Advantages of mesoporous silica based catalysts in methane reforming by CO2 from kinetic perspective

Abstract

Nickel confined inside mesoporous silica SBA-15 (Ni5/SBA-15), and iridium supported nickel/SBA-15 catalysts (Ir0.1-Ni5/SBA-15) were tested in dry reforming of methane (DRM). Calcined samples were characterized and their structural and morphological properties were obtained and analyzed by N2-sorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Nickel oxide nanoparticles with estimated particle sizes of 3.3 and 4.2 nm were obtained. Their reducibility and active surface area were determined by temperature programed reduction and temperature programed desorption, respectively. Kinetic studies in DRM were then performed at 480 °C and the facile power-law rate expressions attained for Ni5/SBA-15 and Ir0.1-Ni5/SBA-15 confirmed the dependency of both rates on CO2 and CH4 partial pressures, which decreased the formation of carbon deposition due to the confinement effect of nickel inside supports mesopores. Activation energies (Ea) of the catalysts were also calculated by varying the temperature. The values of Ea in this study (8.4 and 6 Kcal.mol−1 for CH4 and CO2 on Ni5/SBA-15 catalyst) were lower than those present in other studies, which were mainly performed on non-porous based catalysts. Such outcome stresses on the importance of mesoporous supports in improving the kinetics of DRM. Finally, long tests duration shows that the presence of Ir is beneficial at high temperature (650 °C) in order to maintain the conversion levels of reactants.