Adsorption on metal

Langmuir One parameter Ignores the interaction adsorbed/adsorbent 

Temkin Intimictimi molecule/surface Undefined layers 

It is important to stress that although the limitations, the Langmuir model is, for simplicity, the preferred equation used in kinetic models. 

The adsorption on metals involves physisorption and chemisorption. In the first case, the interaction is weak, like van der Waals forces, while in the second case, the interaction between the molecules and the metal is strong, involving electrons of both sides and modifying the electronic structure. Molecules can chemisorb in the 

Adsorption studies on well-defined crystal surfaces, films, or flat surfaces were important to explain and correlate the interaction between molecules and surfaces of metals and supported metals. However, adsorption of molecules on crystal surfaces is usually performed under ultrahigh vacuum, free of impurities, and thus under ideal conditions. For example, if the molecule adheres at the surface after each collision, under vacuum at 10 torr, it forms a monolayer in 1 s, which corresponds to one Langmuir unit, or a monolayer. 

Adsorption on Metals. The observed quenching of the Swanson peak by chemisorbed gas 21.133,134 assignment as a surface state. Adsorbed copper is found 

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The second detergent function is to prevent formation of varnishes that come from polymerization of deposits on hot surfaces of the cylinder and the piston. Finally, by adsorption on metallic surfaces, these compounds have anti-corrosion effects. 

Electrolyte adsorption on metals is important in electrochemistry [167,168]. One study reports the adsorption of various anions an Ag, Au, Rh, and Ni electrodes using ellipsometry. Adsorbed film thicknesses now also depend on applied potential. 

We consider first some experimental observations. In general, the initial heats of adsorption on metals tend to follow a common pattern, similar for such common adsorbates as hydrogen, nitrogen, ammonia, carbon monoxide, and ethylene. The usual order of decreasing Q values is Ta > W > Cr > Fe > Ni > Rh > Cu > Au a traditional illustration may be found in Refs. 81, 84, and 165. It appears, first, that transition metals are the most active ones in chemisorption and, second, that the activity correlates with the percent of d character in the metallic bond. What appears to be involved is the ability of a metal to use d orbitals in forming an adsorption bond. An old but still illustrative example is shown in Fig. XVIII-17, for the case of ethylene hydrogenation. 

Volume 13 Adsorption on Metal Surfaces. An Integrated Approach edited by J. Benard... 

The information on inhibitor adsorption, derived from direct measurements and from inhibitive efficiency measurements, considered in conjunction with general knowledge of adsorption from solution indicates that inhibitor adsorption on metals is influenced by the following main factors. 

Fig. 20.3 Adsorption of water dipoles, (a) A water dipole showing the positive hydrogen end and negative oxygen end, b) adsorption on metal with large negative excess charge, (c) adsorption on metal with large positive excess charge and (d) adsorption on metal with small negative...

Adsorption on Metal Surfaces and Its Bearing on Catalysis Joseph A. Becker... 

The effect of the presence of alkali promoters on ethylene adsorption on single crystal metal surfaces has been studied in the case ofPt (111).74 77 The same effect has been also studied for C6H6 and C4H8 on K-covered Pt(l 11).78,79 As ethylene and other unsaturated hydrocarbon molecules show net n- or o-donor behavior it is expected that alkalis will inhibit their adsorption on metal surfaces. The requirement of two free neighboring Pt atoms for adsorption of ethylene in the di-o state is also expected to allow for geometric (steric) hindrance of ethylene adsorption at high alkali coverages. 

Figure 5.22 reveals the ability of solid state electrochemistry to create new types of adsorption on metal catalyst electrodes. Here oxygen has been supplied not from the gas phase but electrochemically, as 02 via current application for a time, denoted tj, of 1=15 pA at 673 K, i.e. at the same temperature used for gaseous O2 adsorption (Fig. 5.21). Figure 5.23 shows the effect of mixed gaseous-electrochemical adsorption. The Pt surface has been initially exposed to po2 =4x1 O 6 Torr for 1800 s (7.2 kL) followed by electrochemical O2 supply (1=15 pA) for various time periods ti shown on the figure, in order to simulate NEMCA conditions. 

T. Aruga, and Y. Murata, Alkali-metal adsorption on metals, Progress in Surface Science 31, 61-130 (1989). 

From the theoretical standpoint the above issues are addressed by quantum chemistry. On the basis of calculations of various cluster models [191] the properties of surfaces of solid body are being studied as well as issues dealing with interaction of gas with the surface of adsorbent. However, fairly good results have been obtained in this area only to calculate adsorption on metals. The necessity to account for more complex structure of the adsorption value as well as availability of various functional groups on the surface of adsorbent in case of adsorption on semiconductors geometrically complicates such calculations. 

No "Jilt has so far been assumed that the semiconductor-electrolyte interphase does not contain either ions adsorbed specifically from the electrolyte or electrons corresponding to an additional system of electron levels. These surface states of electrons are formed either through adsorption (the Shockley levels) or through defects in the crystal lattice of the semiconductor (the Tamm levels). In this case—analogously as for specific adsorption on metal electrodes—three capacitors in series cannot be used to characterize the semiconductor-electrolyte interphase system and Eq. (4.5.6) must include a term describing the potential difference for surface states. 

A discussion along this line has been made in regard to the orientation of the hydrogen molecule in the dissociative adsorption on metals 82>. Thus, the interpretation of the function of heterogeneous catalysis on a molecular basis is no longer beyond our reach. The important role of LU MO in the process of polarographic reductions has also been discussed... 

Gumhalter, B, Milun, M. and Wandelt, K. (1990), Selected Studies of Adsorption on Metal and Semiconductor Surfaces, Forschungszentrum Jiilich GmBH. 

Mn(II) adsorption on metal oxide surfaces. The binding of Mn(II) on y-FeOOH can be understood in a surface coordination chemical framework. The surface groups on a metal oxide are amphoteric and the hydrolysis reactions can be written ... 

Petit C, Mendoza B, Bandosz TJ. Hydrogen sulfide adsorption on metal-organic frameworks and metal-organic frameworks / graphite oxide composites, ChemPhysChem 2010,11, 3678-3684. 

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