Effect of methanol concentration on oxygen reduction reaction activity of Pt/C catalysts

The oxygen reduction reaction (ORR) activity of Pt/C catalysts was investigated in electrolytes of 0.5 mol/L H2SO4 containing varying concentrations of methanol in a half-cell. It was found that the ORR activity was improved notably in an electrolyte of 0.5 mol/L H2SO4 containing 0.1 mol/L CH3OH as compared with that in 0.5 mol/L H2SO4, 0.5 mol/L H2SO4 containing 0.5 mol/L CH3OH, or 0.5 mol/L H2SO4 containing 1.0 mol/L CH3OH electrolytes. The same tendency for improved ORR activity was also apparent after commercial Nafion (R) NRE-212 membrane was hot-pressed onto the catalyst layers. The linear sweep voltammetry results indicate that the ORR activities of the Pt/C catalyst were almost identical in the 0.5 mol/L H2SO4 + 0.1 mol/L CH3OH solution before and after coated with the Nafion (R) membrane. Electrochemical impedance spectroscopy results demonstrated that the resistance of the Nafion (R) membrane is smaller in the electrolyte of 0.5 mol/L H2SO4 + 0.1 mol/L CH3OH than in other electrolytes with oxygen gas feed. This exceptional property of the Nafion (R) membrane is worth investigating and can be applied in fuel cell stacks to improve the system performance. (c) 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Determining the Effect of Plasma Pre-Treatment on Antimony Tin Oxide to Support Pt@Pd and the Oxygen Reduction Reaction Activity

This article reveals the effect of plasma pre-treatment on antimony tin oxide (ATO) nanoparticles. The effect is to allow Pt@Pd to be deposited homogeneously on the ATO surface with high dispersion and narrow particle size distribution. The Pt@Pd core–shell catalyst was prepared using the polyol method and shows a dramatic improvement towards ORR activity and durability.

Oxygen reduction reaction mechanism on nitrogen-doped graphene:A density functional theory study

Nitrogen-doped graphene (N-graphene) was reported to exhibit a good activity experimentally as an electrocatalyst of oxygen reduction reaction (ORR) on the cathode of fuel cells under the condition of electropotential of similar to 0.04 V (vs. NNE) and pH of 14. This material is promising to replace or partially replace the conventionally used Pt. In order to understand the experimental results. ORR catalyzed by N-graphene is studied using density functional theory (DFT) calculations under experimental conditions taking the solvent, surface adsorbates, and coverages into consideration. Two mechanisms, i.e., dissociative and associative mechanisms, over different N-doping configurations are investigated. The results show that N-graphene surface is covered by O with 1/6 monolayer, which is used for reactions in this work. The transition state of each elementary step was identified using four different approaches, which give rise to a similar chemistry. A full energy profile including all the reaction barriers shows that the associative mechanism is more energetically favored than the dissociative one and the removal of O species from the surface is the rate-determining step. (C) 2011 Elsevier Inc. All rights reserved.

Oxygen Reduction Reaction on Metal-Terminated MnCr2O4 Nano-octahedron Catalyzing MnS Dissolution in an Austenitic Stainless Steel

To understand pitting corrosion in stainless steel is very important, and a recent work showed that the MnS dissolution catalyzed by MnCr2O4{111} is a starting point of pit g. This demonstrates the need to understand the oxygen reduction reaction (ORR) on MnCr2O4{111}, which is the other half-reaction to complete pitting corrosion. In this study, the adsorption behaviors of all oxygen-containing species on MnCr2O4{111}, which has several possible terminations, are explored via density functional theory calculations. It is found that O-2 adsorbs on MnCr2O4{111) surfaces very strongly. Many possible reactions are investigated and the favored reaction mechanism of ORR is determined. The interactions between O-2 and H2O on the two metal-terminated MriCr(2)O(4){111} are found to be different according to the atomic configurations of the two surfaces. All the calculated results suggest that ORR can readily occur on the MnCr2O4{111} surfaces.

KINETICS OF REDUCTION OF HEXACYANOFERRATE(III) BY THIOSULFATE IONS MEDIATED BY RUTHENIUM DIOXIDE HYDRATE

The kinetics of reduction of hexacyanoferrate(III) by excess thiosulfate, mediated by RuO2.xH2O, are investigated. At high concentrations of S2O32- (0.1 mol dm-3) the kinetics of Fe(CN)63- reduction are first order with respect to [Fe(CN)63-] and [RuO2.xH2O] and independent of [Fe(CN)64-], [S2O32-] and [S4O62-]. At relatively low concentrations Of S2O32- (0.01 mol dm-3) and in the presence of appreciable concentrations of Fe(CN)64- and S4O62- (0.01 mol dm-3) the kinetics depend directly upon [Fe(CN)63-] and [RuO2.xH2O] and inversely upon [Fe(CN)64-]. Both sets of kinetics can be rationalised using an electrochemical model of redox catalysts in which a reversible reduction reaction [Fe(CN)63- + e- --> Fe(CN)64-] is coupled to an irreversible oxidation reaction (s2O32- - e- --> 1/2S4O62-), by a dispersion of RuO2.xH2O microelectrodes. At high concentrations Of S2O32- this model predicts that the kinetics of Fe(CN)63- reduction are controlled by the rate of diffusion of the Fe(CN)63- ions to the RuO2.xH2O particles. The kinetics observed at low concentrations of S2O32- are predicted by the electrochemical model, assuming that the Tafel slope for the oxidation Of S2O32- to S4O62- on the RuO2.xH2O particles is 56.4 mV decade-1.

Carboxymethylethanolamine, a biomarker of phospholipid modification during the maillard reaction in vivo

Nepsilon-(Carboxymethyl)lysine (CML) is a stable chemical modification of proteins formed from both carbohydrates and lipids during autoxidation reactions. We hypothesized that carboxymethyl lipids such as (carboxymethyl)phosphatidylethanolamine (carboxymethyl-PE) would also be formed in these reactions, and we therefore developed a gas chromatography-mass spectrometry assay for quantification of carboxymethylethanolamine (CME) following hydrolysis of phospholipids. In vitro, CME was formed during glycation of dioleoyl-PE under air and from linoleoylpalmitoyl-PE, but not from dioleoyl-PE, in the absence of glucose. In vivo, CME was detected in lipid extracts of red blood cell membranes, approximately 0.14 mmol of CME/mol of ethanolamine, from control and diabetic subjects, (n = 22, p > 0.5). Levels of CML in erythrocyte membrane proteins were approximately 0.2 mmol/mol of lysine for both control and diabetic subjects (p > 0.5). For this group of diabetic subjects there was no indication of increased oxidative modification of either lipid or protein components of red cell membranes. CME was also detected in fasting urine at 2-3 nmol/mg of creatinine in control and diabetic subjects (p = 0.085). CME inhibited detection of advanced glycation end product (AGE)-modified protein in a competitive enzyme-linked immunosorbent assay using an anti-AGE antibody previously shown to recognize CML, suggesting that carboxymethyl-PE may be a component of AGE lipids detected in AGE low density lipoprotein. Measurement of levels of CME in blood, tissues, and urine should be useful for assessing oxidative damage to membrane lipids during aging and in disease.

Glycation, glycoxidation, and cross-linking of collagen by glucose. Kinetics, mechanisms, and inhibition of late stages of the Maillard reaction

The Maillard or browning reaction between sugar and protein contributes to the increased chemical modification and cross-linking of long-lived tissue proteins in diabetes. To evaluate the role of glycation and oxidation in these reactions, we have studied the effects of oxidative and antioxidative conditions and various types of inhibitors on the reaction of glucose with rat tail tendon collagen in phosphate buffer at physiological pH and temperature. The chemical modifications of collagen that were measured included fructoselysine, the glycoxidation products N epsilon-(carboxymethyl)lysine and pentosidine and fluorescence. Collagen cross-linking was evaluated by analysis of cyanogen bromide peptides using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by changes in collagen solubilization on treatment with pepsin or sodium dodecylsulfate. Although glycation was unaffected, formation of glycoxidation products and cross-linking of collagen were inhibited by antioxidative conditions. The kinetics of formation of glycoxidation products proceeded with a short lag phase and were independent of the amount of Amadori adduct on the protein, suggesting that autoxidative degradation of glucose was a major contributor to glycoxidation and cross-linking reactions. Chelators, sulfhydryl compounds, antioxidants, and aminoguanidine also inhibited formation of glycoxidation products, generation of fluorescence, and cross-linking of collagen without significant effect on the extent of glycation of the protein. We conclude that autoxidation of glucose or Amadori compounds on protein plays a major role in the formation of glycoxidation products and cross-liking of collagen by glucose in vitro and that chelators, sulfhydryl compounds, antioxidants, and aminoguanidine act as uncouplers of glycation from subsequent glycoxidation and cross-linking reactions.

Accumulation of Maillard reaction products in skin collagen in diabetes and aging

To investigate the contribution of glycation and oxidation reactions to the modification of insoluble collagen in aging and diabetes, Maillard reaction products were measured in skin collagen from 39 type 1 diabetic patients and 52 nondiabetic control subjects. Compounds studied included fructoselysine (FL), the initial glycation product, and the glycoxidation products, N epsilon-(carboxymethyl) lysine (CML) and pentosidine, formed during later Maillard reactions. Collagen-linked fluorescence was also studied. In nondiabetic subjects, glycation of collagen (FL content) increased only 33% between 20 and 85 yr of age. In contrast, CML, pentosidine and fluorescence increased five-fold, correlating strongly with age. In diabetic patients, collagen FL was increased threefold compared with nondiabetic subjects, correlating strongly with glycated hemoglobin but not with age. Collagen CML, pentosidine and fluorescence were increased up to twofold in diabetic compared with control patients: this could be explained by the increase in glycation alone, without invoking increased oxidative stress. There were strong correlations among CML, pentosidine and fluorescence in both groups, providing evidence for age-dependent chemical modification of collagen via the Maillard reaction, and acceleration of this process in diabetes. These results support the description of diabetes as a disease characterized by accelerated chemical aging of long-lived tissue proteins.

Evaluation and mechanistic investigation of a AuPd alloy catalyst for the hydrocarbon selective catalytic reduction (HC-SCR) of NOx

The ability of a gold palladium bimetallic catalyst to selectively oxidise toluene has been used to enhance the hydrocarbon selective catalytic reduction of NOx, a reaction in which the interaction of partial oxidation intermediates is considered important. The combination of gold with palladium has a synergistic effect, producing a catalyst that is more active for NOx conversion than the arithmetic sum of the corresponding mono-metallic materials. Three regimes in the conversion profile of the AuPd catalyst are proposed relating to production and consumption of toluene derived species, such as benzaldehyde and benzonitrile. The possible role of these reaction intermediates in the toluene HC-SCR reaction is examined. Using 15NO, the formation of N2 and N2O is observed via the direct interaction between the nitrogen atom of benzonitrile and 15NO. The higher activity of the bimetallic catalyst for the NOx reduction reaction by toluene is discussed in the context of these partial oxidation intermediates.

NO Oxidation on Platinum Group Metals Oxides:First Principles Calculations Combined with Microkinetic Analysis

By combining density functional theory calculation and microkinetic analysis, NO oxidation on the platinum group metal oxides (PtO(2), IrO(2), OsO(2)) is investigated, aiming at shedding light on the activities of metal oxides and exploring the activity variations of metal oxides compared to their corresponding metals. A microkinetic model, taking into account the possible low diffusion of surface species on metal oxide surfaces, is proposed for NO oxidation. The resultant turnover frequencies of NO oxidation show that under the typical experimental condition, T = 600 K, p(O2) = 0.1 atm, p(NO) = 3 x 10(-4) atm, p(NO2) = 1.7 x 10(-4) atm; (i) IrO(2)(110) exhibits higher activity than PtO(2)(110) and OsO(2)(110), and (ii) compared to the corresponding metallic Pt, Ir, and Os, the activity of PtO(2) to catalyze NO oxidation is lower, but interestingly IrO(2) and OsO(2) exhibit higher activities. The reasons for the activity differences between the metals and oxides are addressed. Moreover, other possible reaction pathways of NO oxidation on PtO(2)(110), involving O(2) molecule (NO + O(2) -> OONO) and lattice bridge-O(2c), are also found to give low activities. The origin of the Pt catalyst deactivation is also discussed.

Pretreatment Effect on Pt/CeO2 Catalyst in the Selective Hydrodechlorination of Trichloroethylene

Pt-ceria catalysts present different surface chemistries depending on the preparation method and the pretreatment. The catalytic behavior of Pt/CeO2 catalysts in the hydrodechlorination of trichloroethylene (TCE) to ethylene was examined as a function of the pretreatment conditions and the noble metal precursor salts. Using FTIR and X-ray photoelectron spectroscopy, significant differences were observed in the surface properties of Pt/CeO2 prepared from the H2PtCl6 precursor after different pretreatment procedures (i.e.. reduction or oxidation-reduction). These surface changes are related to chloride residues from the synthesis. Strong changes were observed in the selectivity of the catalysts to ethylene depending on the pretreatment conditions. The 0.5%Pt/CeO2 catalyst showed a 13% selectivity toward ethylene after reduction, whereas alter oxidation, followed by reduction, the selectivity increased up to 85% at the same conversion level. This effect was only observed when a chloride-containing precursor was used in the preparation. In this way, it is demonstrated that the use of a Cl-containing Pt precursor and an air treatment prior to reduction strongly improves the ethylene selectivity of Pt-CeO2 dechlorination catalysts. This can be explained by formation or a CeOCl phase during the synthesis that decomposes upon air tempering, producing oxygen vacancies on the ceria support. We propose that these oxygen vacancies are active for cleaving off Cl from the TCE. Pt then supplies II to clean-off Cl as HCl. Reaction of TCE on Pt produces rather ethane, so Pt may be partly Cl-poisoned for the hydrodechlorination reaction but not for II, dissociation or CO adsorption.

New Cu-Based Catalysts Supported on TiO2 Films for Ullmann SNAr-Type C-O Coupling Reactions

New routes for the preparation of highly active TiO2-supported Cu and CuZn catalysts have been developed for C-O coupling reactions. Slurries of a titania precursor were dip-coated onto glass beads to obtain either structured mesoporous or non-porous titania thin films. The Cu and CuZn nanoparticles, synthesized using a reduction by solvent method, were deposited onto calcined films to obtain a Cu loading of 2 wt%. The catalysts were characterized by inductively coupled plasma (ICP) spectroscopy, temperature-programmed oxidation/reduction (TPO/TPR) techniques, Cu-63 nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (S/TEM-EDX) and X-ray photo-electron spectroscopy (XPS). The activity and stability of the catalysts obtained have been studied in the C-O Ullmann coupling of 4-chloropyridine and potassium phenolate. The titania-supported nanoparticles retained catalyst activity for up to 12 h. However, catalyst deactivation was observed for longer operation times due to oxidation of the Cu nanoparticles. The oxidation rate could be significantly reduced over the CuZn/TiO2 catalytic films due to the presence of Zn. The 4-phenoxypyridine yield was 64% on the Cu/nonporous TiO2 at 120 degrees C. The highest product yield of 84% was obtained on the Cu/mesoporous TiO2 at 140 degrees C, corresponding to an initial reaction rate of 104 mmol g(cat)(-1) s(-1). The activation energy on the Cu/mesoporous TiO2 catalyst was found to be (144 +/- 5) kJ mol(-1), which is close to the value obtained for the reaction over unsupported CuZn nanoparticles (123 +/- 3 kJ mol(-1)) and almost twice the value observed over the catalysts deposited onto the non-porous TiO2 support (75 +/- 2 kJ mol(-1)).

OXYGEN CATALYSIS BY ANHYDROUS RUTHENIUM(IV) OXIDE

The results of a kinetic study of the oxidation of water to oxygen by Ce(IV) ions in different acid media, mediated by anhydrous ruthenium(IV) oxide are described. In an acid medium which is predominantly HClO4 the kinetics are diffusion controlled and first order with respect to both [Ce(IV)] and [RuO2] and exhibit an activation energy of 19 kJ mol-1. In 0.5 mol dm-3 H2SO4 the kinetics are much slower and complex, the rate decreasing with increasing [Ce(III)]. The kinetics of catalysis observed in all the different acid media studied are readily interpreted using an electrochemical model in which the catalyst particles are considered as acting as microelectrodes which mediate electron transfer between a Nernstian reduction reaction (Ce(IV) --> Ce(III)) and an irreversible oxidation reaction (H2O --> 2H+ + 1/2O2). This electrochemical model is used to analyse the complex kinetics observed in 0.5 mol dm-3 H2SO4 and extract mechanistic information concerning the nature of the rate determining step.

Intraretinal Leakage and Oxidation of LDL in Diabetic Retinopathy

Purpose: The pathogenesis of diabetic retinopathy (DR) is not fully understood. Clinical studies suggest that dyslipidemia is associated with the initiation and progression of DR. However, no direct evidence supports this theory.

Methods: Immunostaining of apolipoprotein B100 (ApoB100, a marker of low-density lipoprotein [LDL]), macrophages, and oxidized LDL was performed in retinal sections from four different groups of subjects: nondiabetic, type 2 diabetic without clinical retinopathy, diabetic with moderate nonproliferative diabetic retinopathy (NPDR), and diabetic with proliferative diabetic retinopathy (PDR). Apoptosis was characterized using the TUNEL assay. In addition, in cell culture studies using in vitro-modi?ed LDL, the induction of apoptosis by heavily oxidized-glycated LDL (HOG-LDL) in human retinal capillary
pericytes (HRCPs) was assessed.

Results: Intraretinal immuno?uorescence of ApoB100 increased with the severity of DR. Macrophages were prominent only in sections from diabetic patients with PDR. Merged images revealed that ApoB100 partially colocalized with macrophages. Intraretinal oxidized LDL was absent in nondiabetic subjects but present in all three diabetic groups, increasing with the severity of DR. TUNEL-positive cells were present in retinas from diabetic subjects but absent in those from nondiabetic subjects. In cell culture, HOG-LDL induced the activation of caspase, mitochondrial dysfunction, and apoptosis in
HRCPs.

Conclusions: These ?ndings suggest a potentially important role for extravasated, modi?ed LDL in promoting DR by promoting apoptotic pericyte loss.