Multi-centered adsorption

Numerical calculations for multi-centered adsorption over nonuniform surfaces revealed that tile multi-centered nature of adsorbed species masks the influence of non-uniformity, thus a seven-centered species obeys an almost classical profile. This indication in principle supports the utilization of models of ideal adsorbed layers to treat the adsorption behavior of large organic molecules. 

Other types of isotherms are reported in the literature for multi-centered adsorption on nonuniform surfaces, with inclusion of lateral interactions with an average energy e ... 

In order to understand HDS reactions, it is important to define the ways in which thiophenes are bonded to metal centers on catalytic surfaces. A number of modes in which T interacts with surfaces have been proposed, the most important ones being the one-point adsorption , that is, a strong interaction between the S atom and a vacancy on the surface, and the multi-point adsorption involving the S atom plus one or both of the C=C bonds in a delocalized rr-bonding. While it is difficult to experimentally obtain detailed information on the bonding of thiophenes to surface sites, several coordination modes of thiophenes have been authenticated in metal complexes (Figure 2). 

To illustrate this point, let us discuss the following hypothetical mechanism with two reaction routes and when adsorption of multi-centered species occurs requiring a cluster of several metal surface sites ... 

Multiphase nanosized composites containing metastable y-Fe2O3 phases can be obtained by combined precipitation of Fe(II)/Fe(III)/In(III) hydroxides. These materials are characterized by an increased chemical activity as compared to single-phase composites based on individual oxides or Fe2 xInxO3 solid solutions. The developed surface of the multi-phase materials along with the occurrence of active centers of various nature provide multi-way routes of adsorption and redox processes that results in the growth of gas-sensing response. 

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