Tailoring Properties of Metal-Free Catalysts for the Highly Efficient Desulfurization of Sour Gases under Harsh Conditions

Round 1

Reviewer 1 Report

This article is about the durable catalysts for the selective hydrogen sulfide oxidation to elemental sulfur in the treatment of natural gas. To address these goals new impregnation/thermal sequence for the N-C phase growth on SiC extrudates is proposed to find the ideal chemical and morphological properties of the N-C phase for the desulfurization process to occur. Undoubtedly, this experimental approach is interesting and difficult at the same.

However, I have a number of questions for the authors:

I think that the article title is overwhelmed. The authors should reduce and rewrite it.

The authors should rewrite the abstract of the article. I suggest removing part «Recent findings from our group have unveiled the excellent performance of N-C/SiC based composites obtained by the surface coating of the non-oxide ceramic with a mesoporous N-doped carbon phase, starting from commercially available and cheap food-grade building blocks. In a recent report, we have also demonstrated the high coke-resistance of these metal-free systems in a desulfurization process operated under harsh conditions (relatively high GHSVs and concentrations of aromatics as sour gas stream contaminants)» because the abstract should briefly contain the data presented in this article, and there is no need to describe the information from previous publications.

On page 12 “Although these authors cannot definitively rule out
the generation to a certain extent of low-melting coke deposits, they believe that ....” “These authors” ... Should there be a reference to the literature here? or what authors are we talking about?

What do the authors mean by the term "cheap and food-grade components"?

what are the possible ways to regenerate these catalysts?

Author Response

Referee 1#

Comments:

Referee 1# comment 01: This article is about the durable catalysts for the selective hydrogen sulfide oxidation to elemental sulfur in the treatment of natural gas. To address these goals new impregnation/thermal sequence for the N-C phase growth on SiC extrudates is proposed to find the ideal chemical and morphological properties of the N-C phase for the desulfurization process to occur. Undoubtedly, this experimental approach is interesting and difficult at the same.

Answer 01: We appreciate the positive aptitude of this reviewer and we would like to thank him/her for the positive evaluation of our manuscript.

 

Referee 1# comment 02: However, I have a number of questions for the authors:

I think that the article title is overwhelmed. The authors should reduce and rewrite it.

Answer 02: To meet with this referee the manuscript title has been changed as follows: “Tailoring Properties of Metal-free Catalysts for the Highly Efficient Desulfurization of Sour Gases under Harsh Conditions”

 

Referee 1# comment 03: The authors should rewrite the abstract of the article. I suggest removing part «Recent findings from our group have unveiled the excellent performance of N-C/SiC based composites obtained by the surface coating of the non-oxide ceramic with a mesoporous N-doped carbon phase, starting from commercially available and cheap food-grade building blocks. In a recent report, we have also demonstrated the high coke-resistance of these metal-free systems in a desulfurization process operated under harsh conditions (relatively high GHSVs and concentrations of aromatics as sour gas stream contaminants)» because the abstract should briefly contain the data presented in this article, and there is no need to describe the information from previous publications.

Answer 03: To comply with this referee claim, we re-write the abstract accordingly. The shortened abstract is now reported in the revised version of our manuscript.

 

Referee 1# comment 04: On page 12 “Although these authors cannot definitively rule out the generation to a certain extent of low-melting coke deposits, they believe that ....” “These authors” ... Should there be a reference to the literature here? or what authors are we talking about?

Answer 04: In this sentence, we talked about ourselves in third-person. Thus, no literature references are needed there.

 

Referee 1# comment 05: What do the authors mean by the term "cheap and food-grade components"?

Answer 05: With "cheap and food-grade components" we refer to the three “ingredients” used for preparing the catalyst, i.e.: 1) D-glucose, the most common and simplest sugar, 2) citric acid, a natural component present in several fruits and vegetables and in particular in citrus fruits such as lemon and 3) ammonium carbonate, commonly used as a leavening agent. These elements are ubiquitous in common food and of course they are cheap as you can buy them with the appropriate purity directly at the supermarket.

 

Referee 1# comment 06: what are the possible ways to regenerate these catalysts?

Answer 06: As already demonstrated in our previous papers on the topic,[1] these catalysts can be regenerated under oxidative conditions (typically with 5 vol.% of O₂ at T > 300 °C) and they entirely recover their initial catalytic activity. In this paper, however, we have demonstrate that the catalyst does not suffer of any irreversible deactivation caused by the generation of coke deposits but, instead, toluene removal from the stream is enough to entirely recover the pristine catalyst desulfurization activity.

 

[1] Catal. Sci. Technol., 2020, 10, 5487-5500

Reviewer 2 Report

In this article the optimization of the SiC thermal treatment se-quences for the control of the surface chemistry and morphology of a highly N-rich carbon phase coating for desulfurization of sour gases is presented. This work is interested and should be published.

Author Response

Referee 2#

Referee 2# comment 07: In this article the optimization of the SiC thermal treatment se-quences for the control of the surface chemistry and morphology of a highly N-rich carbon phase coating for desulfurization of sour gases is presented. This work is interested and should be published.

Answer 07: We really thank this reviewer for his/her positive comments on our manuscript.

Round 2

Reviewer 1 Report

 On page 9, line 372: “Although these authors cannot definitively rule out the generation to a certain extent of low-melting coke deposits, they believe that ....” 

 When the authors talk about ourselves in the third-person, it confuses the reader and me. To be clear, you should rewrite in the first person.

I received comprehensive answers to my questions.
I wish the authors success in their scientific research.

Author Response

We understand the concern of this reviewer and we rephrased the sentence accordingly (in first-person). 

The new sentence appears now as follows:

"Although we cannot definitively rule out the generation to a certain extent of low-melting coke deposits, we believe that such a little shoulder in the TGA profile of the exhaust sample is reasonably ascribable to the oxidation of sulfur residues."

We really hope that this amendment will meet with this reviewer. 

Kind regards, Giuliano Giambastiani