Dehydrogenation of Ethanol to Acetaldehyde over Different Metals Supported on Carbon Catalysts
Round 1
Reviewer 1 Report
This work studies an important catalytic conversion of ethanol to acetaldehyde. Catalysts were synthesized by incipient impregnation of copper, cobalt, nickel, or ceria nitrate complex, followed by drying at 110 °C and thermal treatment in N2 at 350 °C. Prior to catalytic reactions, the catalysts were dried in N2 at 200 °C again and reduced in a hydrogen flow at 400 °C. The catalysts were tested at 250–450 °C in the dehydrogenation of ethanol. The results are potentially interesting but there are many issues that need to be addressed. Therefore, major revisions are recommended before possible publication.
1. The authors recognize the importance to minimize the acid sites that cause undesirable secondary reactions like aldol condensation, esterification, and ketonization to convert acetaldehyde. However, at the same time, the importance of high acidity (Lewis acid site?) is claimed in abstract and conclusions. Please modify the statements to avoid potential confusion.
2. Why does the N2 uptake by the activated carbon (ACC) shown in Figure 1 decrease as the relative pressure increases?
3. Please provide information about impurity contained in the original activated carbon as they potentially catalyze the reaction.
4. It is difficult to see peaks at T<400 °C in the NH3- and CO2-TPD data. Please show them clearly by changing the axis scale. If the huge peaks for the supported cobalt and nickel catalysts were not used to calculate the concentrations of acid and basic sites, please describe it in the figure caption in Figure 3.
5. The catalytic reactions were conducted using reduced catalysts. However, the XRD measurements were conducted in ambient air, which probably oxidized metals like copper if they were dispersed on a support. Please discuss this possibility. Wang et al. (ChemCatChem 2015, 7, 2846) observed only metallic copper in their mesoporous carbon-supported copper catalysts in their in-situ XRD data.
6. Ethanol conversions for ACC, Ce/ACC and Co/ACC are all quite low. If the reaction is conducted at much higher conversions, does selectivity to acetaldehyde decrease?
7. Nickel(II) cations in the hydrated form were inferred to be catalytically active species by pointing out the decomposition temperature of nickel(II) aqua complexes at 300 °C at the end of page 9. However, the catalyst seemed to be reduced at 400 °C, which probably decomposed them and reduced them.
8. Table 4 is not very helpful. Please merge the information with those in Figures 5 and 6.
Minor points
1. Change “activated carbons” at upper left corner to “catalysts” in Table 1.
2. “ACC” should be explained in Table 1.
3. Use appropriate significant figures for SBET in Table 1.
4. Font sizes of axis titles in figures are too small.
5. Figure 2 needs scale bars as it is difficult to see them on my file.
6. The column “source” in Table 5 should be omitted because it does not provide useful information. In addition, remove °C after the temperature values because they are redundant.
Author Response
1 | The authors recognize the importance to minimize the acid sites that cause undesirable secondary reactions like aldol condensation, esterification, and ketonization to convert acetaldehyde. However, at the same time, the importance of high acidity (Lewis acid site?) is claimed in abstract and conclusions. Please modify the statements to avoid potential confusion. | Thank you for your suggestion. We have modified the abstract and conclusion as suggested. | Pages 1,14 |
2 | Why does the N2 uptake by the activated carbon (ACC) shown in Figure 1 decrease as the relative pressure increases? | We have rechecked N2-isotherm by another instrument and edited it as seen in Figure 1. | Page 3 |
3 | Please provide information about impurity contained in the original activated carbon as they potentially catalyze the reaction. | We measured the elemental distribution and it indicated that the ACC consists of C = 90.81%wt, O = 9.02%wt and P = 0.18%wt. We have added this information in section 3.1.
| Section 3.1 Page 12 |
4 | It is difficult to see peaks at T<400 °C in the NH3- and CO2-TPD data. Please show them clearly by changing the axis scale. If the huge peaks for the supported cobalt and nickel catalysts were not used to calculate the concentrations of acid and basic sites, please describe it in the figure caption in Figure 3. | Thank you for your suggestion. We have edited both of NH3-TPD and CO2-TPD profiles as shown in Figures 3 and 4. | Pages 6,7 |
No. | Query | Response | Location of the revision |
5 | The catalytic reactions were conducted using reduced catalysts. However, the XRD measurements were conducted in ambient air, which probably oxidized metals like copper if they were dispersed on a support. Please discuss this possibility. Wang et al. (ChemCatChem 2015, 7, 2846) observed only metallic copper in their mesoporous carbon-supported copper catalysts in their in-situ XRD data. | Thank you for your suggestion. We used XRD measurement to prospect the metal oxide form of fresh catalysts. Despite, the catalysts were reduced to metal form. Moreover, in-situ XRD measurement was not available to analysis. | - |
6 | Ethanol conversions for ACC, Ce/ACC and Co/ACC are all quite low. If the reaction is conducted at much higher conversions, does selectivity to acetaldehyde decrease? | The selectivity to acetaldehyde possibly decreased with higher conversion of reaction (high temperature) due to decomposition of acetaldehyde. | - |
7
| Nickel (II) cations in the hydrated form were inferred to be catalytically active species by pointing out the decomposition temperature of nickel (II) aqua complexes at 300 °C at the end of page 9. However, the catalyst seemed to be reduced at 400 °C, which probably decomposed them and reduced them. | The catalyst was activated with H2 before testing at 400oC although this catalyst was not reduced at this temperature. Zielinski et al. [1], reported that nickel catalysts supported on activated carbon were reduced at higher temperature of 400oC. So, the species of this catalyst is Ni2+.
| Supplementary page 5 |
8
| Table 4 is not very helpful. Please merge the information with those in Figures 5 and 6 | We have added the data from Table 4 to Figures 5 and 6. So, we have removed Table 4. | - |
Minor | |||
1 | Change “activated carbons” at upper left corner to “catalysts” in Table 1. | We have edited this word in Table 1. | Table 1 |
2 | “ACC” should be explained in Table 1. | We have explained the data of ACC. | Page 4 |
3 | Use appropriate significant figures for SBET in Table 1. | We have been edited some of text. | Page 3 |
No. | Query | Response | Location of the revision |
4 | Font sizes of axis titles in figures are too small. | We have edited the font sizes of all figures already. | - |
5 | Figure 2 needs scale bars as it is difficult to see them on my file. | We have added scale bars in Figure 2. | Page 5 |
6 | The column “source” in Table 5 should be omitted because it does not provide useful information. In addition, remove °C after the temperature values because they are redundant. | We have already removed column “source” and °C after the temperature values in Table 4. | Table 4 |
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript has been investigated the dehydrogenation of ethanol to acetaldehyde over different metals supported on carbon catalysts.
The reviewer comments are:
1. In figure 3 the authors are asked to introduce the TPD results of support (ACC)
2. Why the catalysts were calcined at 350 °C if the reactions were carried out up to 400 °C?
The catalyst structure has been modified at 400 °C. The authors are asked to do calcination for one of the catalysts at 400-450 °C and to observe the physico-chemical modifications.
3. For the Cu / ACC catalyst, the authors should perform a stability test at 350 °C.
Author Response
Thank you for your careful review, comments and suggestions on our manuscript. The authors would like to respond your comments as follows;
No. | Query | Response | Location of the revision |
1 | In figure 3 the authors are asked to introduce the TPD results of support (ACC) | We are sorry for our mistake. We have added both of NH3-TPD and CO2-TPD profiles of ACC as shown in Figures 3 and 4. | Pages 6,7 |
2 | Why the catalysts were calcined at 350 °C if the reactions were carried out up to 400 °C? The catalyst structure has been modified at 400 °C. The authors are asked to do calcination for one of the catalysts at 400-450 °C and to observe the physico-chemical modifications. | We are sorry for this mistake. We have edited the calcined temperature to 400oC in experimental part. | Page 12 |
3 | For the Cu / ACC catalyst, the authors should perform a stability test at 350 °C. | We have added the stability test of Cu/ACC at 350oC as shown in Figure 9. | Figure 9 |
Author Response File: Author Response.pdf
Reviewer 3 Report
Review of the manuscript
Title: Dehydrogenation of ethanol to acetaldehyde over different metals supported on carbon catalysts
The present paper is devoted to ethanol dehydrogenation to acetaldehyde, in one step reaction, by using commercial activated carbon with four different metals doped catalyst. The topic and experiments seems reasonable, however interpretation of results and discussion are insufficient and sometimes with combination of lower level of English unclear and misleading. There is no explanation of different behavior of different catalysts. There is quite detailed characterization of textural properties of catalysts but the textural properties are not correlated with catalytic results. There is no discussion about type of active sites, possible mechanism, no effort to explain totally different results of composition obtained from SEM, TEM and ICP.
I have these specific remarks and questions:
· The results of catalytic tests given at line 148/149 are mentioned earlier than are presented in chapter 2.2. line 180. I recommend to change the structure of article - at first to present results of characterization and catalytic tests and then discuss it.
· Rounding off: In many cases- SBET, acidity, basicity, conversion etc., too many decimal places are given, but these have no meaning.
· Line 41: additional comma
· Line 74: Why “also” is used?
· Names of Tables and Figures: Full stop is often missing.
· Discussion of structural parameters:
Since the BET theory/method is not designed for the evaluation of surface area of microporous materials but of mesoporous-macroporous materials, thus, the application of BET method for AC-based samples is principally wrong. In this case it is necessary to show besides the volume of micropores, Vmicro, also the external surface (i.e. the surface area of mesopores and macropores). Please, present both these values in your manuscript. The SBET values can be presented in the manuscript for general comparison with other authors, but Vmicro and Sexternal values must be added to Table 1. Moreover, the external surface area is very important from the view of deposition of active species and correlation with catalytic data. Do you think that deposited metals can be also located in micropores?
In the case of ACC sample the nitrogen adsorption-desorption isotherm is not measured correctly as visible from Fig. 1, where the adsorbed amount of nitrogen (the isotherm) is decreasing from p/p0~0.4. This fact results in the wrong values of Vtot and Vmicro (shown in Table 1), when Vmicro is higher than Vtot. Please, re-measure the ACC sample. You have 3 possibilities:
1.) When you have small amount of ACC sample, decrease the cell volume by using the glass stick for the physisorption measurement.
2.) Increase the amount of ACC sample for physisorption experiment.
3.) Check the leaking of the instrument.
· Figure 1: Mistake in the name of Y axis
· Line 89-91: I do not understand the sentence.
· Line 96: “The highest copper metal”? Do you mean “the highest amount of copper”?
· Line 89 “all synthesized catalysts”
· Fig 3: Only the area form where acidity and basicity was evaluated should be shown – the peaks in low temperature region will be more visible. Results for ACC sample are totally missing!
· Line 140-141: why peak above 500 °C? The mentioned peaks are at 400 °C for Ni/ACC and below 500 °C for Co/ACC. What do you mean by decomposition of activated carbon? Decomposition into what? Why the other activated carbons are not decomposed? How is it possible to see the changes below 500 °C when the samples were activated before basicity and acidity measurements at 500 °C?
· Line 142: The sequence of figures in Supporting materials should also correlated with sequence of references given in the text.
· Line 143-144. In view of the diversification of peaks to 175-300 °C and above 300 °C, into which region does belong the peak visible for Co/ACC?
· Line 150-152, 223: Lewis acid sites can´t be simply determined from TPD NH3, so given correlation is not relevant. Moreover what is the meaning of given sentence?
· Line 155: There are only two samples given in order and one of them is not if Fig 3…
· XRD part: There are shown oxide phases visible from XRD. The pretreatment of catalyst before catalytic reaction is reduction by H2? What are the active sites for reaction?
· Line 174:” graphene”
· Line 221, 226-227: Why there is maximum conversion at 350 °C? I suppose that reaction is equilibrious and that is also the reason for further activity decrease. Please add equilibrium values to figure as well. The explanation based on agglomeration and pore blockage can´t be deduced from TGA…Or how did You see that form TGA?
· Line 222: nickel doped catalysts did not improve catalytic performance since it is not selective…
· Line 224-225: Some comment to mechanism should be added. The scheme 1 is unclear- what about H2?
· Line 229: Do you have Cu+ sites on your catalyst? How can you see that?
· Line 243-244: There is not any remarkable change visible from TGA at 300 °C for Ni/ACC sample. Moreover the samples were activated by H2 reduction before catalytic test at 400°C, so what kind of species are then present on the catalyst?
· Table 4: Please add how you expressed yield, since conventionally percent yield is calculated as actual yield divided by theoretical yield.
· Table 5 + line 264, 264: Why did you use for comparison conversion of Cu/ACC at 350 °C, when the other results are for lower temperatures? If we compare conversion at 250 °C, the catalyst activity seems to be worse than others, however for exact comparison also other reaction condition should be added (e.g. W/F).
· Line 295, 296: Why the upper temperature 550 °C, which is above calcination temperature, was selected for acidity evaluation?
· Supporting materials, Figure S2: The scale is missing.
· Supporting materials, Figure S3: The experimental for FTIR is missing. Why there are visible organic groups from FTIR on the fresh prepared catalysts?
Comments for author File: Comments.pdf
Author Response
Thank you for your careful review, comments and suggestions on our manuscript. The authors would like to respond your comments as follows;
No. | Query | Response | Location of the revision |
1 | The results of catalytic tests given at line 148/149 are mentioned earlier than are presented in chapter 2.2. line 180. I recommend to change the structure of article - at first to present results of characterization and catalytic tests and then discuss it. | We have been rearranged the manuscript by removal the catalytic discussion at line 148/149 to section 2.2 (catalytic test). | Page 10 |
2 | Rounding off: In many cases- SBET, acidity, basicity, conversion etc., too many decimal places are given, but these have no meaning. | Thank you for your suggestion. We have edited the values to 1 decimal. | Table 1-4 |
3 | Line 41: additional comma | Sorry from our mistakes. We have removed comma. | Line 41, |
4 | Line 74: Why “also” is used? | The sentence in Line 74 has corrected. | |
5 | Names of Tables and Figures: Full stop is often missing. | We are sorry from our mistakes. We have put all of full stop already. | |
6 | Discussion of structural parameters: Since the BET theory/method is not designed for the evaluation of surface area of microporous materials but of mesoporous-macroporous materials, thus, the application of BET method for AC-based samples is principally wrong. In this case it is necessary to show besides the volume of micropores, Vmicro, also the external surface (i.e. the surface area of mesopores and macropores). Please, present both these values in your manuscript. The SBET values can be presented in the manuscript for general comparison with other authors, but Vmicro and Sexternal values must be added to Table 1. Moreover, the external surface area is very important from the view of deposition of active species and correlation with catalytic data. Do you think that deposited metals be added to Table 1. Moreover, the external surface area is very important from the view of deposition of active species and correlation with catalytic data. | Thank you for your suggestion. We have re-measured the characteristics of pore structure of ACC sample and added Sexternal of all catalysts as seen in Table 1. In addition, we have further discussed the pore characteristics in manuscript. | Pages 3,4 |
No. | Query | Response | Location of the revision |
6
| Do you think that deposited metals can be also located in micropores? In the case of ACC sample the nitrogen adsorption-desorption isotherm is not measured correctly as visible from Fig. 1, where the adsorbed amount of nitrogen (the isotherm) is decreasing from p/p0~0.4. This fact results in the wrong values of Vtot and Vmicro (shown in Table 1), when Vmicrois higher than Vtot. Please, re-measure the ACC sample. You have 3 possibilities: · When you have small amount of ACC sample, decrease the cell volume by using the glass stick for the physisorption measurement. · Increase the amount of ACC sample for physisorption experiment. · Check the leaking of the instrument. | ||
7 | Figure 1: Mistake in the name of Y axis | We have edited the name of Y-axis in Figure1. | Page 3 |
8 | Line 89-91: I do not understand the sentence. | We have edited the sentence. | Lines 91-93 |
9 | Line 96: “The highest copper metal”? Do you mean “the highest amount of copper”? | Yes, We have edited this sentence for correctness. | Line 110 |
10 | Line 89 “all synthesized catalysts” | Please see the answer in No.8. | |
11 | Fig 3: Only the area form where acidity and basicity was evaluated should be shown – the peaks in low temperature region will be more visible. Results for ACC sample are totally missing! | We apologize in our mistake. We have added both of NH3-TPD and CO2-TPD profiles of ACC sample and clearly separated the data as shown in Figures 3 and 4. | Pages 6,7 |
12
| Line 140-141: why peak above 500 °C? The mentioned peaks are at 400 °C for Ni/ACC and below 500 °C for Co/ACC. What do you mean by decomposition of activated carbon? Decomposition into what? Why the other activated carbons are not decomposed? How is it possible to see the changes below 500 °C when the samples were activated before basicity and acidity measurements at 500 °C? | We have edited both of NH3-TPD and CO2-TPD profiles in the range of 40-400oC as follow No.11. | Pages 6,7 |
13 | Line 142: The sequence of figures in Supporting materials should also correlated with sequence of references given in the text. | We are sorry for our mistake. We have edited the sequence of references in all of figures.
| |
No. | Query | Response | Location of the revision |
14 | Line 143-144. In view of the diversification of peaks to 175-300 °C and above 300 °C, into which region does belong the peak visible for Co/ACC? | We have edited the manuscript in the acidity part. | Pages 7,8 |
15 | Line 150-152, 223: Lewis acid sites can´t be simply determined from TPD NH3, so given correlation is not relevant. Moreover what is the meaning of given sentence? | We have edited this sentence in manuscript. | Pages 7,8 |
16 | Line 155: There are only two samples given in order and one of them is not if Fig 3… | We have edited the manuscript in the acidity part. | Pages 7,8 |
17 | XRD part: There are shown oxide phases visible from XRD. The pretreatment of catalyst before catalytic reaction is reduction by H2? What are the active sites for reaction? | In XRD part, the fresh catalysts are in oxide forms. For this reaction, the oxide forms are transformed to the reduced form to catalyze the reaction. However, the in situ condition of reaction was reduced at maximum temperature of 400oC equally, whereas some catalysts were not completely in the reduced form. Moreover, Cu/ACC catalyst had Cu+1 that improved the catalytic reaction. | - |
18 | Line 174:” graphene” | Yes, Figure 4 indicates the graphene structure in ACC sample. | Page 8 |
19
| Line 221, 226-227: Why there is maximum conversion at 350 °C? I suppose that reaction is equilibrious and that is also the reason for further activity decrease. Please add equilibrium values to figure as well. The explanation based on agglomeration and pore blockage can´t be deduced from TGA…Or how did You see that form TGA? | The ethanol dehydrogenation to acetaldehyde is as following equation.
[2]
Kassim [3] reported the equilibrium conversion of ethanol (Xe) at 350oC, which is 97.6%. So, the maximum conversion (65.3%) at 350oC in this study was not equilibrious. After 350oC, the conversion of copper catalyst decreased because of agglomeration and pore blockage by coke, which are similar to other studies [2,3]. Moreover, the fresh Cu/ACC catalyst decomposed above 350oC proven by TGA as shown in Figure S1. So, this catalyst deactivated. | |
No. | Query | Response | Location of the revision |
20 | Line 222: nickel doped catalysts did not improve catalytic performance since it is not selective… | Nickel metal improved the ethanol conversion, but it is selective for ethanol dehydration to ethylene at temperature above 300oC.
| - |
22 | Line 229: Do you have Cu+ sites on your catalyst? How can you see that? | Before the ethanol reaction, Cu/ACC was reduced by H2 at 400 oC resulting in the reduction of bulk CuO (Cu2+) on surface at 160 oC as seen in TPR result in Figure S2 [4], while Cu2O (Cu+) is regularly reduced at high temperature around 580- 590oC [5]. Therefore, Cu/ACC has Cu+ sites that can improve the catalytic activity. | Page 10 |
23 | Line 243-244: There is not any remarkable change visible from TGA at 300 °C for Ni/ACC sample. Moreover the samples were activated by H2 reduction before catalytic test at 400°C, so what kind of species are then present on the catalyst? | Thank you for your suggestion. We have edited the manuscript. The catalyst was activated with H2 before testing at 400oC although this catalyst was not completely reduced at this temperature. Zielinski et al [1], reported that nickel catalysts supported on activated carbon were reduced at higher temperature than 400oC. So, the species of this catalyst is Ni2+. | Page 11 |
24 | Table 4: Please add how you expressed yield, since conventionally percent yield is calculated as actual yield divided by theoretical yield. | We added equation of yield, selectivity and ethanol conversion in the last part of section 3.4. | Page 14 |
25
| Table 5 : line 264, 264: Why did you use for comparison conversion of Cu/ACC at 350 °C, when the other results are for lower temperatures? If we compare conversion at 250 °C, the catalyst activity seems to be worse than others, however for exact comparison also other reaction condition should be added (e.g. W/F). | Thank you for your suggestion. We have edited the same reaction temperature with another study at 250oC. In addition, We have added WSHV value of each catalyst in Table 4. | Page 12 |
27 | Supporting materials, Figure S2: The scale is missing. | EDX picture in Figure S2 have not scale. It just shows the dispersion of element. | - |
28 | Supporting materials, Figure S3: The experimental for FTIR is missing. Why there are visible organic groups from FTIR on the fresh prepared catalysts? | From FTIR measurement, the fresh prepared catalysts after carbonization with N2 at 400oC were visible organic groups, which resemble other studies [6]. Moreover, the decomposition of organic groups of activated carbon appeared in the range of temperature 200-500oC [7,8]. | - |
References
[1] Zielinski, M.; Wojcieszak, R.; Monteverdi, S.; Mercy, M.; Bettahar, M.M. Hydrogen storage in nickel catalysts supported on activated carbon. International Journal of Hydrogen Energy 2007, 32 , 1024 – 1032.
[2] Church, J.M.; Joshp, H.K. Acetaldehyde by Dehydrogenation of Ethyl Alcohol. Industrial and Engineering Chemistry 1951, 1804-1811.
[3] Kassim, M.A. The transport process in the catalytic dehydrogenation of ethyl alcohol. Advancement in Science and Technology Research 2015, 2(2), 19-41.
[4] Sukarawan, N. Oxidative dehydrogenation of ethanol over Cu-AgLi/Al2O3 catalysts. Master of Engineering Program in Chemical Engineering, Chulalongkorn University, Bangkok, 2016.
[5] Goodarznia, S.; Smith, K.J. The effect of Cu loading on the formation of methyl formate and C2-oxygenates from CH3OH and CO over K- or Cs-promoted Cu-MgO catalysts. Journal of Molecular Catalysis A: Chemical 2012, 353–354, 58-66.
[6] El-molla, S.A.; El-Shobaky, G.A.; Ahmed, S.A.S. Catalytic Promotion of Activated carbon by Treatment with Some Transition Metal Cations. CHINESE JOURNAL OF CATALYSIS 2007, 28( 7), 611–616.
[7] Zeriouh, A.; Belkbir, L. Thermal decomposition of a Moroccan wood under a nitrogen atmosphere. Thermochimica Acta 1995, 258, 243-248.
[8] Orfao, J.J.M.; Antunes, F.J.A.; Figueiredo, J.L. Pyrolysis kinetics of lignocellulosic materials-three independent reactions model. Fuel 1999, 78, 349-358.
Round 2
Reviewer 1 Report
The authors addressed my concerns appropriately. The manuscript will be recommended for publication after the following corrections are made.
The first sentence in abstract needs to be corrected.
TPD in abstract should be defined.
Author Response
Reviewer A: Thank you for your careful review, comments and suggestions on our manuscript. The authors would like to respond your comments as follows;
No. | Query | Response | Location of the revision |
1 | The first sentence in abstract needs to be corrected. | Thank you for your suggestion. We have edited the first sentence in abstract as suggested. | Page 1 |
2 | TPD in abstract should be defined. | We have identified the NH3-TPD in abstract. | Page 1 |
Author Response File: Author Response.pdf
Reviewer 2 Report
Agree with publication in this form.
Author Response
Thank you for approved the publication.
Reviewer 3 Report
Review of the manuscript
Title: Dehydrogenation of ethanol to acetaldehyde over different metals supported on carbon catalysts
This is my second review of the above mentioned article. In the first review I have several questions and remarks. The authors answered and commented them and changed the text accordingly.
I have these specific remarks and questions:
· Rounding off: Are you sure that you can measure SBET, acidity, basicity, conversion with accuracy given at first decimal place? I think even first decimal place has no meaning for such a result.
· TPD profiles: Since the number of acidity and basicity differs for individual samples I suppose that in Fig 3 and 4, the y axis (scales) in figures are different for induvial samples, which is confusing for readers. Could you please use the same scale for all samples, or if it is necessary to have different (for better recognition) please add scale bar into the fig (even if a.u. is used) in order to see the differences among figures.
· Line 174: „The order of the total basicity is shown as: Cu/ACC > ACC“. Why just two samples are given?
· Line 186: ”grapheme” , mistake in spelling.
· Line 255-258: I do not agree with such a straightforward conclusion that there are only Cu+ species after catalyst reduction at 400 °C. In TPR-H2 profiles, it is clearly visible that significant catalyst reduction starts below 300 °C. Moreover can you calculate, from H2 consumption, how many Cu2+ species are reduced during reduction below 200 °C? It seems to be enormously lower amount than that which is reduced afterwards…
· Table 4: WHSV: I am wondering what meaning has the value given as gethanol/(h gcat). In the reference 41 there is given LHSV 4 ml/(h gcat). Depending on the ethanol inlet concentration, the volume flow can differ (so does the residence time and subsequently conversion) while keeping constant gethanol/(h gcat). For that reason it is better to express it as “ml/(h gcat)” together with ethanol inlet concentration.
· Supporting materials, Figure S2: I understand that it is dispersion. The scale bar is missing, since the reader does not know, what is the magnification (or given area) used for dispersion determination.
· Conclusions: Lewis acidity was not determined in this article.
Recommendation:
I recommend accepting present paper for publication after minor revisions.
Author Response
Reviewer C: Thank you for your careful review, comments and suggestions on our manuscript. The authors would like to respond your comments as follows;
No. | Query | Response | Location of the revision |
1 | Rounding off : Are you sure that you can measure SBET, acidity, basicity, conversion with accuracy given at first decimal place? I think even first decimal place has no meaning for such a result. | Thank you for your suggestion. We have edited the values to integer. | Tables 1, 2 and 4 |
2 | TPD profiles: Since the number of acidity and basicity differs for individual samples I suppose that in Fig 3 and 4, the y axis (scales) in figures are different for individual samples, which is confusing for readers. Could you please use the same scale for all samples, or if it is necessary to have different (for better recognition) please add scale bar into the fig (even if a.u. is used) in order to see the differences among figures. | Thank you for your suggestion. We have added scales of y-axis in figures 3 and 4. | Figures 3 and 4 |
3 | Line 174: The order of the total basicity is shown as: Cu/ACC > ACC“. Why just two samples are given? | Thank you for your suggestion. We have edited the order of all catalysts. | Line 182, page 8 |
4 | Line 186: ”grapheme” , mistake in spelling. | We are sorry for our mistake. We have edited to “graphene”. | Line 194, page 9 |
5 | Line 255-258: I do not agree with such a straightforward conclusion that there are only Cu+ species after catalyst reduction at 400 °C. In TPR-H2 profiles, it is clearly visible that significant catalyst reduction starts below 300 °C. Moreover can you calculate, from H2 consumption, how many Cu2+ species are reduced during reduction below 200 °C? It seems to be enormously lower amount than that which is reduced afterwards… | Thank you for your suggestion. We have calculated the H2 consumption for reduced Cu2+ is 518 µmol/gcat as following equation (1) and 8.1x1018 atoms of Cu2+ species are reduced as shown in equation (2). Ag2O + H2 → 2Ag + H2O (1) 2CuO + H2 → Cu2O + H2O (2) Thus, Cu/ACC catalyst has not only Cu+ species, but it contains both Cu+ and Cu2+ (not reduced) species. The suitable species to improve the ethanol dehydrogenation is Cu+. | Lines 262, 264 Page 11 |
No. | Query | Response | Location of the revision |
6
| Table 4: WHSV: I am wondering what meaning has the value given as gethanol/(h gcat). In the reference 41 there is given LHSV 4 ml/(h gcat). Depending on the ethanol inlet concentration, the volume flow can differ (so does the residence time and subsequently conversion) while keeping constant gethanol/(h gcat). For that reason it is better to express it as “ml/(h gcat)” together with ethanol inlet concentration. | Thank you for your suggestion. We have edited WSHV to LHSV by the equation as follow.
| Table 4, page 12 |
7 | Supporting materials, Figure S2: I understand that it is dispersion. The scale bar is missing, since the reader does not know, what is the magnification (or given area) used for dispersion determination. | We have edited EDX results in Figure S2. | Supplementary page 3 |
8 | Conclusions: Lewis acidity was not determined in this article. | We have deleted the word “Lewis” in conclusions. | Line 390, page 14 |
Author Response File: Author Response.pdf
