Comparative Catalytic Performance Study of 12-Tungstophosphoric Heteropoly Acid Supported on Mesoporous Supports for Biodiesel Production from Unrefined Green Seed Canola Oil
Round 1
Reviewer 1 Report
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Author Response
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Reviewer 2 Report
The present article dealing with the incorporation of HPW on γ-Al2O3, MAP, and MAS for simultaneous esterification and transesterification reactions of biodiesel production using unrefined green seed canola oil, is in the overall well written and contains interesting results. However, in the introduction some important references on the use of heteropolyacids are missed. Please improve the introduction and discussion citing some recent references dealing with HPW supported on different oxides, such as TiO2, ZrO2, CeO2, SiO2, highlighting the effect of the interaction of the heteropoliacids with the supports.
The part related to NH3-TPD must be revised. The only TCD is not appropriate for the evaluation of the NH3 desorbed, another detector such as QM or specific analysers should be considered. Moreover, no details about experimental details are given. So the suggestion is to revise such part.
Author Response
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Reviewer 3 Report
Manuscript Number: catalysts-1676411
Full Title: Comparative catalytic performance study of HPW/MAP and HPW/MAS catalysts in simultaneous esterification and transesterification of unrefined green seed canola oil
Remarks to the Authors:
The authors studied the esterification and transesterification of unrefined green seed canola oil over HPW/MAP, HPW/MAS, and HPW/γ-Al2O3 catalysts in a 100 mL Parr reactor at 200 °C with 600 rpm for 7 h under 4 MPa. The authors characterized synthesized catalysts by BET, XRD, NH3-TPD, TGA, and TEM analyses. The highest biodiesel yield (82.3%) was achieved over the HPW/MAS catalyst, which possessed the highest acidity and surface area. I think that the topic of this investigation is in the scope of MDPI Catalysts and can be interesting for the journal audience. At the same time, I have found some weaknesses in the manuscript body. In my opinion, this work can be considered for publication in MDPI Catalysts only after major revision. Please find my comments below.
- The title must be corrected/improved. The authors did not mention the HPW/γ-Al2O3 Moreover, I recommend the authors decrypt or exclude abbreviations in the title.
- The authors must mention in the abstract obtained product (biodiesel).
- Did the authors analyze the real catalyst composition? I think this information should be provided in Table 2. ICP-OES or XRF analyses can be useful.
- How the authors can explain the average pore size increasing for the HPW/MAP catalyst compared to MAP (Table 2), while for the other HPW catalysts it was observed opposite effect?
- How the pore size distribution curves were built? Based on adsorption or desorption volume? This information must be presented in the manuscript.
- The carbon and/or mass balance must be provided.
- The authors should decrypt the type of percent for the obtained product yield.
- I recommend the authors compare their achieved catalytic results with well-known literature data in a table format and include it in the Results and Discussion section.
- How the authors can explain decreasing of total acidity (Table 3) over the HPW/Al2O3 catalyst while other HPW supported catalysts showed reverse results?
- How the authors can make a statement about Bronsted acidity based on NH3-TPD? For these conclusions, the authors should utilize a Pyridine-DRIFTS technique.
- What about the Lewis acid sites (LAS)? Why did the authors exclude LAS from the discussion? This must be explained. Moreover, the authors mentioned Lewis site in the proposed mechanism of HPW immobilization on MAS.
- The authors said: “According to them, the intensity of peaks in the range of 100-300 °C, which is related to the mild Bronsted acidity”. What about the weak acid cites in this temperature range? Why did not the authors discuss it? This needs to be elucidated.
Author Response
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Round 2
Reviewer 1 Report
The authors have been cleared all my piont.
Author Response
We thank the Reviewer for the nice consideration.
Reviewer 2 Report
The authors tried to improve their manuscript and new references have been added. However, the characterization of the acidic properties is still very lacking and the manuscript cannot be accepted in the current form. The quality of figures 6 (a, c) is very poor, the signals are really noisy. The authors revised the experimental part, specifing that :"the spectrum for the desorption of NH3 was recorded with TCD with temperature rise 169 from100°C to 700°C for the evaluation of the NH3 desorbed and total acidity" but the signals are stopped at 600 °C. On the other hand considering that supported HPWs have been calcined at 450 °C, a TPD process at temperature > 450 °C doesn't make a sense, unless the authors investigate the thermal stability of their samples at T > 450 °C. Other point: XRD patterns are very poor, except that one for HPW. Please, register again and correct the strange behaviour at 2 theta < 10°.
Author Response
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Reviewer 3 Report
Manuscript Number: catalysts-1676411R1
Full Title: Comparative catalytic performance study of 12-tungstophosphoric heteropoly acid supported on mesoporous supports for biodiesel production from unrefined green seed canola oil
Remarks to the Authors:
The authors significantly improved their manuscript but still some improvements are needed. Please find my comments below.
1. The authors should provide the quantification of Pyridine-DRIFTS results and include these results in Table 3 with additional columns such as BAS, LAS, LAS/BAS. To present just spectra in Fig. 3 is not enough. Also, these results should be discussed and compared with NH3-TPD results. How the authors can explain so big discrepancy between Pyridine-DRIFTS and NH3-TPD analyses for the HPW/Al2O3 and HPW/MAS catalysts?
2. Please include more details about the Pyridine-DRIFTS analysis to the 2.6. Catalyst characterization techniques.
3. The authors said: “Larger average pore size of HPW/MAP compared to that of MAP could be due to the occupation or blockage of the mesopores of the support with HPW anions”. But this statement is against the logic. How the average pore size can INCREASE after occupation or blockage of the mesopores of the support? Why the authors did not observe the same effect for the HPW/Al2O3 and HPW/MAS catalysts? Maybe the authors just have experimental errors for the HPW/MAP catalyst? According to the reference that the authors provided, there was mentioned about “the development of abnormalities in the pores”. It can be another explanation.
Author Response
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