Defect-Rich Nickel Nanoparticles Supported on SiC Derived from Silica Fume with Enhanced Catalytic Performance for CO Methanation

Round 1

Reviewer 1 Report

The current manuscript describes the synthesis of silicon carbide ceramics using waste fumed silica, Ni/SF-SiO₂ and defect-rich Ni/SF-SiC catalysts using conventional impregnation method. The authors demonstrated that the presence of Ni vacancies could enhance the adsorption energy of CO and H₂, which in turn can improve the catalytic performance for methanation. The authors also compared the catalytic performance of Ni/SF-SiO₂ with Ni/SF-SiC, which concluded that Ni/SF-SiC catalyst exhibited higher reactivity and stronger anti-sintering. The authors suggested that this could be due to the high thermal conductivity of SF-SiC and good dispersion as well as stronger metal-support interaction in Ni/SF-SiC catalyst. In overall, the manuscript is written scientifically and systematically with comprehensive characterization and discussion. The manuscript looks sufficiently suitable for publication in this journal with some revisions as indicated below.

(1) In Fig. 1, what does it mean by the 'thermodynamic' system and why it has been compared with other catalysts (Ni/SF-SiO₂ and Ni/SF-SiC)? Wouldn't it be better to provide the catalytic performances data of Ni/SF-SiO₂ and Ni/SF-SiC only rather than showing all the data?

(2) It might be necessary to include N₂ adsorption data and corresponding pore size distributions for the given catalysts. 

(3) The authors mentioned that the catalysts were characterized with XRF in the Experimental Section, but the actual XRF data was not provided in the manuscript. 

(4) English corrections are necessary for clearance. For example, on page 10, line 300, the word 'polluted' should be corrected to 'pollution'. 

Author Response

Dear Reviewers,

We greatly appreciate the time and effort you’ve spent in reviewing our manuscript titled“Defect-rich nickel nanoparticles supported on industrial waste silica fume during metallic silicon production with enhanced carbon monoxide methanation performance”, and your constructive suggestions are valuable to our manuscript and future research work. According to the reviewers’ comments, we have made further analysis and revised the manuscript carefully. We hope the Editor and Reviewers will be satisfied with the revisions for the original manuscript. The followings are the reviewers’ comments and the corresponding point-by-point responses to the concerns.

(1) In Fig. 1, what does it mean by the 'thermodynamic' system and why it has been compared with other catalysts (Ni/SF-SiO2 and Ni/SF-SiC)? Wouldn't it be better to provide the catalytic performances data of Ni/SF-SiO2 and Ni/SF-SiC only rather than showing all the data?

Reply: Thank you very much for the reviewer`s helpful comments to our manuscript. The meaning of “thermodynamic” is “the thermodynamics equilibrium value”, and this is the maximum value obtained by theoretical calculation. In comparison with the theoretical values, we could further find that the reactivity of Ni/SF-SiC are better than Ni/SF-SiO₂. 

(2) It might be necessary to include N2 adsorption data and corresponding pore size distributions for the given catalysts. 

Reply: We thank the reviewer’s comment. As suggested, table 2 has been rearranged.

¹ Surface area derived from BET equation. ² Obtained from BJH desorption average pore volume and pore diameter. ^2* Obtained from BJH adsorption average pore volume and pore diameter. ³ Calculated according to equation D_Ni=∑_NiD_i³/∑_NiD_i² from HRTEM. ⁴ Estimated from the XRD diffraction peak (2θ=44.6) using the Scherrer equation. as follows: L= 0.9λ_kα1/B_(2θ)cosθ_max. Where L denotes the average particle size, 0.9 is the value in radians when B_(2θ) is the full width at half maximum (FWHM) of the peak, kα1 is the wavelength of the X-ray radiation (0.15406 nm), and max is the angular position at the (1 1 1) peak maximum of Ni.

(3) The authors mentioned that the catalysts were characterized with XRF in the Experimental Section, but the actual XRF data was not provided in the manuscript. 

Reply: We are very sorry for our negligence of this, and the XRF date has been checked and added. As shown in the part of 3.1 preparation of catalysts.

The detail for waste silica fume (Hesheng Silicon Industry Co., Ltd. in Western Xinjiang, China) was tested by X-ray fluorescence (XRF) are: (wt %) SiO₂ 97.55, CaO 0.81, K₂O 0.43, Al₂O₃ 0.42, MgO 0.31, SiO₃ 0.12, Na₂O 0.11, Fe₂O₃ 0.08, P₂O₅ 0.06, and others 0.11.

(4) English corrections are necessary for clearance. For example, on page 10, line 300, the word 'polluted' should be corrected to 'pollution'.

Reply: We thank the reviewer for pointing out the writing error. And as suggested, we have checked and corrected the mistakes in our manuscript, as followings.

A large quantity of silica fumes deserted in industrial disposal with the development of metallic silicon industry, which not only bringing about resources wasting, but also results in serious pollution by the dust and powder.

We attached a copy of the revised manuscript at the end of this document. This copy is the same as the revised manuscript, except that some parts are colored to make the revisions notable.

We hope the Reviewers and the Editors will be satisfied with the revisions for the original manuscript.

Thanks and Best regards!

Yours Sincerely,

Feng Yu

Email: [email protected].

Author Response File: Author Response.pdf

Reviewer 2 Report

This article compares two Ni loaded silicon carbide based catalysts, using waste silica fume as precursors. The novelty of the article is undoubtedly reasoned. However, the publication of this paper has many drawbacks. First of all, I would recommend to the authors the review of the English language and style with a native English speaker, due to the several mistakes that can be detected along the paper. Units (separated or not), symbols, section numbers (3.1 is twice, 5. conclusions...)... must be revised.

Going on the presentation quality, I would first recommend the publication of the characterization results and the reaction results. Statements in lines 77-82 are not supported with any citation and previous discussion is needed.

Also, for reaction results discussion CH4 production must be included, instead CH4 selectivity. Product selectivity allows the comparison at different temperature for both catalysts easily, instead deciding if high selectivity values are the best option when we have low activity values. Indeed in Table 1, optical temperature is included. I guess this is the optimal temperature, which would be deciding by the temperature where maximum amount of CH4 is produced. Furthermore, is C balance closed at the reactor outlet? Which are the rest of the products?

Figure 3 must be discussed more deeply, 6 lines are not enough to describe what can be observed in those 6 Figures.

From N2 adsorption-desorption results, Ni addition effect is not well described. Which is the main reason to observe and increase of SBET and Pore Volume in SiF-SiO2 catalyst and a decrease in SF-SIC catalyst? The discussion is vague and unintelligible.

From TPR results, it is stated that below 550 ºC, a great mass of NiO species in both catalysts could be reduced by hydrogen (lines 175-176). This is not true. The amount depends of the reduction temperature and a considerable amount is not reduced until temperature reaches 400 ºC.

XPS results are also unintelligible. A Table with each Ni specie quantification must be included in order to make a good description of what is happening in each catalyst. Instead, qualitative results are also difficult to analyze in this sense.

6 images are included in Figure 7; probably c-d Figures are not necessary.

Finally, Scherrer equation, CO conversion and CH4 production equations must be included in experimental section.

Therefore, I would not recommend the publication this manuscript.

Author Response

Dear Reviewer,

We greatly appreciate the time and effort you’ve spent in reviewing our manuscript titled“Defect-rich nickel nanoparticles supported on industrial waste silica fume during metallic silicon production with enhanced carbon monoxide methanation performance”, and your constructive suggestions are valuable to our manuscript and future research work. According to the reviewers’ comments, we have made further analysis and revised the manuscript carefully. We hope the Editor and Reviewers will be satisfied with the revisions for the original manuscript. The followings are the reviewers’ comments and the corresponding point-by-point responses to the concerns.

(1) the English language and style with a native English speaker, due to the several mistakes that can be detected along the paper. Units (separated or not), symbols, section numbers (3.1 is twice, 5. conclusions...)...

Reply: Thank you very much for the reviewer’s helpful comments to our manuscript. As suggested, we have had the English checked and corrected carefully through the whole manuscript.

(2) Statements in lines 77-82 are not supported with any citation and previous discussion is needed.

Reply: Thank you very much for the reviewer’s helpful comments to our manuscript. As suggested, we have deleted this part, and discussed it in the other part of the paper. Meanwhile, we have reorganized the cited literature.

(3) Also, for reaction results discussion CH4 production must be included, instead CH4 selectivity. Product selectivity allows the comparison at different temperature for both catalysts easily, instead deciding if high selectivity values are the best option when we have low activity values. Indeed in Table 1, optical temperature is included. I guess this is the optimal temperature, which would be deciding by the temperature where maximum amount of CH4 is produced. Furthermore, is C balance closed at the reactor outlet? Which are the rest of the products?

Reply: Thank you very much for your helpful comments to our manuscript. As suggested, CH₄ yield with the different reaction temperature at 0.1 MPa and GHSV of 18000 mL·g^-1·h^-1 was added in Fig.1. And the reaction temperature in Table 1 was explained. In fact, as the reaction temperature raised to 300 ^oC, a small amount of carbon dioxide is produced.

Fig.1. Catalytic performances of catalysts in CO methanation under different reaction temperature at 0.1 MPa and GHSV of 18000 mL·g^-1·h^-1: (d) CH₄ yield of Ni/SF-SiO₂ and Ni/SF-SiC.

(4) Figure 3 must be discussed more deeply, 6 lines are not enough to describe what can be observed in those 6 Figures.

Reply: We thank the reviewer’s comments to our manuscript and positive evaluation of our study. As suggested, We have re-written this part. As the followings:

 From the SEM and HRTEM images, we could clearly observe the fine spherical particles of silica fume, as shown in Fig. 3a and 3c. And the images of the as-prepared SF-SiC powder were shown in Fig. 2b and 2d, which reveal that SF-SiC has porous and irregular particles morphologies, this is due to the large amount of heat released by magnesium thermal reaction, which seriously destroyed the morphology and structure of SF-SiO₂, and at the same time, the thermal effect has greatly improved the values of specific surface areas and average pore volumes of SF-SiC, and such results could also be seen from Table 2. And the larger specific areas of SF-SiC support may could provide more attachment sites for the active component. Compering with the amorphous silica fume, the HRTEM image (Fig. 2f) shows that the SF-SiC has good crystallinity with distinct lattice fringes of 0.251 nm and 0.262 nm corresponds to the SiC (102) and (101) planes, respectively.

(5) From N2 adsorption-desorption results, Ni addition effect is not well described. Which is the main reason to observe and increase of SBET and Pore Volume in SiF-SiO2 catalyst and a decrease in SF-SIC catalyst? The discussion is vague and unintelligible.

Reply: We thank the reviewer’s comments to our manuscript and positive evaluation of our study. As suggested, We have re-written this part. As the followings:

The N₂ adsorption-desorption was employed to measure the physical properties of the catalysts, as shown in Table 2. Comparing with SF-SiO₂-support catalysts, the SF-SiC supporting catalysts show higher specific surface areas and pore volume, which should be attached to the influence of molten-salt-mediated magnesiothermic reduction [14]. As can be seen from Figure 3, the surface of SiO2 was smooth with a few pores. But, after loading Ni species, the specific surface areas and pore volume of Ni/SF-SiO₂ were obviously increased, which may due to the rough surface of Ni/SF-SiO₂ produced by Ni particles loading and many holes were produced among these Ni particles. However, the specific surface areas and pore volume of Ni/SF-SiC were decreased, which probably due to the Ni precursors were introduced to the interior pore walls and the pore of the support was blocked. At the same time, this phenomenon also caused a slight change of average pore diameter in the Ni/SF-SiO₂ and Ni/SF-SiC catalysts [38].

(6) From TPR results, it is stated that below 550 ºC, a great mass of NiO species in both catalysts could be reduced by hydrogen (lines 175-176). This is not true. The amount depends of the reduction temperature and a considerable amount is not reduced until temperature reaches 400 ºC.

Reply: We thank the reviewer’s comment. And we are very sorry for our incorrect writing about it. And to avoid misunderstanding, we deleted this part.

(7) XPS results are also unintelligible. A Table with each Ni specie quantification must be included in order to make a good description of what is happening in each catalyst. Instead, qualitative results are also difficult to analyze in this sense.

Reply: We thank the reviewer’s comment. As suggested, the elemental analysis of Ni, O, Si, and C elements content by X-ray photoelectron spectroscopy (XPS) as follows. From Table 3, there were about 5.2% of Ni elements on the Ni/SF-SiC surface, and that of Ni/SF-SiO₂ was 4.7%, which indicating that Ni was easily exposed to the surface of Ni/SF-SiC. In addition, the radio of Ni⁰/Ni and Ni³⁺/Ni were about 11.2% and 31.0% for Ni/SF-SiC, respectively, which were higher than for Ni/SF-SiO₂ at 11.0% and 27.0%, demonstrating that the Ni species of Ni/SF-SiC were more likely to be reduced for their good dispersity and smaller Ni nanoparticles, and there are more vacancies in Ni/SF-SiC.

Table 3. Elemental analysis of Ni, O, Si, and C elements content by X-ray photoelectron spectroscopy (XPS).

(8) 6 images are included in Figure 7; probably c-d Figures are not necessary.

Reply:  As suggested, Fig. 7 has been rearranged.

Figure 7. SEM images of the samples: (a) used-Ni/SF-SiO₂, (b) used-Ni/SF-SiC; HRTEM images of (c), used-Ni/SF-SiO₂ and (d) used-Ni/SF-SiC.

(9) Scherrer equation, CO conversion and CH4 production equations must be included in experimental section.

Reply: We thank the reviewer for pointing out this. As suggested, theCO conversion, CH4 selectivity and yield were added in the part of 3.3. CO methanation performance test of powdered catalyst. And Scherrer equation was added in the table 2. As follows:

The CO conversion, CH₄ selectivity and yield are defined as follows:

CO conversion: Xco (%) = [CO]_in－[CO]_out/[CO]_in × 100%            (1)

CH₄ selectivity: S_CH4 (%) = [CH4]_out/[CO]_in－[CO]_out × 100%          (2)

CH₄ yield: Y_CH4 = [CH₄]_out/[CO]_in × 100%                          (3)

Here, [CO]_in is the moles of CO in the feed stream, [CO]_out is the moles of CO in the effluent gas; [CH₄]_out is the moles of CH₄ in the effluent gas.

the Debye-Scherrer equation as follows: L= 0.9λ_kα1/B_(2θ)cosθ_max. Where L denotes the average particle size, 0.9 is the value in radians when B_(2θ) is the full width at half maximum (FWHM) of the peak, kα1 is the wavelength of the X-ray radiation (0.15406 nm), and max is the angular position at the (1 1 1) peak maximum of Ni.

We attached a copy of the revised manuscript at the end of this document. This copy is the same as the revised manuscript, except that some parts are colored to make the revisions notable.

We hope the Reviewers and the Editors will be satisfied with the revisions for the original manuscript.

Thanks and Best regards!

Yours Sincerely,

Feng Yu

Email: [email protected].

Reviewer 3 Report

This manuscript details a comparison between two supported nickel catalysts for methanation. In my opinion, major revision is required before the paper can be accepted for publication:

- error bars, carbon balances and degrees of reproducibility are required in relation to all catalysis data

- elemental analysis should be undertaken and comparisons between the two materials presented

- literature comparisons presented on the basis of space time yields should be presented and discussed appropriately

- BET data are presented to a degree of precision which is not tenable

- incorrect reference is made to application of the "Debye-Scherrer equation" which in fact does not exist.  Greater detail relating to the application of the Scherrer equation and the elimination of complicating effects resulting from lattice strain/defect content should be described

- can complications arising from final state effects leading to misassignments in the XPS spectra be discounted?

- the TPR data should be quantified

Author Response

Dear Reviewer,

We greatly appreciate the time and effort you’ve spent in reviewing our manuscript titled“Defect-rich nickel nanoparticles supported on industrial waste silica fume during metallic silicon production with enhanced carbon monoxide methanation performance”, and your constructive suggestions are valuable to our manuscript and future research work. According to the reviewers’ comments, we have made further analysis and revised the manuscript carefully. We hope the Reviewer will be satisfied with the revisions for the original manuscript. The followings are the reviewers’ comments and the corresponding point-by-point responses to the concerns.

(1)  error bars, carbon balances and degrees of reproducibility are required in relation to all catalysis data.

Reply: Thank you very much for your helpful comments to our manuscript. As suggested, error bars were added in Fig. 1 (a) and (b). And the results in this paper can be obtained by repeated experiments. And as the reaction temperature raised to 300 ^oC, a small amount of carbon dioxide is produced. But, as for the more detailed information about carbon balances and degrees of reproducibility, further exploration is needed.

Figure 1. Catalytic performances of catalysts in CO methanation under different reaction temperature at 0.1 MPa and GHSV of 18000 mL·g^-1·h^-1: (a) CO Conversion, (b) CH₄ Selectivity.

(2) elemental analysis should be undertaken and comparisons between the two materials presented

Reply: We thank the reviewer’s comments to our manuscript and positive evaluation of our study. As suggested, the elemental analysis of Ni, O, Si, and C elements content by X-ray photoelectron spectroscopy (XPS) as follows. From Table 3, there were about 5.2% of Ni elements on the Ni/SF-SiC surface, and that of Ni/SF-SiO₂ was 4.7%, which indicating that Ni was easily exposed to the surface of Ni/SF-SiC. In addition, the radio of Ni⁰/Ni and Ni³⁺/Ni were about 11.2% and 31.0% for Ni/SF-SiC, respectively, which were higher than for Ni/SF-SiO₂ at 11.0% and 27.0%, demonstrating that the Ni species of Ni/SF-SiC were more likely to be reduced for their good dispersity and smaller Ni nanoparticles, and there are more vacancies in Ni/SF-SiC.

Table 3. Elemental analysis of Ni, O, Si, and C elements content by X-ray photoelectron spectroscopy (XPS).

(3) literature comparisons presented on the basis of space time yields should be presented and discussed appropriately.

Reply: Thank you very much for your helpful comments to our manuscript. But, the data of space time yields were not available in most of the literature listed in table 1. So we could not supplement this data in Table 1, and we are very sorry for it.

(4) BET data are presented to a degree of precision which is not tenable.

Reply: We are very sorry for this. And the data in table 2 has been corrected.

¹ Surface area derived from BET equation. ² Obtained from BJH desorption average pore volume and pore diameter. ^2* Obtained from BJH adsorption average pore volume and pore diameter. ³ Calculated according to equation D_Ni=∑_NiD_i³/∑_NiD_i² from HRTEM. ⁴ Estimated from the XRD diffraction peak (2θ=44.6) using the Scherrer equation as follows: L= 0.9λ_kα1/B_(2θ)cosθ_max. Where L denotes the average particle size, 0.9 is the value in radians when B_(2θ) is the full width at half maximum (FWHM) of the peak, kα1 is the wavelength of the X-ray radiation (0.15406 nm), and max is the angular position at the (1 1 1) peak maximum of Ni.

(5)  incorrect reference is made to application of the "Debye-Scherrer equation" which in fact does not exist.  Greater detail relating to the application of the Scherrer equation and the elimination of complicating effects resulting from lattice strain/defect content should be described.

Reply：We are very sorry for our incorrect writing about it. As suggested, we have checked and corrected this mistake. And the formula has been added in the paper. The Scherrer equation as follows: L= 0.9λ_kα1/B_(2θ)cosθ_max. Where L denotes the average particle size, 0.9 is the value in radians when B_(2θ) is the full width at half maximum (FWHM) of the peak, kα1 is the wavelength of the X-ray radiation (0.15406 nm), and max is the angular position at the (1 1 1) peak maximum of Ni. And it is not clear about the influence of the lattice strain and defect content of the catalysts, and further exploration is needed.

(6) the TPR data should be quantified.

Reply: We thank the reviewer’s comments to our manuscript and positive evaluation of our study. As suggested, the TPR data has been quantified and Fig.5 has been rearranged. By comparing the consumption of H₂ in the two catalysts, we can clearly see that more H₂ was consumed in the NiO/SF-SiC.

Figure 5. H₂-TPR profiles of the as-prepared NiO/SF-SiO₂ and NiO/SF-SiC catalysts.

We attached a copy of the revised manuscript at the end of this document. This copy is the same as the revised manuscript, except that some parts are colored to make the revisions notable.

We hope the Reviewers and the Editors will be satisfied with the revisions for the original manuscript.

Thanks and Best regards!

Yours Sincerely,

Feng Yu

Email: [email protected].

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Several changes are made in the original manuscript, improving the quality of the paper. The manuscript can be published.

Author Response

Dear Reviewers,

   Thanks very much for the time and effort you’ve spent in reviewing our manuscript On behalf of my co-authors, we would like to express our great appreciation to you.

Thanks and Best regards!

Yours Sincerely,

Feng Yu

Email: [email protected].

Reviewer 3 Report

The authors appear to have misunderstood the point relating to the request for space time yield comparisons - all the data required to calculate space time yields is available from the references presented in Table 1 and making such a comparison and placing their study in the context of them would significantly strengthen this manuscript. In doing this, account will be taken of the various different testing parameters.

The precision to which BET data are quoted is untenable with respect to the limitations of the method.

Quantification of TPR refers to uptake/conversion of H₂ which should be normlaised to Ni content taking into account oxidation state requirements for total reduction.

The XPS oxidation state assignments should be critically and carefully considered in the context of potentially complicating final state effects.

The authors state that below 200C, the catalyst materials were "deactivated",   Surely they do not mean this.

Author Response

Dear Reviewers,

   Thank you for your letter and for the your comments concerning our manuscript entitled “Defect-rich nickel nanoparticles supported on industrial waste silica fume during metallic silicon production with enhanced carbon monoxide methanation performance”. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. The responds to the your comments are as flowing:

Responds to the reviewer’s comments:

(1) The authors appear to have misunderstood the point relating to the request for space time yield comparisons - all the data required to calculate space time yields is available from the references presented in Table 1 and making such a comparison and placing their study in the context of them would significantly strengthen this manuscript. In doing this, account will be taken of the various different testing parameters.

Reply: We thank the reviewer’s comments to our manuscript and positive evaluation of our study. As suggested, table 1 has been rearranged.

Table 1. The comparison of catalytic performance in different work.

(2) The precision to which BET data are quoted is untenable with respect to the limitations of the method.

Reply: We are very sorry for this. And the data in table 2 has been corrected.

¹ Surface area derived from BET equation. ² Obtained from BJH desorption average pore volume and pore diameter. ^2* Obtained from BJH adsorption average pore volume and pore diameter. ³ Calculated according to equation D_Ni=∑_NiD_i³/∑_NiD_i² from HRTEM. ⁴ Estimated from the XRD diffraction peak (2θ=44.6) using the Scherrer equation as follows: L= 0.9λ_kα1/B_(2θ)cosθ_max. Where L denotes the average particle size, 0.9 is the value in radians when B_(2θ) is the full width at half maximum (FWHM) of the peak, kα1 is the wavelength of the X-ray radiation (0.15406 nm), and max is the angular position at the (1 1 1) peak maximum of Ni.

(3) Quantification of TPR refers to uptake/conversion of H2 which should be normlaised to Ni content taking into account oxidation state requirements for total reduction.

Reply: We thank the reviewer’s comments to our manuscript and positive evaluation of our study. As suggested, Fig. 5 has been rearranged. And table 3 of Gaussian fitting analysis of H₂-TPR patterns of different catalysts was added.

In Fig. 5, the curves of the two catalysts are similar, which based on the TPR results. There is a strong peak with a shoulder peak in the NiO/SF-SiO₂, the previous in the low temperature region is related to α-type NiO species and played a dominant role in nickel oxide species, which are assigned to the weaker interaction in Ni/SF-SiO₂ [31], and another peak was corresponded to β-type NiO species, which have a stronger interaction with the SF-SiO₂ [39, 40]. In comparison with NiO/SF-SiO₂ catalyst, the spectrum of the NiO/SF-SiC also has a broader peak, and the peak at higher temperature could be associated to the reduction of nickel silicate, implying the enhanced interaction between NiO and the support of SF-SiC [41, 33]. In addition, the overlapped peaks of TPR profiles were fitted by the Gaussian function and classified into four peaks, the peak positions and the quantitative results of relative content are shown in Table 3. It could be seen that there were four peaks in the NiO/SF-SiC. However, there were just three types reduction peaks in NiO/SF-SiO₂, suggesting that the interaction between NiO and support was weaker. Comparing with NiO/SF-SiO₂, the fraction of β-type NiO species of NiO/SF-SiC was larger, implying that the stronger interaction between NiO and support.

Table 3. Gaussian fitting analysis of H₂ -TPR patterns of different catalysts.

Figure 5. H₂-TPR profiles of the as-prepared NiO/SF-SiO₂ and NiO/SF-SiC catalysts.

(4) The XPS oxidation state assignments should be critically and carefully considered in the context of potentially complicating final state effects.

Reply: We thank reviewer’s comment. In fact, it had been confirmed by researchers reported before. In Ni/SF-SiO₂, the Ni 2p3/2 binding energy (BE) of 852.91 eV was related to metallic Ni⁰ (Sasi, B.; Gopchandran, K.G. Nanostructured mesoporous nickel oxide thin films. Nanotechnol. 2007, 18, 115613.), while the Ni 2p3/2 BE 856.78 eV with the satellite peak of 861.02 eV and the Ni 2p1/2 BE of 870.0 and 879.49 eV were assigned to Ni²⁺ species, which corresponding to the partially oxidized nickel species (Sasi, B.; Gopchandran, K.G. Nanostructured mesoporous nickel oxide thin films. Nanotechnol. 2007, 18, 115613.). Compared with Ni/SF-SiO₂, the Ni 2p3/2 and 2p1/2 BEs (857.02, 861.50, 870.88 and 879.98 eV, respectively) of Ni²⁺ species of Ni/SF-SiC was improved. Furthermore, as for Ni/SF-SiO₂，the spectrum of the Ni 2p3/2 and 2p1/2 shown peaks at 855.24 and 873.26 eV，respectively, which could be ascribed to Ni³⁺ defects species (Zhao, Y.; Jia, X. et al. Ultrafine NiO Nanosheets Stabilized by TiO2 from Monolayer NiTi-LDH Precursors: An Active Water Oxidation Electrocatalyst. J. Am. Chem. Soc. 2016, 138, 6517-6524.). But, the BEs of Ni³⁺ species (855.50 and 873.78 eV) of Ni/SF-SiC was shifted to higher. The numerous Ni³⁺ in the two catalysts, which generated from Ni and O vacancies in the process of calcination for forming the NixOy species (Zhao, Y.; Jia, X. et al. Ultrafine NiO Nanosheets Stabilized by TiO2 from Monolayer NiTi-LDH Precursors: An Active Water Oxidation Electrocatalyst. J. Am. Chem. Soc. 2016, 138, 6517-6524.). The surfaces Ni²⁺ was oxidized to Ni³⁺ for forming charge neutrality around the Ni and O vacancies, and the surface Ni³⁺ active sites, which may facilitate charge-transfer and enhance CO and H₂ adsorption (Zhao, Y.; Jia, X. et al. Ultrafine NiO Nanosheets Stabilized by TiO2 from Monolayer NiTi-LDH Precursors: An Active Water Oxidation Electrocatalyst. J. Am. Chem. Soc. 2016, 138, 6517-6524.).

   In Fig. 6b, the O 1s spectra of Ni/SF-SiO₂ and Ni/SF-SiC catalysts could be distinguished into four sub-peaks: the weakly binding energy peaks (O_Ⅰand O_Ⅱ) was related to the surface lattice oxygen and the adsorbed oxygen (Zhang, M.; Yu, F. et al. High CO Methanation Performance of Two-Dimensional Ni/MgAl Layered Double Oxide with Enhanced Oxygen Vacancies via Flash Nanoprecipitation. Catalysts 2018, 8, 363.), respectively; the higher binding energy (O_Ⅲand O_Ⅳ) corresponding to the defects with a low oxygen coordination and the metal-oxygen bonds (Shuangyin Wang, et al. In Situ Exfoliated, N-Doped, and Edge-Rich Ultrathin Layered Double Hydroxides Nanosheets for Oxygen Evolution Reaction. Adv. Funct. Mater. 2018, 28, 1703363.), respectively. The binding energy of O 1s of Ni/SF-SiC was higher than Ni/SF-SiO₂, demonstrating that the stronger metal-support interactions between Ni and SF-SiC (Jin G, Gu F, Liu Q, et al. Highly stable Ni/SiC catalyst modified by Al2O3 for CO methanation reaction. RSC Adv. 2016, 6, 9631-9.). For the catalysts, the presence of Ni³⁺ and O_Ⅲ could further promote the activity of reactive sites in metahantion (Shuangyin Wang, et al. In Situ Exfoliated, N-Doped, and Edge-Rich Ultrathin Layered Double Hydroxides Nanosheets for Oxygen Evolution Reaction. Adv. Funct. Mater. 2018, 28, 1703363.).

(5) The authors state that below 200oC, the catalyst materials were "deactivated",   Surely they do not mean this.

Reply: We thank the reviewer for pointing this. As suggested, the statement has been corrected. “Below 200 ^oC, these were in inactive state,” And avoid misunderstanding, we deleted it.

Some parts are colored to make the revisions notable in the revised manuscript.

We hope the Reviewers and the Editors will be satisfied with the revisions for the original manuscript.

Thanks and Best regards!

Yours Sincerely,

Feng Yu

Email: [email protected].

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

The previous comments have not been completely addressed:

- quoting BET surface areas to one decimal place is generally viewed as not tenable in view of the uncertainty of the measurement.

- the idea of quoting STYs was to facilitate comparison and benchmarking between the literature and the current manuscript.  Inspection of the Table shows that this has not helped in this regard especially since the units are not consistent etc.   The authors need to confirm that they have calculated the correct parameter taking into account any dilution - i.e. the percentage CO conversion quoted is not the % total gas phase flow converted, etc.

- the response concerning carbon balances is confused/confusing. 

- has the quantification of the H2 uptake been explicitly included?

To give the authors additional time to correct these issues I recommend rejection and possible resubmission.

Author Response

Dear Reviewers,

   Thank you for your letter and for the your comments concerning our manuscript entitled “Defect-rich nickel nanoparticles supported on industrial waste silica fume during metallic silicon production with enhanced carbon monoxide methanation performance”. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. The responds to the your comments are as flowing:

Responds to the reviewer’s comments:

(1) quoting BET surface areas to one decimal place is generally viewed as not tenable in view of the uncertainty of the measurement.

Reply: We thank the reviewer’s comments to our manuscript and positive evaluation of our study. As suggested, table 2 has been rearranged. 

¹ Surface area derived from BET equation. ² Obtained from BJH desorption average pore volume and pore diameter. ^2* Obtained from BJH adsorption average pore volume and pore diameter. ³ Calculated according to equation D_Ni=∑_NiD_i³/∑_NiD_i² from HRTEM. ⁴ Estimated from the XRD diffraction peak (2θ=44.6) using the Scherrer equation as follows: L= 0.9λ_kα1/B_(2θ)cosθ_max. Where L denotes the average particle size, 0.9 is the value in radians when B_(2θ) is the full width at half maximum (FWHM) of the peak, kα1 is the wavelength of the X-ray radiation (0.15406 nm), and max is the angular position at the (1 1 1) peak maximum of Ni.

(2) the idea of quoting STYs was to facilitate comparison and bench marking between the literature and the current manuscript.  Inspection of the Table shows that this has not helped in this regard especially since the units are not consistent etc.   The authors need to confirm that they have calculated the correct parameter taking into account any dilution - i.e. the percentage CO conversion quoted is not the % total gas phase flow converted, etc.

Reply: We thank the reviewer for pointing this. Both of weight hourly space velocity and volume space velocity are common units. As suggested，in order to achieve unit consistency, we replaced some of the references in Table 1.

Table 1. The comparison of catalytic performance in different work.

(3) the response concerning carbon balances is confused/confusing. 

 Reply: Thank you very much for your helpful comments to our manuscript. As suggested, the calculation results for carbon balance are as follows.

Table. S1. The calculation results of Ni/SF-SiO₂ for carbon balance.

¹ Molar flow; ² Mass flow.

Table. S2. The calculation results of Ni/SF-SiC for carbon balance.

¹ Molar flow; ² Mass flow.

(4) has the quantification of the H2 uptake been explicitly included?

Reply: We thank the reviewer’s comments to our manuscript and positive evaluation of our study. As suggested,  table 3 of Gaussian fitting analysis of H₂-TPR patterns of different catalysts has been rearranged. By comparing the H₂ consumption of the αandβ–type reduction peaks for the two catalysts, we can clearly see that more H₂ was consumed in the NiO/SF-SiC.

Table 3. Gaussian fitting analysis of H₂ -TPR patterns of different catalysts.

Some parts are colored to make the revisions notable in the revised manuscript.

We hope the Reviewers will be satisfied with the revisions for the original manuscript.

Thanks and Best regards!

Yours Sincerely,

Feng Yu

Email: [email protected].

Author Response File: Author Response.pdf