Mechanistic Insights into Visible Light-Induced Direct Hydroxylation of Benzene to Phenol with Air and Water over Pt-Modified WO3 Photocatalyst
, Yasuaki Matsuda 1, Yoshihisa Sakata 2, Hisayoshi Kobayashi 3 and Shinya Higashimoto 1,*Round 1
Reviewer 1 Report
The manuscript by Y. Kurikawa et al. describes on the "Mechanistic Insight into Direct Hydroxylation of Benzene to Phenol on the Pt-deposited WO3 Photocatalyst in the presence of Air and Water under Visible-Light Irradiation."
It gives the detailed mechanism for the conversion of benzene to phenol with the aid of visible-light photo-catalyst, Pt-deposited WO3, in presence of water and air. It also a combination of both experimental and theoretical calculations of a synthetic chemical transformation that has many practical implications. The mechanistic insight provided herein are supported by H218O labeling experiments, kinetic isotope effect and DFT calculations. Thus, I find the manuscript suitable for publication in "catalysts".
Author Response
Thank you very much for reading our manuscript and providing our manuscript with high evaluation. Thank you for taking your time.
Reviewer 2 Report
Please see the attached file.
Comments for author File: 
Comments.pdf
Author Response
Thank you very much for reading our manuscript and kindly provide us useful comments. In accordance with your comments, we revised our manuscript.
[Comment 1] The introduction section is too short. It should discuss the background studies in more detail.
[Reply 1] The revised parts are indicated in red (line 42~47). The sentence and references were added into introduction section as follows: Therefore, there is a great challenge to develop a one-step synthesis of phenol from benzene by using homogeneous and heterogeneous inorganic catalysts such as palladium membrane, titanium-containing mesoporous molecular sieves and vanadium-substituted phosphomolybdate using hydrogen peroxide (H2O2) [15-17]. Although H2O2 is often used as environmentally friendly oxidant only to produce H2O in catalytic hydroxylation of benzene, O2 is more ideal oxidant than H2O2 due to its abundance in nature.
[Comment 2] The paper lacks the novelty part that should be included.
[Reply 2] Thank you for your instructive comments to improve our manuscript. We added a novelty in the conclusions (shown in red) as follows: One of novelties in our findings was to demonstrate the reaction mechanisms for photocatalytic hydroxylation of benzene into phenol by experimental and theoretical studies. Investigation of mechanistic insight has been carried out by combination with apparent quantum yields (AQY), H218O isotope labeling experiment, kinetic isotope effects (C6D6, D2O), electrochemical measurements and DFT calculations. It was confirmed that the substitution of the OH derived from H2O with H abstracted from benzene by photo-formed H2O2 indicated a mechanism involving push-pull process for the hydroxylation of benzene into phenol.
[Comment 3] Figure 3 has two y-axes. However, the single data (black circles) is provided. Include the data for the other axis.
[Reply 3] We carefully checked Fig. 3. However, I think that the other axis is provided in Fig. 3. I wish that you could check it again if it is appropriate.
[Comment 4] Conclusion is merely a summary, it should be re-written to better conclude the paper.
[Reply 4] Thank you for your instructive comments to improve our manuscript. We extensively revised in the conclusion section in red. The revised manuscript is as follows: In this study, we provided an understanding of photocatalytic activities for hydroxylation of benzene under irradiation of only visible-light (420 < λ< 540 nm). It was demonstrated that hydroxylation of benzene on the Pt-WO3 photocatalyst in the presence of air and H2O produced several products such as phenol, catechol and phloroglucinol etc., and the selectivity of phenol improved over 70%.
One of novelties in our findings was to confirm the reaction mechanisms for photocatalytic hydroxylation of benzene into phenol by experimental and theoretical studies. Investigation of mechanistic insight has been carried out by combination with apparent quantum yields (AQY), H218O isotope labeling experiment, kinetic isotope effects (C6D6, D2O), electrochemical measurements and DFT calculations. It was proposed that the substitution of the OH derived from H2O with H abstracted from benzene by photo-formed H2O2 indicated a mechanism involving push-pull process for the hydroxylation of benzene into phenol. Our results showed new perspectives for enhancement of yields and selectivity of phenol, as well as deeper understanding of the reaction mechanisms for hydroxylation of benzene into phenol on the Pt-WO3 photocatalyst.
