Synthesis and evaluation of promoted Ni catalysts for enhanced hydrogen production in dry reforming of methane: A response surface methodology study

Abstract

Dry reforming methane (DRM) is a method that produces hydrogen, which is highly promotional and environmentally relevant. In addition to providing a route to cleaner energy production via hydrogen fuel, it offers a double environmental advantage by utilizing two powerful greenhouse gases at the same time: CO₂ and CH₄. The DRM at 700 °C was tested using a series of 5 % Ni-based catalysts promoted with 1 % Rh, La, Au, and Sm and supported on alumina. The catalysts were prepared via the impregnation method. The textural qualities, reducibility, structural features, basicity, carbon deposition, morphology, and surface chemical states were examined using N₂ physisorption, H₂-TPR, XRD, CO₂-TPD, Raman spectroscopy, TEM, and XPS. Rh addition significantly increased the catalytic activity, resulting in the highest H₂ and CO yields (approximately 60 % and 70 %, respectively) and an H₂/CO ratio of 0.85. However, when compared to the unpromoted 5Ni/Al₂O₃ catalyst, the addition of La, Au, and Sm resulted in a decline in catalytic performance, highlighting the selectivity of promoter effectiveness. According to characterization investigations, La, Au, and Sm promotion increased coke deposition, which was validated by Raman spectroscopy, while Rh promotion promoted higher reducibility and improved the dispersion of Ni nanoparticles. TEM investigation of the spent 5Ni-Rh/Al₂O₃ catalyst revealed that carbon nanotubes and nanofibers encapsulated the active sites. XPS analysis revealed the presence of NiAl₂O₄ species in both fresh 5Ni/Al₂O₃ and 5Ni-Rh/Al₂O₃ catalysts. The Rh-promoted catalyst showed a modest shift towards higher binding energies, indicating improved metal-support interactions. Using response surface methods, this study examines how temperature, space velocity (SV), and the ratio of CH₄ to CO₂ affect the CO and H₂ yields and their ratios. The findings indicate that the most important component is temperature, which significantly increases the CO and H₂ output. These yields are also improved by lowering SV and the CH₄/CO₂ ratio. As a result, the H₂/CO ratio increased with higher temperature and lower SV, but it also increased with both temperature and CH₄/CO₂. In DRM, the ideal conditions for the 1 % Rh-promoted Ni catalyst were determined through numerical optimization, yielding over 95 % H₂ yield. The experimental findings closely matched the theoretical expectations.