Most abundant surface intermediate MASI

Boudart (1972) introduced the assumption of the most abundant surface intermediate (masi). This assumption suggests that the sites occupied by all species except the most abundant surface intermediate is regarded as negligible compared to those filled by the most abundant intermediate and to those which are empty. 

A concept of a most abundant catalyst-containing species macs) or most abundant surface intermediate (masi) is often used, which could reduce the complex mutistep reaction to two-step sequence. 

The Most Abundant Surface Intermediate (MASI) Approximation Catalytic transformations may include the formation of many intermediates on the catalyst surface, which are difficult to identify. In these cases, it is impossible to formulate a kinetic model based on all elementary steps. Often, one of the intermediates adsorbs much more strongly in comparison to the other surface species, thus occupying nearly all active sites. This intermediate is called the most abundant surface intermediate masi [24]. For a simple monomolecular reaction, Aj A2, the situation can be illustrated with the following scheme ... 

If, under reaction conditions, one of the adsorbed species dominates on the surface and the fractional coverage of this intermediate on the catalytic sites is much greater than any other species, then it is said to be the most abundant reaction intermediate (MARI). Technically, it may not be the most abundant surface intermediate (MASI) because some adsorbed species may not be participating in the reaction sequence [2], although these two terms tend to be used interchangeably [1]. 

The concept of a predominant cycle member was first introduced in heterogeneous catalysis by Boudart [42], who coined the term "most abundant surface intermediate," abbreviated masi (see Section 8.10). 

The concept of a most abundant catalyst-containing species (macs in this book) was originally introduced by Boudart for heterogeneous catalysis under the name of masi, for "most abundant surface intermediate" [42]. 

MASI) or most abundant reaction intermediate (MARI) are terms to denote the (reactive) intermediate, which is present in the highest concentration on the surface. If the concentration of the MASI/MARI sufficiently exceeds that of the other surface species, simplified rate expressions can be obtained.)(13,14,23). As a result of this microscopic vuiderstanding of the macroscopic phenomena, that is, the observed catalytic activity and selectivity, a more rational design of new catalysts becomes possible, provided that relations can be established between the catalyst synthesis procedure and the surface phenomena on the catalyst (see Fig. 8). 

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