A new method for electrochemical screening basedon the rotating ring disc electrode and its applicationto oxygen reduction catalysts

A new method for electrochemical characterization of composite electrode materials is reported. A paste of the catalytic material in Nafion® is coated on a rotating ring disc electrode (RRDE) to partially simulate the working environment of a proton exchange membrane (PEM)/electrode composite as used in, for example, water electrolysis or PEM fuel cell operation. This allows direct comparison of a wide range of candidate electrocatalysts in a reproducible manner. Problems specific to these volumic electrodes are accommodated satisfactorily by rational modification of the standard expressions used in RRDE analysis. The value of the method is illustrated in studies of various cobalt complexes which show promise in dioxygen reduction; namely, cobalt tetramethoxyphenylporphyrin (CoTMPP), cobalt phthalocyanine (CoPC), and cobalt cyclam (CoCy), supported on a range of particulate carbons BP2000, Printex XE 2 and Vulcan XC-72. Typical electrochemical parameters have been measured or estimated, including half-wave potentials (E1/2), Tafel slopes (b), ‘activation currents’ (Ia) and the average number of electrons transferred (n). The nature of the complex itself and the carbon support have a strong influence on electrode behaviour. Ligands with more aromatic character give better performance. Dramatic improvements in performance result from heat pretreatment, which is tentatively attributed to the formation of dimeric cobalt species via thermally-induced aggregation. In terms of the four electron reduction (to water), the best result was obtained for CoTMPP on Printex XE2 and rationalized on the basis of popular current views on the mechanism and catalyst functionality. CoPC on BP2000 is unusual in showing a strong change in n with reduction potential. Product selectivity ranges between mainly hydrogen peroxide (n=2) and water (n=4) with increasing overpotential.     

Spectroscopic Study of Tempo-Oxidized Deinked Pulp

Abstract

Deinked pulps are not currently used in value-added paper manufacturing. To implement their use, both strength and optical properties must be improved. TEMPO oxidation has been shown to improve strength properties of thermomechanical and deinked pulps. However, a significant reduction of the pulp brightness results due to yellowing of mechanical fibers. Spectroscopic techniques were used to investigate the effect of TEMPO oxidation on deinked fiber properties. Fourier transform infra-red (FTIR) spectroscopy and UV/VIS spectrum showed that oxidation conditions are driving important chemical reactions that affect optical properties. Results indicated that ortho-quinone compounds as well as carboxylic groups are generated depending on oxidation conditions resulting in pulp brightness decrease. Spectroscopic studies also revealed that residual ink detachment from fiber surfaces is occurring during oxidation contributing to improve pulp brightness.     

Brightness Optimization of Ozone Pre-Treatment Followed by Peroxide Bleaching of TMP Pulp from Tamarack (Larix laricina)

This study examines the influence of ozone on a TMP pulp of tamarack in an independent bleaching stage and as a pre-treatment for hydrogen peroxide bleaching. Ozone charges of up to 6% were used on dry pulp. The results were compared to those obtained with 1% H₂O₂ bleaching. Experiments were conducted at 23°C and 55°C, and pH varied from 3.5 to 10.5. The best bleaching results were reached with acidic pH, with interesting behavior observed at an alkaline pH level. Ozone effectively attacks CO groups in lignin, but lacks the chemical selectivity and high reactivity required to become a good bleaching agent.     

Stand reaction of linseed oil

Several theories have been proposed concerning the stand oil reaction but no precise reaction scheme has been described. In this work, the stand reaction of linseed oil was characterized in order to determine the nature of the products formed during this reaction. Using complementary analytical techniques (more especially NMR and mass spectrometry), the existence of two different reactions was demonstrated: the Diels–Alder addition between fatty acid chains and the addition of a methylene radical on double bonds, followed by combination or elimination reactions.     

Highly porous catalytic materials with Pd and ionic liquid supported on chitosan

Chitosan was used to immobilize phosphonium‐based ionic liquids, combined with silica particles, to prepare catalytic materials in the form of highly porous monoliths. These catalytic materials were studied for the hydrogenation of 4‐nitroaniline into p‐phenylenediamine in the presence of formic acid as hydrogen donor in a column reactor. Experimental conditions for the elaboration of the materials were evaluated by their impact on palladium sorption, on the structure of the materials, and on their catalytic efficiency. The concentration of chitosan in the initial solution and the size and concentration of silica particles had to be carefully chosen to elaborate homogeneous materials, with good mechanical resistance and stability in water. The chitosan characteristics and the type of ionic liquid immobilized in the material did not significantly affect the structure of the materials but proved to be crucial for their catalytic efficiency. Higher catalytic performances were obtained using materials prepared from chitosan of high‐deacetylation degree and with Cyphos IL‐101. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Poisoning of Pt/C catalysts by CO and its consequences over the kinetics of hydrogen chemisorption

The initial rate of hydrogen dissociation was studied as a function of irreversible CO coverage at 353 K on 30 wt.% Pt/carbon catalysts (Pt/C) prepared according to different processes. The Pt/C catalysts exhibit similar Pt dispersion (D  0.07) and mean Pt particles size (dp  16 nm). The turnover frequency (number of hydrogen molecules dissociated per CO-free surface Pt atom) was determined as a function of CO coverage from 0.0 to 0.8. The evolution of TOF as a function of CO coverage is in agreement with the model of CO adsorbing on low coordination sites (edges, corners) and then spreading across the faces to grow islands as Brandt suggested in the past (R.K. Brandt, M.R. Hughes, L.P. Bourget, K. Truszkowska, R.G. Greenler, Surf. Sci. 286 (1993) 15–25). At high CO coverage (0.8), TOF depends on the process by which the Pt/C catalyst was prepared. In particular, a Pt/C elaborated according to a colloidal process exhibits a low sensitivity to CO poisoning with an increase of TOF by one order of magnitude.     

Phase Stability,Magnetic Properties,and Martensitic Transformation of Ni2−xMn1+x+ySn1−y Heusler Alloy with Excess Mn by First-Principles Calculations

The phase stability, magnetic properties, martensitic transformation, and electronic properties of the Ni_2−xMn_1+x+ySn_1−y system with excess Mn have been systematically investigated by the first-principles calculations. Results indicate that the excess Mn atoms will directly occupy the sublattices of Ni (Mn_Ni) or Sn (Mn_Sn). The formation energy (E_f) of the austenite has a relationship with the Mn content: E_f = 135.27(1 + x + y) − 293.01, that is, the phase stability of the austenite decreases gradually with the increase in Mn content. According to the results of the formation energy of austenite, there is an antiparallel arrangement of the magnetic moment between the excess and normal Mn atoms in the Ni_2−xMn_1+x+ySn_1−y (x = 0 or y = 0) system, while the magnetic moment direction of the normal Mn atoms arranges antiparallel to that of Mn_Ni atoms and parallel to that of Mn_Sn atoms in the Ni_2−xMn_1+x+ySn_1−y (x, y ≠ 0) system. The martensitic transformation occurs in some Ni_2−xMn_1+x+ySn_1−y (x, y ≠ 0) alloys with large magnetic moments of ferrimagnetic austenite. Besides, the valence electrons tend to distribute around the Ni or Mn_Ni atoms and mainly bond with the normal Mn atoms. The results of this work can lay a theoretical foundation for further development of the Ni_2−xMn_1+x+ySn_1−y system as the potential ferromagnetic shape memory alloys.     

Effects of ingestion of a green seaweed,Ulva lactuca,upon caecal and colonic mucosas in the germ‐free rat and in the heteroxenic rat harbouring a human bacterial flora

Effect of ingestion of green seaweed, Ulva lactuca, (70 g kg⁻¹) during a 6‐week period on caecal and colonic mucosas was studied in germ‐free (GF) rats and in heteroxenic (HE) rats harbouring a human bacterial flora (GF rats associated with a human flora). The pH and sulphide concentration of the caecal contents, crypt morphometry, mitotic index and mucin types in the caecal and distal colonic mucosas were determined. In the GF caecum, Ulva strongly increased crypt depth and mucin‐containing cells irrespective of the mucin type studied (neutral, acidic or sulphated) compared to the control diet but had no significant effect on mitotic index. The crypt depth and mucin‐containing cells in the caecum were higher in HE than in GF control rats. They were slightly but significantly increased by Ulva. In the distal colon mucosa of GF rats, Ulva decreased crypt depth and cell number as well as sulphomucin‐containing cells. Conversely, in the HE rats, it increased crypt depth and reduced the number of neutral mucin‐containing cells. These results show that Ulva lactuca exerts an intrinsic effect on mucosal morphometry and on mucin biosynthesis in GF rats. No pathological alteration was observed in the mucosas and no significant modification of the mitotic index or sulphide production was observed in HE rats. © 1999 Society of Chemical Industry