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A-site and B-site substitutions are effective methods towards improving well-studied oxygen carrier materials that are vital for emerging gasification technologies. Such materials include SrFeO3 , which greatly benefits from the inclusion of calcium and/or cobalt, and Sr0.8 Ca0.2 Fe0.4 Co0.6 O3 has been regarded as the best-performing composition. In this study, systems with higher calcium and lower cobalt contents are investigated with a view to lessening the societal and economic burdens of these dual-doped carriers. Density functional theory calculations are performed to illustrate the Fe-O bonding and relaxation contributions to the oxygen vacancy formation energy in Sr1-x Cax Fe1-y Coy O3 systems (x=0.1875, 0.25, 0.3125; y=0.125, 0.25, 0.375, 0.5) and determine that increased calcium A-site substitution requires the use of less cobalt B-site doping to reach the same oxygen vacancy formation. These findings are experimentally validated in situ and ex situ characterization of bulk Sr0.7 Ca0.3 Fe1-y Coy O3 materials. Sr0.7 Ca0.3 Fe0.7 Co0.3 O3 is found to have similar O2 adsorption/desorption rates and storage capacity to Sr0.8 Ca0.2 Fe0.4 Co0.6 O3 in air/N2 cycling experiments. Additionally, both materials are outperformed by Sr0.7 Ca0.3 Fe1-y Coy O3 systems with y=0-0.10 at 400-500 °C, which cycle 1.5 wt% O2 in under ten minutes.

CeO2-Catalyzed esterification of CO2, a well-known greenhouse gas, with methanol has been widely recognized as a promising alternative method to produce dimethyl carbonate (DMC). Herein, we performed a comprehensive study of catalytic mechanisms underlying the formation of DMC from CO2 and methanol on both stoichiometric and reduced CeO2(111) and (110) surfaces. To this end, the saddle-point searching algorithm is employed. Specifically, using the monomethyl carbonate (MMC) as the key intermediate, a three-step Langmuir-Hinshelwood (LH) mechanism, including the formation and esterification of monomethyl carbonate and removal of water molecule, is identified for the catalytic DMC formation on either the reduced or the stoichiometric CeO2(111) and (110) surfaces. For both CeO2(111) and (110) surfaces, our study indicates that the presence of oxygen vacancies can markedly lower the activation energy barrier. Different rate-limiting steps are identified, however, for the reduced CeO2(111) and (110) surfaces. Successful identification of the rate-limiting step and the associated active CO2 species will provide atomic-level guidance on selection of metal-oxide-based catalysts toward direct synthesis of DMC from the green-house gas CO2 and methanol.

Reversible oxygen absorption/desorption in earth-abundant materials is fundamental towards many advanced technologies that require a pure oxygen stream including oxy-combustion via chemical looping and oxygen-blown coal gasification. The Sr1−xCaxFeO3 system is one of many perovskite oxides that have drawn attention given the large quantities of oxygen it can produce during mild cycling conditions. In this work, we employ hybrid functional based DFT calculations to establish the oxygen vacancy formation energy, ΔEf,vac, as an effective parameter for describing the Sr1−xCaxFeO3 system. We validate these calculations experimentally using XPS, O2-TPD, TGA, and synchrotron pXRD. In all cases, we find that increasing calcium content lowers both the oxygen desorption temperature and preferred operating temperature for the system. Importantly, we are able to experimentally show the structural and functional cyclability of these materials, achieving rapidly accessible maximum oxygen storage capacities of 1.51–2.41 wt% for temperatures of 400–700 °C.

Transition metal oxides have gained attention as promising oxygen evolution reaction (OER) electrocatalysts in alkaline electrolytes, but heterogeneities in typical catalyst samples often obscure k...

CeO2-Catalyzed esterification of CO2, a well-known greenhouse gas, with methanol has been widely recognized as a promising alternative method to produce dimethyl carbonate (DMC). Herein, we performed a comprehensive study of catalytic mechanisms underlying the formation of DMC from CO2 and methanol on both stoichiometric and reduced CeO2(111) and (110) surfaces. To this end, the saddle-point searching algorithm is employed. Specifically, using the monomethyl carbonate (MMC) as the key intermediate, a three-step Langmuir-Hinshelwood (LH) mechanism, including the formation and esterification of monomethyl carbonate and removal of water molecule, is identified for the catalytic DMC formation on either the reduced or the stoichiometric CeO2(111) and (110) surfaces. For both CeO2(111) and (110) surfaces, our study indicates that the presence of oxygen vacancies can markedly lower the activation energy barrier. Different rate-limiting steps are identified, however, for the reduced CeO2(111) and (110) surfaces. Successful identification of the rate-limiting step and the associated active CO2 species will provide atomic-level guidance on selection of metal-oxide-based catalysts toward direct synthesis of DMC from the green-house gas CO2 and methanol.

A-site and B-site substitutions are effective methods towards improving well-studied oxygen carrier materials that are vital for emerging gasification technologies. Such materials include SrFeO

In this work, we have investigated a hierarchical CuO-derived inverse opal (CuO-IO) catalyst with high CO selectivity up to 80–90% and minimal H2 evolution at moderate potentials for CO2 electroreduction. The three-dimensionally (3D) structured, porous catalyst was composed of small CuO nanoparticles and exhibited a peak CO faradaic efficiency (FE) of 72.5% (±1.8), complete suppression of H2 formation, and good stability over 24 hours operation at −0.6 V versus the reversible hydrogen electrode (RHE). In situ Raman, X-ray absorption spectroscopy and X-ray diffraction measurements indicated reduction of the catalyst into metallic Cu0 oxidation state with dominant Cu(111) orientation under electrocatalytic conditions. We suggest that rapid depletion of CO2 and protons at the highly roughened catalyst surface likely increased the local pH during the electrolysis. The combination of C1 favoring Cu(111) surfaces and reduced local proton/CO2 availability facilitated selective conversion of CO2 into CO and reduced H2 and C2 products. Our work provides additional understanding of the structure–property relationships of 3D porous electrocatalysts for CO2 reduction applications by evaluating the crystallographic orientation, oxidation state, and crystallite size of a CO-selective CuO-IO catalyst under realistic working conditions.

Oxygen (O2) storage materials often rely on the presence of cobalt (Co) to reduce the thermodynamic penalty and increase the kinetics necessary for efficient O2 storage and release. In this work, we investigate nickel (Ni) as an alternative B-site dopant in Sr1-xCaxFeO3 to identify Co-free carriers that still show improved kinetics at low temperatures. In fact, we show a substantial increase in the reversible O2 release rate through mild Ni B-site substitution (y = 0.06) in select Sr1-xCaxFe1-yNiyO3 systems at 400 to 500°C, reaching 2.00 wt.% O2 release up to approximately 75% faster than Ni-free systems. To explain the role of Ni in these systems, we use density functional theory to calculate the O2 vacancy (VO) formation energy from separate metal-oxygen (M-O) bonding and relaxation components. We computationally show elongated Ni-O bonds are directly responsible for the decrease in VO upon Ni substitution.

Diisopropylammonium bromide (DIPAB) molecular ferroelectric crystals were synthesized and examined to exhibit a large electric polarization (∼23μC/cm2), a large dielectric constant in the α-phase. Although the PXRD pattern indicates that the α-DIPAB sample has an overall excellent crystallinity, our analysis of its FT-IR and Raman vibrational spectra suggests the presence of disorder in the synthesized crystals as indicated by the presence of broad features in the Raman spectrum. Using vdW+DF2 calculations, we identified the majority of vibrational modes in the experimental spectra and analyzed the ones due to Br-disorder. We found that the bromine (Br) deficiency strongly affects the electric properties of α-DIPAB. Particularly, the experimentally measured dielectric constant of α-DIPAB is large (∼20), whereas the DFT-based calculations of the ideal DIPAB give much smaller values (∼2-3). We find that Br-deficiency is responsible for large dielectric constant of the DIPAB crystal with calculated value of ∼15-20. Furthermore, we showed that the van der Waals forces have a slight effect on the structural parameters, only causing a small shift in the vibrational frequencies. The main vibrational features of the DIPAB crystal in the Raman spectrum were shown to be driven by covalent bonding in the DIPA molecules and hydrogen bonds between the molecules with Br.

The dry reforming of methane (DRM) is a promising process for generating syngas (CO + H2) while consuming CO2, but industrial applications have been limited due to the high temperatures required to prevent coke formation. Microwave-assisted DRM (MW-DRM) is a promising approach to enable high temperature reactions because it can utilize excess renewable electrons to rapidly and selectively heat the catalyst bed without wasting time and energy heating the entire reactor. Here we demonstrate the MW-DRM reaction by modifying lanthanum strontium cobaltite (LSC) to serve as both microwave absorber and catalyst. Catalyst doping studies revealed the addition of oxophilic transition metals prevented over-reduction and stabilized the perovskitic phases under reaction conditions. In situ, synchrotron-based x-ray diffraction revealed the catalyst becomes active once metallic cobalt forms on a retained perovskitic support. The best performing Mn doped LSC catalyst showed 80–90 % single-pass conversions, stable operation for over 10 h, and easy microwave regeneration.

An ion-moderated partition high-performance liquid chromatography method was developed for the separation and identification of common organic carbonates. The separation of organic carbonates was achieved on an ion exclusion column with an exchangeable hydrogen ion. An isocratic, aqueous mobile phase was used for elution and detection was performed with a refractive index detector. The developed method was validated for specificity, linearity, limits of detection and quantification, precision and accuracy. All calibration curves showed excellent linear regression (R2 > 0.9990) within the testing range. The limits of detection were 3.8-30.8 ppm for the analyzed carbonates. Improvements in the peak resolution of the chromatograms were achieved by decreasing the column temperature. Addition of the organic modifier, acetonitrile, to the eluent was found to have insignificant effects on the peak resolution. The developed method was demonstrated for analyzing organic carbonate components in the electrolyte system of a commercial lithium ion battery.

The direct conversion of carbon dioxide (CO 2 ) to organic carbonates such as dimethyl carbonate (DMC) is favored only at low temperatures. However, these reactions are typically conducted at high temperatures due to poor reaction kinetics. In this article, the reaction kinetics were experimentally investigated for the direct conversion of CO 2 and methanol to DMC using a ceria nanorod catalyst and were compared with those of a highly crystalline commercial ceria catalyst. The apparent activation energy for this reaction over our nanorod catalyst was determined to be 65 kJ/mol whereas that of a commercial ceria catalyst was measured to be 117 kJ/mol. The reaction rate law was found to be approximately first order with respect to both catalysts, with an apparent negative one reaction order with respect to methanol. These results were found to be consistent with a Langmuir–Hinshelwood type reaction mechanism where CO 2 and methanol adsorption occurs in separate reaction steps.

We report a rapid, room temperature methodology to synthesize fluorite-structured ceria nanoparticles using cerium(III) salts and ozone in the presence of short chain primary, secondary, and tertiary alcohols. This simple technique produced nanoparticles with higher oxygen vacancy compared to that of bulk ceria.

A hybrid catalyst composed of phosphotungstic acid coated cerium oxide nanoparticles was demonstrated to catalyze the one-pot conversion of cellobiose, the disaccharide unit of cellulose, to a monosaccharide mixture of glucose and mannose. A high % conversion of cellobiose (up to 99%) was achieved resulting in a yield of mannose up to 15.8%. The yield of mannose from a glucose starting material was 22.8%, exceeding those of previous cerium-based glucose epimerization catalysts. The components of the hybrid material were revealed to function synergistically via a two-step process. Cellobiose was hypothesized to be first hydrolyzed to glucose, which was subsequently epimerized to mannose by the cerium ions leached from the catalyst. The 13C NMR spectroscopic study suggested that the epimerization likely occurred by way of a 1,2-carbon shift reaction mechanism.

The ability to control the morphology of fluorite-structured cerium oxide nanomaterials is an important step in the design of cerium oxide-based catalysts. Herein, we report an additive-free synthesis of cerium oxide nanorods with highly tunable aspect ratios from ~6:1 to 40:1. The use of a microwave hydrothermal method allows for both rapid synthesis and temperature control. The ability to control the length of the nanorods from 1.7 μm by varying only the reaction temperature was demonstrated over a temperature range of 80°C to 200°C. The formation of the resulting nanorods was investigated using selected-area electron-diffraction and high-resolution transmission electron microscopy. The surface area of nanorod products was found to decrease from 117 to 22 m2/g as the reaction temperature increased from 80°C to 200°C, complementing the general trend of the increasing aspect ratios of these products.

Multi-functional anode catalysts composed of platinum (Pt) nanoparticles electrodeposited on 2 wt% Pt decorated ceria (Pt:CeO2−x) nanorod supports were shown to enhance the alkaline electrocatalytic oxidation of methanol, ethanol and n-butanol over electrodeposited Pt nanoparticles alone or ones supported with pure ceria nanorods. The Pt:CeO2−x nanorod support was demonstrated to increase the current density of the investigated alkaline electrooxidation of methanol, ethanol and n-butanol by more than 30% over the other two catalysts.

The lanthanide sulfides have long been a promising class of semiconductors because of their infrared-to-visible range band gaps and excellent thermoelectric properties. However, their applications have been limited due to their time consuming conventional synthetic processes and the lack of sufficient understanding of their electronic properties. To address these shortcomings, here we report a rapid, chemical vapor deposition route which results in thin films of crystalline α-phase samarium sesquisulfide (α-Sm 2 S 3 ) nanowires within a few hours, rather than the typical 4–7 days required in previous synthetic processes. In addition, density functional theory was, for the first time, utilized to calculate the electronic band structure of α-Sm 2 S 3 in order to shed insight into the interpretation of their UV–Vis absorption spectrum. We found that the theoretical direct gap in the band states of α-Sm 2 S 3 is 1.7 eV. Computation results suggest that this gap can be tuned to a solar optimal ∼1.3 eV via systematic sulfur vacancy sites engineered into the crystal structure. Most significantly, the degenerate semiconductor-like behavior long observed in lanthanide sulfide samples have been shown to be present even in the ideal α-Sm 2 S 3 structure, suggesting that the observed heavily p -type behavior is an unusual intrinsic property of the material resulting from the Fermi level being located significantly below the optically active 1.7 eV band edge.

An ion-moderated partition high-performance liquid chromatography method was developed for the separation and identification of common organic carbonates. The separation of organic carbonates was achieved on an ion exclusion column with an exchangeable hydrogen ion. An isocratic, aqueous mobile phase was used for elution and detection was performed with a refractive index detector. The developed method was validated for specificity, linearity, limits of detection and quantification, precision and accuracy. All calibration curves showed excellent linear regression (R