Platinum chemisorption

Ultraviolet photoelectron spectroscopy (UPS) results have provided detailed infomiation about CO adsorption on many surfaces. Figure A3.10.24 shows UPS results for CO adsorption on Pd(l 10) [58] that are representative of molecular CO adsorption on platinum surfaces. The difference result in (c) between the clean surface and the CO-covered surface shows a strong negative feature just below the Femii level ( p), and two positive features at 8 and 11 eV below E. The negative feature is due to suppression of emission from the metal d states as a result of an anti-resonance phenomenon. The positive features can be attributed to the 4a molecular orbital of CO and the overlap of tire 5a and 1 k molecular orbitals. The observation of features due to CO molecular orbitals clearly indicates that CO molecularly adsorbs. The overlap of the 5a and 1 ti levels is caused by a stabilization of the 5 a molecular orbital as a consequence of fomiing the surface-CO chemisorption bond. 

Trevor D J, Whetten R L, Cox D M and Kaldor A 1985 Gas-phase platinum cluster reactions with benzene and several hexanes evidence of extensive dehydrogenation and size-dependent chemisorption J. Am. Chem. Soc. 107 518... 

F1 NMR of chemisorbed hydrogen can also be used for the study of alloys. For example, in mixed Pt-Pd nanoparticles in NaY zeolite comparaison of the results of hydrogen chemisorption and F1 NMR with the formation energy of the alloy indicates that the alloy with platinum concentration of 40% has the most stable metal-metal bonds. The highest stability of the particles and a lowest reactivity of the metal surface are due to a strong alloying effect. 

Although considerable study has been devoted to oxygen chemisorption (mainly on platinum) there is considerable ambiguity in the surface stoichiometry of the reaction. In some cases Pt20 is formed, in others PtO, the particular compound... 

Standard Test Methodfor Surface Area of Catalysts. (D3663—78) Standard Test Method for Hydrogen Chemisorption on Supported Platinum on Alumina Catalysts. (D3908-80) American Society for Testing and Materials (ASTM), Philadelphia, PA. 

Westermark, G., Kariis, H., Persson, 1. and Liedberg, B. (1999) An infrared study on the chemisorption of tertiary phosphines on coinage and platinum group metal surfaces. Colloids and Surfaces A - Physicochemical and Engineering Aspects, 150, 31-43. 

Adsorption due to the operation of chemical forces is called chemisorption. A typical example of chemisorption is also the adsorption of methanol on platinum electrodes, which is accompanied by a deep destruction of the methanol molecule. 

The first step of oxide-layer formation is oxygen adsorption (chemisorption). In the case of platinum, the process stops at this stage, and depending on the conditions, an incomplete or complete monolayer of adsorbed oxygen is present on the platinum surface. In the case of other metals, layer formation continues. When its thickness 5 has attained two to three atomic diameters, the layer is converted to an individual surface phase that is crystalline (more seldom, amorphous) and has properties analogous to those of the corresponding bulk oxides. 

Bagotzky VS, Vassiliev YB, Khazova OA. 1977. Generalized scheme of chemisorption, electrooxidation and electroieduction of simple organic compounds on platinum group metals. J Electroanal Chem 81 229-238. 

Kardash D, Korzeniewski C. 2000. Temperature effects on methanol dissociative chemisorption and water activation at polycrystalhne platinum electrodes. Langmuir 16 ... 

Shin J, Tomquist WJ, Korzeniewski C, Hoaglund CS. 1996. Elementary steps in the oxidation and dissociative chemisorption of ethanol on smooth and stepped surface planes of platinum electrodes. Surf Sci 364 122. 

Lopes MIS, Beden B, Hahn F, Leger J-M, Lamy C. 1991. On the nature of the adsorbates resulting from the chemisorption of methanol at a platinum electrode in acid medium An EMIRS study. J Electroanal Chem 313 323-339. 

Park S, Tong YY, Wieckowski A, Weaver MJ. 2002a. Infrared spectral comparison of electrochemical carhon monoxide adlayers formed by direct chemisorption and methanol dissociation on carbon-supported platinum nanoparticles. Langmuir 18 3233-3240. 

Chemisorption of oxygen at Pt(lll) has been studied in detail by Ertl s group25 and the STM evidence is for complex structural features present in the temperature range 54M60K (Figure 4.14). The limitations of the Langmuir model, frequently invoked for reactions at platinum surfaces, is obvious from... 

This reduction step can be readily observed at a mercury electrode in an aprotic solvent or even in aqueous medium at an electrode covered with a suitable surfactant. However, in the absence of a surface-active substance, nitrobenzene is reduced in aqueous media in a four-electron wave, as the first step (Eq. 5.9.3) is followed by fast electrochemical and chemical reactions yielding phenylhydroxylamine. At even more negative potentials phenylhydroxylamine is further reduced to aniline. The same process occurs at lead and zinc electrodes, where phenylhydroxylamine can even be oxidized to yield nitrobenzene again. At electrodes such as platinum, nickel or iron, where chemisorption bonds can be formed with the products of the... 

Perrichon, V., Retailleau, L., Bazin, P. et al. (2004) Metal dispersion of Ce02—Zr02 supported platinum catalysts measured by H2 or CO chemisorption, Appl. Catal. A, 260, 1. 

Benzene chemisorption on platinum-alumina in the range 26°-470°C has been measured in a flow system by Pitkethly and Goble (7). A small dose of benzene was injected into a stream of inert carrier gas and transported to the reactor the effluent was then sampled repeatedly and analyzed by gas-liquid chromatography. Information concerning the adsorption and desorption of benzene was obtained from the shape of the subsequent benzene concentration versus time curves. Evidence was obtained for four types of adsorption of benzene ... 

Analogous studies of the chemisorption of 14C-labeled benzene on copper powder and on platinum powder showed no chemisorption on the former, and the establishment of a low surface coverage over a range of temperature on the latter (Fig. 1). Again the surface coverage of hydrogen on platinum appeared to be about three times that achieved by benzene. 

Resistance changes upon benzene chemisorption have also been used by Gryaznov et al. (20) in an attempt to characterize adsorption sites at the surfaces of thin (< 10, 10-20, and 20-30 A) platinum films. 

---