Lignin as a Bio-Sourced Secondary Template for ZSM-5 Zeolite Synthesis
Round 1
Reviewer 1 Report
The declared aim of this study was ‘to rationally design ZSM-5 zeolites using lignin as a BSST and investigate the effect of synthesis duration on crystallinity and structural properties’. What was the target of this rational design? The chosen system is definitely not one that can be considered for any kind of practical application (scale-up) since the use of TEOS as the silica source disqualifies it almost from the start, except for lab experimentation. TEOS is too expensive in comparison to other silica sources, harmful upon inhalation and susceptible to hydrolysis upon storing, so it is generally avoided. This point should be touched on and explained to readers.
In my opinion the lignin-based synthesis does not produce ZSM-5 equivalent to the TPA-based synthesis as indicated by lower microporosities and acid site concentration, which translates into lower activity. In short, the former (lignin) is not only different but inferior, based on the presented data and this should be the theme of the discussion. There is a general problem with the results because they vary (fluctuate) very much even when they are expected to be stable, like the crystallinity and textural properties. They are being analyzed at the ‘face value’, i.e., based on the numbers, without consideration that there may be something inconsistent about this all. The crystallinity discussed below is illustrative of this. The authors carried out a lot of syntheses, characterization and testing but there is hardly any trend in the data. It must be tackled, somehow, in the discussion.
The way the crystallinity of products is evaluated, relying exclusively on the measured intensity of the peak around 23 degree gives very erratic results. During the reported syntheses this value fluctuated with time so one begins to wonder if it has any meaning in this case. Typically, when the crystallization is complete, i.e., all gel phase is converted, the X-ray diffraction pattern remains stable except when there is recrystallization. Visual assessments of the patterns indicates that the regular ZSM-5 is fully crystalline after 8 hrs. (no amorphous halo) while the LZSM-8 after 12 hrs. I cannot understand why there is so much variation with time, and especially why the microporosity data do not match the crystallinity trends. Maybe the crystals change but maybe the measurements are somehow flawed or the static preparation influences heterogeneity of solids and sampling. Another measure of crystallinity mentioned above is micropore volume but in this case there is a lot of unexplained variation also, especially after the maximum value was reached (12 hrs. for ZSM-5 and 16 hrs. LZSM-5). Frankly, I am not sure how this could be explained and I am looking forward to the authors opinion. This part requires a new look and complete revision. It is my opinion the normal ZSM-5 synthesis proceeds faster than LZSM-5, which maybe because the latter has less TPAOH, and lignin plays a marginal templating role or none at all. This could be tested by performing synthesis with reduced amount of TPAOH and no lignin. I think the entire discussion in lines 106 to 129 can be eliminated as basically speculation based on selected results from the literature. It tries to rationalize behavior of the crystallizing system, which is obscure except that it happens (somehow). It is not relevant in this case.
The reported acid sites concentrations are much greater for the normal ZSM-5 than those obtained in the presence of lignin. This suggests that with lignin much less active catalysts are obtained so the replacement of TPAOH has detrimental effect. It also changes the catalytic activity towards a product favored by less active environment. The authors focus on discussing specific quantitative results but should also make evaluation based on pros and cons of each synthesis, since obviously they do not produce comparable results.
Author Response
Dear reviewer,
Please see the attachment.
Kind Regards,
Camila
Author Response File: 
Author Response.pdf
Reviewer 2 Report
I previously reviewed this paper and felt it was publishable after minor revisions, which the authors have address satisfactorily. I believe that the authors should add their explanations in the response letter to the manuscript, and after that it will be publishable.
Author Response
Dear reviewer,
Thank you for your contributions.
Kind Regards,
Camila
Reviewer 3 Report
I think this manuscript version needs no further revisions. I agree to be considered for publication in the current form.
Author Response
Dear reviewer,
Thank you for your contributions.
Best Regards,
Camila
Round 2
Reviewer 1 Report
I am satisfied with the responses and changes made by the authors and can support acceptance of this manuscript.
