The role of oxidants in the activation of methane to methanol over a Ni–Mo/Al 2 O 3 catalyst

• Published in: Catalysis science & technology 2025
• Main Authors: Viswanadham, Balaga, Dasireddy, Venkata D. B. C., Likozar, Blaz, Valand, Jignesh
• Format: Article
• Language: English
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/D4CY01339E

A commercially available Ni–Mo/Al 2 O 3 catalyst was evaluated for its effectiveness in the partial CH 4 oxidation to methanol by using various oxidants, including O 2 , H 2 O, and N 2 O. The main products from the reactions were methanol, formaldehyde, hydrogen and carbon oxide gases. The study revealed that the one-step activation of CH 4 into oxygenates on the Ni–Mo/Al 2 O 3 catalyst depended on the type of oxidant utilized. The research examined how the mobility and storage of lattice oxygen within the catalyst influenced its performance in methane conversion. High oxygen storage and release improved catalytic activity but reduced selectivity. Methane conversion without oxygenated products occurred when H 2 O or N 2 O was used, while O 2 promoted the formation of CO x . The highest methanol yield was obtained at a 2 : 1 molar ratio of oxidant to methane, at reaction temperatures of 250 °C and 350 °C. When H 2 O was used, significant quantities of H 2 and CO were produced, likely due to a simultaneous reforming reaction. Partial oxidation of nickel and molybdenum was observed under H 2 O and N 2 O conditions. Temperature-programmed reduction (TPR) indicated the transformation of higher-valence oxides into different sub-oxides. In temperature-programmed reduction–oxidation (TPRO), three peaks were detected, corresponding to oxygen surface sites and two framework locations. These peaks shifted to lower temperatures with N 2 O, suggesting improved oxygen migration from the bulk to the surface. X-ray diffraction (XRD) analysis identified an active α-NiMoO 4 phase, which facilitated oxygen termination on molybdenum atoms. Under O 2 conditions, nickel also underwent oxidation. Overall, the Ni–Mo/Al 2 O 3 catalyst showed notable methanol productivity, reaching up to 9.85 g of methanol per gram of catalyst per hour with N 2 O as the oxidant, surpassing other catalysts reported in the literature.