Synthesis of Ni-alkaline earth metals particles encapsulated by porous SiO2 (NiMO@SiO2) and their catalytic performances on ethanol steam reforming

Abstract

This study examined hydrogen generation by ethanol steam reforming over 30wt% Ni-alkaline earth metal (Ni1M0.33O2.66@SiO2, M=Mg, Ca, Sr, and Ba) oxide catalysts encapsulated by 70wt% porous SiO2 to depress the sintering that can occur between the nickel particles during the ethanol steam reforming reaction. Transmission electron microscopy of a mixture of NiMO (alkaline earth metal/Ni molar ratio=1/3) and SiO2 particles revealed a core@shell shape with cubic NiMO particles, 100–200nm in size, encapsulated by spherical, porous SiO2 nanoparticles. In contrast, whisker-shaped silica encapsulated the Ni1Sr0.3O2.66@SiO2 and Ni1Ba0.3O2.66@SiO2 samples. The shape of the hydrogen-reduced samples changed to a nanowire-like shape. The catalytic performance over the hydrogen-reduced samples varied according to the alkaline earth metal oxide loading. The Ni1Mg0.3O2.66@SiO2 catalyst exhibited significantly higher reforming reactivity than the other catalysts, NiO@SiO2, Ni1Sr0.3O2.66@SiO2, and Ni1Ba0.3O2.66@SiO2 because of the synergy between the nickel metal and magnesium oxide ions. H2 production was maximized to 88% over Ni1Mg0.3O2.66@SiO2 under the following conditions: reaction temperature of 700°C, CH3CH2OH:H2O of 1:3, and GHSV (gas hourly space velocity) of 4500h−1. The nickel in the catalyst had absolute catalytic activity but its activity was improved by the presence of MgO. MgO might provide oxygen to the nickel species, resulting in an increase in the rate of the CO–water gas shift reaction.