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The contribution of carbon functional groups (CFG) to methanol oxidation at carbon-supported Pt catalysts is studied in this work. Platinum black, attached in a form of a thin layer to electrochemically treated glassy carbon (GC), is investigated as a model system. Impedance measurements reveal significant changes in capacitive response of GC anodically polarized in H2SO4 solution in comparison to unoxidized state. XPS analyses show the increased fraction of oxygen-containing CFGs upon electrochemical treatment of GC. The activity of Pt black attached to oxidized GC for methanol oxidation is more than two times larger in comparison to the catalyst attached to unoxidized GC. Increased activity is most likely due to the promotion of COads removal by increased content of CFGs. Keywords: Carbon functional groups, Electrochemical activation, Platinum catalyst, Methanol oxidation, EIS

This is the post-print version of the final paper published in Chemical Engineering Journal. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2008 Elsevier B.V. The work described in this paper has been undertaken as part of the design of an integrated system comprising a diesel engine, an exhaust-gas fuel reformer and a NOx aftertreatment unit. The exhaust-gas reformer is used to provide hydrogen-rich reformate to the NOx aftertreatment unit, containing a hydrocarbon-SCR catalyst, in order to improve its NOx reduction activity at low exhaust-gas temperatures. The reformer configuration and operating parameters have been examined in order to optimise the performance of the hydrocarbon-SCR catalyst, which is promoted by the presence of H2 but inhibited by CO. The length of the catalyst bed inside the reformer is a key factor in determining the extent to which the water-gas shift reaction can contribute to the reforming process, and therefore strongly influences the proportions of CO and H2 in the reformate. However, it is also necessary for the reactant ratios at the reformer inlet to be controlled in response to changes in the engine operating conditions. In practice, this means that the rate of fuel addition to the reformer needs to be optimised for different exhaust gas compositions and space velocities.

A microstructured catalytic reactor/heat exchanger has been developed, based on the microstructured heat exchanger of the Forschungszentrum Karlsruhe. One channel set of a crossflow device is coated with a platinum catalyst supported on Al 2 O 3 , the other channel set is used for heat removal, either by a gaseous or a liquid fluid. Stoichiometric mixtures of hydrogen and oxygen can be safely combusted in this device, while heat can be transferred either to a heat exchanger oil or used to evaporate water or methanol. Such a system can be useful as part of the fuel processor for fuel cell driven cars.

Catalytic activity and selectivity is shown to be critically dependent on the hydrogen concentration. The surface processes responsible for propane formation are shown to be decoupled from those responsible for the selective formation of the alkene, with the observed chemistry adequately described by a 2-site model.

Platinum catalyst deactivation during aqueous alcohol oxidation is discussed, using the oxidation of methyl α-D-glucopyranoside as an example. The most important causes of platinum deactivation are catalyst over-oxidation and catalyst poisoning. Deactivation by over-oxidation can be reversed by applying a redox-cycle, i.e. cyclic exposure to oxidative and reductive circumstances. A kinetic model for methyl α-D-glycopyranoside oxidation, platinum deactivation, and reactivation is presented and implemented into a three-phase stirred slurry reactor model, clearly showing the advantages of redox-cycles.

The selective reduction of NO by hydrocarbon in an excess of oxygen was studied using a platinum catalyst doped or not with zinc. Successive impregnetion or co-impregnation of Pt and Zn on alumina were made. In some cases, in the presence of Zn, the NO conversion is increased in parallel with N 2 formation. A better conversion of hydrocarbons was also observed. EXAFS experiments and N 2 O decomposition experiments have been carried out to explain these observations.

Poisoning of noble metal catalysts by sulfur-containing organic compounds is a well-known phenomenon. These compounds are frequently present in hydrotreating feedstocks and cause a selective decrease in the metal hydrogenation function of noblemetal-based hydrotreating catalysts. The effects of H 2 S, considered as a model sulfiding compound, were studied on a supported platinum catalyst. Low coverages of H 2 S are found to cause a selective poisoning of noble metal particles, which with increasing coverage becomes unable to chemisorb H 2 at room temperature. At higher coverages H 2 S spills over to the support, modifying its acidic properties. Eventually new weak acid sites are formed.

Oxidation of carbon monoxide on a silica-supported platinum catalyst was studied from 438° to 483°K, from 0.7 to 2.1 Torr carbon monoxide, and from 0.1 to 0.6 Torr oxygen in a differential flow reactor. The amount of chemisorbed CO was monitored during reaction by infrared transmission spectroscopy. Transitions were observed between two kinetic regimes — one characterized by moderate rates and nearly full CO surface coverage; the other, by higher rates and low surface coverage.

The dehydrogenation of methylcyclohexane on an industrial Platinum catalyst carried out by using an integral reactor is represented by a simple kinetic model applicable for a large range of temperatures (300-450°C) and conversions (0-100%). Beside the hydrogen necessary in the feed to assure the constant activity of the catalyst, the rate of dehydrogenation depends only on the pressure of methylcyclohexane. A reaction mechanism compatible with the kinetic model is proposed.

An experimental study of feed composition square-wave cycling during CO oxidation on a supported platinum catalyst was performed. Significant rate enhancement relative to steady-state reactor operation was achieved. It was found that the phasing of the oxygen and CO input cycles had a dramatic effect on the time-average reaction rates. The maximum rates occurred when the oxygen input led the CO input, with the oxygen and CO inputs in-phase for a portion of the overall cycle. The observed rate enhancement could be quantitatively described only by a surface phase transformation model incorporating CO self-exclusion.

The oxidation of carbon monoxide over a 0.5 wt% supported platinum catalyst in a recycle reactor is examined. The reaction rate behavior during both steady-state operation and during forced feed composition cycling is studied in detail. It is shown that, during forced composition cycling, the time-average reaction rate passes through a resonant maximum while the frequency of the forced cycle is varied. This resonant maximum greatly exceeds the bounds of the steady state and the quasi-steady state. In the second part of this study, the experimental data are used to validate a model for this reaction system. The steady-state data are used to determine the reaction parameters, and a comparison is made between the model predictions and the experimental observations during forced composition cycling.