Ni mesostructured catalysts obtained from rice husk ashes by microwave-Assisted synthesis for CO2methanation

Abstract

In this work, rice husk ashes were used to obtain a high purity silica precursor to synthesize mesoporous silica frameworks. A novel route for the synthesis of mesocellular silica foam (MCF) was developed using microwave irradiation during the hydrothermal treatment. Cyclohexane and cetyltrimethylammonium bromide were employed as swelling and structure-directing agents, respectively. Ni-based catalysts supported on MCM-41 and MCF mesostructured materials were obtained using two methods, one-pot and incipient wetness impregnation. The catalysts prepared for both methods presented noticeable differences in the metal-support interaction, which were observed by TEM, SAXRD, TPR and XPS. The impregnated catalysts showed preferentially Ni particles inside the pore structure of the support while the one-pot catalysts also showed Ni particles within the silica framework. The catalysts were evaluated in the CO2 methanation reaction between 200 and 500 °C at atmospheric pressure. The samples prepared by impregnation showed better catalytic performance than those prepared by the one-pot method. Thereby, the Ni particles highly distributed within the pore improved the CO2 methanation reaction. The Ni/MCF_ch_iwi presented the best catalytic performance reaching CO2 conversions and CH4 selectivities close to the reaction equilibrium, from 350 to 500 °C. The Ni/MCF_ch_iwi also showed high structure and catalytic stability, as well as coke resistance formation under reaction conditions.