The catalytic performance is deactivated by aging. Is there a method to estimate the equivalent deactivation under different aging conditions?
For example, what is the estimated duration for aging at 850C, if we want to keep the same catalyst deactivation with the aging condition of 800C/20H?
When the kinetics and activity are separable, it is possible to study catalyst decay and reaction kinetics independently. However, nonseparability, Nonseparable kinetics: (Past history, Fresh catalyst) must be accounted for by assuming the existence of a nonideal surface or by describing deactivation by a mechanism composed of several elementary steps.
You may refer to "Elements of Chemical Reaction Engineering", Fourth Edition, by H. Scott Fogler for more information Junfei Weng
Junfei Weng ,What is "equivalent deactivation". Can you give a definition. Moreover, it is impossible to answer the second part of the question without carrying out experiments. You also use too many shortcuts. For example, what does "the same catalyst deactivation" refer to: time, or maybe rate?
First of all it depends on the mechanism of catalyst deactivation. If the deactivation is primarily caused by active metal sintering, you can estimate the sintering rate/activation energy in a set of experiments at lower temperatures and then re-calculate it for higher temperature (although this is also not so correct since the sintering is related to the Tamman temperature which is mostly an empirical value). This is just on example, but of course the deactivation can be caused by several other factors. If you know exactly the deactivation mechanism, you can estimate for other temperatures, but it will be difficult (almost impossible) to correctly predict what will happen at that temperatures.
Of course, there is no way to answer the formulated question without experimenting. It may be that at 800oC there will be no structural changes or the observed changes will be slight, and at 850oC the catalyst will sinter. We are waiting for more details.
Thanks for your responses, Prof. Mirosław Grzesik , Dr. Hundessa Dessalegn Demsash, and Danghyan Vardan . I understand that the deactivation of the catalysts is a complicated process involving different mechanisms and could be affected by many factors. It's impossible to give out a clear demonstration without the experiments.
Let me clarify and simplify the questions a little bit, and I apologize for causing the confusion.
If we only consider the sintering effects caused by thermal aging, how could we estimate the deactivation or deterioration effects at different aging conditions (temperature/time)?
For example, a fresh PGM catalyst has a reaction rate of R0. After aging at a specific temperature(T1) and time (t1), the catalysts become deactivated to some extent and now its reaction rate turns to R1. Similarly, for another aging at T2/t2, the reaction rate turns to R2. Assume T1 and T2 are high enough to cause the deactivation, and only sintering effects are considered here for the deactivation.
Q1: Is it possible to compare R1 and R2? If yes, How to do that?
Q2: If we want to achieve R1=R2, and T1/t1 and T2 is known, could we estimate the time we need at T2?
Hopefully I have explained my question clear. Thank you for your answers again.
There are two variables here: time on stream and temperature. Changes in catalyst activity in the case of sintering with respect to these two variables may be discontinuous. Even if you perform many experiments, e.g. in a differential reactor for different times on stream and temperatures, the subsequent interpolation of the results, due to possible step changes may be impossible.
Hi Prof. Mirosław Grzesik, I agree that the change in catalytic activity may be discontinuous, and the mechanism could also be different, especially for aging along with higher temperatures or longer duration. Here I just wonder, could we estimate the aging equivalent of different protocol, in the simplest case or if we make some assumptions?
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