Coal Fly Ash and Acid Mine Drainage-Based Fe-BEA Catalysts for the Friedel–Crafts Alkylation of Benzene

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this work, authors reported a Fe-HBEA catalyst that was prepared using coal fly ash and acid mine drainage as precursors. This manuscript can be accepted for publication, but the below issues should be addressed.

1.     Which ion in the HBEA was exchanged with the metal ion in AMD?

2.     I find that the metal loading amount increased as increasing the used AMD volume. So, what is the theoretic maximum ion-exchange amount?

3.     The stability and reusability of their catalyst should be considered.

4.     The morphology, structure and valence state of active species has great influence on the catalyst performance. Thus, their catalysts should be systematically characterized.

5.     There are many typos and errors in the manuscript. Authors should carefully check the manuscript.

Author Response

1. Which ion in the HBEA was exchanged with the metal ion in AMD?

The hydrothermal synthesised zeolite was converted to the H-form, thus the metals were exchanged with the proton. Section 3.2 presents the conversion of the Na-Zeolite to the H-Form.

2. I find that the metal loading amount increased as increasing the used AMD volume. So, what is the theoretic maximum ion-exchange amount?

The cation exchange capacity of the zeolite was not determined. However, the Si/Al ratio can give an idea of how many exchange sites are available per gram of zeolite assuming that all the framework positions occupied by Al are Bronsted acid exchange sites and accessible to the cations or metals being exchanged. Reviewer 2 also pointed out the need to present the Si/Al ratio. The Si/Al ratio was presented in Section 2.1.

3. The stability and reusability of their catalyst should be considered.

Determination of catalyst stability was not done since the objective was to explore the feasibility of using acid mine drainage as a metal precursor, and the FC alkylation of benzene was used as a probe reaction. Also considering that the most abundant metal that got loaded onto the zeolite was Fe with traces of other metals, in the case of those catalysts prepared via wet impregnation, it would be assumed that the reusability and stability of these catalysts would be comparable to those prepared using conventional feedstocks. Mostly stability and reusability of catalysts are affected by coking and heat sintering, and in the study the experiments were carried out under mild conditions which may render these effects less likely. It however was recommended under the Conclusion section that the stability and reusability studies ought to be undertaken  in future on these catalysts before their potential industrial application. The last statement in the conclusion section reads, “Furthermore, it is recommended that the stability and reusability of these catalysts are further investigated before their full industrial application can be considered.’

 

4. The morphology, structure and valence state of active species has great influence on the catalyst performance. Thus, their catalysts should be systematically characterized.

The Fe, when loaded onto a zeolite is either incorporated in Ferric or Ferrous form. Upon calcining the Fe loaded sample in air, most, if not all the Fe species convert to the Fe (III) species. It was however unfortunate that the XRD analysis done could not detect the nature of the Fe crystallites due to low concentration and good dispersion. A statement was made under section 3.3 and it reads, “When either ferrous sulphate or ferric sulphate is used as Fe solution precursor and exchanged onto the zeolite, calcination in air at 550 ˚C converts the Fe species to Fe³⁺ species via oxidation (Li, et al, 2023).

 

5. There are many typos and errors in the manuscript. Authors should carefully check the manuscript.

The typos and errors were attended to, it should however be noted that the language used in the article is English (UK). This may make certain spellings to be wrong if considered in English (US).

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This work deals with the simultaneous valorization of wo wastes: coal fly ashes to produce BEA zeolite and mine drainage as a metal precursor. The idea is very interesting and fits the interest of “Catalyst” readers but, in my opinion, there are some issues that need to be polished before publication. Accordingly, I recommend a “Major Revision”.

The issues that need to be reviewed are:

-          The Si/Al ratio of HBEA zeolite that is produced from coal fly ash needs to be presented. Indeed, the acidity of the zeolite is fundamental for this type of reactions, so the Si/Al ratio is an important parameter required for this study.

-          Catalyst characterization – Line183: the experimental technique used for textural characterization is N2 adsorption isotherms at -196 ºC. The BET method is a model that is used to estimate the surface area from the raw data obtained from the isotherms. Please correct. Also, in the discussion of the textural parameters (Line 285), please add the method that was used to calculate the mesopore size distribution and the micropore surface area (Table 5).

-          Catalytic test: I cannot agree with chosen type of plots (experimental points connected by lines). As the experimental points were not acquired in continuum mode, a dispersion plot is more adequate. The authors can add a smooth dashed line to guide the viewer eyes. This procedure should be performed in all plots making them “cleaner” and easier to interpretate. I also believe that the interpretation of the catalytic results would be easier if the authors could add reaction schemes to elucidate the reaction route and side products.

-          Effect of various metal in AMD on the FC alkylation reaction (Line437). It is very difficult to me to understand the idea and the results for these experiments because the values presented on Figures 6 are very close and probably within the experimental error (again the lines connecting the dots contribute for confusing the readers eyes). I ask if the errors associated with the catalytic assays were taken into consideration. If not, the interpretation of this section can be seriously compromised.

Author Response

The issues that need to be reviewed are:

-          The Si/Al ratio of HBEA zeolite that is produced from coal fly ash needs to be presented. Indeed, the acidity of the zeolite is fundamental for this type of reactions, so the Si/Al ratio is an important parameter required for this study.

The Si/Al ratio obtained by ICP-OES was stated in Section 2.1 under elemental composition.

-          Catalyst characterization – Line183: the experimental technique used for textural characterization is N2 adsorption isotherms at -196 ºC. The BET method is a model that is used to estimate the surface area from the raw data obtained from the isotherms. Please correct. Also, in the discussion of the textural parameters (Line 285), please add the method that was used to calculate the mesopore size distribution and the micropore surface area (Table 5).

The rectification under “Catalyst characterisation” was made and BET was replaced with N₂-adsorption. With regard to the equations used to calculate the mesopore size distribution, the statement was added…”Surface area determination was performed using the Brunauer-Emmett-Teller (BET) equation and the pore size distribution determined using the Barrett, Joyner, Halenda (BJH) equation”

 

-          Catalytic test: I cannot agree with chosen type of plots (experimental points connected by lines). As the experimental points were not acquired in continuum mode, a dispersion plot is more adequate. The authors can add a smooth dashed line to guide the viewer eyes. This procedure should be performed in all plots making them “cleaner” and easier to interpretate. I also believe that the interpretation of the catalytic results would be easier if the authors could add reaction schemes to elucidate the reaction route and side products.

The plots were changed as recommended and these are: Figure 3, Figure 4, Figure 5 and Figure 6. Reaction Scheme 2 was presented to clarify the issue of product distribution and a brief description of the by-products was presented prior to presenting the scheme.

 

-          Effect of various metal in AMD on the FC alkylation reaction (Line437). It is very difficult to me to understand the idea and the results for these experiments because the values presented on Figures 6 are very close and probably within the experimental error (again the lines connecting the dots contribute for confusing the readers eyes). I ask if the errors associated with the catalytic assays were taken into consideration. If not, the interpretation of this section can be seriously compromised.

The plots were changed as recommended and the scale of the graphs was also changed to enhance

visibility of the data points. It should be noted that after 1 hr on stream for most of the tested catalysts the activity (based on conversion of t-butyl chloride) increased rapidly, so effective comparison on the effect of other metals can probably be assessed based on the outcomes obtained after 0.5 hr on stream.  

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The paper can be accepted in present form