Novel Polymer–Silica Composite-Based Bifunctional Catalysts for Hydrodeoxygenation of 4-(2-Furyl)-3-Buten-2-One as Model Substance for Furfural–Acetone Aldol Condensation Products
Round 1
Reviewer 1 Report
In this paper, the authors study the hydrodeoxygenation of 4-(2-furyl)-3-buten-2-one, potentially obtainable from the aldol condensation of furfural and acetone.
The authors study the influence of catalyst composition on the product distribution. Different aspects are here considered, such as the metal loading and its chemical nature. Particular attention is devoted to the role of polymer-silica composite supports and their acidic properties.
The methodology and the data presented are sound and the conclusions are supported by the experiments. At the same time, the manuscript lacks of any morphological characterization technique or determination of the support acidity. I encourage the authors to complement their future studies with other characterization techniques.
Overall, this is a good quality paper that can be further improved by considering some minor comments (see below). For these reasons, I recommend this work for publication on Applied Sciences, pending the consideration of minor revisions by the authors.
Comment 1: Figure 2 is not useful in the main text. I recommend to move it in the SI.
Comment 2: The authors should discuss more in details their findings in the Discussion part. For example: i. Which catalyst/support composition promotes the most the formation of octane over the other products and why? ii. What is the influence of changing metal on the product distribution? It seems that using Ru instead of Pt or Pd considerably decrease the amount of C8-OH produced. The authors could comment on this evidence also on the basis of previous literature in the field.
Author Response
We thank the reviewer for their comments. We addressed them in the following fashion:
Comment 1:
The reviewer is right. The figure was moved to the ESI. Figure numeration was adapted accordingly.
Comment 2:
i) The formation of octane as product of the full hydrodeoxygenation (HDO) is affected by both the acid and redox properties of the catalyst. Their effect on the HDO process cannot be easily distinguished from one another. As discussed in the manuscript (chapter 3.2.2., lines 257-261) the acid catalyzed ring opening step seems to be rate limiting for the full HDO (to n-octane). This was also suggested in the literature and is cited ibidem. This means that increasing the hydrogenation (i.e. redox) activity further (via increasing metal-content) does not increase HDO-yield (as opposed to increasing acid site density by increasing polymer loading (see chapter 3.2.1)). A sentence was added to chapter 3.2.2. to further stress these findings (lines 259-261).
ii) The influence of the noble metal of bifunctional acid-redox catalysts was already investigated by Xia et al. Their findings are discussed in the framework of the current findings and are cited in chapter 3.2.3 lines 283-291. The outstanding performance of Ru as an HDO catalyst is also addressed in the recent literature. A corresponding remark and two citations were added to chapter 3.2.3 (lines 291-292).
Reviewer 2 Report
Title: Novel polymer-silica composite based bifunctional catalysts for
hydrodeoxygenation of 4-(2-furyl)-3-buten-2-one as model substance for
furfural-acetone aldol condensation products
Journal: Applied Sciences
The present manuscript deals with the hydrodeoxygenation of 4-(2-furyl)-3-buten-2-one using Nafion-silica catalysts. It is a very interesting topic and the manuscript is well-written and the conclusions supported by the results. Also, the experimental work is nicely described. The influence of different variables such as hydrogen pressure, Nafion content, Pt content and the metal type (Pt, Pd or Ru) has been studied. Therefore, I recommend its publication after minor revisions. Please, consider these comments:
- Compound E in Figure 1 has 9 carbon atoms. Please, revise it.
- Considering the strong acidity of these catalysts, are there any branched hydrocarbons among the reaction products?
- Please, provide a recyclability test.
Author Response
We thank the reviewer for their comments. We addressed them in the following fashion:
Comment 1 (Compound E in Figure 1 has 9 carbon atoms. Please, revise it.):
The reviewer is right. The figure was adapted accordingly.
Comment 2 (Considering the strong acidity of these catalysts, are there any branched hydrocarbons among the reaction products?):
No branched hydrocarbons were observed. They have also not been reported in the literature that was cited in the manuscript dealing with similar HDO-reactions.
Comment 3 (Please, provide a recyclability test.):
A recycleabilty test hast been added to the ESI.
