Oxidation in Flow Using an Ionic Immobilized TEMPO Catalyst on an Ion Exchange Resin

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript entitles “Oxidation in Flow using an ionic immobilized TEMPO catalyst on an Ion Exchange Resin” deals with an interesting topic. Prior to publication, the following points are recommended.

 

Further comparisons of the catalytic results to literature data are required: e.g., DOI 10.1039/c3gc40159f , “Intensification of TEMPO-mediated aerobic alcohol oxidations under three-phase flow conditions”.

 

The English usage and scientific terms need to be revised: multiples of “residence times” should be revised throughout the manuscript since it is not clear what that means. Do the authors mean time on-stream? Please write rigorously.

Other terms or sentences requiring revision for the sake of rigor and clarity: “ regeneration of reactivity”, “ oxidations are partially under harsh conditions”, “ significant for effectivity and with that also the costs”, “kinetic loading”, “regression of the specific bands”, “latter educt”. “explainable by the equilibration”.

 

The following sentence in the Conclusions is very confusing, “by equilibria within the batch, with kinetic 320 loading having the expected enhanced absorption of catalytic entities.”.

 

What if the fate of hydroxyl ions (from NaOH) in Figure 1?

 

A detailed mechanism involving Br- and the cocatalyst BIAB, besides TEMPO may be presented for benzyl alcohol oxidation.

 

Page 3: It is not clear why the loading is superior to 100%. Is the washing after the ion-exchange, inefficient? On the other hand, the excess TEMPO may leach because it is not in electrostatic interactions (the resin may have different types of supported species). This discussion is somewhat confusing.

 

Page 6: for clarity, “ln2/k” should be “(ln2)/k”.

 

Details on how the resins were packed in the column (filters, wool?) seem missing.

Details on how the swelling of the resin was measured and the pressure of the reactor seem missing.

Were the resins used as received for supporting TEMPO?

In section 3.5, please indicate the mass of resin, volume of glass column, volume of brine solution.

In section 4.6.2, it is missing: mass of resin, flow rates of TEMPO solution.

 

Please indicate the reactor volume in “residence time 𝜏𝑅 of 6 min”.

 

Results for control experiments without BIAB or without bromide may be presented.

Comments on the Quality of English Language

can be improved

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

 This work successfully prepared the Ion Exchange Resin supported TEMPO catalysts, and these samples demonstrated high conversion rates for the oxidation reaction. The topic is promising and the discussion is elaborate. The paper could be published as long as the following concerns are well addressed.

1. the format of the references should be consistent, some references have DOI but some not. Also the authors should take notice of the subscript of chemicals (i.e. TIO2), and the abbreviation of journal names.
2. As for FIgure 2, the authors states that “The substitution of chloride ions by TEMPO-4 sulfate results in swelling of the beads and increases the volume of the ion exchange resins by roughly 20%”, could the the author provide the particle size distribution or average particle sizes to quantify this finding. For me, the particle size is slightly changed after the loading.
3. As for Table 1, could the authors also include the selectivity or productivity data to make a better comparision. The oxidation reaction may also contain lots of side products, so that the selectivity is also important for the oxidation catalysts.
4. Achieving the 84% of the continuous reaction conversion for such reactions is very promising. Could the authors utlize the in-situ DRIFTS to analyze the active center of the TEMPO catalysts to better demonstrate the mechanism of the catalystic reaction?

 

Comments on the Quality of English Language

the paper contains some minor grammar mistakes, the authors should double-check the writings.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript describes the loading of TEMPO onto a typical anionic ion-exchange resin using ionic bonds, which facilitates easy desorption and reloading. This approach enables highly selective catalytic oxidation of alcohols to aldehydes. The continuous flow method allowed for 56% more TEMPO loading onto the ion-exchange resin compared to the batch method. The catalytic performance was evaluated in both batch and packed-bed reactor, showing the catalyst's versatility in catalyzing the Anelli oxidation reaction, with reaction-separation coupling also achieved in the packed-bed reactor (PBR). 

The overall content of the article is substantial, with a clear structure that demonstrates a certain degree of innovation and practical value. However, there are a few areas that could benefit from minor revisions to enhance the clarity and impact of the manuscript. Here are my suggestions for improvement:

(1) The manuscript should clearly differentiate whether the catalysts used in sections 2.2, 2.3, and 2.4 were obtained through batch or continuous flow methods. This differentiation is crucial for understanding the preparation and application of the catalyst.

(2) In section 2.3, it is noted that the catalytic activity decreases with repeated use. It would be beneficial to provide a detailed explanation of the potential reasons for this decline, such as the reduction in the loading of TEMPO.

(3) Section 2.4, which covers the reactions in the packed-bed reactor (PBR), would be benefit from a discussion on the impact of space velocity. Including this information would offer a more comprehensive understanding of the reaction in the PBR.

(4) Formatting and Minor Corrections:

Table 1 should be expressed in three-line form for consistency and clarity.

Some of the level 3 heading numbers in section 3.6 are incorrect and need to be revised.

 

Author Response

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Author Response File: Author Response.pdf