Hydrogenation of toluene over Pt and Pt?Cu alloys in NaY

The hydrogenation of toluene is performed over small Pt and Pt–Cu particles in a NaY zeolite. For toluene hydrogenation the T.O.N. of Pt and Pt alloyed with Cu are very different at room temperature but at high temperature (530 K) they are of the same order of magnitude.

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Pt Pt–Cu NaY. ( ) Pt Pt, , , , (530 K) .

     

Effect of the Pt/Pt Electrode Roughness on the Interaction of CO with Oads

Transients of potential E during the CO-O_ads interaction on Pt/Pt electrodes of different roughness (f = 20-1200), measured in 0.5 M H₂SO₄ under open-circuit conditions, slow down with increasing f. Dependence of specific activity of Pt/Pt on f cannot be described by one CO-O_ads interaction mechanism in a wide range of f. At f < 100, more acceptable is the mechanism suggested earlier for polycrystalline (smooth) Pt, and at larger f—mechanism of conjugated reactions. Presumably, increasing f at small f reduces intrinsic electrocatalytic activity of the Pt surface, while at large f inner-diffusion limitations can arise.     

Carbon monoxide adsorption on Pt/Pt electrodes modified with silver adatoms

Adsorption of carbon monoxide on the Pt/Pt surface in the presence of preliminarily accumulated different amounts of UPD silver (_Ag) is studied by using voltammetry, electrode washings, and analytical techniques. It is found that carbon monoxide is adsorbed only on the sites unoccupied by Ag_ad and rather than displacing the latter atoms to the noticeable extent. The fraction of carbon monoxide chemisorbed in the linear form increases with _Ag. The shape of anodic voltammetric curves and the number of peaks in the region where the mixed layer CO_ads + Ag_ad is desorbed strongly depend on the CO_ads : Ag_ad ratio; at small and medium _Ag, three and more peaks are observed. Electroanalytic detection of silver passed to solution in various potential ranges in the course of the mixed-layer oxidation allowed us to identify the processes corresponding to different peaks.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 241–246.Original Russian Text Copyright © 2005 by Maksimov, Podlovchenko.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Study of CO chemisorption on polycrystalline Pt

The chemisorption of CO on a sputtered and annealed polycrystalline Pt surface has been examined using ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD). Data obtained from an isotopic TPD experiment indicate that adsorption is molecular with no detectable CO dissociation. ISS data demonstrate that the CO bonds to the Pt through the C with the O pointing away from the surface and that about 80% of the Pt surface is covered at saturation based on the relative sizes of the ISS Pt peak heights obtained from the clean and CO-saturated surfaces. Coverage versus exposure plots have been determined from both the ISS and TPD data, and the agreement is generally good. The sticking coefficient is close to 1 up to =0.5 and than falls rapidly with increasing exposure to the saturation exposure of 90 L. The Kisliuk adsorption model, which assumes adsorption at a single type of site, is able to provide a good fit of the ISS uptake data but is not as successful in fitting the TPD uptake data.     

Improved deactivation profile observed for Pt/H-chabazites and Pt/H-Y zeolite

The presence of small platinum crystallites in the framework of protonic offretite, erionite and Y-zeolite causes an improved deactivation profile during n-butane conversion and reflects a stronger shape-selectivity compared to the analogous behavior of the monofuctional (protonic) zeolites.

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Nitrate electroreduction on Pt in metatungstate-containing solution

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Encapsulation of Pt(iv) prodrugs within a Pt(ii) cage for drug delivery

This report presents a novel strategy that facilitates delivery of multiple, specific payloads of Pt(iv) prodrugs using a well-defined supramolecular system. This delivery system comprises a hexanuclear Pt(ii) cage that can host four Pt(iv) prodrug guest molecules. Relying on host–guest interactions between adamantyl units tethered to the Pt(iv) molecules and the cage, four prodrugs could be encapsulated within one cage. This host–guest complex, exhibiting a diameter of about 3 nm, has been characterized by detailed NMR spectroscopic measurements. Owing to the high positive charge, this nanostructure exhibits high cellular uptake. Upon entering cells and reacting with biological reductants such as ascorbic acid, the host–guest complex releases cisplatin, which leads to cell cycle arrest and apoptosis. The fully assembled complex displays cytotoxicity comparable to that of cisplatin against a panel of human cancer cell lines, whereas the cage or the Pt(iv) guest alone exhibit lower cytotoxicity. These findings indicate the potential of utilising well-defined supramolecular constructs for the delivery of prodrug molecules.     

Pt羰基簇合物在NaY内的合成机理

利用IR，EXAFS, ~(13)CO同位素交换反应及与NO作用等手段研究了Pt羰基簇合物[Pt_3(CO)_6]~(2-)_n(n＝3,4)在NaY分子筛超笼内的合成机理．在氧化样品Pt~(2+)/NaY上300－373 K的还愿羰基化过程中，首先Pt~(2+)与CO反应生成PtO(CO)物种(波数σ_(CO)＝2110 cm~(-1))，然后聚集成“Pt_3(CO)_6”(σ_(CO)＝2112，1896和1841 cm~(-1))，最后生成深绿色的Pt羰基簇合物Pt_(12)(CO)_(24)]~(2-)/NaY(σ_(CO)＝2080，1824 cm~(-1))．“Pt_3(CO)_6”的羰基在室温下能迅速地与~(13)CO发生交换，而[Pt_3(CO)_6]~(2-)_n(n＝3,4)的羰基与~(13)CO的同位素交换即使在343 K也进行得很慢，室温下，NO能逐步破坏Pt羰基簇合物的层间和层内Pt－Pt键，得到中间物种“Pt_3(CO)_6”和PtO(CO)，同时在气相产生CO_2和N_2O．而由上述两中间物种出发，300－353 K温度下，在CO气氛中的还原羰基化又能可逆地得到原羰基簇合物．     

On the kinetics of oxygen adsorption over stepped Pt surface

A model of adsorption kinetics is considered in which adsorption proceeds at a high rate (s_o=1.0) on steps only, and then Oads can migrate to terraces and back. For E_dif from steps on terraces 75 kJ/mol, the lg s vs. () dependence at 300 K is close to linear.     

Bromide ion oxidation of various Pt surfaces

At variance with the absence of an orientation effect in the hydrogen evolution reaction, aclear difference in the electrocatalytic effect of various parts of the surface on bromide ion oxidation is observed.

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Selective cytotoxic Pt(II) complexes of phenanthroline derivatives

A new dichloroplatinum(II) complex with 5-methyl-1,10-phenanthroline (1) has been obtained and characterized by X-ray diffraction. MTT assay was used for in vitro cytotoxicity evaluation of this complex, along with a similar complex with 4,7-diphenyl-1,10-phenanthroline (2) against normal and cancerous cell lines. Interestingly, the IC₅₀ values of the new complexes were higher for normal cells and in the case of complex 2, lower against all studied human cancer cells, in comparison with cisplatin.     

STM针尖诱导构筑-置换两步法制备Pt表面纳米结构

STM“Jump-to-contact”针尖诱导表面纳米构筑是目前水溶液中具有最高分辨率的一种表面纳米构筑技术.然而,一些金属因其具有较高的内聚能而难以发生针尖原子向表面的转移,限制了该技术的广泛应用.本文建立了以STM构筑-置换两步法获得不能直接利用“Jump-to-contact”原理进行构筑的金属表面纳米团簇阵列,利用STM针尖“Jump-to-contact”诱导在Au(111)表面构筑Cu纳米团簇阵列,然后通过Pt-Cu置换的方法,制备出Au(111)表面的Pt纳米团簇阵列.     

Kinetics of decalin dehydrogenation on Pt/C catalyst

Catalytic dehydrogenation of decalin (decahydronaphtalene), a promising material for hydrogen storage, has been investigated. The amount of hydrogen produced on a Pt (3 wt.%)/C catalyst has been studied as a function of pressure, temperature, and the substrate feed rate in a flow-type reactor. The maximum volume of the released hydrogen is achieved at atmospheric pressure, a temperature of 320 °C and a substrate LHSV of 1 h^–1. The dehydrogenation occurs mainly by conversion of cis(97%) and partial conversion of trans-decalin (66%) with a selectivity of 97% to naphthalene. The amount of the released hydrogen corresponds to the decalin hydrogen capacity (5.5 wt. %). The obtained results are consistent with the calculated thermodynamic characteristics of the studied reaction.     

Die Kristallstruktur von Li2Pt(OH)6 und Na2Pt(OH)6

The Crystal Structure of Li₂Pt(OH)₆ and Na₂Pt(OH)₆ The crystal structure of Li₂Pt(OH)₆ and Na₂Pt(OH)₆, trigonal, space group P3 1m-D, is closely related to that of Li₂ZrF₆, with alkali atoms occupying different positions. Electrostatic lattice energies are calculated in order to predict probale hydrogen positions and to discuss this structural difference.     

Modification of a Pt surface by spontaneous Sn deposition for electrocatalytic applications

In the present communication we explored a simple dip-coating method for spontaneous (without applying an external current or additional reducing agents) modification of Pt surface by both tin oxy-species and tin metal based on hydrolysis of tin chloride complex and autocatalytic (electroless) deposition of tin for fabrication of the fuel cell catalysts with improved CO tolerance. It consisted of (i) Pt immersion into SnCl₂/HCl solution under open-circuit conditions; (ii) subsequent rinsing of the surface by pure water. The resulting Sn-modified Pt surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). Two types of tin species, namely, tin oxide/hydroxide species and metallic tin were identified at Pt surface. Tin oxide/hydroxide species were assumed to be derived as a result of Sn(II) chloride complex hydrolysis, while tin metal particles were most likely deposited spontaneously on Pt surface due to disproportionation of Sn(II) to Sn(IV) and metallic tin, competing with dissolution of the Sn deposit in strongly acidic medium. Modifying tin species show a satisfactory stability in 0.5-M H₂SO₄ solution at potentials relevant to low-temperature fuel cell operating conditions (below 0.6 V vs. a standard hydrogen electrode, SHE).     

Reaction of sterically hindered arylmercury compounds with Pt(IV), Pt(II), and Pd(II) chloride complexes

Conclusion Heating of a solution of the PtCl₆ ^2– ion and an arylmercury compound containing a substituent in the ortho position to mercury leads to the formation of a diaryl (in the case of -naphthylmercury) or arene (in the case of the mesityl or pentamethylphenyl mercury derivatives).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2374–2376, October, 1986.The authors express their gratitude to A. E. Shilov and A. K. Yatsimirskii for a useful discussion of these results.     

Ring opening of ehtylcyclopentane over supported Pt catalysts

Ring opening of ethylcyclopentane (ECP) was studied over 6.3% Pt/SiO₂ (EUROPT-1) and 10% Pt/Al₂O₃, as a function of the hydrogen pressure. Both catalysts gave almost nonselective ring opening. Pt/Al₂O₃ produced also olefins, more side dealkylation and less fragmentation products. It is likely, that adlineation sites are operative over both catalysts.

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