Kinetic Relevance of Surface Reactions and Lattice Diffusion in the Dynamics of Ce–Zr Oxides Reduction–Oxidation Cycles

Reduction–oxidation cycles in oxides are ubiquitous in oxygen storage and transport, chemical looping processes, and fuel cells. O-atom addition and removal are mediated by coupling reactions of oxidants and reductants at surfaces with diffusion of O-atoms within oxide crystals, with either or both processes as limiting steps. CeO2–ZrO2 solid solutions (CZO) are ubiquitous in practice. They are used here to illustrate general experimental strategies and reaction–diffusion formalisms for nonideal systems that enable assessments of the kinetic relevance of the steps that mediate O-atom addition and removal in these materials; these experiments are described within the context of models that describe the driving forces for reaction and diffusion rigorously in terms of oxygen chemical potentials (μO). These strategies assess the rate consequences of varying the fluid phase redox potential, through changes in the identity and pressures of the reactants and products used in redox cycles (O2; CO/CO2; H2/H2O; N2O/N2), of introducing dispersed metal nanoparticles that capture and react lattice O-atoms in CZO using CO or H2, and of imposing intervening dwells without reaction within redox cycles. O-removal rates depend on reductant pressures, even when CO/CO2 and H2/H2O ratios are chosen to maintain the same surface μO if surface reactions were quasi-equilibrated. These data, taken together with significant rate enhancements in O-removal when Pt nanoparticles are present at CZO crystal surfaces and with similar rates before and after inert dwells, demonstrate that reduction rates by both CO and H2 are limited by surface reactions without the presence of consequential spatial gradients in μO within CZO crystals. In contrast, O-addition rates to partially reduced CZO crystals are similar for N2O and O2 reactants and are not affected by the presence of Pt nanoparticles; O-addition rates are significantly higher after intervening inert dwells during CZO oxidation, indicative of spatial gradients in μO, which relax during nonreactive periods. These methods and models, illustrated here for CZO redox cycles at conditions relevant to oxygen storage practice, allow systematic assessments of the kinetic relevance of lattice diffusion and surface reactions for systems that use solids for the reversible storage and release of atoms, irrespective of the identity of the solids or the atoms (e.g., O, H, N, and S)

Additional file 1: of ‘The university should promote health, but not enforce it’: opinions and attitudes about the regulation of sugar-sweetened beverages in a university setting

Copy of study survey. (PDF 351 kb

Facile Synthesis and Evaluation of Nanofibrous Iron–Carbon Based Non-Precious Oxygen Reduction Reaction Catalysts for Li–O₂ Battery Applications

Development of low cost active catalysts toward oxygen reduction reaction (ORR) is critical for the effective operation of Li–O₂ battery. Porous nonprecious iron–carbon based nanofiber catalysts have been developed by electrospinning method. The catalysts demonstrated similar ORR catalytic activity for ORR as the commercial Pt-based catalysts in the aqueous half-cell voltammetry sweeps. In the Li–O₂ aprotic environment, the catalyst exhibited higher on-set potentials when compared to glassy carbon and Pt disk electrodes. The results show that the nonprecious electrospun nanofiber could be an effective low cost ORR catalyst at the cathode for Li–O₂ battery

Additional files 2: of Protocol for a cluster-randomised trial to determine the effects of advocacy actions on the salt content of processed foods

Interim outcomes: examples of the types and sources of data, and measures. Description of data: description of the interim measures, examples of the types of data to be collected, the data sources, and the measure. (PDF 175 kb

Determination of Iron Active Sites in Pyrolyzed Iron-Based Catalysts for the Oxygen Reduction Reaction

Fe-based oxygen reduction reaction (ORR) catalyst materials are considered promising nonprecious alternatives to traditional platinum-based catalysts. These catalyst materials are generally produced by high-temperature pyrolysis treatments of readily available carbon, nitrogen, and iron sources. Adequate control of the structure and active site formation during pyrolysis methods is nearly impossible. Thus, the chemical nature, structure, and ORR mechanism of catalytically active sites in these materials is a subject of significant debate. We have proposed a method, utilizing CN^– ions as ORR inhibitors on Fe-based catalysts, to provide insight into the exact nature and chemistry of the catalytically active sites. Moreover, we propose two possible catalytically active site formation mechanisms occurring during high-temperature pyrolysis treatments, dependent on the specific type of precursor and synthesis methods utilized. We have further provided direct evidence of our proposed active site formations using ToF-SIMS negative and positive ion imaging. This knowledge will be beneficial to future work directed at the development of Fe-based catalysts with improved ORR activity and operational stabilities for fuel cell and battery applications

DBP-maf inhibits tumor cell migration.

<p>LNCaP (<b>A</b>), LNCaPLN3 (<b>B</b>), PC3M (<b>C</b>) or PC3MLN4 (<b>D</b>) cells were added (150,000/well) to the top chamber of a modified Boyden chamber (+/− DBP-maf) with 10% FBS in the bottom chamber. After 6 hours cells were removed that had not migrated and remaining cells were quantitated using an acid phosphatase assay. Results were normalized to control. Experiments were performed a minimum of three times and error is shown as +/− SD. Compared to cell growth without DBP-maf, adding DBP-maf had a statistically significant overall reduction of cell migration at 30% (P = 0.0003) for the combined four tumor cell types. Individual significant reduction rates were found with each of these tumor cell types. Compared to control, significant reduction was seen with DBP-maf at (<b>A</b>) 20% P = 0.0022 (<b>B</b>) 20% P = 0.0029 (<b>C</b>) 10% P = .0045 (<b>D</b>) 30% P = .0094. n = 3.</p

DBP-maf peptide does not inhibit expression of uPAR in PC3M or LNCaPLN3 cells.

<p>LNCaPLN3 (<b>A</b>) and PC3M cells (<b>B</b>) were treated with DBP or DBP-maf (0.001 and 1 µg/mL) and incubated for 24 hours then harvested. RT products (cDNA), identified as uPAR1, 2, and 3, were amplified by real-time quantitative PCR. p<0.05.</p

FACS analysis of apoptosis or necrosis.

<p>Cells were treated with or without 1 µg/mL DBP-maf for 48 hours, propidium iodide and annexin V were added and cells were analyzed using flow cytometry. Results are representative of three experiments.</p

DBP-maf inhibits tumor cell proliferation.

<p>LNCaP (<b>A</b>), LNCaPLN3 (<b>B</b>), PC3M (<b>C</b>) or PC3MLN4 (<b>D</b>) cells were seeded in 24 well dishes overnight, then medium +/− DBP-maf was added with 1% FBS. After 72 hours cells were quantitated using an acid phosphatase assay. Results were normalized to control. Experiments were performed a minimum of three times and error is shown as +/− SD. Compared to control, significant reduction was seen with DBP-maf at (<b>A</b>) 50% P = 0.0001 (<b>B</b>) 50% P = 0.0001 (<b>C</b>) no significant reduction (<b>D</b>) 40% P = .0073. n = 3.</p

DBP-maf inhibits expression of uPAR in PC3M cells.

<p>PC3M, and PC3MLN4 cells were treated with DBP or DBP-maf (0.001 and 1 µg/mL) and incubated for 24 hours then harvested. RT products (cDNA), identified as uPAR1, 2, and 3, were amplified by real-time quantitative PCR. p<0.05.</p