Highly Dispersed Ni Nanoparticles on Anhydrous Calcium Silicate (ACS) Nanosheets for Catalytic Dry Reforming of Methane: Tuning the Activity by Different Ways of Ni Introduction

Three kinds of nickel-loaded anhydrous calcium silicate nanocatalysts (ACS), including Ni-ACS-Dop, Ni-ACS-Iex and Ni-ACS-Im, were prepared by introducing Ni species through doping in the synthesis of calcium silicate hydrate (CSH) nanosheets, ion-exchange with premade CSH nanosheets and deposition on calcined ACS nanosheets, respectively. Although Ni species were introduced in different ways, all the Ni-ACS catalysts showed similar chemical compositions and microstructures, where Ni nanoparticles were highly dispersed on the ultrathin ACS nanosheets with a large surface area and good thermal stability. However, the differences in the way of Ni introduction did produce Ni with different electronic states. The Ni-ACS-Iex catalyst with "surface Ni" as a dominant form had more electrons enriched on the surface of Ni, which led to the highest activity in the dry reforming of methane (DRM) reaction among the three catalysts, whereas the Ni-ACS-Dop catalyst with "lattice Ni" as a dominant form showed an electron-deficient property and lowest activity. Different from the introduction of a more favourable nanostructure or chemical component to the catalyst system, this work controlled the chemical environment of metal precursors and created metal catalysts with a preferred surface electronic state during synthesis, which could be a new strategy to improve the catalytic activity.