Aging rate deactivation kinetics

The same criteria were used for start-of-cycle and deactivation lumping. Start-of-cycle lumping was based on thermodynamics and molecular-reaction similarity. The deactivation kinetic lumps contain the start-of-cycle lumps as a subset. The additional deactivation lumps were required to properly describe the effect of carbon number on aging rate. 

The elements of range in value from 0 to 1 and are the ratio of the reformer kinetic constants at time on stream t to the values at start of cycle. At any time on stream t, the deactivation rate constant matrix K(a) is determined by modifying the start-of-cycle K with a. From the catalytic chemistry, it is known that each reaction class—dehydrogenation, isomerization, ring closure, and cracking—takes place on a different combination of metal and acid sites (see Section II). As the catalyst ages, the catalytic sites deactivate at... 

This mechanism includes reversible adsorptions of NO and CO, steps (1) and (2), and the dissociation of adsorbed NO, step (3) as rate determining step. The values of tlie rate constant of step (3) and of the equilibrium adsorption constants of CO and NO determined on these different Pt catalysts were discussed in terms of changes in the adsorption properties of Pt induced by support effects [10]. Hence kinetics could be useful to state on the modifications in the extent of such interactions when Rh is added to Pt, in particular when the deactivation proceeds during the CO+NO reactions. This study reports kinetic data on a fresh and on an aged bimetallic Pt-Rh/AljO, catalyst which have been further interpreted with kinetic models including competitive adsorptions of NO and CO on a single kind of active site as well as non-competitive adsorptions in accordance with preferential adsorptions of the reactants on Pt and Rh sites as suggested by Van Slooten and Nieuwenhuys [11]. 

To understand the deactivation trend of the Cu/beta catalyst as a function of exposure time to the 670 °C/4.5 %H20 hydrothermal aging, SCR activities of the aged catalysts at 200 °C were measured at a very high space velocity (SV = 1,00,000 h ). This would render the overall NOx conversions low enough for a SCR reaction rate constant (k) to be calculated based on pseudo first-order kinetics for NO [39]. The results are plotted in Fig. 5.4. The initial 64 h of hydrothermal exposure causes a rapid deactivation of the catalyst as demonstrated by a sharp decline in the SCR reaction rate constant. Extending the aging time beyond 64 h further reduces the activity of the catalyst but at a slower rate. 

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