Effect of Mono-, Di-, and Triethylene Glycol on the Activity of Phosphate-Doped NiMo/Al2O3 Hydrotreating Catalysts
, Galina A. Bukhtiyarova 1,2, Aleksander A. Porsin 1, Igor P. Prosvirin 1, Irina V. Deliy 1,2, Vladimir A. Volodin 2,3, Evgeny Yu. Gerasimov 1,2, Evgeniya N. Vlasova 1,2 and Valerii I. Bukhtiyarov 1,2Round 1
Reviewer 1 Report
This manuscript entitled “Effect of mono-, di- and triethylene glycol on the activity of phosphate-doped NiMo/Al2O3 hydrotreating catalysts” deals on the study of the effect of the presence of different glycols in the hydrotretaing properties of phosphate-doped NiMo catalysts. The research is original, contains interesting information and is into the scope of Catalysts. However, many parts of the paper require improvements and major changes to consider the paper as publishable.
1.- The preparation of the different catalysts is not totally reproducible . This part must be rewritten giving complete details. Please, identify the used support, alumina, giving full details.
2.- The XPS source is or not monochromatic.
3.- Information concerning the spent catalysts is mandatory, specially the surface composition determined by XPS and the corresponding chemical state of the active phases.
4.- The catalytic results and their discussion are very scarce and poor. This part must be expanded giving information about conversion and stability after longer reaction periods.
5.- The main effect of the studied glycols is a higher active phase dispersion, and this parameter is not reported along the text of the manuscript.
Author Response
Response 1. We agree with Reviewer. Section "3.1 Catalyst preparation" supplemented.
Response 2. Non-monochromatic Al Ka radiation (was specified in the manuscript)
Response3. The sulfide catalysts were studied by XPS, XRD and TEM methods after liquid-phase sulfidation and evaluation of catalytic activity in the hydrotreating of SRGO (the reaction was continued until constant level of sulfur). The initial state of catalysts was not studied, because liquied-phase sulfidation is time-consuming procedure.
Response 4. We agree with Reviewer. Section "2.3. The catalytic properties were determined at 330 and 340°C, but only rate constants calculated for the data at 330°C were specified in the first version of manuscript as more representative results, reflecting the difference in the behavior of the catalysts. The sulfur level obtained after SRGO hydrotreating is not suitable for the calculation of HDS constant (too little sulfur level), but doesn’t correspond ULSD level. Revised manuscript is supplemented by catalytic results obtained at 340 °C (Table 5) and some other details. According to the results obtained, the sulfur level was decreased after temperature increase from 330 to 340°C, reached steady-state level after 8 hours of operation and was kept at the same level for 24 hours.
Response 5. The classical definition of dispersion expressed as the ratio of surface metal atoms to the total number of atoms cannot be applied to the molybdenum sulfide nanoparticles, which have layered anisotropic structure. The XPS method is used to evaluate qualitatively the dispersion of Ni (or Co) and Mo in hydrotreating catalysts:
1. Iwamoto, R.; Kagami, N.; Sakoda, Y.; Iino, A. Effect of polyethylene glycol addition on NiO-MoO3/Al2O3 and NiO-MoO3-P2O5/Al2O3 hydrodesulfurization catalyst. J. Jpn. Petrol. Inst. 2005, 48, 351–357
2. Iwamoto, R., N. Kagami, et al. (2005). "Effect of polyethylene glycol addition on hydrodesulfurization activity over CoO-MoO3/Al2O3 catalyst." Journal of the Japan Petroleum Institute 48(4): 237-242
3. Escobar, J.; Barrera, M.C.; Toledo, J.A.; Cortes-Jacome, M.A.; Angeles-Chavez, C.; Nunez, S.; Santes, V.; Gomez, E.; Dıaz, L.; Romero, E.; Pacheco, J.G. Effect of ethyleneglycol addition on the properties of P-doped NiMo/Al2O3 HDS catalysts: Part I. Materials preparation and characterization. Appl. Catal. B: Environ. 2009, 88, 564–575.
The change of Ni(Co)/Al and Mo/Al surface ratios was used to follow the effect of different parameters (glycol addition) on the metal species “dispersion” on the support surfaces (both in oxide and sulfide catalyst). Indeed, the smaller is the sizes and stacking of MoS2 particles, the higher is Mo/Al surface ratio. We used the Ni/Al and Mo/Al surface ratios to follow, how the addition of different additives on the Ni and Mo surface distribution in the oxide and sulfide state. The change of Ni/Al and Mo/Al surface ratios was also evaluated after sulfidation of the catalysts.
Section “2.2. Catalyst characterization” (Page 5) contains following sentence “The Mo dispersion in the sulfided catalysts in the term of Mo/Al ratio is decreased in the following order: NiMoP-DEG/Al2O3 > NiMoP-EG/Al2O3 > NiMoP-TEG/Al2O3 > NiMoP/Al2O3.”
Section “2.3. Catalytic activity” (Page 7) contains following sentences “…the addition of EG, DEG and TEG in the impregnation solution increases the catalytic activity by a factor of 2.2, 2.8 and 1.3, respectively. These results can be explained by the influence of organic additives on the dispersion of Mo in the sulfide catalyst (Table 2). Besides, the activity of NiMoP-DEG/Al2O3 exceeding that of NiMoP-EG/Al2O3 may be associated with a higher Ni dispersion.”
Thus, the correlation between the dispersion of active metals and catalytic activity is discussed in the text of the manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript deals with the effect of poly-alcohols (glycols) additives on the catalytic activity of NiMoP/Al2O3 materials in the hydrotreatment of a SRGO fraction. The addition of EG, DEG and TEG compounds during the metallic species impregnation onto the g-Al2O3 support is studied. Characterization of materials by chemical analysis, N2 adsorption isotherms, XPS, Raman, UV-Vis, and HR-TEM has been made by the authors. Results indicate that the addition of DEG, EG and TEG (in this order) increase the HDS and HDN activity of the sulfided NiMoP/g-Al2O3 catalyst when comparing with the non-modified analogous sample. This fact is mainly due to a better dispersion of metallic species when the additive is present, although a redistribution of Mo species is observed after sulfidation.
The paper is of interest for both academic and industrial viewpoints. Its quality is adequate, although the originality of research work is less remarkable. Moreover, some important points need further explanations and discussions by the authors (see major comments and remarks listed below):
i) As above-mentioned, the research work is interesting but the idea of using poly-alcohols (glycols) as additives is just revisited (see at least Refs. 6-12 and 14-17 cited in this manuscript). The more relevant point, the study and evaluation of the redistribution of Mo species after sulfidation remains uncertain, and authors say that further studies are needed to assess this point. In my opinion, these data should be shown in this manuscript. Authors must solve this important concern.
ii) Authors conclude that the best results are observed with NiMoP-DEG/g-Al2O3, arguing that a higher dispersion of Mo on the surface of the catalyst is achieved. The question is Why DEG is better than EG or TEG to perform this Mo dispersion? What is the the chemical or physical reason for that? Authors must address this issue.
iii) With respect to the Raman spectra of aqueous solutions (Figure 2, page 3) authors comment that impregnation solutions containing EG and DEG showed the same results. These data should be provided at least as Supplementary Information (SI).
iv) In Table 1, the type of measurement performed for chemical composition determination must be mentioned (at least as a foot-note text of the table).
v) Which type of SRGO fraction is used by the authors? Although a very brief description of the petroleum fraction is given in section 3.3. Catalyst tests, main properties and composition (including the amount of S and N) must be provided by the authors (for example in a proper table).
vi) English version is right, although several grammatical and type-settings faults are encountered all along the text. Authors must carefully revise them.
Summarizing, I could consider the manuscript suitable for publication but further enhancements are needed. Authors must carefully revise the paper by following this reviewer’s comments and remarks above-mentioned.
Author Response
Response i) and ii). We agree with Reviewer that poly-alcohols were used in the several works early, but there were not found the comparison of all studied glycols (EG, DEG, TEG) in the same reactions, using the same support and experimental methods for catalyst preparation and study. Moreover, the model reactions, such as toluene hydrogenation and HDS of DBT were used to estimate the glycol effect in most cases. To our knowledge, there is no reference in the scientific literature, comparing the effect of different glycols on the activity of sulfide NiMo(P)/Al2O3 catalysts and disclosing the benefit of DEG compared with other studied glycols. So, the new experimental results were described in the manuscript. We also agree with Reviewer, that study and evaluation of the redistribution of Mo species after sulfidation is relevant issue. The study of the influence of glycol nature on the sulfidation is a major work that requires a lot of time and the development of special research methods. For example, the work [1] is fully dedicated to the effect of phosphate and glycol on the sulfidation mechanism of CoMo/Al2O3 hydrotreating catalysts. To understand the effect of glycol nature on Mo dispersion and catalytic properties of NiMo(P)/Al2O3 catalysts, a detailed study of the sulfidation mechanism will be conducted. We can speculate, that physical properties of glycol, such as viscosity and boiling temperature can effect on the redistribution of oxide species during drying, the water and glycol content in the dried samples, and on sulfidation process. The above listed issues will be considered in the future studies.
[1] Nicosia, D.; Prins, R. J. Catal. 2005, 231, 259–268.
Response iii) Raman spectrum of NiMoP-TEG solution is added to Supplementary Information. Spectrum of NiMoP-EG solution is similar.
Response iv) The type of measurement performed for determination of chemical composition of the catalysts is added to footnote text of the table 1.
Response v) We agree with Reviewer. Table 4 “Characteristics of the feedstock” is added.
Response vi) The text is corrected.
Author Response File: Author Response.pdf
Reviewer 3 Report
I only have minor comments for the authors:
1. A comparison of the current catalytic activity with similar literature data should be inserted, for a better evaluation of the accomplished results;
2. Please explain the acronyms (HDS and HDN) when introduced for the first time in the text.
Author Response
Response 1.
It is well known that nature and content of sulfur, nitrogen and aromatic compounds in feedstocks as well as the sulfidation procedure have a significant influence on the HDS activity. The glycol-modified catalysts were investigated in the HDS of model compounds [ref. # 6−12,16,17 in manuscript] and gasoil fractions [ref. # 10,12,16,17 in manuscript]. In these papers the different feedstocks and sulfidation procedure were used. Therefore, comparison of the catalytic activity with similar literature data is difficult.
Meanwhile, our results show that the catalysts prepared using glycols show a higher HDS activity than the catalyst prepared without the additive. This is consistent with the results, obtained in [ref # 6-12 in manuscript].
Response 2
We agree with Reviewer.
Author Response File: Author Response.pdf
Reviewer 4 Report
In the paper “Effect of mono-, di- and triethylene glycol on the activity of phosphate-doped NiMo/Al2O3 hydrotreating catalysts”, authors studied the effect on the catalytic activity for the hydrotreating of the straight-run gas oil (SRGO), using ethylene glycol (EG), diethylene glycol (DEG) and triethylene glycol (TEG) in the synthesis of catalysts. The argument might be of great interest for commercial applications to refining fuels.
Although the results provide interesting preliminary indications regarding the beneficial effect of glycols, I found several problems in this manuscript. The authors devote sufficient attention to the characterization of glycol solutions and to the adsorption process by Raman and UV-Vis, but the characterization of the surface of catalysts is less thorough, and the catalysis is limited to a single condition test.
Catalysts were studied by XPS in oxide form, and by BET(??), XPS and TEM after testing in hydrotreating. The TEM results could be better described and analyzed: the average particles (which nature?) sizes determined by statistical processing in the range 4.5–5.2 nm did not give direct information on Ni dispersion. In particular, the concept of dispersion is limited to the XPS Me/Al and ratio, failing to deepen or clarify what the true effect of glycol addition is. Characterization should be completed at least by XRD and/or CO adsorption to have an evaluation of the metallic surface area (Ni/Mo dispersion) on the surface.
Experimental: The sample treatment procedure after catalysis to perform XPS and TEM analysis is missing.
Samples were tested in only one catalytic test, that is not sufficient to have an idea of catalytic properties of the materials.
It is my opinion that this study does not meet the scientific quality requirements of the "Catalysts" journal and should be extended in the characterization, in the study of the catalytic activity and in the discussion before being published.
Figure S5. Better deconvolution instead of decomposition
Author Response
Point 1:
Catalysts were studied by XPS in oxide form, and by BET(??), XPS and TEM after testing in hydrotreating. The TEM results could be better described and analyzed: the average particles (which nature?) sizes determined by statistical processing in the range 4.5–5.2 nm did not give direct information on Ni dispersion. In particular, the concept of dispersion is limited to the XPS Me/Al and ratio, failing to deepen or clarify what the true effect of glycol addition is.
Response 1
According to TEM data, the morphology of the samples is typical of NiМо/Al2O3 sulfide catalysts and corresponds to the structure of molybdenum disulfide МоS2 (lines 170-171 in manuscript).
The XPS method can be used to determine the dispersion of Ni (or Co) and Mo in hydrotreating catalysts.
1. Escobar, J.; Barrera, M.C.; Toledo, J.A.; Cortes-Jacome, M.A.; Angeles-Chavez, C.; Nunez, S.; Santes, V.; Gomez, E.; Dıaz, L.; Romero, E.; Pacheco, J.G. Appl. Catal. B: Environ. 2009, 88, 564–575
2. van Haandel, L.; Bremmer, G.M.; Hensen, E.J.M.; Weber, Th. J. Catal. 2017, 351, 95–106
3. Iwamoto, R.; Kagami, N.; Sakoda, Y.; Iino, A. J. Jpn. Petrol. Inst. 2005, 48, 351–357
4. Nguyen, T.S.; Loridant, S.; Chantal, L.; Cholley, T.; Geantet, C. Appl. Catal. B: Environ. 2011, 107, 59
According to the alternative approach, “the extent of the sulfide phase dispersion” can be estimated, using the average fraction of Mo atoms at the MoS2 edge surface, calculated, assuming that the MoS2 slabs were perfect hexagons:
1. S. Kasztelan, H. Toulhoat, J. Grimblot, J.P. Bonnelle, Appl. Catal. 13 (1984) 127.
2. G. Berhault, M. Perez De la Rosa, A. Mehta, M.J. Yácaman, R.R. Chianelli, Appl.Catal. A 345 (2008) 80.
3. Pimerzin, A., A. Mozhaev, et al. (2017). "Comparison of citric acid and glycol effects on the state of active phase species and catalytic properties of CoPMo/Al2O3 hydrotreating catalysts." Applied Catalysis B-Environmental 205: 93-103.
But at least two assumptions should be assumed in this case. Firstly, the statement about morphology of MoS2 slabs as perfect hexagons is questioned in the present-day studies, that describe sulfide nanoparticles as truncated triangles with the changing ratio of M and S edges, depending on the preparation, sulfidation and working conditions. Some examples of such articles are given below:
1. Chen, J. J., E. D. Garcia, et al. (2016). "Effect of high pressure sulfidation on the morphology and reactivity of MoS2 slabs on MoS2/Al2O3 catalyst prepared with citric acid." Journal of Catalysis 339: 153-162.
2. Chen, J. J., L. Oliviero, et al. (2015). "On the morphology of MoS2 slabs on MoS2/Al2O3 catalysts: the influence of Mo loading." Rsc Advances 5(99): 81038-81044.
3. Schweiger, H., P. Raybaud, et al. (2002). "Shape and edge sites modifications of MoS2 catalytic nanoparticles induced by working conditions: A theoretical study." Journal of Catalysis 207(1): 76-87.
Then, it is known, that only part of sulfide nanoparticles is observable by means of transmission electron microscopy (TEM). The thread-like fringes corresponding to the MoS2 edges is visible on TEM picture, while the particle situated with basal plane are missing.
So, we tried to use impartial method for the dispersion evaluation, free of speculative assumptions.
Point 2:
Characterization should be completed at least by XRD and/or CO adsorption to have an evaluation of the metallic surface area (Ni/Mo dispersion) on the surface.
Response 2.
The NiMo(P)/Al2O3 sulfide catalysts were characterized by XRD. The XRD patterns are added to Supplementary Materials. Currently, we cannot conduct research on CO adsorption.
Besides, the classical definition of dispersion expressed as the ratio of surface metal atoms to the total number of atoms (or metallic surface area) cannot be applied to the molybdenum sulfide nanoparticles, which have layered anisotropic structure.
Point 3:
Experimental: The sample treatment procedure after catalysis to perform XPS and TEM analysis is missing.
Response 3.
The sample treatment procedure after catalysis to perform XPS and TEM analysis is added.
Point 4:
Samples were tested in only one catalytic test, that is not sufficient to have an idea of catalytic properties of the materials.
Response 4.
We agree with Reviewer only partly. It is usual practice in the catalytic study to use only one catalytic reaction for the catalytic properties study. There are a lot of works, where one reaction (toluene hydrogenation, thiophene HDS, DBT HDS) was used for catalytic properties evaluation and comparison. In our case the catalytic properties in SRGO HDS were determined at 330 and 340°C, but only rate constants calculated for the data at 330°C were specified in the first version of manuscript as more representative results, reflecting the difference in the behavior of the catalysts. The sulfur level obtained after SRGO hydrotreating is not suitable for the calculation of HDS constant (too little sulfur level), but doesn’t correspond to ULSD level. Revised manuscript is supplemented by catalytic results obtained at 340 °C (Table 5) and some other details. According to the results obtained, the sulfur level was decreased after temperature increase from 330 to 340°C, reached steady-state level after 8 hours of operation and was kept at the same level for 24 hours.
Point 5:
Figure S5. Better deconvolution instead of decomposition
Response 5.
We agree with Reviewer
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have considered all my suggestions and the manuscript has been improved. Now, I recommend it publication in Catalysts.
Author Response
This Review Report contains no comments.
Reviewer 4 Report
The paper is partly improved based on all the comments of all reviewers. The answers of the authors are only partially exhaustive and some critical aspects remain. In particular, the characterization of samples is poor. The catalytic results and their discussion are poor. No valid conclusions were presented on the role of different glycols in catalytic activity.
I wish to point out some aspects of the author’s answers (in red color):
Response 1
The XPS method can be used to determine the dispersion of Ni (or Co) and Mo in hydrotreating catalysts.
1. Escobar, J.; Barrera, M.C.; Toledo, J.A.; Cortes-Jacome, M.A.; Angeles-Chavez, C.; Nunez, S.; Santes, V.; Gomez, E.; Dıaz, L.; Romero, E.; Pacheco, J.G. Appl. Catal. B: Environ. 2009, 88, 564–575
2. van Haandel, L.; Bremmer, G.M.; Hensen, E.J.M.; Weber, Th. J. Catal. 2017, 351, 95–106
In that paper (2.) the XPS is not used to evaluate the dispersion but only the degree of sulphidation at different temperatures during the activation process of Mo/Al2O3 and CoMo/Al2O3 catalysts; whereas UV–Vis DRS was used to estimate the dispersion of supported molybdenum oxides. Samples were extensively characterized by many technics XPS, UV-Vis, EXAFS, XRD
3. Iwamoto, R.; Kagami, N.; Sakoda, Y.; Iino, A. J. Jpn. Petrol. Inst. 2005, 48, 351–357
4. Nguyen, T.S.; Loridant, S.; Chantal, L.; Cholley, T.; Geantet, C. Appl. Catal. B: Environ.2011, 107, 59
On that paper (4.) a comparative Co/Mo..etc.. atomic ratios were obtained by XPS but oxide and sulphide particles were extensively characterized by correlations between many technics XPS, UV-Vis, EXAFS, XAS, RAMAN.
Response 2.
The NiMo(P)/Al2O3 sulfide catalysts were characterized by XRD. The XRD patterns are added to Supplementary Materials. Currently, we cannot conduct research on CO adsorption.
Besides, the classical definition of dispersion expressed as the ratio of surface metal atoms to the total number of atoms (or metallic surface area) cannot be applied to the molybdenum sulfide nanoparticles, which have layered anisotropic structure.
It is clear that in the present case, a parameter like the dispersion should be connected to the particle size, ie to grow with the decrease of the particle size. Hence, given the difficulty of obtaining information on dispersion, my suggestion to use XRD took for granted to consider to use the Debye Sherrer equation to evaluate the size of MoS2 particles (if Ni sulphides are not detected). The XRD data had to be exploited to obtain structural information.
Response 4.
We agree with Reviewer only partly. It is usual practice in the catalytic study to use only one catalytic reaction for the catalytic properties study. There are a lot of works, where one reaction (toluene hydrogenation, thiophene HDS, DBT HDS) was used for catalytic properties evaluation and comparison. In our case the catalytic properties in SRGO HDS were determined at 330 and 340°C, but only rate constants calculated for the data at 330°C were specified in the first version of manuscript as more representative results, reflecting the difference in the behavior of the catalysts. The sulfur level obtained after SRGO hydrotreating is not suitable for the calculation of HDS constant (too little sulfur level), but doesn’t correspond to ULSD level. Revised manuscript is supplemented by catalytic results obtained at 340 °C (Table 5) and some other details. According to the results obtained, the sulfur level was decreased after temperature increase from 330 to 340°C, reached steady-state level after 8 hours of operation and was kept at the same level for 24 hours.
I completely agree that it s usual to study only one catalytic reaction. As reviewer I did not ask to study more reactions but only to test more experimental conditions.
Addition of activity at 340 °C has improved the activity information, but is to much close to 330 °C. But why not calculate the speed constant K in table 5? Why “not detected”? it is not a calculation?
Only 10 degrees of temperature 330-340 have increased the efficiency of the catalysts so much. Why to use 330? I think it is an aspect to be better explored and commented.
Author Response
Point 1: Hence, given the difficulty of obtaining information on dispersion, my suggestion to use XRD took for granted to consider to use the Debye Sherrer equation to evaluate the size of MoS2 particles (if Ni sulphides are not detected). The XRD data had to be exploited to obtain structural information.
Response 1: We agree with Reviewer. The average crystallite sizes were evaluated based on the XRD patterns of the sulfide catalysts.
Point 2: As reviewer I did not ask to study more reactions but only to test more experimental conditions. Addition of activity at 340 °C has improved the activity information, but is to much close to 330 °C. But why not calculate the speed constant K in table 5? Why “not detected”? it is not a calculation?
Response 2: The primary goal of our work was the comparison of the effect of the different glycols on the HDS activity of NiMo(P)/Al2O3 catalyst. It is well known, that the study of HDS of real feed using the granulated catalysts and liquid-phase sulfidation is a time-consuming procedure; the sulfidation procedure takes about 30 hours. We have chosen the conditions close to the conditions of the refinery operation to the comparison of the catalysts. And testing the catalysts in the chosen conditions let us rank the catalysts according their activity. It is unclear, how the wider range of experimental conditions can “improve” the conclusion of our manuscript.
The rate constants (k) were calculated to compare the hydrodesulfurization activity. When the reaction was carried out over the NiMoP-DEG/Al2O3 catalyst at 340°C, the residual amount of sulfur was 34 ppm (Table 5, Entry 6). This corresponds to a conversion of 99.6%. The calculation of the rate constant gives a large error at such a high conversion.
Point 3: Only 10 degrees of temperature 330-340 have increased the efficiency of the catalysts so much.
Response 3: It is experimental results, but it is not surprising, because the apparent activation energy for the hydrodesulfurization of straight-run gas oil in the presence of NiMo/Al2O3 sulfide catalysts is approximately 120-140 kJ mol-1. The sulfur level in the presence of the less active catalyst is decreased from 340 to 166 ppm, but the conversion is increased by 2%, from 96,2 to 98,1%.
Point 4: Why to use 330? I think it is an aspect to be better explored and commented.
Response 4: We started our experiments from 340°C, but the residual sulfur level was too low at this condition, especially in the case NiMoP-DEG/Al2O3 catalyst, to calculate the reaction rate constant. The higher level of sulfur in the resulting feed, obtained at the temperature of 330°C, allowed us to use the reaction rate constants to compare the activity of the catalysts, while too low sulfur gives a large error in constant calculation. Besides, a temperature of 330-335 °C (hydrogen pressure of 3.5 MPa) is commonly used in industry as the starting (SOR, Start of run) temperature for production of ULSD (Ultra low sulfur diesel) from straight-run gas oil using advanced sulfided Ni(Co)Mo/Al2O3 catalysts.
