Palladium adsorption

Attard GA, Al-Akl A. Palladium adsorption on Pt(lll) a combined electrochemical and ultra-high vacuum study. Electtochim Acta 1994 39 1525-30. 

Figure Bl.22.1. Reflection-absorption IR spectra (RAIRS) from palladium flat surfaces in the presence of a 1 X 10 Torr 1 1 NO CO mixture at 200 K. Data are shown here for tluee different surfaces, namely, for Pd (100) (bottom) and Pd(l 11) (middle) single crystals and for palladium particles (about 500 A m diameter) deposited on a 100 A diick Si02 film grown on top of a Mo(l 10) single crystal. These experiments illustrate how RAIRS titration experiments can be used for the identification of specific surface sites in supported catalysts. On Pd(lOO) CO and NO each adsorbs on twofold sites, as indicated by their stretching bands at about 1970 and 1670 cm, respectively. On Pd(l 11), on the other hand, the main IR peaks are seen around 1745 for NO (on-top adsorption) and about 1915 for CO (tlueefold coordination). Using those two spectra as references, the data from the supported Pd system can be analysed to obtain estimates of the relative fractions of (100) and (111) planes exposed in the metal particles [26].

Conrad FI, ErtI G and Latta E E 1974 Adsorption of hydrogen on palladium single crystal surfaces Surf. Sc/41 435-46... 

The impurities usually found in raw hydrogen are CO2, CO, N2, H2O, CH, and higher hydrocarbons. Removal of these impurities by shift catalysis, H2S and CO2 removal, and the pressure-swing adsorption (PSA) process have been described (vide supra). Traces of oxygen in electrolytic hydrogen are usually removed on a palladium or platinum catalyst at room temperature. 

A variety of catalysts including copper, nickel, cobalt, and the platinum metals group have been used successfully in carbonyl reduction. Palladium, an excellent catalyst for hydrogenation of aromatic carbonyls is relatively ineffective for aliphatic carbonyls this latter group has a low strength of adsorption on palladium relative to other metals (72,91). Nonetheless, palladium can be used very well with aliphatic carbonyls with sufficient patience, as illustrated by the difficult-to-reduce vinylogous amide I to 2 (9). 

In some cases, the catalyst is a solid substance on whose surface a reactant molecule can be held (adsorbed) in a position favorable for reaction until a molecule of another reactant reaches the same point on the solid. Metals such as iron, nickel, platinum and palladium seem to act in this way in reactions involving gases. There is evidence that in some cases of surface adsorption, bonds of reactant particles are weakened or actually broken, thus aiding reaction with another reactant particle. 

S.W. Jorgensen, N.D.S. Canning, and R.J. Madix, A HREELS, TPD study of nitric oxide adsorption, desorption and reaction on clean and sulfur covered palladium (100), Surf. Sci. 179, 322-350 (1987). 

Y. Matsumoto, T. Onishi, and K. Tamam, Effects of Sulphur on a Palladium Surface on the Adsorption of Carbon Monoxide and the Adsorption and decomposition of nitric oxide, J.C.S. Faraday I 76, 1116-1121 (1980). 

There are several methods used to purify gases catalytic adsorption, palladium diffusion, gettering, chemisorption, and filtration. 

As an introductory example we take one of the key reactions in cleaning automotive exhaust, the catalytic oxidation of CO on the surface of noble metals such as platinum, palladium and rhodium. To describe the process, we will assume that the metal surface consists of active sites, denoted as We define them properly later on. The catalytic reaction cycle begins with the adsorption of CO and O2 on the surface of platinum, whereby the O2 molecule dissociates into two O atoms (X indicates that the atom or molecule is adsorbed on the surface, i.e. bound to the site ) ... 

Neurock and coworkers [M. Neurock, V. Pallassana and R.A. van Santen, J. Am. Chem. Soc. 122 (2000) 1150] performed density functional calculations for this reaction scheme up to the formation of the ethyl fragment, for a palladium(lll) surface. Figure 6.38(a) shows the potential energy diagram, starting from point at which H atoms are already at the surface. As the diagram shows, ethylene adsorbs in the Jt-bonded mode with a heat adsorption of 30 kj mol and conversion of the latter into the di-a bonded mode stabilizes the molecule by a further 32 kJ mol . ... 

In their electrochemical surface properties, a number of metals (lead, tin, cadmium, and others) resemble mercury, whereas other metals of the platinum group resemble platinum itself. Within each of these groups, trends in the behavior observed coincide qualitatively, sometimes even semiquantitatively. Some of the differences between mercury and other. y- or p-metals are due to their solid state. Among the platinum group metals, palladium is exceptional, since strong bulk absorption of hydrogen is observed here in addition to surface adsorption, an effect that makes it difficult to study the surface itself. 

Tateishi N, Yahikozawa K, Nishimura K, Masato S, Iwanaga Y, Watanahe M, Enami E, Matsuda Y, Takasu Y. 1991. Electrochemical properties of ultra-fine palladium particles for adsorption and absorption of hydrogen in an aqueous HCIO4 solution. Electrochim Acta 36 1235-1240. 

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