H-Beta Zeolite as Catalyst for the Conversion of Carbohydrates into 5-Hydroxymethylfurfural: The Role of Calcination Temperature

Round 1

Reviewer 1 Report

The authors offer an interesting analysis of the effect of calcination temperature on the performance of the H-Beta zeolite catalyst in the isomerization/dehydration of glucose to 5-hydroxymethylfurfural (HMF). The experiments have demonstrated that calcination accounts for the loss of catalyst activity due to the depletion of acid sites, mainly Lewis acidic. This has a profound impact on the isomerization of glucose and follow-up transformation into HMF. The study was well-structured and was sufficiently exhaustive (given the scope). Thus, I recommend the publication upon minor revisions. I leave a few comments for the authors' consideration:

·       I find the term dealumination rather confusing since calcination does not remove any aluminum atoms from the material but impacts the coordination environment of the aluminum centers. Since I understand it is perhaps common practice to use the term "dealumination," I will not discourage its use. However, I would avoid the use of expressions such as "removal" or "elimination" and use "depletion" when referring to extra or intra-framework aluminum centers. This should improve the clarity of some passages.

·       No feedstock widely used in the food industry represents a good starting material for producing HMF or other newly designed platform molecules for the chemical industry. Do the authors agree with this statement? If so, can the authors specify more precisely which feedstocks are most convenient for producing HMF and their corresponding natural sources? This will significantly improve the introduction section.

·       The HMF productivity is often defined in a limited time frame, which is within the first hours of the reaction. This makes clear that the catalyst is prone to deactivation, most likely due to the accumulation of humins, from which the requirement of regenerating the catalyst. Do the authors agree with this statement? If so, can the authors specify more clearly which is the most common deactivation mechanism for H-Beta catalysts where more appropriate across the manuscript? Also, can they indicate what the typical regeneration protocol is?

·       The authors make an interesting observation: the procedures involved in catalyst regeneration (calcination) can affect the catalyst's stability cycle after cycle. To improve the value of the work, I suggest highlighting this finding already in the abstract. 

·       Figures 5 and 6 do not describe the difference between detail (a) and (b). 

Thanks in advance for your attention and consideration. I hope that my input will help further improve the present contribution to the satisfaction of the authors and readers.

Occasionally, uncommon words are used. I simply suggest sticking to a simple vocabulary (e.g., increased instead of augmented).

Author Response

First of all, thank you very much for listening to our manuscripts during your busy schedule. This is our pleasure. We have done our best to respond to your valuable comments in a peer-to-peer manner, as shown in the uploaded file. We hope that our work will be recognized by you. Looking forward to your feedback.

Author Response File: Author Response.pdf

Reviewer 2 Report

Zeolites are widely used in the conversion of biomass and individual products of its processing, like glucose. The paper presents interesting results on the use of H-Beta zeolites calcined at different temperatures in the conversion of glucose and cellulose to 5-hydroxymethylfurfural. In general, the conclusions are based on reliable results of catalyst characterization and testing. The methods used for characterization are adequate and provide information about the state of catalystsm including the neature and content of acid sites, texture parameters and products formed in the course of the catalytic conversion. The only comment that should be made is related to the observed fact of the decreasing concentration of Lewis acid sites with increasing calcination temperature. It is known that while increasing the calcination temperature, the Broensted acid sites (bridged OH groups) are removed and thus are converted into Lewis acid sites (low coordinated framework or extra-framework Al ions). THus, an increase in the content of Lewis acid sites should be expected at temperatures of pretreatment higher than 700oC. The authors should comment on this discrepancy.

Minor editing may be needed

Author Response

First of all, thank you very much for listening to our manuscripts during your busy schedule. This is our pleasure. We have done our best to respond to your valuable comments in a peer-to-peer manner, as shown in the uploaded file. We hope that our work will be recognized by you. Looking forward to your feedback.

Author Response File: Author Response.pdf