Surface metal atom, adsorption-induced

So far, it has been accepted that molecules or atoms are adsorbed on sites being in registry with the substrate lattice, and the catalysis is explained by their reaction over the surface. By the adsorption of molecules or atoms, surface metal atom undergoes so often short distance shift from their equilibrium position, which is the adsorption induced reconstruction. It should be pointed out that such short distance shift of the... 

Adsorption-induced reconstruction, surface metal atom, 245 Adsorption isotherms, development, 4/,5 Alcohols, role in photooxidation reaction of water on n-Ti02 electrode, 297-308 Alloy single-crystal surface, thin anodic oxide overlayers, 236-244 Alloy surfaces, chemical reconstruction, 246-247... 

The results mentioned together with data outlined in Section 1.11 indicate that adsorption induced change in electric conductivity of sintered and partially reduced oxide is mostly dependent on adsorption related change in concentration of stoichiometric metal atoms which are responsible for dope electric conductivity rather than by charging of the surface of adsorbent due to transformation of radicals of O2 and O". 

Gas-induced morphological changes have been reported, and there is growing evidence that this may be a common occurrence with supported metal catalysts. There is further evidence that a small metal particle may consists of a solid core having a fluid-like surface layer of metal atoms. This raises the possibility that in addition to having catalytic reactions which are structure sensitive it may be necessary to allow that structures are sensitive to catalytic reactions, i.e., reaction-sensitive structures. It is possible that during the initial adsorption of the reactants a small particle will change its surface structure into one which best suits those particular reactants. 

On metallic catalysts, sulfur is strongly adsorbed, and even if only minute amounts are found in the feedstock, accumulation can occur on a significant part of the metallic surface area. In the adsorbed state, the poison molecule will deactivate the surface on which it is adsorbed then the toxicity will depend on the number of geometrically blocked metal atoms. On the other hand, the chemisorption bond between the poison and the metal can modify the properties of the neighboring metallic atoms responsible for the adsorption of reactants. If the interaction between the poison and the metal is weak, the structure of the metal will remain unchanged, but it can induce a perturbation all around the adsorption site, which will be able to modify the catalytic properties of this surface. Yet if the interaction between the metal and the adsorbate is strong, it can go as far as to modify the metal-metal bond. The mobility of the surface atoms can be increased and a new superficial structure can appear. 

There is clear evidence that adsorbate and alloyed metal atoms on platinum surface promote CO electro-oxidation. The reduced overpotential is primarily a result of the promotion of the activation of water. The subsequent kinetics are determined by the details of a Langmuir-Hinshelwood reaction between the adsorbed oxidant (OH) and adsorbed CO. Evidence is also presented that relates this promotion (or poisoning) of CO electro-oxidation to tolerate CO in hydrogen feeds in the hydrogen electro-oxidation reaction. An alternative mechanism that may operate at low potentials [79,113] may be that the reduction in CO adsorption energy on platinum induced by Ru [86,113,114] results in a higher equilibrium concentration of nonpoisoned sites. The relative importance of these mechanisms is a function... 

The ready alleviation of surface distortion by adsorption of foreign atoms is of course only a special case of induced atomic displacement. Small motions of substrate atoms away from regular lattice sites can frequently be expected also. These are probably rather common after adsorption on any type of substrate, whether a metal, semiconductor or... 

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