Effect of combining Al, Mg, Ce or La oxides to extracted rice husk nanosilica on the catalytic performance of NiO during COX-free hydrogen production via methane decomposition

摘要

Amorphous nanosilica powder was extracted from rice husk and used as a catalyst support as well as a starting material for the preparation of different binary oxides, i.e., SiO2 Al2O3, SiO2 MgO, SiO2-CeO2 and SiO2 La2O3. A series of supported nickel catalysts with the metal loading of 50 wt % were prepared by wet impregnation method and evaluated in methane decomposition to "COx -free" hydrogen production. The fresh and spent catalysts were extensively characterized by different techniques. Among the evaluated catalysts, both Ni/SiO2 Al2O3 and Ni/SiO2 La2O3 catalysts were the most active with an over-all H-2 yield of ca. 80% at the initial period of the reaction. This distinguishable higher catalytic activity is mainly referred to the presence of free mobile surface NiO and/or that NiO fraction weakly interacted with the support easily reducible at low temperatures. The Ni/ SiO2-CeO2 catalyst has proven a great potential for application in the hydrogen production in terms of its catalytic stability. The formation of MgxNi(1-x)O solid solution caused the Ni/ SiO2-MgO catalyst to lose its activity and stability at a long reaction time. Various types of carbon materials were formed on the catalyst surface depending on the type of support used. TEM images of as -deposited carbon showed that multi-walled carbon nanotubes (MWCNTs) and graphene platelets were formed on Ni/SiO2, while only MWCNTs were deposited on all binary oxide supported Ni catalysts. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.