Requirement of initial long-range substrate structure in unusual CO pre-oxidation on Pt(111) electrodes

The activation pathway of CO electro-oxidation at low potentials is frequently favored on a catalyst with surface defects. Here, we report a discovery in which an initial long-range substrate structure is required for the activation of an unusual CO pre-oxidation reaction pathway on Pt(111) surfaces which have been flame annealed and then cooled in a CO atmosphere. Different to current understanding about the oxidation of CO on Pt, the activation of this reaction pathway is inhibited as the (111) planes become defect-rich.M.J.S.F and A.A.T. thanks the CAPES (Brazil) Finance Code 001. J.M.F. thanks the MINECO (Spain) CTQ2013-44083-P project

Redukcija kiseonika na monokristalnim platinskim elektrodama u rastvorima fosforne kiseline

Oxygen reduction reaction has been studied on Pt low index planes in 0.1 M and 85% H3PO4 using hanging meniscus rotating disc electrode technique. The first-order kinetics of O2 reduction reaction was found for all three surfaces in a four-electron process with the first electron transfer rate determining in both 0.1 M and 85% H2PO4 solutions. Catalytic activity for O2 reduction follows the sequence Pt (110)>Pt (100)>Pt (111). Structural dependence is predominantly determined by the adsorption of phosphoric acid anions, which is strongly structure-dependent on Pt surfaces.Ispitivana je reakcija redukcije kiseonika na niskoindeksnim monokristalima platine u 85%i0.1 M rastvoru H3PO4 tehnikom rotirajućeg meniska. Utvrđeno je da je u oba rastvora reakcija prvog reda i da se odigrava 4-elektronskim putem u kome je prenos prvog elektrona spori stupanj. Katalitička aktivnost za redukciju kiseonika sledi niz Pt(110) > Pt(100) > Pt(111). Strukturna zavisnost aktivnosti dominantno je određena strukturno zavisnom adsorpcijom anjona fosforne kiseline na Pt(hkl) ravnima

Electrocatalytic oxidation of hydrazine in alkaline media promoted by iron tetrapyridinoporphyrazine adsorbed on graphite surface

The electrocatalytic oxidation of hydrazine was studied using an ordinary pyrolytic graphite electrode modified with iron tetrapyridinoporphyrazine complex (FeTPyPz), employing cyclic voltammetry and rotating disk electrode techniques. Analyses of the voltammograms recorded at different potential scan rates and the polarization curves at different electrode rotation rates showed that the reaction of electrooxidation of hydrazine on FeTPyPz occurs via 4-electrons with the formation of N2 as main product. The kinetic parameters suggest that the second electron transfer step is rate controlling. The activity of FeTPyPz depends on its Fe(II)/Fe(I) formal potential and fits well in a volcano plot that includes several iron phthalocyanines, indicating that such formal potential is a good reactivity index for these complexes

Nonuniform Synergistic Effect of Sn and Ru in Site-Specific Catalytic Activity of Pt at Bimetallic Surfaces toward CO Electro-oxidation

This work investigates the mechanisms by which Sn and Ru can improve or inhibit the site-specific catalytic activity of Pt (neighboring or distant from foreign atoms) at bimetallic surfaces. For this purpose, we decorated Pt stepped surfaces (nonequivalent sites) by site-selective electrodeposition of different coverages of either Sn or Ru on (110) Pt steps, forming Snsteps/Pt(hkl) and Rusteps/Pt(hkl) bimetallic surfaces, and we used CO adlayer electro-oxidation as a surface probe reaction, monitored by in situ FTIR and cyclic voltammetry techniques. The results showed that both Sn and Ru selectively accelerated the reaction pathway of CO electro-oxidation only at the (111) Pt terrace sites but importantly played different underlying roles in favoring activity at these active sites. In the case of Snsteps/Pt(hkl) catalysts, the CO adlayer oxidation started at potentials lower than those on Rusteps/Pt(hkl), but Sn only improved the activity at sites on atoms of the first rows of (111) Pt terraces, while the catalytic benefit of Ru seemed to extend further along the (111) Pt terraces. In comparison to unmodified Pt surfaces, Ru did not influence the activity at the line of the (110) Pt steps, while Sn slightly inhibited the activity there, which characterized a slight contrasting effect in catalytic activity at the (111) terraces in comparison to the (110) step sites. In this regard, the chemical modification by irreversible deposition of either Sn or Ru at lines of Pt steps on a stepped Pt surface interestingly resulted in a nonuniform synergistic effect or balancing of energies involving different site-specific catalytic activities at nonequivalent Pt surface sites. Since the electro-oxidation of CO takes place at the (111) Pt terrace sites away from Sn or Ru, and because COads behaves as an immobile species during its oxidation, it is reasonable to assume that the classical bifunctional mechanism completely fails as a model to interpret the enhancement of catalytic activity toward CO electro-oxidation at Snsteps/Pt(hkl) or Rusteps/Pt(hkl) catalysts. The selective alteration in site-specific catalytic activity of Pt was related to (i) the type and coverage of foreign atoms (Sn or Ru) at the lines of Pt steps, (ii) the crystallographic orientation of Pt sites, whether (111) terraces or steps, and (iii) the width of the (111) Pt terraces.M.J.S.F. acknowledges financial support from PNPD/CAPES (Brazil). A.A.T. acknowledges support from CAPES (PROCAD 2013) and CNPq (grant #309066/2013-1). J.M.F. thanks MINECO (Project CTQ2016-76221-P) and GV (Project PROMETEOII/2014/013) for financial support. W.C. is grateful for the award of an F.P.I. grant associated with project CTQ2009-13142

Unraveling the Nature of Active Sites in Ethanol Electro-oxidation by Site-Specific Marking of a Pt Catalyst with Isotope-Labeled 13CO

This works deals with the identification of preferential site-specific activation at a model Pt surface during a multiproduct reaction. The (110)-type steps of a Pt(332) surface were selectively marked by attaching isotope-labeled 13CO molecules to them, and ethanol oxidation was probed by in situ Foureir transfrom infrared spectroscopy in order to precisely determine the specific sites at which CO2, acetic acid, and acetaldehyde were preferentially formed. The (110) steps were active for splitting the C–C bond, but unexpectedly, we provide evidence that the pathway of CO2 formation was preferentially activated at (111) terraces, rather than at (110) steps. Acetaldehyde was formed at (111) terraces at potentials comparable to those for CO2 formation also at (111) terraces, while the acetic acid formation pathway became active only when the (110) steps were released by the oxidation of adsorbed 13CO, at potentials higher than for the formation of CO2 at (111) terraces of the stepped surface.M.J.S.F. is grateful to PNPD/CAPES (Brazil). A.A.T. acknowledges CAPES (PROCAD-2013) and CNPq (309066/2013-1). J.M.F. thanks the MINECO (Spain) project-CTQ2013-44083-P

Site-specific catalytic activity of model platinum surfaces in different electrolytic environments as monitored by the CO oxidation reaction

Stepped Pt surfaces having different width (1 1 1) terraces interrupted by (1 1 0) or (1 0 0) monoatomic steps were employed to evaluate the catalytic activity toward CO oxidation at Pt specific sites in HClO4, H2SO4, and H3PO4 solutions, as well as in phosphate buffer and alkaline solution. The catalytic activity at the (1 1 1) terraces was sensitive to the nature of the anions derived from the electrolyte dissociation, while no effect on activity was detected at the monoatomic steps. A change in solution pH, passing from acid to alkaline solutions, had contrasting effects on catalytic activity at the (1 1 1) terraces and the step sites, with the catalytic activity of the (1 1 1) terraces improving, while activity at the step sites deteriorated. During the CO adlayer oxidation, the release of surface sites occurred preferentially from the (1 1 1) terraces of the Pt(s) − [(n − 1)(1 1 1) × (1 1 0)] surfaces, while from Pt(s) − [(n)(1 1 1) × (1 0 0)] surfaces, (1 1 1) terrace and (1 0 0) step sites were released simultaneously.M.J.S. Farias acknowledges financial support from PNPD/CAPES (Brazil). G.A.B.M. received a post-doctorate fellowship from CNPq (grant no. PDE 233268/2014-6). A.A.T. acknowledges support from CAPES (PROCAD 2013) and CNPq (grant no. 309066/2013-1). J.M.F. thanks MICINN (Project CTQ2016-76221-P) and Generalitat Valenciana (Project PROMETEOII/2014/013) for financial support

Construction and application of an electrochemical sensor for paracetamol determination based on iron tetrapyridinoporphyrazine as a biomimetic catalyst of P450 enzyme

This work describes the construction and application of a biomimetic sensor for paracetamol determination in different samples . The sensor was prepared by modifying a glassy carbon electrode surface with a Nafion® membrane doped with FeTPyPz. The best performance of the sensor in 0.1 mol L-1 acetate buffer was at pH 3.6. Under these conditions, an oxidation potential of paracetamol was observed at 445 mV vs. Ag|AgCl. The sensor presented a linear response range between 4.0 and 420 µmol L-1, a sensitivity of 46.015 mA L mol-1 cm-2, quantification and detection limits of 4.0 µmol L-1 and 1.2 µmol L-1, respectively. A detailed investigation about its electrochemical behavior and selectivity was carried out. The results suggested that FeTPyPz presents catalytic properties similar to P450 enzyme for paracetamol oxidation. Finally, the sensor was applied for paracetamol determination in commercial drugs and for the monitoring of its degradation in an electrochemical batch reactor effluent.Descreve-se a construção e aplicação de um sensor biomimético para determinação de paracetamol em diversos tipos de amostras. O sensor foi construído modificando a superfície de um eletrodo de carbono vítreo com membrana de Nafion® dopada com tetrapiridinoporfirazina de ferro (FeTPyPz). Esse sensor apresentou melhor desempenho em tampão acetato 0,1 mol L-1 e pH 3,6. Nessas condições o potencial de oxidação do paracetamol foi de 445 mV vs. Ag|AgCl. O sensor apresentou uma faixa de resposta linear entre 4,0 e 420 µmol L-1, sensibilidade de 46,015 mA L mol-1 cm-2, limite de quantificação de 4,0 µmol L-1 e limite de detecção de 1,2 µmol L-1. Estudos eletroquímicos e de seletividade demonstraram a propriedade catalítica da FeTPyPz como sendo similares a da enzima P450 na oxidação do paracetamol. O sensor foi usado na determinação de paracetamol em formulações comerciais e no acompanhamento de sua degradação eletroquímica em efluentes provenientes de um reator em escala piloto.734743Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

MnO2-Ir Nanowires: Combining Ultrasmall Nanoparticle Sizes, O-Vacancies, and Low Noble-Metal Loading with Improved Activities towards the Oxygen Reduction Reaction

"Although clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can be considered a promising strategy, this approach remains challenging by the dependence on high loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or alloying) or replace them completely in these systems. The present investigation shows that high catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs) deposited onto MnO2 nanowires surface under low Ir loadings (1.2 wt.%). Interestingly, we observed that the MnO2 -Ir nanohybrid presented high catalytic activity for the ORR close to commercial Pt/C (20.0 wt.% of Pt), indicating that it could obtain efficient performance using a simple synthetic procedure. The MnO2 -Ir electrocatalyst also showed improved stability relative to commercial Pt/C, in which only a slight activity loss was observed after 50 reaction cycles. Considering our findings, the superior performance delivered by the MnO2 -Ir nanohybrid may be related to (i) the significant concentration of reduced Mn3+ species, leading to increased concentration of oxygen vacancies at its surface; (ii) the presence of strong metal-support interactions (SMSI), in which the electronic effect between MnOx and Ir may enhance the ORR process; and (iii) the unique structure comprised by Ir ultrasmall sizes at the nanowire surface that enable the exposure of high energy surface/facets, high surface-to-volume ratios, and their uniform dispersion.

Genetic insights into resting heart rate and its role in cardiovascular disease

Resting heart rate is associated with cardiovascular diseases and mortality in observational and Mendelian randomization studies. The aims of this study are to extend the number of resting heart rate associated genetic variants and to obtain further insights in resting heart rate biology and its clinical consequences. A genome-wide meta-analysis of 100 studies in up to 835,465 individuals reveals 493 independent genetic variants in 352 loci, including 68 genetic variants outside previously identified resting heart rate associated loci. We prioritize 670 genes and in silico annotations point to their enrichment in cardiomyocytes and provide insights in their ECG signature. Two-sample Mendelian randomization analyses indicate that higher genetically predicted resting heart rate increases risk of dilated cardiomyopathy, but decreases risk of developing atrial fibrillation, ischemic stroke, and cardio-embolic stroke. We do not find evidence for a linear or non-linear genetic association between resting heart rate and all-cause mortality in contrast to our previous Mendelian randomization study. Systematic alteration of key differences between the current and previous Mendelian randomization study indicates that the most likely cause of the discrepancy between these studies arises from false positive findings in previous one-sample MR analyses caused by weak-instrument bias at lower P-value thresholds. The results extend our understanding of resting heart rate biology and give additional insights in its role in cardiovascular disease development.</p