Catalytic Activity Of Platinum Research Articles

Graphite Electrodes Modified with Platinum‐Nickel Nano‐Particles for Methanol Oxidation

AbstractMethanol electro‐oxidation is investigated at graphite electrodes modified with various platinum and nickel nano‐particle deposits using cyclic voltammetry. The modified electrodes are prepared by the simultaneous electrodeposition of metals from their salt solutions using potentiostatic and galvanostatic techniques. They show enhanced catalytic activity towards methanol oxidation in KOH solution. The catalytic activity of platinum nano‐particles is found to be significantly affected by the presence of relatively small amounts of nickel deposits. A comparison is made between the electrocatalytic activity of Pt/C and (Pt‐Ni)/C electrodes. The results show that the methanol electro‐oxidation current increases with an increase in the nickel content. In particular, the highest catalytic activity is achieved for platinum to nickel deposits of 95%:5% (wt.‐%), in other cases the catalytic activity decreases. It is found that Ni enhances the catalytic activity of Pt by increasing the number of active sites, as well as through an electron donation process from Ni to Pt. This process takes place once the nickel hydroxide (Ni(OH)2)/nickel oxy‐hydroxide (NiOOH) transformation begins. The effect of the methanol concentration on the methanol oxidation reaction is investigated. The order of reaction, with respect to methanol, at the modified (Pt‐Ni)/C electrode is found to be 0.5.

Unique Catalytic Activity of Platinum Eluted into Perovskite in the Solid Phase

It has been found that Pt eluted into the (La0.7Sr0.2Ba0.1)ScO3-δ perovskite oxide exhibited higher catalytic activity for CO oxidation than for H2 oxidation under separate reaction conditions, a behaviour which differs from that of conventional Pt catalysts. The unique activity appeared when ionic Pt in the perovskite lattice was partly reduced, forming Pt nanoparticles on the surface.

Synthesis, characterization, and catalytic activity in the n-heptane conversion over Pt/In–Al2O3 sol–gel prepared catalysts

Platinum catalysts supported on indium-doped alumina were prepared by the sol–gel method. The method allows the incorporation of In3+ in the alumina network. The indium-doped alumina supports showed narrow pore size distribution (5.4–4.0 nm) and high specific surface areas (258–280 m2/g). The 27Al NMR-MAS spectroscopy identified aluminum in tetrahedral, pentahedral, and octahedral coordination; however, the intensity of the signal assigned to aluminum in pentahedral coordination diminishes with the increase of the content of indium. Total acidity determined by ammonia thermodesorption diminishes strongly in Pt/In–Al2O3 catalysts, suggesting a selective deposit of platinum over the acid sites of the support. The effect of the support in the platinum catalytic activity was evaluated in the n-heptane dehydrocyclization reaction. The selectivity patterns for such reaction were modified substantially in the doped Pt/In–Al2O3 catalysts, in comparison with the Pt-In/Al2O3–I coimpregnated reference catalyst. As an important result, the formation of benzene was suppressed totally over the indium-doped alumina sol–gel supports with a high content (3 wt%) of indium.

Activity of Closed d-Shells in Noble Metal Atoms

The Periodic Table has the column of the noble gas atoms (He, Ne, Ar, Kr, Xe, Rn) as one of its main pillars. Indeed the inert chemical nature of their closed shell structure is so striking that it is sometimes extended to all such structures. Is it true however that any closed shell, say a closed d-subshell will denote a lack of chemical activity? Take the noble metals for instance, so renowned for their catalytic capacity. Platinum has 10 electrons in its valence shell which makes one of its excited states to be a closed 5d10–6s0 state. Surely this state would not be expected to be crucial to the catalytic activity of platinum, or would it? Or take palladium whose ground state is precisely the 4d10–5s0 state, should we expect that an isolated Pd atom at near zero-point temperature would attack a closed-shell hydrogen molecule efficiently? We shall here show that this is precisely the case; the closed-shell excited states of nickel and platinum are indeed crucial, through symmetry avoided crossings, for their reactivity. Other valuable catalysts as ruthenium depend on their excited states with maximal d-shell occupancy for their activity. The most notable confirmation of this new finding; that closed d-shells are vital to the catalytic activity of noble metals however, is the case of palladium whose closed-shell ground state is indeed capable of attacking hydrogen and hydrocarbon molecules even at temperatures well below 10 K as was predicted theoretically and immediately confirmed experimentally.

Catalytic Activity of Platinum on Ruthenium Electrodes with Modified (Electro)chemical States

Using Pt on Ru thin-film electrodes with various (electro)chemical states designed by the sputtering method, the effect of Ru states on the catalytic activity of Pt was investigated. The chemical and electrochemical properties of Pt/Ru thin-film samples were confirmed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. In addition, Pt nanoparticles on Ru metal or oxide for an actual fuel cell system showed an effect of Ru states on the catalytic activity of Pt in methanol electrooxidation. Finally, it was concluded that such an enhancement of methanol electrooxidation on the Pt is responsible for Ru metallic and/or oxidation sites compared to pure Pt without any Ru state.

Addition of Tetrachloromethane to Alkenes, Catalyzed by Pt(II) Complexes

Platinum(II) complexes [dichlorobis(triphenylphosphine)platinum(II), dichlorobis(tri-m-tolylphosphine)platinum(II), dichloro(2,9-dimethyl-1,10-N, N′-phenanthroline)platinum(II), etc.] showed catalytic activity in addition of tetrachloromethane across the double bond in 1-hexene, 1-heptene, 1-octene, 1-decene, and cyclohexene. The stability of the platinum catalysts was evaluated by GLC, gas chromatography-mass spectrometry, and 31P NMR and IR spectroscopy; the kinetic relationships of the addition reactions were determined. A reaction mechanism involving formation of trichloromethyl radical was suggested. A correlation was revealed for the first time between the catalytic activity of platinum, palladium, and rhodium complexes and the capability of these complexes to generate hexachloroethane.

Chemisorption of alkyl thiols and S-alkyl thiosulfates on Pt(1 1 1) and polycrystalline platinum surfaces

The self-assembled monolayers prepared from 1-dodecanethiol (C 12SH) or S-dodecylthiosulfate (Bunte salt, C 12SSO 3Na) have been characterised on polycrystalline gold and platinum surfaces and on Pt(1 1 1). Contact angle and impedance measurements show that the film quality decreases in the order Au/C 12SH > Pt/C 12SH ∼ Au/C 12SSO 3Na > Pt/C 12S SO 3Na. XPS measurements show that the S–SO 3 bond of organic thiosulfates is broken on platinum surfaces and the state of the surface-bound sulfur is indistinguishable from that of thiolate. On platinum three sulfur species are formed upon SAM formation and we suggest that the catalytic activity of platinum is responsible for their existence in pristine monolayers.

Imaging of catalytic activity of platinum on p-InP for photocathodical hydrogen evolution

Abstract Platinum was deposited photocathodically on single-crystalline p-type indium phosphide from aqueous hexachloroplatinic acid. The laser-induced deposition was performed with a scanning optical microscope set-up equipped with a He/Ne-laser. This technique allowed the formation of deposits at different positions of the electrode along laser scanned lines in a single combinatorial experiment under variation of potential, light intensity and time of exposure. Subsequent spatially resolved photocurrent measurements in sulphuric acid at different potentials and comparison with optical micrographs of the deposits revealed the different catalytic activity for hydrogen evolution of platinum deposits precipitated under different conditions. The catalytically most active deposits were formed at low light intensity (45 mW/cm 2 ) and relatively negative potentials (−0.3 V vs. SCE). With increasing light intensity and negative potentials corrosion of p-InP dominated platinum deposition, while high light intensities and more positive potentials resulted in more densely deposited platinum of low catalytic activity.

Mechanistic Investigation and New Catalyst Design in Palladium- and Platinum-Catalyzed Se−Se Bond Addition to Alkynes

The present study explains the different catalytic activities of platinum and palladium in Se−Se addition reactions with alkynes. Under the catalytic conditions cis-[Pt(SePh)2(PPh3)2] undergoes fast isomerization to the trans isomer, which does not react with alkynes. Palladium complexes maintain their catalytic activity, due to the formation of the dinuclear structure [Pd2(SePh)4(PPh3)2]. It was shown that the palladium intermediate involved in the catalytic cycle can be prepared directly in the reaction mixture starting from the simple [PdCl2(PPh3)2] precursor, thus allowing replacement for the traditional Pd(PPh3)4 catalyst. X-ray analysis shows that the products of Se−Se addition reactions with alkynes possess the necessary geometry parameters for coordination as bidentate ligands.

Kinetic study of support effect in the propane combustion over platinum catalyst

The support effect on the low-temperature propane combustion over platinum catalysts was investigated by kinetic study. The catalytic activity of supported platinum catalysts varied with the support material, and Pt/SiO2–Al2O3 showed much higher activity than Pt/ZrO2, as already reported. The reaction order for oxygen was negative and that for propane was positive. The reaction order for propane and oxygen also greatly depended on the support material: Pt/ZrO2 gave anomalous reaction orders, i.e., −2.9 for oxygen and 3.4 for propane. Further, oxidized Pt/ZrO2 showed a long-term change of the catalytic activity with time-on-stream, compared with oxidized Pt/SiO2–Al2O3. From these results, it was concluded that high catalytic activity of platinum on acidic support is attributed to high ability to maintain the metallic state of platinum with high oxidation-resistance and high reducibility of platinum oxide.

Electrocatalytic Activity of Platinum modified Polypyrrole Films for the Methanol Oxidation reaction

The catalytic activity of platinum modified polypyrrole films prepared in different ways was studied for the methanol oxidation reaction. Surprisingly, no catalytic activity was observed for films modified with colloidal platinum particles incorporated into the film during its synthesis or for the film synthesised with tetrachloroplatinate complex as a nucleophilic counter-ion, which was subsequently cathodically reduced. On the other hand, high catalytic activity was observed for platinum deposited onto pre-synthesised polypyrrole film. The platinum load, film thickness and potential of platinum deposition were found to be important parameters. High electrocatalytic activity was also observed for platinum layers deposited directly onto the glassy carbon (GC) support. However, in the latter case the stability of the electrocatalytic activity was lower when compared with the polypyrrole film modified by cathodically deposited Pt.

Electrochemical reactions of benzoic acid on platinum and palladium studied by DEMS. Comparison with benzyl alcohol

The electrochemical reactivity of benzoic acid on porous platinum and palladium electrodes has been studied by cyclic voltammetry and differential electrochemical mass spectrometry (DEMS) in aqueous 0.1 M HClO 4 . The objective of this work is to investigate the adsorption processes and the reactivity of this compound on different noble metals, in order to compare these results with those obtained for related aromatic compounds. On-line mass spectroscopy analysis of volatile products reveals that the adsorption of benzoic acid is irreversible at platinum while it is mainly reversible on palladium. Accordingly, different catalytic activity of platinum and palladium is demonstrated during the electrooxidation process. The anodic stripping of the adsorbates formed from benzoic acid yields CO 2 as the sole oxidation product of platinum. Cathodic stripping of the residues results in the partial desorption of the organic adlayer from the electrode. At palladium, only small amounts of irreversibly adsorbed species, which also oxidise to CO 2 are detected. The effect of the nature of the electrode on the electrochemical behaviour of these substances is also analysed.

Investigation of the electrochemical reactivity of benzyl alcohol at platinum and palladium electrodes

The electrochemical reactions of 2 mM benzyl alcohol (BA) on platinum and palladium electrodes in 0.1 M HClO 4 were studied by means of differential electrochemical mass spectrometry (DEMS) and cyclic voltammetry. The objective of this work is to investigate the influence of electrode nature on the reactivity of BA. On-line mass spectroscopy analysis of volatile products reveals that the interaction of BA with these metals partially occurs dissociatively producing benzene. CO 2 is the sole oxidation product detected. The corresponding mass signal exhibits three different contributions. The extent of each contribution is found to depend strongly on the electrode nature, though in the case of palladium, it also varies with changes in the electrode potential range covered during the voltammetric scan. The different catalytic activity of platinum and palladium is demonstrated during the electroreduction process. Both hydrogenolysis of the molecule and hydrogenation of the aromatic ring occur on platinum, whereas the latest process is of little significance on palladium.

The effect of sulphur containing pollutants on the oxidation activity of precious metals used in vehicle exhaust catalysts

The effect of traces of hydrogen sulphide and of sulphur dioxide on the oxidation of methane over supported precious metals has been examined. Both gases inhibited catalytic oxidation over Pd and Rh, apparently as a result of sulphate formation. However, the catalytic activity of platinum was slightly enhanced by the pollutants.

The influence of the preparation methods on the catalytic activity of platinum and gold supported on TiO2 for CO oxidation

The influence of the preparation methods on the catalytic activity for CO oxidation was markedly large for Au-TiO2 and negligible for Pt-TiO2 catalysts. Platinum and gold were deposited on TiO2 by deposition-precipitation (DP), photodeposition (FD) and impregnation (IMP). The DP method gave the most active catalysts for both Pt and Au. Gold catalysts prepared by DP were active at temperatures below 273 K and showed a much greater activity than Pt catalysts.

ChemInform Abstract: Catalytic Activity of Platinum After Exchange with Surface Active Functional Groups of Carbon Blacks.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Catalytic Activities of Platinum‐ and Nickel‐Doped Magnesium Oxide for Steam Reforming of Ethanol.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Structure Sensitivity of Methane Oxidation Over Platinum and Palladium.

Abstract A series of supported platinum and palladium catalysts were tested for methane oxidation at 260 to 370°C, 50 Torr methane, 110 Torr oxygen, 900 Torr helium, and conversions below 2%. The intrinsic rate varies by more than 5000 from the least active to the most active catalyst, indicating that the reaction is structure sensitive. The catalytic activity of platinum depends on the distribution of the metal between a dispersed and a crystalline phase. These two phases are distinguished by absorbances at 2068 and 2080 cm−1, respectively, in the infrared spectrum of adsorbed carbon monoxide. The catalytic activity of palladium depends on the metal particle size. For the different classes of catalysts, the mean steady state turnover frequency (TOF) at 335°C and the mean apparent activation energy (Ea) are as follows: dispersed phase of platinum, TOF = 0.005 s−1 and Ea = 36 kcal/mole; crystalline phase of platinum, TOF = 0.08 s−1 and Ea = 28 kcal/mole; small particles of palladium, TOF = 0.02 s−1 and Ea = 27 kcal/mole; and large particles of palladium, TOF = 1.3 s−1 and Ea = 29 kcal/mole. The structure sensitivity may be explained by differences in the reactivity of the adsorbed oxygen on these metal surfaces.

Catalytic activity of platinum applied on fibrous carbon materials during hydrogenation of carbon monoxide

1. Platinum applied on cloth made of carbon fibers exhibits activity in hydrogenation of carbon monoxide; the activity of the samples is a function of the concentration of platinum in the sample. 2. The amount of platinum applied on the carbon fibers is a function of the acidic-basic properties of the surface of the carbon fibers.

Influence of adsorbed sulfur on the catalytic activity of platinum in the ethylene hydrogenation reaction

Influence of adsorbed sulfur on the catalytic activity of platinum in the ethylene hydrogenation reaction