Impact of Oxygen Storage Components in Prototype Pd-Based Three-Way Catalysts under Exhaust Conditions Relevant to Propane Engines^†

Round 1

Reviewer 1 Report

The manuscript, titled "Impact of Oxygen Storage Components in Prototype Pd-Based Three-Way Catalysts under Exhaust Conditions Relevant to Propane Engines," explores the application of Pd-based three-way catalysts integrated with oxygen storage materials, highlighting the benefits derived from increased surface area and porosity. Nevertheless, several critical points require attention before the publication of this work:

1. The abstract contains many abbreviated terms that necessitate correction and expansion for clarity.

2. It is noted that the operational stability of Pd-OSC (Oxygen Storage Component) appears to be less favourable when compared to other catalyst counterparts. The authors need to elaborate on the novelty and unique attributes of using Pd-OSC, especially in terms of its operational stability, to provide a more comprehensive understanding.

3. To underscore the impact of surface area and porosity on catalytic activities, it is recommended to include a surface area-normalized activity plot. This will help in demonstrating how these factors influence the catalytic performance.

4. To enhance the manuscript's depth and insight, a mechanistic evaluation would be a valuable addition.

Author Response

Thank you for your insightful feedback on the revisions to the abstract and other aspects of the paper. We have prepared a revised version of the manuscript incorporating your suggestions, and our response to your feedback is as follows:

1. The abstract contains many abbreviated terms that necessitate correction and expansion for clarity.
   -> Thank you for your suggestion. It has been addressed.
2. It is noted that the operational stability of Pd-OSC (Oxygen Storage Component) appears to be less favourable when compared to other catalyst counterparts. The authors need to elaborate on the novelty and unique attributes of using Pd-OSC, especially in terms of its operational stability, to provide a more comprehensive understanding.
   -> Despite the experiments being conducted under stoichiometric conditions, the performance results show that both fresh and aged samples of Pd-OSC outperformed other samples. The primary purpose of OSC materials is to store oxygen under lean conditions and release the stored oxygen under rich conditions to enhance catalytic performance. Considering this, it is anticipated that the performance of Pd-OSC samples would be even better under dithering conditions. However, as our experiments were not conducted to confirm this, we did not make any specific mention of this aspect. The relevant information has been mentioned in the results section (lines 349-352, marked in yellow), so please refer to that section for details.
3. To underscore the impact of surface area and porosity on catalytic activities, it is recommended to include a surface area-normalized activity plot. This will help in demonstrating how these factors influence the catalytic performance.
   -> Thank you for the suggestion. This is a reasonable approach when considering the reactivity of a homogeneous metal oxide, but since the reactivity on these samples is primarily carried out on the Pd surface or on the surrounding support, this normalization will not provide insight, or at least would be misleading.
4. To enhance the manuscript's depth and insight, a mechanistic evaluation would be a valuable addition.
   -> We would have liked to be able to complete this, but detailed mechanistic studies of TWC reactivity are complex and not straightforward and thus has eluded researchers for years.  Thus, this is not possible to undertake in the scope of our research described here.

Reviewer 2 Report

The manuscript by Daekun Kim et al provides a detailed study of the performance of three-way catalysts for propane engines. The study is certainly relevant and can be published in the Catalysts journal with two important additions.

1. It is necessary to more clearly demonstrate the relevance of developing three- way catalysts directly for the propane engine. In this regard, the introduction should be supplemented. Why is it necessary to develop new catalytic compositions specifically for propane engines and why it is not possible to use existing TWC for gasoline engines?

2. Only three types of catalyst compositions were studied in this work. In view of such a relatively small set of samples, the reason for choosing such compositions should be more clearly explained. The nature of the OSC component and its content are not given (in particularly, in Table 2). Why was this particular composition chosen?

Author Response

Thank you for your constructive comments and for considering our manuscript for publication in the Catalysts journal. We appreciate the opportunity to enhance our paper and agree that the two points raised are crucial for establishing the study's relevance and robustness. Please find below our responses to each of the revision requests:

1. It is necessary to more clearly demonstrate the relevance of developing three-way catalysts directly for the propane engine. In this regard, the introduction should be supplemented. Why is it necessary to develop new catalytic compositions specifically for propane engines and why it is not possible to use existing TWC for gasoline engines?
   -> Thank you for your suggestion. This has been addressed in the introduction part (marked in yellow).
   -> Although its not necessarily to develop, but to see what are the key factors that aid propane reactivity.  Each fuel used could have a TWC formulation that is ideal for its reactivity.  This is just to highlight importance of OSC versus Rh.  Another goal was to down select which one would be used in an engine experiment for the project.
2. Only three types of catalyst compositions were studied in this work. In view of such a relatively small set of samples, the reason for choosing such compositions should be more clearly explained. The nature of the OSC component and its content are not given (in particularly, in Table 2). Why was this particular composition chosen?
   -> First of all, as we mentioned in our response to the first comment, I'd like to mention that our manuscript is not focused on the role of new catalytic compositions in the development of catalysts for propane engines. Because the catalyst samples used in our study are prototypes provided by Cummins, which unfortunately means that specific compositional details remain proprietary. Despite the limited information available, Cummins has disclosed the presence of an Oxygen Storage Capacity (OSC) material and the loading of Pd or Rh for this project. Therefore, instead, our aim is to comparatively analyze the impact of the OSC material and/or the presence of Rh on catalyst performance. This is a critical aspect of our study, as the presence of an OSC material and the use of Pd-only catalysts have shown the most promising performance for propane engines.

Round 2

Reviewer 2 Report

Accept in present form