Can oxygen vacancies in ceria surfaces be measured by O1s photoemission spectroscopy?

X-ray photoemission spectroscopy is a standard technique for materials characterization and the O 1s binding energy is commonly measured for oxides. Here we use density functional theory calculations to investigate how the O 1s binding energy in CeO2(111) is influenced by the presence of oxygen vacancies. The case with point vacancies in CeO2(111) is compared to complete reduction to Ce2O3. Reduction of CeO2by oxygen vacancies is found to have a minor effect on the O 1s binding energy. The O 1s binding energy is instead clearly changed when the character of the chemical bond for the considered oxygen atom is modified by, for example, the formation of OH-groups or carbonates

On the signatures of oxygen vacancies in O1s core level shifts

Density functional theory calculations are used to investigate O1s surface core level shifts for MgO(100), ZnO(101\uaf0), In2O3(111) and CeO2(111). Shifts are calculated for the pristine surfaces together with surfaces containing oxygen vacancies and dissociated H2. Pristine surfaces show small negative shifts with respect to the bulk components and vacancies are found to have a minor effect on the O1s binding energies of neighboring oxygen atoms. OH-groups formed by H2 dissociation yield binding energies shifted to higher energies as compared to the oxygen atoms in the bulk. The results stress the difficulties in assigning core-level shifts and suggest that assignments of shifts in O1s binding energies to neighboring oxygen vacancies for the explored oxides should be reconsidered

Interface Reactions Dominate Low-Temperature CO Oxidation Activity over Pt/CeO2

First-principles-based kinetic Monte Carlo simulations and kinetic experiments are used to explore CO oxidation over Pt/CeO2. The simulations compare CO oxidation over a ceria-supported 1 nm particle with simulations of a free-standing particle and Pt(111). The onset of the CO oxidation over ceria supported Pt is shifted to lower temperatures compared to the unsupported systems thanks to a Mars-van Krevelen mechanism at the Pt/CeO2 interface perimeter, which is not sensitive to CO poisoning. Both the Mars-van Krevelen mechanism and the conventional Langmuir-Hinshelwood mechanism over the Pt nanoparticle are contributing to the conversion after the reaction onset. The reaction orders in CO and O2 are compared experimentally for Pt/CeO2 and Pt/Al2O3. The reaction orders over Pt/CeO2 are close to zero for both CO and O2, whereas the corresponding reaction orders are-0.75 and 0.68 over Pt/Al2O3. The measured zero orders for Pt/CeO2 show the absence of CO/O2 site competition and underline the relevance of interface reactions. The measurements for Pt/Al2O3 indicate that the main reaction path for CO oxidation over Pt is a conventional Langmuir-Hinshelwood reaction. The results elucidate the interplay between condition-dependent reaction mechanisms for CO oxidation over Pt supported on reducible oxides

Riociguat treatment in patients with chronic thromboembolic pulmonary hypertension: Final safety data from the EXPERT registry

Objective: The soluble guanylate cyclase stimulator riociguat is approved for the treatment of adult patients with pulmonary arterial hypertension (PAH) and inoperable or persistent/recurrent chronic thromboembolic pulmonary hypertension (CTEPH) following Phase

Low temperature CO oxidation over Pt/CeO2

The oxidation of CO to CO2 is a widely studied reaction not only for its practical applications but also for its apparent simplicity. CO oxidation is, in fact, often used as a model reaction for other oxidation reactions. On metal surfaces, the reaction is known to follow a Langmuir-Hinsenlwood mechanism where CO and dissociated O2 react to form CO2 that desorbs. Despite the high cost of platinum catalysts, it is hard to match the activity of CO oxidation using other metals. Instead of changing the catalysts, the approach is to reduce the amount of necessary metal to carry out the reaction. In this thesis, density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations are used to investigate the reaction energetics and kinetics on model systems, with a focus on the low temperature regime.Stimulated by the experimental evidence that CO may dissociate at low temperatures, CO dissociation has been studied as a possible initial competing reaction to oxidation. Our results show that CO dissociation does not occur directly, even on stepped surfaces. Instead, we propose that dissociation is facilitated at high coverages by a Boudouard reaction path at undercoordinated sites.In order to study the reaction kinetics, a complete description of the energy landscape is necessary. To describe the reaction landscape, scaling relations like the Bronsted-Evans-Polanyi and structure sensitive relations that link the adsorption energy of the reactants with a chosen descriptor, can be used to reduce the computational cost. Scaling relations are used in this work together with kinetic Monte Carlo to study CO oxidation over Pt nanoparticles. The sensitivity of the kinetic behaviours on scaling relations and on the oxygen sticking probability is investigated. Our results show that varying the slope of the scaling relations changes the turnover frequency (TOF) of the reaction, but the general behaviour is maintained, and clear trends are established between the reaction kinetics and the slope of the scaling relations.\ua0It is known that reducible oxides like ceria can increase the reaction\u27s activity at low temperatures, by allowing for a Mars-van Krevelen path. In this way, the issue with CO poisoning is reduced. We explore the effect of Mars-van Krevelen reaction steps for CO oxidation over Pt/CeO2. Additionally, we show that the common experimental assignment of XPS spectra shifts for the O 1s to the formation of oxygen vacancies might need reconsideration. Such shift could instead be due to OH groups adsorbed on the surface

Low temperature CO oxidation: Effects of support, composition and structure

Carbon monoxide is a tasteless, colorless and in-odorous toxic gas, which is formed during incomplete combustion. Due to its toxicity, efficient methods for CO oxidation to CO2 are required. One of the most active catalysts for this reaction is platinum, and the technological catalyst is generally based on nanosized platinum, yielding a high atom efficiency.In this thesis, density functional theory (DFT) calculations, mean field micro kinetic models and kinetic Monte Carlo (kMC) simulations are used to investigate the reaction energetics and kinetics on model systems, to understand and enhance the low temperature reaction regime.Experimental evidence of CO disproportionation stimulated the study of CO dissociation as a possible competing reaction to oxidation at low temperature. Our results show that dissociation of CO is facilitated at high coverages by a Boudouard reaction path at under-coordinated sites. To study the reaction kinetics over nanoparticles, a complete description of the energy landscape is necessary. In order to reduce the computational cost, it is possible to describe the energy landscape through scaling relations like the Br\uf8nsted-Evans-Polanyi and structure sensitive relations that link the adsorption energy of the reactants with a chosen descriptor. The sensitivity of scaling relations and sticking coefficient on CO oxidation is investigated, showing that varying the slope of the scaling relations results only in minor modifications of the reaction kinetics. It is known that reducible oxides like ceria can increase the reaction\u27s activity at low temperatures, by allowing for a Mars-van Krevelen (MVK) path. The effect of Mars-van Krevelen reaction steps for CO oxidation over Pt/CeO2 is explored. Our results show that the high activity for CO oxidation at low temperatures is due to the possibility of following the MVK mechanism at low temperatures and not to overall lower reaction barriers. The nature of oxygen vacancies in ceria is furthermore investigated, and we show that the common assignment of XPS spectra shifts for the O 1s to the formation of oxygen vacancies might need reconsideration. Such shift could be instead due to the presence of adsorbed OH groups on the surface. More on the fundamental description of CO oxidation, we investigate the possibility of predicting reaction paths from the experimental measurements of reaction orders. Exploring different reaction pathways by mean field simulations shows that reaction orders alone do not reveal the reaction mechanism. Lastly, we investigate CO oxidation on dilute Pt-Au alloy nanoparticles

Sensitivity of Monte Carlo Simulations to Linear Scaling Relations

One approach to study reaction kinetics over metal nanoparticles is to combine linear scaling relations with kinetic Monte Carlo simulations. This methodology is based on the observation that adsorption energies commonly scale linearly with descriptors such as the generalized coordination number and that reaction barriers are related to the adsorption energies via the Brionsted-Evans-Polanyi relation. In this work, the sensitivity of the reaction kinetics on the slopes of the scaling relations is investigated for CO oxidation over Pt-nanoparticles. The obtained trends between the slope and the turnover frequency suggest a modest dependency and that a flat energy landscape with energies corresponding to edge-sites yields a high catalytic activity. We also explore the sensitivity of the O-2 sticking probability on the turnover frequency. This parameter is found to have a minor influence on the kinetics of the studied reaction

Kinetics of the interaction of sulfate and hydrogen phosphate radicals with small peptides of glycine, alanine, tyrosine and tryptophan

The kinetics and mechanism of the oxidation of Glycine (Gly), Alanine (Ala), Tyrosine (Tyr), Tryptophan (Trp) and some di-(Gly-Gly, Ala-Ala, Gly-Ala, Gly-Trp, Trp-Gly, Gly-Tyr, Tyr-Gly), tri-(Gly-Gly-Gly, Ala-Gly-Gly) and tetrapeptides (Gly-Gly-Gly-Gly) mediated by sulfate (SO44 •−) and hydrogen phosphate (HPO4−) and hydrogen phosphate (HPO4 •−) radicals was studied, employing the flash-photolysis technique. The substrates were found to react with sulfate radicals (SO4 employing the flash-photolysis technique. The substrates were found to react with sulfate radicals (SO4 −) radicals was studied, employing the flash-photolysis technique. The substrates were found to react with sulfate radicals (SO44 •−, produced by photolysis of the S2O8 2−) faster than with hydrogen phosphate radicals (HPO4 2−) faster than with hydrogen phosphate radicals (HPO4 by photolysis of the S2O8 2−) faster than with hydrogen phosphate radicals (HPO4 2−) faster than with hydrogen phosphate radicals (HPO4 −, produced by photolysis of the S2O8 2−) faster than with hydrogen phosphate radicals (HPO4 2−) faster than with hydrogen phosphate radicals (HPO4 2O8 2−) faster than with hydrogen phosphate radicals (HPO4−) faster than with hydrogen phosphate radicals (HPO4 •−, generated by photolysis of P2O8 4− 4− −, generated by photolysis of P2O8 4−− at pH = 7.1). The reactions of the zwitterions of the aliphatic amino acids and peptides with SO4= 7.1). The reactions of the zwitterions of the aliphatic amino acids and peptides with SO4 •− radicals take place by electron transfer from the carboxylate moiety to the inorganic radical, whereas those of the HPO4 by electron transfer from the carboxylate moiety to the inorganic radical, whereas those of the HPO4 − radicals take place by electron transfer from the carboxylate moiety to the inorganic radical, whereas those of the HPO44 •− proceed by H-abstraction from the a carbon atom. The phenoxyl radical of Tyr-Gly and Gly-Tyr are formed as intermediate species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO4 oxidation of these peptides with SO4 species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO4 oxidation of these peptides with SO4 H-abstraction from the a carbon atom. The phenoxyl radical of Tyr-Gly and Gly-Tyr are formed as intermediate species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO4 oxidation of these peptides with SO4 species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO4 oxidation of these peptides with SO4 − proceed by H-abstraction from the a carbon atom. The phenoxyl radical of Tyr-Gly and Gly-Tyr are formed as intermediate species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO4 oxidation of these peptides with SO4 species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO4 oxidation of these peptides with SO4 a carbon atom. The phenoxyl radical of Tyr-Gly and Gly-Tyr are formed as intermediate species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO4 oxidation of these peptides with SO4 = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO44 •− and HPO4− and HPO4 •−. Reaction mechanisms which account for the observed intermediates are proposed. intermediates are proposed. −. Reaction mechanisms which account for the observed intermediates are proposed.Fil: Bosio, Gabriela Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Criado, Susana Noemi. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Massad, Walter Alfredo. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Rodríguez Nieto, Felipe Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Gonzalez, Monica Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Garcia, Norman Andino. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Martire, Daniel Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Plasmonic versus All-Dielectric Nanoantennas for Refractometric Sensing: A Direct Comparison

In comparison to nanoplasmonic structures, resonant high-index dielectric nanoantennas hold several advantages that may benefit nanophotonic applications, including CMOS compatibility and low ohmic losses. One such application area might be label-free refractometric sensing, where changes in individual antenna resonance properties are used to quantify changes in the surrounding refractive index, for example, due to biomolecular binding. Here, we analyze and compare the sensing performance of silicon and gold nanodisks using a common and unbiased testing framework. We find that the all-dielectric system is fully capable of effectively monitoring small changes in bulk refractive index and biomolecular coverage, but the sensitivity is five to ten times lower than the plasmonic counterpart. However, this drawback is partly compensated for by a more linear response to adsorbate layer thickness changes and an approximately four times smaller susceptibility to photothermal heating. Finally, dielectric sensors may show promise if certain strategies are employed to improve their performance, which could thus bridge the gap between the two systems

Riociguat treatment in patients with chronic thromboembolic pulmonary hypertension: Final safety data from the EXPERT registry

Objective: The soluble guanylate cyclase stimulator riociguat is approved for the treatment of adult patients with pulmonary arterial hypertension (PAH) and inoperable or persistent/recurrent chronic thromboembolic pulmonary hypertension (CTEPH) following Phase 3 randomized trials. The EXPosurE Registry RiociguaT in patients with pulmonary hypertension (EXPERT) study was designed to monitor the long-term safety of riociguat in clinical practice. Methods: EXPERT was an international, multicenter, prospective, uncontrolled, non-interventional cohort study of patients treated with riociguat. Patients were followed for at least 1 year and up to 4 years from enrollment or until 30 days after stopping riociguat treatment. Primary safety outcomes were adverse events (AEs) and serious adverse events (SAEs) coded using Medical Dictionary for Regulatory Activities preferred terms and System Organ Classes version 21.0, collected during routine clinic visits and collated via case report forms. Results: In total, 956 patients with CTEPH were included in the analysis. The most common AEs in these patients were peripheral edema/edema (11.7%), dizziness (7.5%), right ventricular (RV)/cardiac failure (7.7%), and pneumonia (5.0%). The most common SAEs were RV/cardiac failure (7.4%), pneumonia (4.1%), dyspnea (3.6%), and syncope (2.5%). Exposure-adjusted rates of hemoptysis/pulmonary hemorrhage and hypotension were low and comparable to those in the long-term extension study of riociguat (Chronic Thromboembolic Pulmonary Hypertension Soluble Guanylate Cyclase-Stimulator Trial [CHEST-2]). Conclusion: Data from EXPERT show that in patients with CTEPH, the safety of riociguat in routine practice was consistent with the known safety profile of the drug, and no new safety concerns were identified