Transient catalysts definition

In the absence of aging (deactivation) of the catalyst, a phenomenological definition of catalysis would be enhancement of chemical reactions or a change of their rate under the influence of substances — catalysts — which several times enter into transient chemical interactions with reaction participants and then, after each cycle of transient interactions, regenerate their chemical identity [1]. 

In conclusion, it must be noted that the equations to describe the transient behaviour of heterogeneous catalytic reactions, usually have a small parameter e = Altsot/Alt t. Here Atsot = bsS = the number of active sites (mole) in the system and Nfot = bg V = gas quantity (mole). Of most importance is the solution asymptotes for kinetic equations at A/,tsot/7Vtflt - 0, 6S, bg and vin/S being constant. Here we deal with the parameter SjV which is readily controlled in experiments. The case is different for the majority of the asymptotes examined. The parameters with respect to which we examine the asymptotes are difficult for control. For example, we cannot, even in principle, provide an infinite increase (or decrease) of such a parameter as the density of active sites, bs. Moreover, this parameter cannot be varied essentially without radical changes in the physico-chemical properties of the catalyst. Quasi-stationarity can be claimed when these parameters lie in a definite range which does not depend on the experimental conditions. 

These mixed metal systems have also been tested with the transient method for catalytic activity in the Fischer-Tropsch reaction. We would like to remark here that the nature of the cation, anion, and zeolite are all important factors in the Fischer-Tropsch reactions that we have studied. Further details of these catalytic studies can be found elsewhere (23). We do observe here, however, that some catalysts that are completely reduced to the metallic state are not necessarily the most active catalysts. Also, even though the Mossbauer experiments suggest that 400°C is sufficient for complete reduction, higher activation temperatures can increase the activity and selectivity of these reactions. We have also observed that the cation definitely changes the product distribution and the activity. 

Reversibility begets reusability. The transient nature of complexes is an absolute requirement for all molecules that function as reusable machines. Enzymes are molecule-sized lathes that bind to their substrates, catalyze a reaction, and release the product when done, the enzyme is ready for reuse. Indeed, any chemical catalyst must meet this criterion based on the very definition of a catalyst a species that enhances the rate of a chemical process without itself being changed. Enzymatic... 

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