Assessment on the Effect of Sulfuric Acid Concentration on Physicochemical Properties of Sulfated-Titania Catalyst and Glycerol Acetylation Performance

Round 1

Reviewer 1 Report

Glycerol acetylation via sulfated titania catalyst: Effect of sulfonating concentration

Review decision

Major revision

General comments

The authors study the effect of sulfonation of a TiO2 support to improve the acidity of the material in glycerol to acetins reaction. The work is nicely done, with appropriate analysis and discussion. However, several points of attentions needs major revision:

The authors should include some repetition tests and analysis to attribute error bars and statistical significance to their results

The text needs major English syntax revision, the authors use a mix of present, past, active form and passive form. And the text results difficult to read and grammatically incorrect. The text cannot be accepted in its current state. I advise the use a proofreading service.

The authors needs to use a consistent citation style with numerical lists [n] instead of the author-year style ex: “According to Nda-Umar et al., (2020)”

Abstract

475 – and in abstract line 31 – The authors do not prove the higher thermal stability of the catalyst. Either remove such claims or proceed with an appropriate test to measure thermal stability of the catalyst under reaction conditions (a time on stream test measures deactivation). TGA measures thermal stability under non-reactive conditions. It is unknown if the catalyst would be stable overtime under reaction conditions.

Introduction

38 – space missing

39 – check additional space

Rephrase introduction – “…phenomena were occurred due to the emission of unwanted and harmful gasses to the 39 environment such as carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides 40 (NOx), and sulfur dioxide (SO2)[2].” – poorly written. Plus global warming and pollution are two separate problems, and in the sentence it seems to be the same.

43 - Biodiesel is a high-value fuel that has zero adverse effect on the ecosystem due to no 43 sulfur and no aromatics in its composition [2,4].- That’s incorrect. Biodiesel is more polluting that regular diesel from a CO2 emission. But it’s true that the absence of aromatics and sulfur compounds results in less toxic gases emissions.

37-46 – needs major English syntax revision

55 – wrong reference formatting [number]

58 – same

Fig 1 should be placed right below where it is first mentioned. Fig quality needs to be improved (resolution)

80 – rephrase sentence, or explain better

83-85 – check syntax

90 – same

96 – what’s a “using a non-microwave instant heating condition.”? Is it normal thermal heating?

100 – check syntax

107 – too many significant digits

Materials and methods

158-159 – “which use Cu Kα radiation source of 27.7 kW and electricity of 30 Ma,” those units and values are wrong and they make no sense

180 – it’s kV not Kv

181 – 1000x-10000x

186 – the t-plot ONLY measures the micropore volume (which are absent), not the overall pore volume of the cat. Be more precise. Use BJH for mesopore-volume. Or the final point of the adsorption branch as total pore volume (usually pores below 300 nm)

194 – use ml min-1

196-198 – incorrect “At this stage, the physisorption is occurred. To proceed with chemisorption, 196 the prepared sample was further heated to 950 °C” – rephrase and make it more clear

200 – “The amount of element in the synthesized catalyst was identified” – poorly written, rephrase

213 – “The reaction was carried out at 100 – 120 °C for 2 - 4 h UNDER REFLUX CONDITIONS.”

227-229 – do you use internal standard? Calibration curves? Please improve methodology discussion

Results and Discussion

Fig4 – it would be nice to quantify the amount of S=O and S-O bands.

262-264 – what about the dissolution of titania into titanium sulphate ?

271 – unclear

275-on – too many significant digits. The TGA lacks at least one repetition experiment to assign error bars and uncertainty. Repeat exp 20SA.

298-300 – I would mention as cause the formation of titanium sulphate or Titanyl sulfate. You should check those in XRD in 20SA

Fig 5 – Add a separate XRD plot of sample 20SA and search for titanium sulphate or Titanyl sulfate peaks, if present. Then discuss previous point.

404 – It’s table 3. The mentioned table 2 is referring to another table. Plus add also the other experiments in table 3 as follows: blank, TC, 5SA, 10SA, 15SA, 20SA

411 – “a significant improvement of the GC,” GC glycerol or instrument? Use a different acronym (GL)?

413 – “corrosion of the 413 equipment,” well, not really, you still use the same acid. remove

420 – table 3

Fig 10 – Also in this case, the authors have to repeat AT LEAST one experiment to assess repeatability and confidence intervals of the analysis. Preferably on the best material.

Conclusion

475 – and in abstract line 31 – The authors do not prove the higher thermal stability of the catalyst. Either remove such claims or proceed with an appropriate test to measure thermal stability of the catalyst under reaction conditions (a time on stream test measures deactivation). TGA measures thermal stability under non-reactive conditions. It is unknown if the catalyst would be stable overtime under reaction conditions.

References

appropriate

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

I send my comments in the report attached

Comments for author File: Comments.docx

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Review of the manuscript Catalysts-1451256 for the Authors: This article presents a study of preparation of titania catalysts used to catalyze glycerol acetylation into acetins. Sulfated Titania catalysts were prepared at different acid concentrations and the influence of concentration on catalytic performance is studied. One of the catalysts (15SA) showed high glycerol conversion (>90%) and high selectivity to TA (42%): how high are the values in comparison to the literature? Obtained results should be more connected and correlated to the various methods which were used in the sample characterization. In this way, not sufficient explanation is given, how does sulfate affect the catalytic performance, other than general, high acid site density and high thermal stability? Also, in the last sentence in the Conclusion it is stated “15SA catalyst shows the highest glycerol conversion (99.42 %) and highest selectivity of triacetin (41.98 %) as compared to TC, 5SA, 10SA and 20SA catalyst.” Why is there no explanation of the advantages of this feature? The language and writing style need to be worked on. In the present form the manuscript provides convincing results but the main goal should be more explained and followed through manuscript. I recommend major revision of the manuscript.

Title – Could be more accurate.

Abstract – First part general, however second part is expected to comment on results and give possible explanation: Should be more details why 15SA catalyst shows best catalytic performance among others catalysts in this study.

Introduction – Too long, offers information to the reader, however it seems it burdens the text and goal of the study. Needs to be rewritten with explanation why this study is needed based on the lack of literature in this area, with more insight. I am lost in reference lists, numbers and names, and different styles.

Materials and methods – Appropriate, but can be improved with more details. Also, Figure quality should be improved.

Results – FTIR – sulfation has successfully occurred in all samples. Could you comment on the amount of sulfate anions bounded? Trend regarding the acid concentration? Are Quantitative analysis and comments possible?

XRD – Crystallinity is decreasing with increase in concentration of sulfuric acid impregnated to titania. Explanation is given as “could be” related to acid concentration and covered surface with sulfate groups. For that extent of the intensity change that does not seem to be very convincing. Is there any other thing you think could be related? Please explain.

TGA-DTGA – different stages of decomposition are observed: Catalysts with 15 and 20 have 3^rd stage at highest temperature, as authors said, related to higher amounts of sulfate groups. Could we see the difference between SA15 and SA20 as we see SA15 has better catalytic properties? Level of instability?

SEM – Sulfur is observed in EDX, and concentration is increasing with samples, the same trend was observed with FTIR? Is agglomeration increasing also? Could you provide some additional differences? Please add bars and Figures are blurry.

Catalytic study: Why literature text placed in the part with results? For highest sulfur concentration SA20 it is stated that the catalyst is deactivated and as can be seen in SEM? How? Please explain. Especially correlation to samples S15 and S20 which are similar. Only selectivity to TA decreases from SA15 to SA20. For example, selectivity to MA and DA are similar. Parameter which should also be commented on is the conversion and why it decreases for highest acid samples. This was not mentioned?

Explanation as “15SA was selected for further studies because the researcher was more interested in getting higher 430 selectivity of TA” seems not sufficient and does not have scientific background.

Conclusions – As in Abstract, it is shown that 15SA catalyst shows best catalytic performance among other catalysts in this study: However, could you back it up with more possible explanations other than high acid site density and high thermal stability? Consider that a 20SA sample has higher sulfuric acid concentrations but does not perform better. Should be better connected and explained.

Literature – Based on the Introduction part, too long. Should be better used in the text and follow the text with the author's thoughts why this investigation is needed and will provide interesting results.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Check formatting of Fig 5 and XRF analysis table during final editing

Best regards

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Review of the manuscript Catalysts-1451256-R1 for the Authors: This article presents a revised study of preparation of titania catalysts used to catalyze glycerol acetylation into acetins. The presentation of the revision is not appropriate, namely the print-to-pdf of the word track-changes option becomes useless for the case of many changes. However, it is obvious the authors devoted some time and corrected the problematic issues of the last version. Please correct few remaining typos, and thereafter I can recommend the manuscript for publication.

Author Response

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Author Response File: Author Response.pdf