Dry reforming of methane over Ni/MgO-Al_2O_3 catalysts: Thermodynamic equilibrium analysis and experimental application

摘要

In this study, dry reforming of methane (DRM) employing a Ni/MgO-Al2O3 catalyst was undertaken to evaluate the effects of temperature (650, 700 and 750 degrees C), weight hourly space velocity (7.5, 15 and 30 L h(-1) at) and catalyst MgO content (3, 5 and 10 wt%) on catalytic activity and coke-resistance. The catalysts were prepared by the wet impregnation method and were characterized by wavelength dispersive X-ray fluorescence (XRF),N-2 physisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR-H-2), temperature-programmed desorption (TPD-NH3), H-2 chemisorption, thermogravimetric/derivative thermogravimetry analysis (TG/DTG) and scanning electron microscopy (SEM). The best conversions of methane (CH4) and carbon dioxide (CO2) and lower coke formation were obtained using higher temperatures, lower WHSV and 5 wt% MgO in the catalyst. The H-2/CO molar ratios obtained were within the expected range for the DRM reaction. The experimental yields of H-2 and CO differed from chemical equilibrium, mainly due to occurrence of the reverse water-gas shift reaction. Thermodynamic analysis of the reaction system, based on minimization of the Gibbs free energy, was performed in order to compare the experimental results with the optimal values for chemical equilibrium conditions, which has indicated that the DRM reaction was favored by higher temperature, lower pressure, and lower CH4/CO2 molar ratio. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.