Recent Manganese Oxide Octahedral Molecular Sieves (OMS–2) with Isomorphically Substituted Cationic Dopants and Their Catalytic Applications

Round 1

Reviewer 1 Report

The authors reviewed the structural and physic-chemical features of the [M]–K–OMS2 oxides (M = Ag, Ce, Mo, V, Nb, W, In, Zr and Ru) and their applications in pollutants degradation, fine chemistry, and electrocatalysis, proposed their potential alternative applications. This review work contains some useful information and could be considered for publication. However, the authors should revise their manuscript before acceptance for publication according to the following comments:

1. What are the substitution degrees of K by M in the [M]–K–OMS2 oxides? It should be discussed in the effect of substitution degree of K by M on physicochemical property of [M]–K–OMS2.
2. Some tables should be needed to summarize the main preparation methods, chemical compositions, typical physicochemical property, performance, and references of the [M]–K–OMS2 oxides.
3. The catalytic mechanisms should be discussed. What are the active sites for the addressed reactions?
4. There are a large number of inappropriate English words or expressions in the manuscript. The authors should carefully polish the English of the whole manuscript.

Author Response

RESPONSE TO REFEREE# 1

The authors reviewed the structural and physic-chemical features of the [M]–K–OMS2 oxides (M = Ag, Ce, Mo, V, Nb, W, In, Zr and Ru) and their applications in pollutants degradation, fine chemistry, and electrocatalysis, proposed their potential alternative applications. This review work contains some useful information and could be considered for publication. However, the authors should revise their manuscript before acceptance for publication according to the following comments:

• Comment 1 What are the substitution degrees of K by M in the [M]–K–OMS2 oxides? It should be discussed in the effect of substitution degree of K by M on physicochemical property of [M]–K–OMS2.

Response: As we have commented in the manuscript, doping processes can take place at three levels: a) at the level of framework, b) on the surface and c) in the tunnels. In OMS materials, K⁺ and other alkali/alkali earth metal cations occupy tunnel positions (VIII – coordination) due to their largest size, which gives stability to the tunnel structure. For this reason, K⁺ is replaced through post-synthesis processes, which are outside the scope of the review. In other words, K⁺ is not replaced by cationic dopants M since all the cations mentioned in the review have been incorporated from the beginning of the synthesis giving rise to structural (isomorphic) substitutions. We have added a comment and new extra-references in the introduction to clarify this point and for a better understanding of the doping process.

Besides, we have extended the discussion for the [Ce]– K – OMS2 oxide according to the information extracted from the reference, Applied Catalysis B: Environmental 201 (2017) 503–510, order to show the difference between both doping processes (in the tunnel or in the structure) (section 3.1.2). The main consequences regarding physic chemical properties and catalytic activity have also been addressed.

• Comment 2: Some tables should be needed to summarize the main preparation methods, chemical compositions, typical physicochemical property, performance, and references of the [M]–K–OMS2 oxides.

Response: We thank the referee for his/her constructive comment. We have incorporated new data in the tables throughout the manuscript. Besides, we have included new tables (tables 2 and 7) in section 3.1, giving more details in order to better describe the materials. We have tried to standardize data according to the available literature in order to avoid wrong conclusions.

• Comment 3: The catalytic mechanisms should be discussed. What are the active sites for the addressed reactions?

Response: We agree with the referee and we have made the proper changes. For completing this part, we have included new references about the respective mechanisms and we have discussed about the active species in each particular case.

• Comment 4: There are a large number of inappropriate English words or expressions in the manuscript. The authors should carefully polish the English of the whole manuscript

Response: We appreciate this comment. We have fixed some grammar errors and we have rewritten some sentences. We think that the general redaction has improved after these changes.

Reviewer 2 Report

The manuscript “Recent manganese oxide octahedral molecular sieves OMS-2 with isomorphically substituted cationic dopants and their catalytic applications” represents review describing the structural and physico-chemical properties of K-OMS2 with different transition metal cations. Authors analyzed the structure propertied of MnO2 oxides, the synthesis methods to get isomorphic substituted materials, catalytic application of these oxides. Although it is an interesting review, there are several aspects that must be reviewed before it can be accepted for publication.

• Information about differences of MnO2 forms should be improved. For examples, cell or space group of MnO2 (Table 1) should be added. Table 1, instead of «name» it is better to use «structure type», since spinet is MgAl2O4 ets. It would be nice if authors indicate some correlation between way of octahedral organization and oxidation state of Mn ions.
• Some repetitions and typos.

Lines 148,184 (AOS)

337, 348. 396, 456, 507 [.  ]

401 (XRPD diffraction instead of XRPD)

Author Response

RESPONSE TO REFEREE #2

The manuscript “Recent manganese oxide octahedral molecular sieves OMS-2 with isomorphically substituted cationic dopants and their catalytic applications” represents review describing the structural and physico-chemical properties of K-OMS2 with different transition metal cations. Authors analyzed the structure propertied of MnO2 oxides, the synthesis methods to get isomorphic substituted materials, catalytic application of these oxides. Although it is an interesting review, there are several aspects that must be reviewed before it can be accepted for publication:

• Comment 1: Information about differences of MnO2 forms should be improved. For examples, cell or space group of MnO2 (Table 1) should be added. Table 1, instead of «name» it is better to use «structure type», since spinet is MgAl2O4 ets. It would be nice if authors indicate some correlation between way of octahedral organization and oxidation state of Mn ions.

As suggested by the referee we have expanded the structural information of Mn oxides in Table 1. For this, we have included information regarding the formula, space group and manganese oxidation states distribution in order to facilitate the understanding. Besides, we have also included new bibliographic citations. Our approach is that Table 1 can give a general idea to the readers. Then if they want to deepen into any of the allotropic forms presented, they should search for the referenced literature.

Nonetheless, we have kept the “name” column (in Table 1) provided all the MnO₂ materials reported in the review come from the same mineral analog, so we think that this nomenclature can be useful to understand the structure and composition of the oxides.

As requested by the referee, we have also included information about the structure and manganese oxidation state distribution in Table 1. In this regard, it is important to indicate that there is not a clear correlation between these two parameters (structure/Mn oxidation state). Finally, we have also described the reaction mechanisms in each particular case.

• Comment 2: Some repetitions and typos. Lines 148,184 (AOS). 337, 348. 396, 456, 507 [. ].401 (XRPD diffraction instead of XRPD)

Response: We appreciate the interest of the referee in correcting all the details.

We have corrected these mistakes as well as others that had gone previously unnoticed.