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[Display omitted] • NiW/γ-Al 2 O 3 catalysts were prepared at different pHs and in presence of a chelating agent (CyDTA). • The influence of sulfurization pressure and its effect on the active species for hydrodesulfurization. • The surface species of sulfided catalysts was studied by several characterization techniques. • Sulfided catalysts were tested in HDS of thiophene. In this paper NiW/γ-Al 2 O 3 catalysts were prepared by consecutive impregnation of a W/γ-Al 2 O 3 catalyst with an aqueous solution of nickel salt. The structural control of the nickel ion precursor in the impregnation solution was achieved by the addition of 1, 2-cyclohexanediamine-N, N, N', N'-tetraacetic acid (CyDTA) as a chelating agent at different pH. The influence of the sulfidation pressure (1 bar vs 40 bar) on the activity and structure of the NiW catalysts was investigated. The catalysts performances were tested in hydrodesulfurization (HDS) of thiophene after sulfidation at atmospheric or high pressure. The catalysts were characterized by X-Ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and infrared spectroscopy of adsorbed CO (IR/CO) to explain the modification in surface species composition due to the chelating agent CyDTA and sulfiding conditions. NiW catalysts prepared in presence of CydTA and sulfided under high pressure displayed the highest HDS activity. These two factors enhanced the sulfidation degree of W-based species as characterized by XPS. A linear correlation was found between the HDS activity and the sulfidation degree. In addition, chelating agent addition induced a decrease on metal-support interaction, as pointed out by TPR, and strongly favored the creation of CUS sites on the NiWS phase as seen by IR/CO. All these features favored a high catalytic activity. In addition, high pressure sulfidation not only leads to more active NiW catalysts but improved the butene-over-butane ratio. [ABSTRACT FROM AUTHOR]

In this manuscript, the potential of zero charge (pzc) of platinum single-crystal electrodes has been determined using the impinging jet system and recording the transient associated with the interphase formation. Initially, the Pt(111), Pt(110), and Pt(100) electrodes covered with CO were used. To demonstrate the validity of the procedure, the values obtained for the pzc of these electrodes were compared with those previously reported in the literature and also with those expected from work function changes. An excellent agreement has been found. After that, the values for the pzc of the stepped surfaces having (111) terraces and (110) steps were determined. For these surfaces, the pzc initially diminishes as the step density increases, in accordance with the expected diminution of the work function due to the Smoluchowski effect on the step site. However, for the shorter terraces, the pzc value increases with the step density, probably because of step dipole-dipole coupling due to the presence of a CO layer on the electrode. [ABSTRACT FROM AUTHOR]

CO 2 electroreduction using a Pt catalyst in an aqueous solution system is known to produce only H 2 . Recently, a remarkable result has been reported that CH 4 can be obtained by reducing CO 2 using a membrane electrode assembly (MEA) containing a Pt catalyst. A big difference that exists between the two systems is the number of water molecules. Therefore, this study investigated the influence of water molecules on the CO 2 -reduction process at the Pt electrocatalyst in the MEA system. As a result, cyclic voltammetry indicated that adsorbed CO (CO ads ) was formed by CO 2 reduction in the MEA system more preferably than the aqueous solution system. In detail, the ratio of CO ads at the atop sites (linear CO, CO L ) on Pt, which participates in the CH 4 generation reaction, to the total CO ads formed by the CO 2 reduction became higher as the lower relative humidity (RH) at 50 °C in the MEA system. Cyclic voltammetry combined with in-line mass spectrometry revealed that the amount of CO L and CH 4 generated by the CO 2 reduction reached their maximums at 63.1% RH. CH 4 production by the extremely low-overpotential CO 2 reduction was significantly achieved under all the RH conditions. Consequently, the Faradaic efficiency of the CH 4 production at 63.1% RH was improved by 1.35 times compared to that at 100% RH. These results would be mainly obtained based on the H 2 O-involved chemical equilibrium of the reactions for the CO ads and CH 4 formation. Overall, the present study experimentally clarified that the formation of CO ads (particularly CO L ) and the following CH 4 from the CO 2 reduction at the Pt electrocatalyst in the MEA system was facilitated by appropriately controlling the water-molecule content.

Abstract: Inhibition by CO of the corrosion of Fe, Ni, and three alloys, containing either Fe and large amounts of Ni (Incoloy 825) or large amounts of Fe (Uniloy-420 and N80 steels) in solutions containing between 7.5% and 28% HCl was studied using potentiodynamic polarization curves, gravimetric tests, and FTIRS. In all cases, but Uniloy-420 in 28% HCl, a clear inhibition of corrosion in the presence of CO in the solution was shown by the gravimetric tests and from cyclic voltammetry, the inhibition being higher in the case of Ni and Ni-containing alloys. CO chemisorbed on Fe and/or Ni atoms present on the alloy surface was identified as the species responsible for corrosion inhibition. The inhibition of corrosion is higher in the cases of Ni and Incoloy 825. [Copyright &y& Elsevier]

Abstract: Pt-K/Al2O3 (Pt 1%; K 5.4% wt/wt) catalyst active for the simultaneous Diesel particulate oxidation and NO x reduction have been characterized in comparison with 1% Pt/Al2O3 catalyst. IR spectra of adsorbed CO at −140°C and at room temperature allowed the detection of oxidized Pt centers and of their very strong oxidizing ability. TPD and IR spectra of adsorbed CO2 allowed to characterize the basicity of the samples. The data indicate that Pt centers lie in close proximity of potassium oxide species generating basicity. [Copyright &y& Elsevier]

Abstract: Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) measurements were conducted to analyze the electrochemical oxidation of CO dissolved in bulk electrolyte solution on a polycrystalline Pt electrode during linear sweep (cyclic) voltammetry (CV) in 1% and 100% CO-saturated 0.1M HClO4. A CO adlayer was first formed on Pt at 0.05V vs. the reversible hydrogen electrode (RHE) during CO bubbling in each electrolyte, followed by the CV measurement. In 1% CO-saturated 0.1M HClO4, a well-developed prepeak was found, showing an onset and a peak at around 0.25–0.3V and 0.42V, respectively. A major contribution of bridge-bonded CO, CO(B), to the prepeak is concluded based on a decrease in the corresponding band intensity. In 100% CO-saturated 0.1M HClO4, the onset of bulk CO oxidation takes place around 0.25–0.3V, which is closely associated with a band intensity decrease of CO(B), whereas atop (linear) CO, CO(L), did not exhibit intensity change in this potential region. This suggests that vacant sites made available upon oxidation of CO(B) serve as active sites for bulk CO oxidation. The oxidation of CO(B) at such low potentials is interpreted in terms of an adsorption energy on Pt that is lower than that for CO(L) and also of the specific structure of an adlayer that consists of intermixed CO(L) and CO(B). The bulk CO oxidation becomes diffusion-limited by dissolved CO above ca. 0.72V, where we observed hardly any infrared spectral features ascribed to reaction intermediates. During a negative-going scan back to 0.05V from 1.2V, a steep decrease of the bulk CO oxidation current takes place around 0.66V, at which preferential adsorption of CO(L) is observed. A rigid CO(L) island formation is strongly suggested from its high Cing frequency vs. its very small initial coverage and from its subsequent dependence on potential, with a linear Stark shift characterized by a slope of −29cm−1/V. Such an island formation is in marked contrast to the adlayer structure with intermixed CO(L) and CO(B) initially formed at 0.05V during CO bubbling. It is concluded that the Pt surface saturated with the CO adlayer formed initially at 0.05V exhibits a low overpotential for bulk CO oxidation owing to its adlayer structure with intermixed atop and bridge-bonded CO. [Copyright &y& Elsevier]

Abstract: Methanol adsorption/oxidation on a polycrystalline platinum electrode was investigated by ATR-FTIRAS combined with linear potential sweep voltammetry after initial adsorption at 0.05V in 0.05–1.0M HClO4 containing 0.04–1.0M methanol. Methanol adsorption exhibits a pronounced maximum around 0.56V, which coincides with the onset potential of the oxidation. This suggests that adsorbed CO is not a catalytic poison but an intermediate of the oxidation. The low methanol oxidation activity on Pt is not ascribed to the poisoning action by the adsorbed CO but to inability of Pt to dissociate water to adsorbed OH species needed for the CO and methanol oxidation. It was found for the first time that methanol adsorption at 0.05V is significantly diminished in dilute perchloric acids. This was interpreted in terms of reduced physisorption of methanol at the adsorption potential which becomes more negative with respect to the pzc. Band intensity of the formate species with a symmetric O–C–O vibration around 1320cm−1 remains unchanged with increase of methanol concentration from 0.04M to 1M, while the peak current of methanol oxidation increases by ca. three times in 1M HClO4. The result suggests a minor role of the formate in the methanol oxidation mechanism. [Copyright &y& Elsevier]

Abstract: The behavior of 2% Pd catalyst supported on ceria–zirconia, prepared by solution combustion synthesis, was investigated in fresh and aged status, after severe hydro-thermal ageing in presence of SO2. A surface chemical characterization study was performed using methane temperature programmed combustion, oxygen temperature-programmed desorption, hydrogen temperature-programmed reduction and infrared spectroscopy of low temperature carbon monoxide adsorption. The fresh catalyst is mostly constituted by partly oxidized very small Pd metal particles and dispersed Pd oxide species. This situation gives rise to high catalytic activity for methane combustion at low temperature. The progressive oxidation of highly dispersed small Pd particles to PdO x , as well as the coalescence of dispersed Pd oxide species result in PdO x particles fully oxidized at least at the surface which are less active (in the low temperature range) with respect to the active species of the original catalyst. [Copyright &y& Elsevier]

FTIR absorption spectra of CO, of 12CO–13CO isotopic mixtures and of CO–18O2 interaction on gold catalysts supported on group IV oxides are reported together with CO quantitative chemisorption data. On Au/TiO2 two kinds of metallic gold surface sites, mutually interacting, adsorb CO in spite of the low CO/Au ratio (0.03). On Au/ZrO2, where a CO/Au ratio of 0.30 has been determined, mutually interacting corner sites on non-metallic gold nanoclusters are present. Finally, isolated and negatively charged gold nanoclusters have been evidenced on Au/CeO2. Different absorption coefficients have been found. On all samples, by contacting CO–18O2 at 90 K, only C16O18O is produced: gold sites are involved in the activation of both molecules. The largest amount of C16O18O is produced on the CeO2 supported sample, as a consequence of an easier activation of the oxygen on the anionic gold clusters and on the support. [Copyright &y& Elsevier]

Abstract: The effect of chloride ions (10−7 to 10−1 M) on the potential oscillation generated by the oxidation of formaldehyde is investigated with polycrystalline platinum at 315K in a sulfuric acid solution containing 0.1M formaldehyde. When the chloride ion concentration is 10−5 M or lower, between the two current regions for the appearance of relaxational oscillations, a large-amplitude trapezoidal oscillation appears, which is alternately accompanied by a relaxational one at a lower current. At a still lower current, the relaxational oscillation changes to a sinusoidal one, which then produces a well-known chaos. When the chloride ion concentration is between 10−4 and 3×10−4 M, the relaxational oscillations disappear and the alternating oscillation shows chaos, the properties of which are different from those of the chaos already stated. When the chloride ion concentration is 10−3 M or greater, a simple large-amplitude trapezoidal oscillation prevails without alternation with the relaxational one, along with much less chaos. The surface adsorption state during the various observed oscillations is discussed on the basis of voltammograms measured at various chloride ion concentrations. [Copyright &y& Elsevier]

Abstract: The effect of chloride ions (10−7–100 M) on the potential oscillation generated by the oxidation of formic acid is investigated with polycrystalline platinum at 315K in a sulfuric acid solution containing 1M formic acid. It is found that at very low concentrations of chloride ions (less than or equal to 10−7 M), at a current near the maximum one for the appearance of oscillation, the potential shows small oscillations at and near the peak potential of a relaxational oscillation. In the chloride ion concentration range of 5×10−7–10−5 M, a chaotic oscillation appears in the portion of the small oscillations. When the chloride ion concentration is 5×10−5 M or above, the potential shows a very stable periodic oscillation with an amplitude larger than 0.5V and without small oscillations. In particular, at a concentration higher than or equal to 10−2 M, the increasing potential velocity in the oscillation becomes faster than the decreasing one, although the reverse is true at a lower concentration. A bifurcation diagram is sketched with the applied current as the abscissa and the chloride ion concentration as the ordinate. The reasons for the appearance of the small oscillations and the large-amplitude oscillations are discussed on the basis of the voltammograms measured systematically. [Copyright &y& Elsevier]

Abstract: We report on surface CO diffusion processes in relation to properties of nanoparticle Pt and Pt/Ru fuel cell catalysts. The COad diffusion was studied by the use of 13C electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy. Measurements were carried out in the temperature range 253–293K, where the solution side of the nanoparticle–electrolyte interface is liquid, in contrast to previous measurements, in ice. We offer a concerted view of the effect of particle size and surface coverage on COad diffusion, and find that both are important. We also found that the diffusion parameters were influenced by the variations in the distribution of chemisorption energies on particles of different sizes, and by the CO–CO lateral interactions. On all Pt nanoparticle surfaces investigated, we conclude that CO surface diffusion is too fast to be considered as the rate-limiting factor in methanol reactivity. The addition of Ru to Pt increases the surface diffusion rates of CO, and there is a direct correlation between the Fermi level local density of states (E f-LDOS) of the 2π* molecular orbital of adsorbed CO and the activation energy for surface diffusion. These results are of interest since they improve our knowledge of surface dynamics of molecules at electrochemical interfaces, and may help to formulate better models for the electrooxidation of adsorbed CO on nanoparticle surfaces. [Copyright &y& Elsevier]

Abstract: Surface structure of Pt(310)=3(100)–(110), which contains kink atoms in the step, has been determined with the use of in situ surface X-ray scattering (SXS) in the double layer region (0.50V(RHE)) in 0.1M HClO4. Clean Pt(310) surface has pseudo (1×1) structure on which lateral displacements of 2–9% and 0.3–1% are found along a and b directions, respectively, whereas the surfaces of Pt(110)=2(111)–(111) and Pt(311)=2(100)–(111) are reconstructed to (1×2) according to previous reports. Interlayer spacing between the first and the second layers d 12 is contracted about 5% compared with the bulk spacing, whereas those between underlying layers are expanded down to fourth layer. Fully adsorbed CO has no effect on the surface structure of Pt(310). This result differs from that on Pt(111), where d 12 is expanded after CO adsorption. [Copyright &y& Elsevier]

Abstract: Partial oxidation of methane was studied by pulsing O2 into a CH4 flow over Rh/Al2O3 in a sequence of in situ infrared (IR) cell and fixed bed reactor at 773K. The results obtained from the sequence of an IR cell followed by a fixed bed reactor show that (i) adsorbed CO produced possesses a long residence time, indicating that adsorbed oxygen leading to the formation of CO is significantly different from those leading to CO2 and (ii) CO2 is not an intermediate species for the formation of CO. The results obtained from the reversed reactor sequence show the water–gas shift reaction as the dominant pathway in the downstream of the catalyst bed. Pulsing oxygen into varying partial pressure of methane revealed that H2 oxidation is more sensitive to the partial pressure of the reactant than CO oxidation. In situ IR of pulse reaction coupled with alternating reactor sequence is an effective approach to study the primary and secondary reactions as well as the nature of their adsorbed species. [Copyright &y& Elsevier]

Abstract: The influence of dissolved oxygen on the potential oscillation patterns is investigated during the oxidation of 0.1M formaldehyde on polycrystalline platinum in an acidic solution at 315K under galvanostatic conditions. We have found that, with increasing dissolved oxygen concentration from 0 to 1mM, chaotic oscillations persist to appear as well as periodic ones, both oscillations show fluctuations in their amplitude and the period length doubles. Voltammograms show that a current peak appears at ca. 0.6V and becomes large, which is found to be due to the oxidation of the adsorbed CO with oxygen but not due to the slowing down of the formation velocity of the adsorbed CO. The results are discussed regarding the conditions for the appearance of chaos. [Copyright &y& Elsevier]

Abstract: The general aspects of CO bonding in carbonyls and on metal surfaces are discussed in terms of a molecular orbital description, based on calculations and direct experimental measurements. In particular, the excellent agreement between experiment and theory for CO adsorbed on Ni(100) is the starting point to derive in the same theoretical approach the orbital-based electronic structure of the carbonyls Ni(CO)4, Fe(CO)5, Cr(CO)6 and CO coordinated to the heme group. A frontier orbital interaction scheme involving only the 2π* and the 5σ orbitals is shown to be inadequate for the description of the electronic structure; all orbitals change due to the interaction. Instead, we demonstrate how the formation of an allylic configuration in the π-system, involving both the 1π and 2π* orbitals, gives a more complete description of the π electronic structure. The rearrangement of the σ orbitals involves mainly mixing of occupied CO and metal orbitals resulting in Pauli repulsion. The latter is minimized by polarization of charge away from the CO–Me bond. The bonding picture for CO in organometallic systems is very similar to the surface adsorption case; the main idea of repulsive σ and bonding π interactions seems generally valid when CO interacts with metals. [Copyright &y& Elsevier]

Abstract: We present results of a combined electrochemical and in situ spectroscopy study on kinetic and mechanistic aspects of the reduction of CO2 on Pt model electrodes and compare these with the performance of a Pt/C membrane electrode assembly (MEA) in a polymer electrolyte fuel cell (PEFC) for using pure H2 or H2/CO2(25%) mixtures (synthetic reformate). Based on highly sensitive surface enhanced IR absorption spectrocopy (SEIRAS) measurements on a thin film Pt electrode and on-line differential electrochemical mass spectrometry (DEMS) results obtained on a carbon supported Pt catalyst electrode we conclude that (i) linearly and multiply bonded COad is the only adsorbed reaction product, that (ii) COad formation by CO2 reduction saturates after about 30min at coverages of about 0.45 monolayers (ML) at potentials between 0.06 and 0.2VRHE, and drops down to zero at 0.35VRHE, that (iii) in acidic solution COad formation is independent of the presence of H2 in the electrolyte, and that (iv) even at saturation COad coverage (0.45ML), under steady state conditions, hydrogen oxidation is hardly affected by the presence of CO2 in H2/CO2(20–25%) mixtures. The results indicate that CO2 reduction proceeds by reaction with coadsorbed Had rather than by reaction with dissolved H2 and is therefore favored in the H-upd region, i.e., at fuel cell relevant anode potentials. CO2 reduction is kinetically hindered by self-poisoning and blocking of Pt ensembles at COad coverages, which are still low enough for H2 oxidation. These limitations in CO2 reduction are responsible for the relatively small performance losses for PEFCs operating on H2/CO2 mixtures, compatible with a picture where H2 oxidation proceeds in holes of the CO adlayer, which are too small for CO2 reduction. [Copyright &y& Elsevier]

This paper examines the reaction pathways and the nature of active sites for CO hydrogenation in general and C2+ oxygenate synthesis over Rh catalysts in particular. [ABSTRACT FROM AUTHOR]

• SFG spectra of adsorbed CO on Pt(111) showed on-top peak in HClO 4 and NaOH solutions. • The on-top SFG peak totally disappeared in pre-peak region in NaOH solution. • The on-top SFG peak totally disappeared in the main peak region in HClO 4 solution. • Adsorbed CO was oxidized by reacting with OH− in solution via Eley-Rideal mechanism. • SFG inactive adsorbed CO was oxidized in the main peak region in NaOH solution. In situ broad band sum frequency generation (SFG) spectroscopy was applied to clarify the oxidation mechanism of adsorbed CO on Pt(1 1 1) electrode in alkaline solution in comparison with that in acidic solution. A single SFG peak due to CO adsorbed on-top site of Pt(1 1 1) was observed in the region of 1950 – 2150 cm−1. While oxidation of adsorbed CO proceeded in a nucleation-growth mode via Langmuir–Hinshelwood (L-H) mechanism by reacting with adsorbed OH in the main peak region in 0.1 M HClO 4 solution, adsorbed CO was oxidized in a random oxidation model via Eley-Rideal (E-R) mechanism by reacting with OH− in the solution in the pre-peak region in 0.1 M NaOH solution. The main anodic peak was still observed even after the SFG peak due to on-top CO was totally disappeared by anodic oxidation in the pre-peak region, showing there existed SFG inactive adsorbed CO, although its structure was not clear. [ABSTRACT FROM AUTHOR]

The strong effect of the electrolyte cation on the activity and selectivity of the CO 2 reduction reaction (CO 2 RR) can only be understood and controlled if the cation's effect on the interfacial potential distribution is known. Using CO (the key intermediate in the CO 2 RR) adsorbed on Pt as a probe molecule, and combining IR spectroscopy, capacitance measurements and ab initio molecular dynamics, we show that the cation size determines the location of the outer Helmholtz plane, whereby smaller cations increase not just the polarisation but, most importantly, the polarizability of adsorbed CO (CO ad) and the accumulation of electronic density on the oxygen atom of CO ad. This strongly affects its adsorption energy, the degree of hydrogen bonding of interfacial water to CO ad and the degree of polarisation of water molecules in the cation's solvation shell, all of which can deeply affect the subsequent steps of the CO 2 RR. Image 1 [ABSTRACT FROM AUTHOR]