One-Step Ethanol Conversion for 1,3-Butadiene Synthesis over Two-Dimensional VMT-SiO₂ Nanomesh Loaded with Magnesium and Copper Oxide

Round 1

Reviewer 1 Report

1. What are the advantages of the current method compared to other on-purpose production methods

2. What is the ramping rate utilizing for calcining the catalysts

3. The authors need to revise the equations used for calculating the conversion and selectivity

4. There is need for correlating the catalytic properties (based on characterization results) to the catalytic performance obtained

5. The authors should provide the possible reaction mechanism for the ethanol to 1,3-butadiene conversion process 

The authors should revise the entire manuscript for grammatical and typographical errors

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors prepared a series of vermiculite-based materials modified with SiO2, CuO, and MgO, and evaluated their catalytic performances in the direct conversion of ethanol into 1,3-butadiene in flow conditions. The results indicate that an optimal balance between acid and basic sites is critical to achieve high 1,3-butadiene productivity. The authors consider the calcination procedure of the catalysts as the pivotal factor affecting such balance.

The topic of this manuscript is timely since it deals with the production of a fundamental chemical building block from a potentially renewable source like ethanol.

Although silica-magnesia catalysts modified with copper are not new for this application, the use of vermiculite is interesting since it’s a readily available material (indeed the authors purchased it) and offers a tailorable platform to shape active catalysts.

However, the manuscript in the present form has some issues that need to be addressed before publication.

Here is a bulleted list of minor issues:

-          The English language must be checked—some parts are quite hard to read.

-          The quality of the figures is low, and it is hard to read them, especially in black and white coloring.

-          Some citations are incorrectly reported in the text, both in the writing and in the content. For example, Page 1 rows 36 and 44, Carlo and Trees are the first names of the authors. Please use surnames. In page 2, besides the poor English language, I guess the authors meant that ZrO2 weakens the dehydration ability of Zn (II) and not of ethanol.

-          The catalyst preparation section is not clear and should be rewritten in a better way.

-          About the test unit, what is the internal diameter of the reactor? And were the catalysts in powder or pelletized form during the tests?

-          In Page 5 row 202, can the authors explain what the mean with, quote, “slight clusters”?

-          I page 7 row 268, why an infrared adsorption peak should show, quote, “similar strikingly adsorption peaks”? What do the authors mean by “strikingly”?

-          In Figure 7 the Y axis does not account for the STY.

-          In Figure 8a check both the Y axis.

-          Reference 26 is impossible to retrieve. Please substitute it.

Major issues:

-          The authors stressed in several passages that CuO is in the form of clusters but could see the corresponding XRD peak. EDX analyses on a wide area are needed to clarify this discrepancy and would be insightful to ascertain the presence of isolated Cu sites, as claimed by the authors on the sole basis of UV-Vis analyses. CO infrared analyses are highly recommended in these cases. The same applies to verify the location of MgO.

-          The NH3-TPD analyses show that upon modification of the VMT-SiO2 material with MgO the acidity increases. That is curious as MgO is notoriously a basic material, particularly considered that a 10 wt.% of MgO loading results in a roughly 5-fold increase in the number of acid sites (Table 2). Please explain.

-          Another thing about the NH3-TPD analyses: by looking at Figure 6a, one would expect only minor differences in total number of acid sites in all the modified VMT-SiO2 materials, and yet in Table 2 major differences are reported. Please explain.

-          Page 10 rows 362-373. The authors state that, quote, “CuO poisons the majority of acid sites”. What is the poisoning of an acid site? What is then responsible for such acid sites? Maybe MgO (!?). Please explain.

-          In Table 4 the catalytic results are listed. I need clarification from the authors because the 1,3-BD STY does not seem to reflect the conversion and selectivity numbers. Specifically, CuO/MgO-VMT-SiO2 (450℃) has a conversion of 15.8% and a 1,3-BD selectivity of 36.7 with STY of 91.4 g·kgcat-1·h-1, whereas CuO/MgO-VMT-SiO2 (500℃), which converts twice as much with a higher selectivity, produces only 70% more 1,3-BD. The same applies to CuO/MgO-VMT-SiO2 (550℃). Unless it’s a (repeated) typo, could it be that the authors used the same volumes of catalysts? In doing so, however, the amount of catalyst might have been different due to different densities. If that is the case, reactions with the same amount of catalyst should be performed.

-          Did the authors verify that the reaction conditions used are in the kinetic regime? This is particularly relevant considering the precedent comment.

-          Long run reaction tests should be reported to investigate the stability of the catalysts or, at least, of the best performing one.

-          There is no comparison whatsoever with previous works about the catalytic activity. Please add it and discuss accordingly.

There is a relavant number of typos and some phrases are hard to read. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors addressed all the points raised during the review process and thus the paper can be published. 

The quality of English language improved from the original version of the manuscript.