Electrochemical sulphur dioxide oxidation with platinum-aluminum electrocatalysts

Platinum-aluminum electrocatalysts supported on carbon black were investigated for electrogenerative sulfur dioxide (SO₂) oxidation in hybrid type, liquid-phase SO₂/O₂ cells. Incorporation of aluminum with platinum electrocatalysts on carbon resulted in an electrocatalytic activity increase for S02 oxidation over the whole investigated range (1–30 at % aluminum). Significant synergistic effect from aluminum was observed when even a small amount, as little as 1 at %, was incorporated in the platinum. A maximum 68 % improvement was obtained when 10 at % aluminum was incorporated in the platinum. Results of an ESCA study and electrochemical platinum surface area measurement supported the hypothesis of an electronic interaction between platinum and aluminum.     

Electrocatalytic oxidation of methanol on platinum microparticles in polypyrrole

The oxidation of methanol on gold electrodes modified with polypyrrole and platinum is reported. These electrodes were characterized by cyclic voltammetry and by 12h polarizations in methanol solutions. They were found to give higher currents and lower rates of drift than electrodes of platinum and platinized gold. The effect of varying the amount of platinum deposited is also discussed.     

Platinum deactivation: in situ EXAFS during aqueous alcohol oxidation reaction

With a new set‐up for in situ EXAFS spectroscopy the state of a carbon‐supported platinum catalyst during aqueous alcohol oxidation has been observed. The catalyst deactivation during platinum‐catalysed cyclohexanol oxidation is caused by platinum surface oxide formation. The detected Pt–O co‐ordination at 2.10 Å during exposure to nitrogen‐saturated cyclohexanol solution is different from what is observed for the pure oxidised platinum surface (2.06 Å).     

Some kinetic aspects of the oxidation of graphite and platinum graphimet

The catalytic effect of platinum on the oxidation of graphite has been examined for 1 wt% Pt-graphimet with the use of temperature programmed desorption technique. Analyses of results show that the addition of platinum particles enhances the overall rate of carbon oxides evolution by increasing the active surface area, with little or no change in the apparent activation energy of desorption. This is attributed to the scission of carbon-carbon bonds by platinum. Results of the mathematical modelling based on controlled atmosphere electron microscopy studies by Baker and his co-workers seem to suggest the existence of a viscous oxide layer and surface diffusion on the metal surface and a possibility that both electron and oxygen transfer mechanisms are operating in the carbon-oxygen reactions catalysed by platinum group metals.     

Platinum modification of gold and electrocatalytic oxidation of ethylene glycol on Pt-modified Au electrodes

The surface modification of gold electrodes with platinum and the electrocatalytic oxidation of ethylene glycol on Pt-modified Au electrodes are investigated by cyclic voltammetry. Platinum modification is performed by the electrochemical deposition of platinum on polycrystalline gold electrodes, and the Pt-modified Au electrodes with different amount of the deposited platinum are used for the ethylene glycol oxidation in alkaline and acidic solutions. It is shown that oxidation potential for the ethylene glycol oxidation on the Pt-modified Au electrodes shifts significantly negative compared with that on Au electrodes, nearly same oxidation potentials as that on Pt electrodes are observed, and peak current density of the ethylene glycol oxidation is dependent on the amounts of the deposited platinum on gold surface, much higher peak current densities than that on Au and Pt electrodes can be obtained. The low oxidation potential and high peak current density indicate the enhanced reactivity of Au electrodes by the platinum modification. The characteristics of the Pt-modified Au electrodes are found to be similar to that of Pt electrodes, and the reactivity of the Pt-modified Au electrodes is mainly attributed to the deposited platinum.     

The anodic oxidation of allyl alcohol in acetonitrile

The kinetics of the anodic oxidation of allyl alcohol in acetonitrile has been studied. At a platinum electrode at low potentials, < 2·6 V, the reaction is charge transfer controlled and at higher potentials the process becomes diffusion controlled. The reaction is not a simple charge-transfer process, but may proceed via an adsorption step. Controlled potential electrolysis yielded acrolein and polymers as products. The oxidation of allyl alcohol on platinum is probably electrocatalysed by “surface oxides”.     

Effect of platinum particle size and catalyst support on the platinum catalyzed selective oxidation of carbohydrates

The effect of the platinum particle diameter and the catalyst support was investigated for the aqueous phase selective oxidation of methyl α-D-glucopyranoside, octyl α-D-glucopyranoside and α-cyclodextrin with molecular oxygen. No platinum particle size effect was observed in the platinum particle diameter range of 1.4 to 3.0 nm. The structure-insensitivity is attributed to the high degree of surface coverage by oxygen. The rate of deactivation due to over-oxidation of the catalyst increases to a small extent with decreasing platinum particle diameter. The effect of the catalyst support is much larger than the platinum particle size effect. The turnover frequency for platinum on activated carbon and carbon fibrils supported catalyst is 3-7 times higher than for graphite as the catalyst support. The support effect is attributed to the hydrophilic character of the support. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gold and platinum catalysed oxidation of methanol

A comparative study was made of the vapour phase oxidation of methanol in presence of gold and platinum, using a flow system at temperatures below 500°C. Over gold there is a stoichiometric conversion to formaldehyde and water. In presence of platinum, the reaction is the same up to 200°C, but at higher temperatures other oxidation products appear. Mechanisms are suggested involving interaction between chemisorbed oxygen and methanol fragments.     

Selective electrogenerative oxidation of benzyl alcohol with platinum–graphite packed-bed anodes

The selective electrogenerative oxidation of benzyl alcohol in 1M sulfuric acid solutions was studied on several types of graphite supported platinum packed-bed anodes in a hybrid continuous-flow cell with an oxygen gas diffusion cathode. Benzaldehyde formed preferentially on all three catalytic packed-beds under electrogenerative conditions (Eanode<0.75V) where the platinum catalyst was not irreversibly oxidized. Tin–palladium chloride graphite-pretreatment before platinum deposition through ethanol reduction significantly enhanced catalytic activity. This electrocatalyst provided current densities as high as 77mAcm-2 (superficial packed-bed cross sectional area) with a platinum loading of 0.89wt% Pt on graphite at relative low polarization. The origin of the catalytic activity is discussed and evidence is presented on the roles of tin and palladium. Benzyl alcohol oxidation appears to provide a sensitive probe reaction for demonstrating the existence of special types of catalytic centres.     

Plasmonic energy transformation in the photocatalytic oxidation of ammonium

The plasmonic transformation of light into energy for a chemical reaction is demonstrated in the endothermic oxidation of ammonium ions. The plasmonic heating effect physically triggers a platinum thin film, which becomes an active catalyst for the plasmonic catalytic reaction. The amount of chemical energy consumed in the plasmonic photocatalytic reaction was less than that in the normal chemical process. A homogeneous, condensed, pinhole-less 8 nm platinum thin film fabricated via plasma-enhanced atomic layer deposition served as a medium that transformed the energy in two steps.     

The characterization of Pt/Sn catalyst for the electrochemical oxidation of methanol

Pt/Sn electrodeposited catalysts have been prepared, characterized and tested for the electro-oxidation of methanol. Catalyst activities were measured in 3 M H₂SO₄ electrolyte between ambient temperature and 95°C. Enhancement in specific activity by a factor of about 50 was found over electrodeposited platinum black. This behaviour is in contrast to that of alloys of platinum and tin which were found to have very low activities compared with platinum catalysts and to be readily corroded in H₂SO₄ electrolyte.ESCA (electron spectroscopy for chemical analysis) studies and Mössbauer spectroscopy showed the majority of the tin in the deposit to be present in an oxidized form. A small amount (17%) was present as a dilute alloy of tin in platinum. Surface area measurements and X-ray powder diffraction indicated that the increase in activity over platinum black was not attributable to smaller platinum particle size. It seems that the combination of platinum and tin results in a decrease in the poisoning effect by strongly adsorbed organic residues. Whether this arises from the operation of a cyclic Sn(II)/Sn(IV) redox system or from modification of the platinum surface remains unresolved.     

On the anodic oxidation of cyclohexene on platinized platinum electrodes

Cyclic voltammetry experiments performed in acid solutions of cyclohexene on platinized platinum anodes show that platinum oxide must play a role in the anodic oxidation of the hydrocarbon through a mechanistic scheme of the type proposed by Gilman[10]. This fact would explain results obtained with other unsaturated hydrocarbons     

Metal-support interactions in the catalytic oxidation of carbon monoxide

The catalytic oxidation of carbon monoxide has been studied over transition metal oxides in the absence and presence of platinum. A characteristic activity pattern was observed in both cases, with platinum reducing the temperature at which oxidation was initiated by between 20 and 200 K. The results show that platinum-metal oxide interactions are important in the system. These appear to involve the reaction of carbon monoxide adsorbed on the metal with oxygen associated with the metal oxide lattice. This revised version was published online in July 2006 with corrections to the Cover Date.     

Binary systems of platinum and a second metal as oxidation catalysts for methanol fuel cells

A large number of platinum based binary catalysts has been prepared by deposition of submonolayer amounts of the second components onto the surface of platinum catalysts via an immersion method. Of the hitherto unknown systems, platinum—titanium showed an activity close to that of the best systems known so far, viz platinum—tin and platinum—ruthenium. The various systems could be classified according to their electrosorption behaviour. It was found that the group of catalysts exhibiting redox behaviour at low potential were not more active than pure Pt, although this would be expected if the redox mechanism for enhanced methanol oxidation was valid. Highest activity was observed for systems displaying stabilization of the adsorbed second element in the zero—valent state and hence modified Pt adsorption behaviour. These observations suggest that an adsorption mechanism could account for the effect of the second metal.     

The oxidation of carbon monoxide at platinum and gold metallized membrane electrodes

The oxidation of carbon monoxide at gold platinum membrane electrodes is discussed and it is shown that the electrochemical characteristics of these electrodes are similar to massive electrodes. At platinum the short time response is determined by the oxidation of a surface monolayer of carbon monoxide by a reactant pair mechanism occuring at the edges of growing islands of an oxidised platinum species whilst at gold, the process is diffusion controlled. On both metals the longer timescale response is complicated by poisoning of the surface by a reaction intermediate but it is also shown that a gold anode may be reactivated by potential cycling. The relevance of these results to the construction of an analytical device is discussed.     

Optimization of experimental conditions for the catalytic oxidation of furfural to furoic acid

Oxidation of furfural in a stream of oxygen in aqueous alkaline medium in the presence of a lead–platinum catalyst leads to the formation of furan 2-carboxylic acid. The influence of five factors was studied using a Doehlert matrix. The analysis of the areas of responses allowed the optimal operating conditions to be determined: platinum metal mass/furfural mass introduced × 100:1·7%; lead diacetate mass/platinum on carbon mass: 20%; initial furfural concentration 0·8 M; temperature 55°C. After 1 h of reaction, the whole of the furfural is then selectively transformed into furoic acid.     

载铂聚苯胺/聚砜复合膜修饰电极对甲醇的电催化氧化行为研究

采用循环伏安法制备聚苯胺(PAN)/聚砜(PSF)复合膜修饰电极,在其上电沉积铂粒子,制得载铂聚苯胺/聚砜复合膜修饰电极,用循环伏安法和交流阻抗法研究它对甲醇的电催化氧化行为。复合膜的化学组分用FTIR进行表征,复合膜内层载铂后的表面形态用SEM进行表征。结果表明,复合膜的内层(与工作电极接触的一面)是聚苯胺,外层(与溶液接触的一面)是聚砜,铂粒子在复合膜内层的多孔聚苯胺上均匀沉积,从而使载铂聚苯胺/聚砜复合膜修饰电极对甲醇有好的电催化氧化性能。     

The electrocatalytic oxidation of methanol in acid electrolyte: preparation and characterization of noble metal electrocatalysts supported on pre-treated carbon-fibre papers

The electrocatalytic aspects of direct oxidation of methanol in acid electrolyte in relation to fuel cell applications is briefly reviewed. The reaction requires noble metal catalysts (in particular platinum) in large quantities (several mg cm^–2 of electrode area) to produce steady state current densities of commercial interest. Initial activities are about 10⁴ times greater than steady state values, thus the problem in methanol electro-oxidation is to stabilize the initial activity.The approaches generally taken are to develop methods of dispersing platinum more effectively, e.g. by depositing the metal on a conducting support, or to modify the properties of platinum by alloying it with a second component. The latter approach can have the effect of simply isolating platinum atoms from each other, thus limiting the size of the platinum clusters, or of electronically modifying the properties of platinum by virtue of the ligand effect of the second component in the alloy.We have developed platinum and platinum-ruthenium catalysts supported on specially treated carbon-fibre paper which have substantially higher steady state activities than conventional catalysts. The method of preparation involves an ion-exchange procedure whereby noble metal cations become chemically bound to acidic surface oxide groups on the pre-oxidized carbon-paper surface. This produces platinum with increased surface area and high specific activity. It is proposed that the highly active form of platinum is involved in an interaction with the carbon support leading to improved performance. This modified form of platinum has been shown by cyclic voltammetry to have different characteristics of hydrogen adsorption/desorption and platinum oxide reduction from those of unsupported and conventionally supported platinum.This paper was first presented at the meetingElectrochemistry: Material Recovery and the Environment held at the Thornton Centre, Chester in January 1979 and organized by the Electrochemistry Group of the Chemical Society.     

Platinum crystallite size effects on the electrocatalytic oxidation and deposition of adsorbed hydrogen—III

Kinetic parameters for the oxidation and deposition of the two adsorbed hydrogen species on platinum in acid were examined using rapid linear potentiodynamic scans with good agreement between the theory and experimental data. Specific rate constants obtained from the magnitudes of the current peak potential shifts from quasi-equilibrium with potential scan rates were shown to be dependent upon the surface areas of the platinum electrocatalysts. It is postulated that the decrease in the specific rate constant with decreasing platinum crystallite size is caused by an increasing preponderance of surface platinum atoms as a fraction of the total atom content in the crystallites. Changes in the electronic, “metallic” or ionic—co-valent character of the surface platinum atoms are reflected in the changes of this specific rate constant and is an indication of the importance of the electronic structure due to the electrocatalyst sites in determining the electrocatalytic activity.     

Electrocatalytic oxidation of methanol: carbon-supported gold–platinum nanoparticle catalysts prepared by two-phase protocol

This paper describes recent results of an investigation of the electrocatalytic oxidation of methanol at carbon-supported gold and gold–platinum nanoparticle catalysts. The exploration of the bimetallic composition on carbon black support is aimed at modifying the catalytic properties for methanol oxidation reaction (MOR) at the anode in methanol oxidation fuel cells. Gold and gold–platinum nanoparticles of 2–3 nm core sizes with organic monolayer encapsulation were prepared by two-phase protocol. The nanoparticles were assembled on carbon black materials and thermally treated. The electrocatalytic MOR activities were characterized using voltammetric techniques, and were compared with commercial catalysts under several conditions. The results have revealed some initial insights into the catalytic activity of gold–platinum nanoparticle catalysts. Implications of our findings to the design and manipulation of highly-active gold–platinum nanoparticle catalysts for fuel cell applications are also discussed.