How catalytic mechanisms reveal themselves in multiple steady-state data: II. An ethylene hydrogenation example

Many mechanisms have been proposed for ethylene hydrogenation on catalytic surfaces. In a companion article we discussed how isothermal multiple stead y-state data can be used to discriminate between rival candidate mechanisms . While most catalytic mechanisms have the capacity to support some pair of steady states, they will not usually have the capacity to support a partic ular pair of steady states observed in the laboratory. The companion articl e described how chemical reaction network theory can be used to determine w hether multiple steady-state data are consistent with a given mechanism. Mu ltiple steady-state data had been obtained previously for ethylene hydrogen ation over a rhodium catalyst in an isothermal CFSTR. In this article, thes e data are used to discriminate between a total of 80 single- and multiple- pathway mechanisms. Given certain assumptions, it will be seen that only ni ne of the 80 mechanisms are consistent with the data. The purpose of this a rticle is not to favor one mechanism over another, but to demonstrate the t ype of refined mechanism discrimination that is possible using even fragmen tary multiple steady-state data. (C) 2000 Elsevier Science B.V. All rights reserved.