Pseudo-elementary step concept

Scheme 15.5 The pseudo-elementary step concept proposed by Finke and coworkers to monitor transition-metal nanoparticle formation.

In both cases (Scheme 6.1) the formation of the NPs follows the auto-catalytic mechanism developed by Finke and coworkers [81]. For example, for Ir or Pt(0) NPs, the catalytic hydrogenation (H2 uptake) of 1-decene and cyclohexene, respectively, is used as a reporter reaction via the pseudo-elementary step concept. Scheme 6.3 (where A is the precatalyst [lr(cod)Cl]2 or Pt2(dba)3 and B is the catalyti-cally active lr(0) or Pt(0) nanoclusters. Scheme 6.3). 

Later, it became clear that the concentrations of surface substances must be treated not as an equilibrium but as a pseudo-steady state with respect to the substance concentrations in the gas phase. According to Bodenstein, the pseudo-steady state of intermediates is the equality of their formation and consumption rates (a strict analysis of the conception of "pseudo-steady states , in particular for catalytic reactions, will be given later). The assumption of the pseudo-steady state which serves as a basis for the derivation of kinetic equations for most commercial catalysts led to kinetic equations that are practically identical to eqn. (4). The difference is that the denominator is no longer an equilibrium constant for adsorption-desorption steps but, in general, they are the sums of the products of rate constants for elementary reactions in the detailed mechanism. The parameters of these equations for some typical mechanisms will be analysed below. 

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