There are several reasons for deactivation. The most important of these are too high temperature (sintering), structural changes during long-term use (aging), fouling and poisoning. I associate such a rapid change in activity with poisoning of active sites. You should check the purity of the substrates. Unless some mistake has been made in the manufacture of the catalyst.

I agree with Mirosław Grzesik, there several reasons for catalyst deactivation including coke formation. Catalyst deactivation by coke formation is very common under tail-end conditions as is the formation of C4 byproducts.

Any kind of deactivation is possible here until proven. In the case of coking, there should be traces of blackening of the used catalyst. In turn, a rapid decrease in activity to zero could indicate poisioning. But that's just a guess.

Mr. Mirosław Grzesik thanks for your detailed answer. the problem is that I have 2 samples that the first one is an industrial catalyst and does not lose activity overtime or the deactivation is slow, but the sample that I synthesized with the same amount of Pd-Ag loadings, lose activity. is there a certain impregnation condition that i may not know.

It can be due to the presence of oxidant in the medium that can provide redox reaction

The deactivation rate with the commercial catalyst is much slower than the synthesized catalyst indicating that it is (i) deactivated more rapidly by poisons; and/or (ii) more active for polymer/carbon formation side reactions; and/or (iii) subject to rapid change in the active metal structure (e.g. loss of metal SA). Therefore, I suggest examining any structural differences between the catalysts such as the support type (e.g. both alumina? If so, alumina phase such as alpha or gamma) and support properties (e.g. SA; PV); metal level (reported as same for both Pd & Ag) and dispersion (e.g. crystallite size). There are different means of metal impregnation (e.g. dipping into a metal salt solution; incipient wetness) including the use of additives and whether both metals are added at the same time (co-impregnation) or sequentially (e.g. Pd first followed by calcination and then the Ag). The condition used for calcination are another variable. Unfortunately, I don't have detailed knowledge of these areas for this type of catalyst but others may be able to advise.

Also, this article may be useful and one of the authors is listed at Iran University of Science and Technology; "Acetylene selective hydrogenation: a technical review on catalytic aspects"( Article Acetylene selective hydrogenation: a technical review on cat...

Farzad Jokar Abnavi, Designing catalysts is a kind of art. In our laboratory, we had laboratories who could do this. But it is not an easy task. There may be gaps in the way you are dealing. Not all information is published. By the way, how long the catalyst you synthesized is stable?

The intended duty for the acetylene hydrogenation catalyst and associated test conditions may also be relevant. In olefin plants, the flowsheets options divide into "front-end" or "tail-end" acetylene hydrog designs. The former types operate with excess H2 present whereas the latter operates on a purified C2 stream with controlled addition of H2. This may also have an influence on the cause of catalyst deactivation.

My memory is that Ag promotion of the Pd front-end catalyst was developed by Phillips Petroleum in about the early 1990s and an early version of this (or a very similar) catalyst was sold by Sud Chemie (now Clariant) as G-83C. Catalysts offered by others are now "promoted" maybe still with Ag. In terms of catalyst preparation, there may be some technical papers or patents assigned to the initial companies that may provide clues on catalyst preparation.

If the conditions of the experiment and the method are the same for both catalysts, the reason for the rapid deactivation of the synthesized catalyst is the catalyst itself, and not the method and conditions.

Mirosław Grzesik, I think you are right, by changing the impregnation procedure, the activity and selectivity are improved. responding to your former question, the catalyst is stable for about 3 hr and then gradually loses its stability. the rate of deactivation in our catalyst is faster than the commercial one.

Farzad Jokar Abnavi, In a word, those who designed the catalyst, currently used in practice, know some secrets related to its production. I don't think that's common knowledge. When changing the conditions of the process, you should try to determine what factor/s is/are causing the loss of activity. Worse if these are structural changes e.g. under the influence of temperature or reactants.