Enhanced performance and carbon resistance of mechanochemically synthesized 15 %Ni/Al₂O₃ catalysts in combined methane reforming: Effects of transition metal promoters (Fe, Mn, and Cr) and operating conditions

In this study, 15 wt% Ni/Al₂O₃ catalysts promoted with Fe, Mn, and Cr were synthesized through a mechanochemical route and evaluated for the combined dry and steam reforming of methane reaction. Structural and physicochemical properties were examined using XRD, BET, TPR, TPO, and FESEM analyses. The catalysts exhibited high BET surface areas ranging from 220.82 to 233.6 m²/g and mesoporous structures with pore sizes of 2–10 nm. The incorporation of Cr notably improved the catalyst’s performance, delivering CH₄ and CO₂ conversions of 66.7 % and 33.5 %, respectively, with excellent stability (H₂/CO ∼ 2.1) maintained over 7 h of reaction at 700 °C. TPO results revealed that both Mn and Cr minimized carbon deposition by improving Ni dispersion and enhancing carbon oxidation, leading mainly to filamentous carbon, as confirmed by FESEM images. Increasing Cr loading from 3 % to 7 % significantly improved activity and minimized carbon formation, attributed to oxygen-rich lattice sites promoting carbon oxidation. Upon raising the GHSV from 6000 to 24,000 mL/g cat .h, CH₄ conversion in combined reforming decreased, falling from 85.2 % to 68.6 %. Increasing the steam content in the CH₄:CO₂ feed enhanced CH₄ conversion but slightly suppressed CO₂ conversion, owing to the stronger oxidizing ability of steam. • Fe, Mn, Cr-promoted 15 %Ni/Al₂O₃ catalysts boost SCO₂-MRe process efficiency. • Chromium incorporation promoted lattice oxygen formation in the catalyst structure. • Cr(7)-NiAl showed highest activity with improved methane conversion and lower carbon buildup. • Steam’s high stability and oxidizing power vs CO₂ lowers carbon formation. • Effect of operating conditions on catalyst performance was studied.