The electrocatalytic reduction of 0.5 M nitrate in 1 M HClO 4 over carbon-supported palladium nanoparticles ͑mean size 10.5 nm͒ was studied with differential electrochemical mass spectrometry ͑DEMS͒ as a function of reaction temperature between 0 and 55°C. The palladium nanoparticles are active for the electrocatalytic reduction of nitrate as evidenced by the detection of N 2 O and NO in DEMS. NO is produced during the anodic scan between 0.8 and 1.0 V vs reversible hydrogen electrode ͑RHE͒ and also during the cathodic scan between 0.3 and 0.0 V vs RHE. In contrast, N 2 O is only produced during the cathodic scan between 0.4 and 0.0 V vs RHE. While the reduction of NO 3 − to NO and N 2 O during the cathodic scan occurs only at significant overpotentials, the required overpotential decreases with increasing temperature. The potential dependencies of the apparent activation energies for the cathodic NO and N 2 O production indicate that at potentials above 0.1 and 0.075 V vs RHE, the respective kinetics of NO and N 2 O evolution are primarily determined by the potential. At potentials below 0.1 and 0.075 V vs RHE, respectively, the apparent activation energies for the evolution of NO and N 2 O are largely potential independent.
The adsorption and reaction of n-propanol was investigated using in situ Fourier transform IR spectroscopy and on-line differential electrochemical mass spectrometry on electrodeposited Pt, Rh, and PtRh with different compositions. It has been observed that the bimetallic electrodes were more active than pure platinum below 0.9 V. The pure rhodium electrode was practically inactive. Differences in product yield show that platinum is more active than the bimetallic electrodes for propionic acid formation, but the bimetallic electrodes show higher activity for CO 2 and propanal production. The electrochemical reduction of the strongly adsorbed intermediates on pure platinum and on the two bimetallic electrodes gave products with 1, 2, and 3 carbons, while the pure rhodium electrode produced only methane. The degree of coverage by the irreversibly adsorbed species is about ten times higher on platinum than on the bimetallic electrodes or rhodium, showing that on the bimetallic electrodes the intermediates are not as strongly adsorbed as on pure platinum.The electrochemical oxidation of n-propanol on platinum electrodes has been the subject of a detailed study 1 using auxiliary techniques like in situ Fourier transform infrared spectroscopy ͑FTIRS͒ and on-line mass spectrometry to detect products and intermediates. It was found that the oxidation leads to CO 2 , propanal, and propionic acid for the oxidation products. Stable intermediates with C-H stretching bands were observed and the adsorbed species may contain CH 3 and CH 2 stretching vibrations. However, a very characteristic band from adsorbed alkoxy species, the C-O-H deformation band at ca. 1430 cm Ϫ1 , was not reported and a definitive identification of the adsorbed species was not given. However, it is clear that the reduction of the adsorbed intermediates gives ethane and propane. Ethane is ca. 3.5 more abundant than propane. Detection of ethane and propane show that C2 and C3 adsorbates are very likely, because reduction products from adsorbed CO on platinum electrodes, generally yield only C 1 hydrocarbon compounds. 2 The key step for total oxidation of a multicarbon atom alcohol is the C-C bond dissociation and the C-O coupling reactions, while partial oxidation requires only C-H dissociation for propanal and C-H bond dissociation followed by C-O bond formation for the acid. Thus a good catalyst for total oxidation must provide sites for C-H and C-C bond dissociation and sites for active oxygen at low potentials to promote the C-O bond formation, in order to carry out the oxidation to CO 2 . Therefore, a more complete oxidation to CO 2 or acid entails the supply of oxygen species, which may come from the water in solution or from surface oxides formed on the electrode surface at different potentials. Indeed, oxides on platinum electrode surfaces, depending on the oxidation state ͓Pt-OH, Pt-(OH) 2 and PtO͔, can be classified as active species. Oxides of platinum at higher oxidation states ͓Pt(OH) 3 and PtO 2 ] poison the reaction. 3 Ruthenium has been ad...
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