Hi, I'm working on Co3O4 catalysts now. When I do H2-TPR to determine the reducibility of Co3O4, I could observe two peaks, one at ~350C, and the other one at ~405C. However, I could not fit the results with two peaks. On the other hand, there is an obvious peak shoulder at ~450C inside the higher temperature peak, and I could fit the reduction peak well using these three peaks.
From the literature, it always indicates the existence of two peaks, a lower one for the reduction of Co3+ to Co2+, and a higher one for the reduction of Co2+ to metallic Co. Is there any literature talking about the three peaks? Is it possible that the two higher peaks may be due to the reduction of Co2+ that are originally formed in the catalyst and from the reduction of Co3+.
Do you know the amount of H2 consumed in moles in each peak? What is the average size of Co3O4 particles? Are you sure that you have a pure Co3O4?
Dear Junfei Weng many thanks for your interesting technical question. According to the relevant literature, the reduction of Co3O4 with elemental H2 occurs in two steps:
1. Reduction of tricobalt tetraoxide (Co3O4) to cobalt(II) oxide (CoO)
2. Reduction of CoO to metallic cobalt
In this context please have a look at the following useful Open Access article:
Cobalt Catalyst Reduction Thermodynamics in Fischer Tropsch: An Attainable Region Approach
(see attached pdf file)
Junfei Weng, I think only two peaks are possible. However, in order to give a credible answer, one should know whether the catalyst you are using is pure cobalt (III) oxide or if cobalt (III) oxide is e.g. an active ingredient in a more complex system.
Thanks for your reply, Dr. Yurii V Geletii .
I'm afraid I could not give out the amount of H2 consumed here as we do not have a CuO standard sample. But at least we could see the relative ratio of different peaks. Co3O4 is synthesized via the hydrothermal method with CoCl2 and urea. The XRD proves the pure Co3O4. The particle size is around 10-20nm by TEM.
The attached graph1 is my H2-TPR result regarding the Co3O4 and a series of Co3O4/zeolite (Co3O4/Z1-4, in-situ growth of Co3O4 with Zeolite1-4). The high-temperature peak of Co3O4 is very broad, while a shoulder could also be observed in the high-temp peak of Co3O4/Z1-4.
From the literature (attached graph2, Co/ZSM-5 by impregnation, DOI: 10.1007/s10562-020-03324-7), it roughly ascribed the peaks into two regions (lower than 350C, Co3+ to Co2+; and 350-500C, Co2+ to metallic Co), although several sharp peaks are observed. Could you please put some comments on it?
Thanks for your replies, Dr. Frank T. Edelmann and Dr. Mirosław Grzesik . Please see my further explanation to Dr. Yurii V Geletii above. Any comments are appreciated if you may have regarding my H2-TPR results.
I'm not an expert in this area. I guess that the surface of so small particles is not uniform. You may see several badly resolved peaks as a single broad peak. I would check the reproducibility of your data for one of the sample.
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