Reasonable harmony of Ni and Mn in core@shell-structured NiMn@SiO2 catalysts prepared for hydrogen production from ethanol steam reforming

Abstract

To improve the long term catalytic stability without catalytic deactivation during ethanol steam reforming (ESR), this study considered two main areas; the role of the redox promoter of the Mn component in a Ni-based catalyst and the stability of the core@shell structure. Five different core@shell 30NixMny@70SiO2 catalysts were prepared and applied to the ESR reaction. The hydrogen selectivity was highest on the core@shell-structured 30Ni8.5Mn1.5@70SiO2 catalyst compared to those of the other catalysts. During ESR, the amount of evolved CO gas, which is related directly to catalyst deterioration, was large over the 30Ni@70SiO2 catalyst, but it was relatively low on the 30NixMny@70SiO2 catalysts. The carbon types deposited on the catalyst surface after the ESR reactions varied. Carbon nanotubes were produced on the 30Ni@70SiO2 catalyst, whereas carbon lumps were produced predominantly over the 30NixMny@70SiO2 catalysts. In particular, the amounts of carbon deposited were smallest over the 30Ni8.5Mn1.5@70SiO2 catalyst. An ESR model over the core@shell-structured 30NixMny@70SiO2 catalysts was suggested from the results of CH4-, CO- and H2O-TPD. CH4 and CO molecules, as intermediates, were adsorbed predominantly on the surface of Ni sites, but water molecules were adsorbed easily on the surface of the Mn sites, leading to a CO to CO2 transformation through a water gas shift (WGS).