Quantum chemistry and in situ FTir spectroscopy studies on potential-dependent properties of CO adsorbed on Pt electrodes

The electronic and vibrational properties of CO adsorbed on Pt electrodes at different potentials have been studied, by using methods of self-consistent-charge discrete variational Xa (SCC-DV-Xa) cluster calculations and in situ FTir spectroscopy. Two new models have been developed and verified to be successful: (1) using a "metallic state cluster" to imitate a metal (electrode) surface; and (2) charging the cluster and shifting its Fermi level (e{lunate}) to simulate, according to the relation of -d e{lunate}e dE, quantitatively the variation of the electrode potential (E). It is shown that the binding of PtCO is dominated by the electric charge transfer of dp ? 2p, while that of s ? Pt is less important in this binding. The electron occupancy of the 2p orbital of CO weakens the CO bond and decreases the v. Variation of E mainly influences the charge transfer process of dp ? 2p, but hardly influences that of s ? Pt. A linear potential-dependence of v has been shown and the calculated dv/dE = 35.0 cm V. All results of calculations coincide with the ir experimental data. © 1993.

PtRuO/Ti anodes with a varying Pt:Ru ratio for direct methanol fuel cells

PtRuO/Ti anodes with a varying Pt:Ru ratio were prepared by thermal deposition of a PtRuO catalyst layer onto a Ti mesh for the direct methanol fuel cell (DMFC). The morphology and structure of the catalyst layers were analyzed by SEM, EDX, and XRD. The catalyst coating layers became porous with increase of the Ru content, and showed oxide and alloy characteristics. The relative activities of the PtRuO/Ti electrodes were assessed and compared using half-cell tests and single DMFC experiments. The results showed that these electrodes were very active for the methanol oxidation and that the optimum Ru surface coverage was ca. 38% for a DMFC operating at 20-60 °C. © 2006 Elsevier B.V. All rights reserved.

PtRu/Ti anodes with varying Pt:Ru ratio prepared by electrodeposition for the direct methanol fuel cell

PtRu/Ti anodes with varying Pt : Ru ratio were prepared by electrodeposition of a thin PtRu catalyst layer onto Ti mesh for a direct methanol fuel cell (DMFC). The morphology and structure of the catalyst layers were analyzed by SEM, EDX and XRD. The catalyst coating layer shows an alloy character. The relative activities of the PtRu/Ti electrodes were assessed and compared in half cell and single DMFC experiments. The results show that these electrodes are very active for the methanol oxidation and that the optimum Ru surface coverage was ca. 9 at.% for DMFC operating at 20°C and 11 at.% at 60°C. The PtRu/Ti anode shows a performance comparable to that of the conventional carbon-based anode in a DMFC operating with 0.25 M or 0.5 M methanol solution and atmosphere oxygen gas at 90°C. © the Owner Societies 2006.

An investigation of the role of surface nitrate species in the oxidation of propene on a Pt-based diesel oxidation catalyst

Enhancing the low temperature activity of diesel oxidation catalysts is important for cold-start conditions and the possible importance of nitrate species in oxidation reactions has been proposed although definitive evidence has not been reported. To investigate the possible role of surface nitrates, their adsorption and reactivity on a Pt-based diesel oxidation catalyst have been investigated using the Short Time on Stream (STOS) transient kinetic technique. The results provide for the first time definitive evidence for the oxidation of propene by some of these nitrate-type species. © The Royal Society of Chemistry 2013.

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.

Aqueous phase reforming of xylitol over Pt-Re bimetallic catalyst: Effect of the Re addition

The aqueous phase reforming (APR) of xylitol was studied in a continuous fixed bed reactor over three catalysts: Pt/Al2O3, Pt/TiO2 and Pt-Re/TiO2. The data obtained in the case of the monometallic Pt catalysts was compared to the bimetallic Pt-Re sample. The effect of Re addition on the catalyst stability, activity, product formation and selectivity toward hydrogen and alkanes was studied. The bimetallic catalyst demonstrated a higher selectivity to alkanes compared to the monometallic samples. The monometallic catalyst was more selective toward hydrogen formation. A plausible reaction scheme explaining differences in selectivity toward hydrogen and alkanes was proposed and discussed.

WC/CNT, WC/CNT/Pt Composite Material and Preparation Process Therefor and Use Thereof. (International Patent)

(EN)Disclosed are a WC/CNT， WC/CNT/Pt composite material and a preparation process therefor and use thereof. The WC/CNT/Pt composite material comprises mesoporous spherical tungsten carbide with a diameter of 1-5 microns, carbon nanotubes and platinum nano particles, with the carbon nanotubes growing on the surface of the mesoporous spherical tungsten carbide and expanding outward, and the platinum nano particles growing on the surfaces of the mesoporous spherical tungsten carbide and carbon nanotubes. The WC/CNT composite material comprises mesoporous spherical tungsten carbide with a diameter of 1-5 microns, and carbon nanotubes, with the carbon nanotubes growing on the surface of the mesoporous spherical tungsten carbide and expanding outward. The WC/CNT/Pt composite material of the present invention can be used as an electro-catalyst in a methanol flue battery, significantly improving the catalytic conversion rate and the service life of the catalyst. The WC/CNT composite material can be used as an electro-catalyst in the electro-reduction of a nitro aromatic compound, significantly improving the efficiency of organic electro-synthesis.

WC/CNT, WC/CNT/Pt Composite Material and Preparation Process Therefor and Use Thereof. (US patent)

Disclosed are a WC/CNT， WC/CNT/Pt composite material and a preparation process therefor and use thereof. The WC/CNT/Pt composite material comprises mesoporous spherical tungsten carbide with a diameter of 1-5 microns, carbon nanotubes and platinum nano particles, with the carbon nanotubes growing on the surface of the mesoporous spherical tungsten carbide and expanding outward, and the platinum nano particles growing on the surfaces of the mesoporous spherical tungsten carbide and carbon nanotubes. The WC/CNT composite material comprises mesoporous spherical tungsten carbide with a diameter of 1-5 microns, and carbon nanotubes, with the carbon nanotubes growing on the surface of the mesoporous spherical tungsten carbide and expanding outward. The WC/CNT/Pt composite material of the present invention can be used as an electro-catalyst in a methanol flue battery, significantly improving the catalytic conversion rate and the service life of the catalyst. The WC/CNT composite material can be used as an electro-catalyst in the electro-reduction of a nitro aromatic compound, significantly improving the efficiency of organic electro-synthesis.

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.

Acrolein hydrogenation on Pt(211) and Au(211) surfaces:a density functional theory study

Partial hydrogenation of acrolein, the simplest alpha, beta-unsaturated aldehyde, is not only a model system to understand the selectivity in heterogeneous catalysis, but also technologically an important reaction. In this work, the reaction on Pt(211) and Au(211) surfaces is thoroughly investigated using density functional theory calculations. The formation routes of three partial hydrogenation products, namely propenol, propanal and enol, on both metals are studied. It is found that the pathway to produce enol is kinetically favoured on Pt while on Au the route of forming propenol is preferred. Our calculations also show that the propanal formation follows an indirect pathway on Pt(211). An energy decomposition method to analyze the barrier is utilized to understand the selectivities at Pt(211) and Au(211), which reveals that the interaction energies between the reactants involved in the transition states play a key role in determining the selectivity difference.

A density functional theory study of CO and atomic oxygen chemisorption on Pt(111)

Ab initio total energy calculations within a density functional theory framework have been performed for CO and atomic oxygen chemisorbed on the Pt(111) surface. Optimised geometries and chemisorption energies for CO and O on four high-symmetry sites, namely the top, bridge, fee hollow and hcp hollow sites, are presented, the coverage in all cases being 0.25 ML. The differences in CO adsorption energies between these sites are found to be small, suggesting that the potential energy surface for CO diffusion across Pt(111) is relatively flat. The 5 sigma and 2 pi molecular orbitals of CO are found to contribute to bonding with the metal. Some mixing of the 4 sigma and 1 pi molecular orbitals with metal states is also observed. For atomic oxygen, the most stable adsorption site is found to be the fee hollow site, followed in decreasing order of stability by the hcp hollow and bridge sites, with the top site being the least stable. The differences in chemisorption energies between sites for oxygen are larger than in the case of CO, suggesting a higher barrier to diffusion for atomic oxygen. The co-adsorption of CO and O has also been investigated. Calculated chemisorption energies for CO on an O/fcc-precovered surface show that of the available chemisorption sites, the top site at the oxygen atom's next-nearest neighbour surface metal atom is the most stable, with the other four sites calculated bring at least 0.29 eV less stable. The trend of CO site stability in the coadsorption system is explained in terms of a 'bonding competition' model. (C) 2000 Elsevier Science B.V. All rights reserved.