Single Metal Atoms Embedded in the Surface of Pt Nanocatalysts: The Effect of Temperature and Hydrogen Pressure

Round 1

Reviewer 1 Report

Comments:

The present manuscript reports on the “Single Metal Atoms Embedded in the Surface of Pt Nanocatalysts: the Effect of Temperature and Hydrogen Pressure”. The work is of some interest but seems to be too primitive and lacks in proper scientific support and justification. Thus, in my opinion, the manuscript in its present form cannot be considered for publication. I recommend major revision.

Following are some of the comments/suggestions which will be useful to the authors.

1. First of all, there are many previous works published on composites of metal nanoparticles. The authors seem deliberately avoid those papers. This is unusual, as the authors need to acknowledge the previous literature and compare their work with the similar ones in the literature and demonstrate their research outcomes in terms of advantages and disadvantages. Some of studies are given below need to cited;

i- Arif, M., Shahid, M., Irfan, A., Nisar, J., Wu, W., Farooqi, Z. H., & Begum, R. (2022). Polymer microgels for the stabilization of gold nanoparticles and their application in the catalytic reduction of nitroarenes in aqueous media. RSC advances, 12(9), 5105-5117.

ii- Arif, M., Shahid, M., Irfan, A., Wang, X., Noor, H., Farooqi, Z. H., & Begum, R. (2022). Catalytic degradation of organic dyes using Au-poly (styrene@N-isopropylmethacrylamide) hybrid microgels. Inorganic Chemistry Communications, 144, 109870.

iii- Arif, M., Tahir, F., Fatima, U., Begum, R., Farooqi, Z. H., Shahid, M., ... & Ali, Z. (2022). Catalytic degradation of methyl orange using bimetallic nanoparticles loaded into poly (N-isopropylmethacrylamide) microgels. Materials Today Communications, 104700.

2. The references of this articles are not correct. They should correct the references. For example, “Roldan et al. [8], reported experimental evidence of seg” as written in line 42 but at reference, it is different as written in line 404,405. References should be needed for correction.

3. The authors should explain the reasons of coagulation at high temperature. The proper explanation of temperature and pressure effect on the cluster is missing.

4. In figure 1, the temperature and hydrogen pressure range are missing.

 

5. The temperature rage and pressure value are missing in the abstract (in line 20).

6. The title of this manuscript should be needed to revise. It is not proper for this work.  

7.  The writing format is not correct in line 199.  Correct “This result” from this line.        

8. The reporting materials is not clear with respect to composites or doped materials or core shell system or alloy. This clarity is missing in this manuscript.  

9. English language of this article should be improved. Some grammatical and typographical mistakes are present. Such as “Adsorption of hydrogen on pure Pt (111) surface si added as reference” written in line 311 and 312.

Author Response

Review 1

The present manuscript reports on the “Single Metal Atoms Embedded in the Surface of Pt Nanocatalysts: the Effect of Temperature and Hydrogen Pressure”. The work is of some interest but seems to be too primitive and lacks in proper scientific support and justification. Thus, in my opinion, the manuscript in its present form cannot be considered for publication. I recommend major revision.

Following are some of the comments/suggestions which will be useful to the authors.

1. First of all, there are many previous works published on composites of metal nanoparticles. The authors seem deliberately avoid those papers. This is unusual, as the authors need to acknowledge the previous literature and compare their work with the similar ones in the literature and demonstrate their research outcomes in terms of advantages and disadvantages. Some of studies are given below need to cited;

i- Arif, M., Shahid, M., Irfan, A., Nisar, J., Wu, W., Farooqi, Z. H., & Begum, R. (2022). Polymer microgels for the stabilization of gold nanoparticles and their application in the catalytic reduction of nitroarenes in aqueous media. RSC advances, 12(9), 5105-5117.

ii- Arif, M., Shahid, M., Irfan, A., Wang, X., Noor, H., Farooqi, Z. H., & Begum, R. (2022). Catalytic degradation of organic dyes using Au-poly (styrene@N-isopropylmethacrylamide) hybrid microgels. Inorganic Chemistry Communications, 144, 109870.

iii- Arif, M., Tahir, F., Fatima, U., Begum, R., Farooqi, Z. H., Shahid, M., ... & Ali, Z. (2022). Catalytic degradation of methyl orange using bimetallic nanoparticles loaded into poly (N-isopropylmethacrylamide) microgels. Materials Today Communications, 104700.

 

Our answer: This work is focusing on the stability of single atoms SAACs in Pt nanoparticles and not on composites of metal nanoparticles. As suggested by the reviewer, we went through the references of Arif, M. and coworkers but we did not see any raison to add them in the revised version of the manuscript. These references related on the « Polymer microgels for the stabilization of gold nanoparticles » and « Catalytic degradation of organic dyes using Au-poly » are out of the scoop of this paper. We think there has been error in copying the references, we would be glad to add the pertinent papers to the article.

 

2. The references of this articles are not correct. They should correct the references. For example, “Roldan et al. [8], reported experimental evidence of seg” as written in line 42 but at reference, it is different as written in line 404,405. References should be needed for correction.

Our answer: We thank the referee for his help to improve the manuscript. The references were carefully revised and corrected.

 

3. The authors should explain the reasons of coagulation at high temperature. The proper explanation of temperature and pressure effect on the cluster is missing.

Our answer: It seems there are problems of misunderstanding. We never talked about coagulation. This term does not exist in material science and in the topic treated in this manuscript. Is it possible that the reviewer mixed up two different review assignments?

 

4. In figure 1, the temperature and hydrogen pressure range are missing.

Our answer: The temperature and pressure ranges P(Pa) and T(K) are indicated in Figure 1.

 

5. The temperature rage and pressure value are missing in the abstract (in line 20).

Our answer: The temperature and pressure ranges are indicated in the main text.

 

6. The title of this manuscript should be needed to revise. It is not proper for this work.

Our answer: We cannot see what should be revised in the title. This work follows our previous work published in the journal of Applied Surface Science (App. Surf. Sci.  548 (2021) 149217) untitled "Mapping Surface Segregation of Single-Atom Pt Dispersed in M Surfaces (M=Cu, Ag, Au, Ni, Pd, Co, Rh and Ir) Under Hydrogen Pressure at Various Temperatures." In that work, we investigated the stability of Pt single atom in M host surfaces and in this work we complete our study by investigating the stability of M single atom in Pt host surfaces.

 

7. The writing format is not correct in line 199.  Correct “This result” from this line. 

       Our answer: The writing format was corrected

 

8. The reporting materials is not clear with respect to composites or doped materials or core shell system or alloy. This clarity is missing in this manuscript.  

Our answer: The manuscript was entirely revised to improve clarity. See corrected version.

 

9. English language of this article should be improved. Some grammatical and typographical mistakes are present. Such as “Adsorption of hydrogen on pure Pt (111) surface si added as reference” written in line 311 and 312.

 

Our answer: Thank you for reviewing our paper. The typos and grammar has been corrected to the best of our knowledge.

Reviewer 2 Report

The present study represents a good work in the improvement of selective engineering of nanoalloys by introducing low precious cations to the Pt metal. Few references in the literature should be added in the introduction part for rationality of the present study. I recommend the acceptance of the current version after this minor addition/updates.

Author Response

Review2

The present study represents a good work in the improvement of selective engineering of nanoalloys by introducing low precious cations to the Pt metal. Few references in the literature should be added in the introduction part for rationality of the present study. I recommend the acceptance of the current version after this minor addition/updates.

Our answer: We thank referee 2 for his/her positive comments. Additional references were added in the introduction part for rationality of the present study.

 

Reviewer 3 Report

 

In this work, an environmental segregation energy model is developed to predict the stability and the surface composition evolution of twenty-four Metal M-promoted Pt surfaces. The authors found coinage single-atoms might be used to tune the catalytic properties of Pt surface under hydrogen media. This work is very interesting and it deserves to be published if the below concerns are addressed. 

1. It is quite important that surface deformation or reconstruction can be induced by adsorbates/gases in alloy system, and I recommend to cite papers on this topics to provide more information for promising readers: Phys. Chem. Chem. Phys., 2017,19, 18010-18017;  J. Phys. Chem. C 2018, 122, 20, 10883–10891.

2. I don't understand the reason of using 400 eV as cutoff energy. It seems the authors attribute the settings to the consideration of valence electrons? However, I don't think this has any connection with the cutoff settings. It would be required to perform comparative studies on different cutoff energies.

3. In addition, the authors need to rephrase the Methodology part, since many sentences are similar with those in the author's work published on Applied Surface Science. I understand it is difficult to write new words based on the same calculation methods, but rephrasing would be acceptable. 

4. From the method description that, the bottom two layer of atoms of a surface structure are fixed during calculations. However this settings may affect the surface energy calculation in Table 1. Have the authors done any convergence test with increasing layers? A normal way to calculate the surface energy is to fix the middle part of the structure while relax the near-surface parts. D Since the surface energy is further used for MSR calculation, a high-level of accuracy is needed to determine the pre-requisite parameters.

5. I disagree with "much stronger repulsive H-H lateral interaction on Pt(111) (-0.13 eV) than on Pt(100) (-0.063 eV)". The difference is negligible and within the DFT error range. The authors may need to provide more details or explanations to support the argument. In addition, how to define/calculate lateral interaction? More description is needed.

6. As a H2 storage material, H may diffuse into sublayer or inner bulk structure of Pt. This may change the lattice and the behavior of surface H. It would also affect the average CN of Pt nanoparticle. Does the author evaluate the effect on their current results?

7. The units of interface tension in Figure 2 is missing. The definition of interface tension is needed.

8. Font sizes in line 199 are inconsistent.

9. The doping concentration of single-atoms in DFT-level of calculations should be provided. In addition, it would be interesting to know the area/ratio of the segregated parts. Can the authors summarize some results on this?

10. Some adsorption results in Table 2 are too small, i.e. 0.00 eV. This is counterintuitive. The authors need to provide the corresponding structures. Or they may need to compare the results with literature. Do the authors only consider one adsorption site? 

11. The ZPE will increase the accuracy of the DFT-energies and it may help to explain the results in Table 2 if involving it into calculation.

12. Are free energies considered in MSR? Otherwise I guess it is needed to provide free-energy calculation. This would make the results, such as Figure 1, selfconsistent at “real” temperature/pressure. 

 

 

Author Response

Review 3 

In this work, an environmental segregation energy model is developed to predict the stability and the surface composition evolution of twenty-four Metal M-promoted Pt surfaces. The authors found coinage single-atoms might be used to tune the catalytic properties of Pt surface under hydrogen media. This work is very interesting and it deserves to be published if the below concerns are addressed. 

Our answer: We thank referee 3 for his/her positive comments and his/her suggestions to help us improving our manuscript.

 

1. It is quite important that surface deformation or reconstruction can be induced by adsorbates/gases in alloy system, and I recommend to cite papers on this topics to provide more information for promising readers: Phys. Chem. Chem. Phys., 2017,19, 18010-18017;  J. Phys. Chem. C 2018, 122, 20, 10883–10891

Our answer: As suggested by the referee, additional references were added to provide more information for promising readers.

 

2. I don't understand the reason of using 400 eV as cutoff energy. It seems the authors attribute the settings to the consideration of valence electrons? However, I don't think this has any connection with the cutoff settings. It would be required to perform comparative studies on different cutoff energies.

Our answer:  There were a mistake in the methodological details and the sentence was rephrased. The cut off energy was fixed to 400eV according to our previous studies on Pt surfaces and clusters and this value is in complete agreement with the literature and validated by the code VASP. References of previous works using this cut off value are added in the manuscript.

 

3. In addition, the authors need to rephrase the Methodology part, since many sentences are similar with those in the author's work published on Applied Surface Science. I understand it is difficult to write new words based on the same calculation methods, but rephrasing would be acceptable. 

Our answer:  We thank the referee for his understanding, the point raised is important and it is now corrected. The Methodological part was entirely rewritten.

 

4. From the method description that, the bottom two layer of atoms of a surface structure are fixed during calculations. However this settings may affect the surface energy calculation in Table 1. Have the authors done any convergence test with increasing layers? A normal way to calculate the surface energy is to fix the middle part of the structure while relax the near-surface parts. D Since the surface energy is further used for MSR calculation, a high-level of accuracy is needed to determine the pre-requisite parameters.

Our answer:  We thank the reviewer for his remark. Indeed, as underlined by the reviewer the convergence of surface energies are very important for the accuracy of the MSR model. Several approaches were reported for the calculations of the surface energies. We can fix the middle part of the slab and increase the number of layers or we fix the bottom layers and increase the number of upper surface layers. The main important thing is to reproduce both the bulk and the surface properties. Our calculation method of surface energies was already tested and compared with other methods and namely with the method of Fiorentini et al.  (V. Fiorentini, et al. J. Phys. Condens. Matter 1996, 8, 6525). The results show negligible effect of the used methodology.

 

5. I disagree with "much stronger repulsive H-H lateral interaction on Pt(111) (-0.13 eV) than on Pt(100) (-0.063 eV)". The difference is negligible and within the DFT error range. The authors may need to provide more details or explanations to support the argument. In addition, how to define/calculate lateral interaction? More description is needed.

Our answer: We agree with the referee, the statement “much stronger” is wrong. This statement is moderated in the new version of the manuscript. Additional details on the calculations of lateral interactions are now provided in the methodological details section.

 

6. As a H2 storage material, H may diffuse into sublayer or inner bulk structure of Pt. This may change the lattice and the behavior of surface H. It would also affect the average CN of Pt nanoparticle. Does the author evaluate the effect on their current results?

 

Our answer: In this work, we did not consider the absorption and diffusion of hydrogen toward the subsurface. This may be the subject of a deeper work on selected materials like Ag and Au single atom promoters on Pt NPs where the study of the effect of H absorption and its effect on the structure and the stability of the promoters may provide important information. This perspective was added in the conclusion of the revised manuscript.

 

7. The units of interface tension in Figure 2 is missing. The definition of interface tension is needed.

Our answer: The units of interface tension (eV/Å2) was added in figure 2. The definition of interface tension is now included in the revised version of the manuscript (see methodological details).

 

8. Font sizes in line 199 are inconsistent.

Our answer: The front size was corrected

 

9. The doping concentration of single-atoms in DFT-level of calculations should be provided. In addition, it would be interesting to know the area/ratio of the segregated parts. Can the authors summarize some results on this?

Our answer: The doping concentration is about 11% of the surface (1 single atom embedded in 3x3 surface). This value is now provided in the paper. As the calculations are focusing on the segregation energy of a M-single atom, the results are relevant for highly diluted atoms in the surface.  The evolution of area/ratio may be calculated if we compute the environmental mixing energies for M-M single atoms in Pt surfaces for all systems and for all considered temperature and pressure. This is out of the scoop of the paper as we only focused on single atoms.

 

10. Some adsorption results in Table 2 are too small, i.e. 0.00 eV. This is counterintuitive. The authors need to provide the corresponding structures. Or they may need to compare the results with literature. Do the authors only consider one adsorption site? 

Our answer: The calculations of adsorption energies of atomic hydrogen were performed on different adsorption sites and the most favorable sites were selected. These values were used to compute tension energy evolution. The endothermic adsorptions are those with positive calculated energy values. These values were set to zero to indicate that the adsorption does not happens. More explanations were added to explain the calculated endothermic adsorptions and references from the literature were added.

 

11. The ZPE will increase the accuracy of the DFT-energies and it may help to explain the results in Table 2 if involving it into calculation.

Our answer: We supposed the ZPE correction would be negligible and would not alter the energy trends. We also took this decision not to include ZPE correction from the price/quality point of view. Although, the accuracy would be improved the price to obtain the corrected energies is too high to obtain the same trends as for the uncorrected energies.

 

12. Are free energies considered in MSR? Otherwise I guess it is needed to provide free-energy calculation. This would make the results, such as Figure 1, selfconsistent at “real” temperature/pressure.

 

Our answer: The considered energies for the MSR construction are free energies involving the effect of entropy. Additional methodological details were added in the revised version of the manuscript and references of our previous works using the MSR and environmental segregations energies are add to provide more information for promising readers.

Round 2

Reviewer 1 Report

Accept

Reviewer 3 Report

Thank you for addressing my concerns.