Single-Site Adsorption of Each Component in a Multicomponent Mixture

14-3 SINGLE-SITE ADSORPTION OF EACH COMPONENT IN A MULTICOMPONENT MIXTURE 

In an effort to predict fractional surface coverage of component in a mixture of reactants and products, it is necessary to analyze adsorption and desorption when several components are present. Each component adsorbs withont preference on a single active surface site. Hence, the available vacant sites a are the same in each reaction. The sequence of reversible elementary steps is 

As a prelude to the development of kinetic rate expressions for heterogeneous chemical reactions, if A reacts with B, for example, then the next step in the mechanism is ha + Ba, forming an activated complex on the snrface. Each reversible step in the seqnence above is characterized by a forward rate constant adsoiption for adsoiption, with units of mol/area time atm, and a backward rate constant A ,desoiption for desorption, with units of mol/area time. The ratio of these rate constants adsorption/ h, desoiption defines the adsorption/desorption equi- 

If the adsorption process is species specific such that the fraction of vacant active sites VA available to gas A is different from those vb available to gas B, and so on, then the net rate of adsorption for component i must be modified as follows  

An additional condition requires that all vacant-site fractions and coverage fractions must sum to unity. If no active sites on the surface are available to more than one species, then  

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