Effects of molybdenum addition to activated carbon supported Ni-based catalysts for CO₂ methanation

Recently, CO₂ methanation has become a technique that aims to reduce anthropogenic CO₂ emissions by converting CO₂ captured from stationary and mobile sources and H₂ produced from renewable sources into CH₄. Due to their excellent performance-to-cost ratio, Ni-based catalysts were frequently used in such conversions. The main drawbacks, however, are that Ni has the propensity to aggregate and deposit carbon during the high-temperature reaction. These issues can be partially resolved by including a support (e.g., MOF, zeolite, activated carbon, etc.) and a second transition metal (e.g., Mo, Co, or Fe) in Ni-based catalysts. Therefore, the activity of Ni-based catalysts at low temperatures needs to be improved. In this study, a series of mesoporous activated carbon (AC) supported bimetallic Ni–Mo catalysts (Ni–xMo/AC, Ni = 13 wt.%, x = 5, 7, 9, 11 wt.%) were synthesized using the incipient wetness impregnation method. The effect of Mo content on the catalyst's activity was examined in a fixed-bed reactor. At 250–650°C, 1-atmosphere pressure, gas hourly space velocity (GHSV): 1200 mL h⁻¹ g⁻¹, and H₂/CO₂ ratio: 4:1, the catalytic efficiency of these catalysts was examined. The catalysts were analyzed using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), N₂-physisorption, and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX). Ni–7%Mo/AC catalyst showed the lowest carbon deposition rate, superior stability, and the best activity. The addition of Mo can improve the heat resistance of the Ni/AC catalyst and the interaction between the metal nickel and the support, which prevents the sintering of the catalyst.