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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]

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]