Synthesis of Catalytic Ni/Cu Nanoparticles from Simulated Wastewater on Li–Al Mixed Metal Oxides for a Two-Stage Catalytic Process in Ethanol Steam Reforming: Catalytic Performance and Coke Properties

Round 1

Reviewer 1 Report

After reading the work of Chen et al., I recommend it for publication upon addressing the following comments:

The introduction has various unlinked stories. The first paragraph is about the plating wastewater problem, the second and third paragraphs are about the hydrogen production from the ESR reaction, the fourth paragraph is about the catalyst support, and the fifth paragraph gets more complex. All these paragraphs are unlinked. The authors should restructure this information to make an introduction more easy-to-understand setting forth the problem and solution they proposed. The first questions that I ask are: what is the problem with the current methods or raw materials for producing catalysts? Why changing the current methods for producing catalysts for the method the authors propose?

In line 311, the authors say “had the ethanol steam firstly reacting…”, but did you mean “ethanol-steam feed”? I do not understand the phrase the way is written.

From line 355, related to the “prolonged” reaction time experiments, why did you test the catalysts only for 5 hours? 5 hour tests are not enough for the ESR since this reaction is usually very stable on various catalysts for many hours. Furthermore, the authors say that the 6Ni catalyst undergoes deactivation because of the decreases in the product yields, but this phenomenon should be treated as a partial deactivation of the catalyst for some reactions since the ethanol conversion remains at 100% despite of the observed change in the product distribution. The authors should analyze other products to see what happens over the course of the experiment (the catalyst partially deactivates for some reactions but it remains active for others, as reported in recent works: https://doi.org/10.1021/acs.energyfuels.1c01670).

For Table 3, the authors warn that the reaction conditions of one of the catalysts is different from the ones they use. Are the reaction conditions the same or similar for the other catalysts reported in the table?

In lines 378-382, the authors comment the results of Figure 11. Although they are conservative on their comments, from a shape perspective, the carbon deposited on the Ni/LiAlO₂@6Ni catalyst is also filamentous with different texture.

In the analysis of deposited carbon (coke), I am missing the quantification of deposited carbon by TPO measurements, which is routine analysis for this. The authors must have carried out TPO analysis in order to quantify and determine the combustion characteristics of deposited carbon. This is helpful to see the relevance of deposited carbon over the product yields and the nature of deposited carbon.

It is curious that the authors prefer to use FTIR spectroscopy instead of TPO analysis. FTIR spectroscopy can be confusing since it is difficult to obtain good spectra of spent catalysts with highly developed coke and the assignation of bands is not always straightforward. For example, the 1640 cm^-1 was assigned to the vibration of C=O bonds in acetyl groups, but it can be also assigned to the vibration of O-H bonds in liquid water. It is likely that this band is actually adsorbed water from the ambient. The authors should be cautious when making conclusions from the FTIR spectroscopy results.

Although the Raman analysis is acceptable, it could be improved by using references related to filamentous carbons. Both catalysts seems to form filamentous carbon with different textures, and different in texture may be associated to the formation and deposition of amorphous carbon in between the filaments. TPO analysis would be interesting to complement the Raman results, because it is expected that the TPO profile of the catalyst with major content of amorphous carbon exhibit a combustion peak at lower temperature.

I was expecting to read an explanation for the differences in the carbon formation on the Ni/LiAlO₂ catalyst using the two configurations. Can the authors be able to provide an explanation for this?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Reviewer’s Comments:

A manuscript entitled:

“Synthesis of catalytic Ni/Cu nanoparticles from simulated wastewater on Li-Al mixed metal oxides for a two-stage catalytic process in ethanol steam reforming: catalytic performance and coke properties” presented by:

[Yu-Jia Chen, Song-Hui Huang, Jun-Yen Uan, and Hao-Tung Lin]

was submitted to Catalysts (an MDPI Journal) for review on 24^th August 2021.

A: General Comments

1. The Title:

The title is appropriate for the article involving catalytic ethanol steam reforming (ESR), with special emphasis on the characterization of the residual coke properties.

2. Introduction:

The literature overview captures contemporary issues surrounding the use of layered double hydroxides (LDHs) as catalyst supports that possess desirable properties (high surface area, high thermal stability, high metal dispersion, and high basicity), which are suitable and favour complete and efficient ESR reaction.

3. Research Objective:

The authors will do well if the aim of the study is clearly stated, as in: “The objective of this study (research/work) is to…”  

4. Originality:

The novelty of the study is evidently specified as the work being the first to use aluminum lathe waste as a substrate of a structured catalyst to overcome the problems of pressure drop and poor heat distribution in the reactor bed.

5. Experimental Methods:

Catalyst synthesis by electrodeposition, catalyst testing for ESR, and materials characterization is adequately described and presented. The authors clearly state the use of Ni or Cu cations from “simulated electroplating wastewater” to synthesize the Ni/Cu nano-catalysts.

• Did the authors attempt to use “real wastewater” to synthesize the analogues of these novel catalysts?

6. The Body:

This study highlights the successful electrodeposition of Cu and Ni catalysts on the aluminum-lathe waste surface for ethanol steam reforming. The experimental set-up, catalyst synthesis, testing and characterization is well documented through scientifically sound methodologies, with notable findings.

7. Summaries:

The outlines of the study in the abstract and conclusion are well summarized to capture the main outcomes of the investigation. The “Conclusion” contains some very long complex sentences that can be shortened to keep the ideas separate and more concise. For example, Lines 565 – 568 can be broken into several sentences, with each sentence dealing with one aspect/idea at a time.

8. Conclusion: Good work that should be published, but with minor corrections.

B: Minor Issues

9. Line 164: The calculation of the value 1.44 is not clear from Table 1.
10. Line 189: Why is the Al peak at 2-theta angle of 45^o longer than that at 38^o in Figure 3(b)?
11. Lines 285, 304, 330, 362, and 364: What is ‘S/E’ in S/E = 10?
12. Line 290: Use “rises” instead of “rising” in “as the temperature rising from”.
13. Line 581: Change the word “can” to “to” in: “making the reaction can perform effectively”... to read: “making the reaction to perform effectively”.
14. Line 590: Revise the phrase: “…pre-reaction of ethanol steam with Cu catalyst...” because it is not clear what “ethanol steam” is.
15. The Supplementary Materials referred to in Figures S1, S2, S3, S4, S5 and S6 are not available in the manuscript:
    1. Lines 118, 121, 477, 498, 593 (S1);
    2. Lines 261 and 600 (S2);
    3. Lines 264, 273 and 603 (S3);
    4. Lines 368, 369, 370 and 608 (S4);
    5. Lines 393 and 608 (S5);
    6. Lines 463, 465, 467 and 611 (S6).
16. Line 604: in H2O; use the subscript for the 2.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors made most of the suggested corrections with minimum work. However, I still think they must set forth better the problem in the introduction.