewable H 2 to methanol represents a promising pathway for reducing anthropogenic CO 2 emissions. Catalysts play a key role in enhancing both the hydrogenation rate and methanol selectivity. ZrO 2 is a promising catalyst support, promoter and even active species for CO 2 hydrogenation due to its versatile properties and weak hydrophilic character. Over the past decades substantial progress has been made in designing high performance catalysts and understanding the hydrogenation mechanisms over ZrO 2 -supported catalysts. ZrO 2 interacts with metals and/or other oxides and consequently may affect the CO 2 adsorption and activation, enhance the dissociation of H 2 and spillover of atomic hydrogen, change the reaction pathways and/or the binding of key reaction intermediates for further conversion. The synergistic effects induced by ZrO 2 could be achieved by improving the metal dispersion, modifying surface basicity and interacting with other components (metals, cosupports or promoters). However, although experimental and computational investigations have been extensively performed, the multiple roles of ZrO 2 in the catalytic process are still under debate. In the current Perspective, we use ZrO 2 -containing catalysts as a model system to elucidate the governing principles for designing high performance catalysts with multiple active components for CO 2 hydrogenation to methanol.

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

CeO 2 Promoted CuO/MgO-Al 2 O 3 Catalyst with Enhanced Activity and Water-Resistance for CO Oxidation

Copper (Cu)-based catalysts have emerged as cost-effective and sustainable alternatives to noble metal systems (e.g., Pt, Pd) for catalytic CO oxidation. However, their practical application is hindered by insufficient low-temperature activity and rapid deactivation under wet conditions containing moisture. To address these challenges, this work introduces CeO 2 -modified CuO/MgO-Al 2 O 3 (Cu-Ce/MA) catalysts, strategically designed to enhance the catalytic performance and water resistance simultaneously. These catalytic materials were evaluated for CO oxidation under both dry and humid conditions, revealing that CeO 2 modification significantly improves the low-temperature activity. Specifically, the optimal catalyst, Cu-30Ce/MA, achieved a 50% CO conversion temperature (T 50 ) of 151 °C, a marked reduction from 218 °C on Cu/MA reference catalyst. Furthermore, the water resistance improves in a CeO 2 content-dependent manner, with higher CeO 2 loadings imparting greater stability in humid environments. Detailed characterizations demonstrate that CeO 2 promotes the dispersion of CuO and stabilizes Cu sites, while also enhancing the low-temperature reducibility and CO adsorption capacity. Crucially, CeO 2 modification suppresses the competitive H 2 O adsorption, mitigating water-induced deactivation. These synergistic effects collectively rationalize the superior activity and durability of Cu-Ce/MA catalysts. By elucidating the dual role of CeO 2 in optimizing Cu-based systems, this study advances the rational design of cost-effective catalysts for real-world CO emission control, particularly under water-rich industrial conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗