Effects of Phosphorus Addition on the Hydrophobicity and Catalytic Performance in Methane Combustion of θ-Al2O3 Supported Pd Catalysts
, Gurong Shen 3,* and Meiqing Shen 1,4,*
Round 1
Reviewer 1 Report
10.03.2023
The revision of manuscript catalysts-2282380 entitled:
"Effect of phosphorus addition on the hydrophobicity and catalytic performance for methane oxidation of θ-Al2O3 supported Pd catalysts Reactor for COx Methanation”
The manuscript deals with the preparation of P-modified Pd/q-Al2O3 catalysts and investigation of P addition on physicochemical properties and finally the efficiency toward CH4 oxidation. P modified q-Al2O3 supports and final catalysts differing in P content were characterized with several techniques (ICP-OS, XRD, TG, NH3-TPD, BET/BJH, FT-IR, XPS), and CH4 oxidation activity was estimated using self-made fixed-bed reactor with fine grained catalysts’ samples. Authors found Pd/q-Al2O3 catalyst modified with P (up to 0,6 wt. %) as an efficient system useful for CH4 oxidation comparing to reference catalyst. It was also concluded that the incorporation of relatively low content of P improves activity as a consequence of surface hydrophobicity enhancement leading to decrease of H2O inhibiting effect.
This work follows the scope of Catalysts journal. Before consideration of acceptance, major revisions should be conducted. Specific comments are shown below.
a) I haven’t found “Supplementary Materials” which are referenced in the text. Probably it was not attached to the manuscript.
b) Another issue concerns hydrophobicity investigation method. What is the accuracy of hydrophobicity measurement? The difference of mass loss between catalysts determined by TGA is quite low – Δm variation between all of investigated catalysts in temperature range of RT-300 °C do not exceed 1.5%. Authors should explain the accuracy of methodology applied to evaluate the surface hydrophobicity since it is crucial for the conclusions made.
c) The term “peak center” should be replaced with “peak maximum”.
d) It is not clear why the “..slurry was stirred…” at the stage of P precursor deposition onto the q-Al2O3 surface in case of using the incipient wetness impregnation. Using a slurry excludes “wetness impregnation”. That issue should be explained and corrected.
e) “P element”, “Phosphorus addition” should be corrected since the catalysts contain just P compounds instead of P elemental form.
I recommend major revision of this manuscript before publication.
Author Response
Please see the attachment.Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
After carefully reviewing the paper “Effect of phosphorus addition on the hydrophobicity and catalytic performance for methane oxidation of θ-Al2O3 supported Pd catalysts” I recommend that it should be accepted after major revision. Here are some recommendations:
- I think that the process is more correctly named “catalytic combustion” rather than “oxidation”, since methane oxidation is usually considered to lead to oxygenated compounds such as formaldehyde and methanol;
- the main problem with this manuscript is the lack of access to the supplementary information (Tables S1-S9 and Figures S1-S6), not made available by the authors. They were discussed in detail in the manuscript, but the reader cannot verify these results – please provide the supplementary material;
- some of the information from the supplementary material could be added to the main manuscript, e.g. the XRD patterns of the solids;
- when commenting Figure 2, the authors claim that “The peak center of the second peak is about 280°C, which is classified as strong acid”. A reference should be cited, but the temperature probably indicates the presence of medium strength acid sites rather than strong ones;
- in the same paragraph: “the desorption spectrum of NH3 were collected at different temperatures. When the temperature began to rise from 100°C to 150°C, the infrared adsorption peak of NH3 was significantly weakened, which indicated that NH3 had undergone chemical adsorption”. “Spectrum” should be changed to “spectra”, and the authors should explain why they reached this conclusion;
- in the next paragraph: “The infrared absorption peaks in the range of 3000-3500 cm-1 mainly corresponds to the Brønsted acids produced by the hydroxyl groups on the surface of Al2O3, which corresponds to the first peak in the NH3-TPD curve” – reference is needed;
- page 4 of the manuscript: “On the other hand, the law between the content of P element of the supports and the desorption amount of NH3 of the supports was consistent with the law of hydrophobicity reflected in the TG test” – “law” should be replaced with “relationship”;
- page 4: “As shown in Figure 3, the amplification of Figure S4 in the range of 2000 cm-1 - 700 cm-1 …” – the range in Figure 3 is 1600-700 cm-1;
- page 4: “Phosphate has three basic configurations: PO43-，HPO42- and H2PO4-.” – these are different ions, not configurations of the same ion as the sentence suggests. There are several other places in the manuscript where this concept is used (e.g. pages 5 and 6);
- page 6: section 2.2 is named “Characteristic of catalysts”, it should probably be changed to “Characterization of catalysts”;
- page 7: an explanation would be relevant for the readers why did the authors choose the value of 8 % for the water introduced in the reaction;
- page 9: when commenting on Figure 9, the authors write “the relative surface hydroxyl density of supports was correlated with the hydrophobicity of supports and the T50 of methane oxidation ignition test (Figure 9), showing a good linear relationship.” In fact, a change of slope is visible at around 1.2 for the relative surface hydroxyl density, which causes a low value of R2. Could this change of slope have relevance?
- page 10, section 3.3. Catalytic activity test: what was the diameter of the U-shaped reactor?
- the next paragraph: “the reactor was heated to 600°C, and the reaction atmosphere (2000ppm CH4, 5%O2, 8%H2O (0%H2O), N2 was the equilibrium gas, and the space velocity was 36000h-1) was maintained for 1h, so that the samples reached a stable state. The reactor was cooled to 80°C by N2, and reaction atmosphere was switched to the reactor and stabilized, then, the ignition test of methane oxidation was conducted.” – it is not clear why the reactor was heated to 600 °C in the presence of the reaction mixture, then cooled to 80 °C, and what does “reaction atmosphere was switched to the reactor and stabilized” mean. The phrase should be clarified.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The paper can be accepted in the present form.
