**5. Conclusions**

The elimination of greenhouse gases via reforming CH4 with CO2, was investigated via heterogeneous catalysis. Specifically, the role of different supports (alumina and zeolites Y-zeolite and H-ZSM-5) for Ni-based catalysts were investigated for DRM. The activity results showed that Ni deposited onto H-ZSM-5 (NH catalyst) exhibited excellent stability (just 2% deactivation over 9h on-stream) with the least amount of carbon deposition when compared with the Ni deposited onto alumina and Y-zeolite supports. The least amount of carbon deposition was confirmed with TGA and TPO. The favorable metal-support interaction and high basicity of Ni catalytic sites onto the H-ZSM-5 contributed towards its stable performance. A comparison between the prepared NH catalyst with already reported catalysts for DRM reaction showed that the NH catalyst developed here, with 87.3% conversion of CO2, outperformed other Ni based catalysts and even bimetallic catalysts. The catalyst where Ni was deposited onto alumina showed the best conversion of CH4 (80.5%) compared to the zeolite supports, which led to up to 78.5% CH4 conversion. Overall, Ni deposited onto H-ZSM-5 constitutes a catalyst with exceptional performance for the reduction of the greenhouse gases CO2 and CH4 (87.3 and 78.5% conversion, respectively) and generation of syngas. This study provides a platform to further evaluate the performance of hierarchical zeolites synthesized by modifying conventional zeolites.

**Author Contributions:** Conceptualization, W.U.K.; methodology, M.R.K. and N.A.; formal analysis, W.U.K.; writing—original draft preparation, W.U.K.; writing—review and editing, M.R.K., R.B. and N.A.; funding acquisition, M.R.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** The APC was funded by Researchers Supporting Project No. (RSP-2021/138) King Saud University, Riyadh, Saudi Arabia.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank the Researchers Supporting Project No. (RSP-2021/138) King Saud University, Riyadh, Saudi Arabia for funding this project.

**Conflicts of Interest:** The authors declare no conflict of interest.
