Highly porous Ni/MgO-ZrO2 catalysts for dry reforming of methane and the effects of MgO addition on the mechanisms
Dry reforming of methane (DRM) is a promising pathway to convert greenhouse gas into syngas. However, the commonly used Ni based catalysts suffer deactivation due to severe sintering and coking. In this paper, a series of porous Ni/MgO-ZrO 2 catalysts (5Ni/xM(1-x)Z, x = 0, 20, 40, 60, 80 wt%, respectively) with high specific surface area were synthesized by a facile combustion method followed by incipient impregnation. It is found that the appropriate amount of MgO (40 %) addition in ZrO 2 favors high porosity and high specific area. More MgO enhances the basicity of the catalyst as well as the metal-support interaction (MSI) by the formation of NiO-MgO solid solution, thus improving DRM activity and coking resistance. However, excessive MgO addition leads to over-strong MSI and lower porosity, resulting in lower DRM activity. The catalyst with 40 % MgO addition (5Ni/40M60Z) exhibits the best activity (conversions of CH 4 ∼ 76 %, CO 2 ∼ 83 %) and stability (>50 h) at high GHSV = 96000 ml/g cat ·h and 750 °C. in situ DRIFTS reveals the mechanism that MgO addition improves DRM activity and stability. Compared with ZrO 2 where CO 2 adsorbs as monodentate carbonate, CO 2 tends to adsorb on 40 %MgO-60 %ZrO 2 as bidentate carbonate and then easily transfer to more stable intermediate bidentate formate, thus improving DRM activity and coking resistance. This study provides new insights on the role of Mg addition in Ni/MgO-ZrO 2 DRM catalysts.
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