Methane partial oxidation over NiO-MgO/Ce0.75-Zr0.25O₂ mixed oxide catalysts

Abstract

Methane partial oxidation (MPO) is considered as an alternative method to produce hydrogen since it is an exothermic reaction with affording a suitable H2/CO ratio of 2. However, carbon deposition on a catalyst is observed as a major cause of catalyst deactivation. In order to find suitable catalysts that can prevent the carbon deposition. NiO-MgO/Ce0.75Zr0.25O2 (CZO) mixed oxide catalysts were prepared via the co-impregnation (C) and sequential incipient wetness impregnation (S) methods. The Ni loading was fixed at 15 wt% whereas MgO loading was varied from 5 to 15 wt%. The catalysts were characterized by BET surface area measurements, X-ray diffraction (XRD) analysis, H2 chemisorption, temperature programmed reduction (TPR) and oxidation (TPO) techniques, and scanning electron microscopy (SEM). The catalysts were investigated for their catalytic activities and inhibition of carbon deposition on MPO in the temperature range of 400 to 800 ℃ at atmospheric pressure. The results revealed that the addition of Mg caused the light-off temperatures shifted to higher temperatures. This is because the Ni surface was partially covered with MgO, and the strong interaction between NiO and Ni-Mg mixed oxide solid solution over CZO support can lead to the difficulty in reducing NiO resulting in less catalytic activity. However, among the catalysts tested, the 15Ni5Mg/CZO (S) catalyst exhibited the highest catalytic stability for MPO with a prolong time on stream of 18 hours at 750 ℃. Moreover, a better resistance to carbon deposition for such a catalyst was obtained due to its higher metallic Ni dispersion at higher temperature.