Activated Carbons from Fast Pyrolysis Biochar as Novel Catalysts for the Post-Treatment of Pyrolysis Vapors, Studied by Analytical Pyrolysis

Round 1

Reviewer 1 Report

This manuscript described the synthesis of three different biochars derived from willow, birch and pine, and their corresponding activated form. Characterizations were done for these biochars and activated biochars on the surface area, pore size, surface functional group and so on. The so-called catalysis performance on vapor was also analyzed. However, my biggest concern is how to confirm the catalysis effect? The authors fail to exclude the effect from biochar (or AC) sorption, or the releasing of intrinsic chemicals on biochar (or AC) surface. As the catalysis performance is the key part of this manuscript, I would like to suggest a major revision, with the outcome in doubt. Other specific comments were listed as follows:

1) Line 63,64, how to define physical activation and chemical activation? Why >700°C heating was considered as physical activation?

2) Line 118-119, how much catalyst was placed?

3) For the tables that have sample names (specifically, they are table 1,3,4), it is very confusing to understand the sample name. I would suggest the authors add underlines to every single samples.

Author Response

Dear Reviewer 1,

 

Thank you for your comments to the our manuscript. Please see the attachment. 

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

C (ISSN 2311-5629)

 

carbon-931106

 

Activated carbons from fast pyrolysis biochar as novel catalysts for the post-treatment of pyrolysis vapors, studied by analytical pyrolysis

 

This paper reports biochars and their activated porous carbons from a range of biomass precursors. Then studied as catalyst for a post-treatment of pine wood pyrolysis vapors, aiming at stabilizing the vapors before their condensation. Among the samples, activated carbon catalysts with increased surface area and pore volume reduced the oxygen content of the pyrolysis degradation products. The residual high mineral contents also show profound effect.

 

Note that the reported surface area and porosity values of the activated carbon catalyst samples in Table 4 are significantly lower than the commonly achieved values (authors statements at line 30 and 52) of over 1000 m2/g to up to 4000 m2/g, for instance refer to “Superior Multifunctional Activity of Nanoporous Carbons with Widely Tunable Porosity: Enhanced Storage Capacities for Carbon‐Dioxide, Hydrogen, Water, and Electric Charge. Adv. Energy Mater. 2020, 10, 1903649. https://doi.org/10.1002/aenm.201903649, which comprehensively summarises hundreds of activated/templated carbon porous structures with significantly increased specific surface areas along with pore size and pore volumes, and surface functional groups. Such carbon structures show significantly enhanced adsorption binding and uptake capacities for vapours, liquids and other small gaseous molecules.

Such relevant reference works in the introduction (lines 29-35, 60-65, etc) can boost the understanding of the structures.

 

It is suggested to provide N2 adsorption-desorption isotherms and pore-size, pore-volume plots to understand the true nature of porous characteristics if the active carbon samples reported in Table 4.

 

Then the influence of particular porosity characteristic can be attributed to catalytic activity – currently it is not fully clear as what is main factor in the paper. For example, there are metal-organic framewroks and graphene carbons in addition to the biomass carbons. For instance, Size‐Related Electrochemical Performance in Active Carbon Nanostructures: A MOFs‐Derived Carbons Case Study. Adv. Sci. 2019, 6, 1901517. https://doi.org/10.1002/advs.201901517

 

This paper maybe accepted for a publication after incorporating the above stated but highly relevant structural/porosity information, for the applicability of the reported work for a wide range of activated carbons.

Author Response

Dear Reviewer,

 

Thank you for your comments and suggestions to the our manuscript. Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I am still not satisfied with the reply on the catalyst/adsorption. Please provide more solid proof.

The authors say that (Pd/C) and activated carbon (Maxorb) could have significant contribution by sorption, but the carbon used in this work could not. Please explain why?

To my understanding, it is quite normal that the lower surface area, the less contribution of the sorption. And different compounds generaly show different sorption behaviors onto biochars. The author fails to provide convincing and quantifiying data to differentiate sorption and catalysis.

My suggestions are that:

1) provide the data that no compounds were injected into the biochar/activated biochars. This is to prove that there is no compounds desorb out of the biochars/activated biochars surface.

2) continuesly flow the compounds to the biochars/activated biochars, normally, the outlet gas compounds will show a increasing concentration if the sorption dominate the process; otherwise, the outlet gas concentration should maintained at a relatively low concentration if it is a catalysis process.

 

 

Author Response

Please see the attachment 

Author Response File: Author Response.pdf

Reviewer 2 Report

This MS can be accepted for a publication.

Author Response

Dear Reviewer,

 

Thank you for the positive response for the first revision. Now some minor changes and corrections has been made in second revision. 

Round 3

Reviewer 1 Report

Accept, no comments