Production of Alkyl Levulinates from Carbohydrate-Derived Chemical Intermediates Using Phosphotungstic Acid Supported on Humin-Derived Activated Carbon (PTA/HAC) as a Recyclable Heterogeneous Acid Catalyst
Round 1
Reviewer 1 Report
This manuscript reports a Production of alkyl levulinates from carbohydrate-derived chemical intermediates using phosphotungstic acid supported on humin-derived activated carbon (PTA/HAC) as a recyclable heterogeneous acid catalyst. A series of characterizations and results of PTA/HAC prepared by this method are systematically described. This is an interesting and meaningful finding and the manuscript is well organized and can be accepted for publication after minor revisions.
1. Standard cards can make the PXRD data look more intuitive. It is recommended to add standard cards to the PXRD diagram to facilitate analysis.
2. Some pictures in the text are scattered. It is suggested that the pictures should be further spliced, and each group of pictures should be spliced neatly to make them look clearer and more beautiful.
3. This paper focuses on the samples with the best catalytic performance. In some performance analysis diagrams, such as Fig.5 and Fig.6, there is only 20% PTA / HAC-600 performance. Adding the performance of the other two groups of samples ( HAC-500, HAC-600 ) in the text is more likely to be more convincing. The reason for the best performance of 20% PTA / HAC-600 should be further explained.
4. It is shown in 3.2 that temperature is one of the important parameters of the reaction, so how does the change of temperature affect the reaction? How to affect the yield?
Author Response
Please find the attached file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript includes some good performance of phosphotungstic acid supported on humin-derived activated carbon (PTA/HAC) catalysts, and this work looks interesting. However, this manuscript is of some significance and maybe accepted after major revision.
1. The literature review regarding utilizing phosphotungstic acid on esterification reaction in the introduction section is inadequate. It is necessary to mention this aspect from the previous study (optional for authors): Journal of Environmental Chemical Engineering, 2019, 7, 103243; Catalysts 2023, 13, 40; Carbohydrate polymers, 2020, 237, 116128; Sustainable Chemistry and Pharmacy, 2023, 33, 101038; RSC Advances, 2021, 11, 33416-33424; Fuel, 2023, 334, 126768.
2. Although the manuscript is well defined, a minor grammar check is required.
3. The reference in the catalyst preparation should be provided.
4. The NH3-TPD patterns of different types of catalysts should be added.
5. The levels and factors of the independent variable in the esterification reaction procedure should be stated clearly. Also, how many repeated measurements?
6. It is strongly recommended that experimental error for all the data should be added (Figure 5, 6, 7 and Table 3 and Table 4).
7. In Section 3.3. Catalyst recyclability, the hot filtration test and ICP characterization is needed.
Author Response
Please find the attached file.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Authors have addressed my comments convincingly. Hence, the revised version may now be recommended for publication.
